The maintenance of a clear airway in an anaesthetized patient can often be achieved by a simple elevation of the jaw (jaw thrust) and/or extension of the head on the cervical spine. These movements tend to separate the tongue, epiglottis and soft palate from one another and away from the posterior pharyngeal wall (Fig. 6.1). However, in many patients maintenance of the airway in this manner is either ineffective or impractical for surgery. Patients with anatomical reasons for such manoeuvres to fail include those whose ‘pharyngeal spaces’ are absolutely or relatively small (e.g. a large tongue, small lower jaw, large diameter neck, obesity and also those with large adenoid or palatine tonsils). In such patients the obstruction must be relieved and the easiest way to achieve this is by inserting a device that separates these structures and thus creates an artificial airway. These airway adjuncts may be inserted via the mouth (oropharyngeal airway) or via the nose (nasopharyngeal airway) (Fig. 6.2).

Figure 6.1 A. The obstructed airway following the administration of a general anaesthetic if the jaw is unsupported. The airway may be obstructed by (i) epiglottis and/or (ii) tongue pressing on the posterior pharyngeal wall, or by (iii) the soft palate, occluding the oral or nasal airways. B. The effect of simple elevation of the jaw in a patient with normal anatomy.

Figure 6.2 A. An unobstructed air passage produced with an oropharyngeal airway. B. An unobstructed air passage produced with a nasopharyngeal airway.

Oropharyngeal airway

These devices are shaped to emulate and so restore the space present in the pharynx during consciousness by pushing the tongue and epiglottis away from the posterior pharyngeal wall. Oropharyngeal airways are usually oval-shaped, occasionally circular, in cross-section and are produced in varying lengths and diameters to suit different patient sizes from premature neonate to large adult. The proximal end has a flange to limit the depth of insertion and prevent its loss into the pharynx. Devices are sufficiently rigid to prevent collapse should the patient bite down and indeed they may be used as a ‘bite block’ in an intubated patient (to prevent airway obstruction as a result of the tracheal tube being obstructed by biting). When inserted, the distal end should lie at the posterior of the tongue but above the epiglottis. Insertion too deep may in itself lead to airway obstruction either by mechanically pushing the epiglottis back or by irritating the sensitive laryngeal inlet leading to laryngospasm. There is a standard colour and number coding for size. The most popular oropharyngeal airway type is the Guedel pattern (Fig. 6.3). To select the correct size of Guedel airway, the distance from the flange to the distal tip of the airway should be about the same as from the patient’s lips to the tragus of the ear.

Figure 6.3 Guedel airways in sizes 00, 0, 1, 2, 3, 4 (a smaller size 000 is not shown here).

Nasopharyngeal airway

The nasopharyngeal airway is designed to be passed through the nares and along the floor of the nose to deliver the tip beyond the soft palate to lie in the oropharynx, above the epiglottis. It can bypass nasal, soft palate and tongue base obstruction. The tubes have either a fixed or adjustable flange (Fig. 6.6) at the proximal end to prevent loss of the device into the nose and to limit insertion of an excessive length. The tip is bevelled to make its passage through the nose less traumatic. Some designs have a hole cut in the wall opposite the bevel to maintain patency if the tip becomes obstructed. They are produced in a range of sizes with the length of the airway governed by the internal diameter of the tube.

Figure 6.6 Nasopharyngeal airways (from top to bottom) Portex and Rusch designs, the lower with an adjustable flange.

Nasopharyngeal airways are often indicated where a patient has limited jaw opening, awkward or fragile dentition or where an oropharyngeal airway is frequently displaced by a marked overbite. They are well tolerated by patients during relatively light levels of anaesthesia and during emergence. To avoid traumatic insertion and heavy bleeding nasopharyngeal airways are ideally soft (plastic, polyurethane or latex rubber). Avoiding excessively large tubes also minimizes complications during use, but the tube must be long enough to extend well into the oropharynx. An estimate of appropriate length is the distance from the tip of the nose to the tragus of the ear.

The use of nasopharyngeal airways has reduced dramatically with the rise in popularity of the LMA. They retain an important role in patients in whom the oropharynx cannot be accessed and in sedated patients who would not tolerate an oropharyngeal airway.

Complications

The commonest complication is trauma causing bleeding, which can be extensive and may compromise the airway further. They should not be used where there is evidence of coagulopathy or other potential causes of epistaxis. Inappropriate sizes may either fail to clear the airway (too short) or lead to coughing, laryngospasm or retching (too long).

Facemasks

Anaesthetic facemasks are designed to fit over the patient’s nose and mouth and enable the creation of a low pressure seal. This should not require excessive force. The facemask (Fig. 6.7) consists of three parts: the mount, the body and the edge. A snug fit is achieved by incorporating one or more of the following features into the design: by anatomically shaping the body, by the use of an air-filled cuff at the edge (Figs 6.8B, D and E) that has a soft cushioning effect or by a soft pliable flap (Figs 6.8A and C) that takes up the contour of the face.

Figure 6.7 The parts of an anaesthetic facemask: A, the mount; B, the body; C, the edge.

Figure 6.8 A selection of facemasks: A. black rubber ‘Everseal’ mask with soft pliable flap (designed by MIE Ltd in 1953 for the British Everest expedition); B. ‘anatomical’ facemask in black rubber with air filled cushion; C. single-use facemask with flap; D. single-use facemask with adjustable air filled cushion; E. single-use facemask with pre-filled air cushion. Note: A, D and E carry attachments for use with a harness (see text).

The mount should be a 22 mm female taper if made to the standards of ISO (International Organization for Standardization) or BS (British Standards). It is usually constructed of hard synthetic rubber but may be plastic or metal. The former two wear more easily with repeated use and eventually produce a leak or potential for accidental disconnection.

The body may be made from black rubber, neoprene, plastic, polycarbonate or silicone rubber. In some cases, a malleable wire stiffener or wire gauze is incorporated in the body so that the shape may be altered to fit the patient’s face. The transparent body of a polycarbonate or plastic facemask permits continuous inspection of the airway and respiration to be monitored by the appearance of condensation during exhalation. This is useful during anaesthesia and particularly during resuscitation. A transparent facemask also affords the possibility of seeing regurgitant matter or vomitus emerging from the mouth. Such masks are perhaps less threatening to children and anxious adults (Figs 6.8C, D and E).

The internal volume (apparatus dead space) within the body of the facemask is relatively unimportant in adults but may assume significance in neonates and infants where it can constitute 30% or more of their tidal volume. Several designs shape the paediatric facemask to minimize the apparatus dead space (Fig. 6.9). In spite of this, good fit may be more important than theoretical apparatus dead space: paradoxically in paediatrics, a larger facemask particularly of the Rendell-Baker or Laerdal type, may allow the face to fit further into the mask with improved fit and reduced effective apparatus dead space.

Figure 6.9 The full range of Rendell-Baker paediatric facemasks, sizes 00, 0, 1, 2, 3.

The edge may be anatomically shaped and fitted with a cuff or flap. A good fit is essential to prevent dilution of administered gasses by room air during spontaneous respiration and to allow positive pressure ventilation without gas leak. A variety of types and sizes of facemask must be available, since none will be a good fit for every face. Edentulous or bearded patients may be especially difficult. The former are best managed by leaving any dentures in place to prevent the cheeks from falling away from the mask and by using a smaller mask. Beards often prevent a good seal around the edge of the mask and a leak-free fit may sometimes be achieved with a bigger mask held firmly with two hands. Anaesthetists have often had to go to bizarre lengths to achieve a useful seal in heavily bearded patients (e.g. using a pierced defibrillator gel pad on the face ³ or even wrapping the entire head in clingfilm⁴). Reusable masks with a cuff have a small filling tube fitted with a plug to enable the degree of inflation to be regulated. The plug must be removed to allow the cuff to deflate if the mask is to be autoclaved.

Whereas some facemasks withstand the high temperatures of autoclaving, others do not. Since these are not easily distinguished, many adopt uniform policies of disinfection. Care must be taken if chemical disinfection is used as some chemicals, e.g. chloroxylenol (Dettol), are known to have been absorbed by the material of the facemask and have resulted in injury to the patient’s skin.

The shift towards disposable single-use facemasks avoids the cost of sterilization (increasingly performed off-site for many hospitals) packaging, and mandatory tracking and trace systems, but risks a reduction in quality. The same principles of design nevertheless apply to plastic disposable facemasks (Figs 6.8C, D and E). Materials and components are cheaper and of lower quality, but more importantly there is a much more limited range of designs and sizes. Most, even those for paediatric use, are essentially based on the one design of air-filled cuff and cone-shaped body. As they are reproduced with differing quality and materials by numerous manufacturers, uniformity of performance cannot be assumed. They may be advertised with bold claims of high performance and popularity but formal clinical evaluation is not a pre-requisite to bringing them to market. Several new designs have been found to be substandard and it is wise to assess performance before changing devices. Sizes do not necessarily equate between manufacturers. Some single-use masks do not allow adjustment of the volume of the air-filled cuffs and these may be both under filled and of less pliable plastic leading to a poor-quality seal. Poor design or poor fit, even in the absence of a leak, can cause areas of high pressure on the skin, which if unchecked, could lead to ulceration. Single-use masks do, however, have a number of advantages beyond sterility. These include use of inert plastics (eliminating risk of allergy to latex), transparency and even the potential to add scent to the plastic making the products more readily accepted by patients.

Many anaesthesia masks are supplied with a ring device that has several lugs protruding to allow attachment of a head harness. Older black rubber masks have a similar metal harness ring (Figs 6.8A, D and E). A head harness may be used to allow facemask anaesthesia while allowing the anaesthetist to keep both hands free. Since the introduction of supraglottic airways head harnesses are rarely used, if ever, except during non-invasive ventilation (see below).

Masks for some dental anaesthetic techniques are designed to fit the nose only, so that the dentist has unimpeded access to the mouth (Fig. 6.10). They are also known as nasal inhalers.

Figure 6.10 A McKesson comfort cushion nasal inhaler.

Facemasks are also used for non-invasive ventilation (NIV) or continuous positive airway pressure (CPAP) in differing scenarios, both in and out of hospital (see Chapter 7, Fig. 7.17). These are similar to anaesthesia facemasks and may cover the mouth and nose (conventional CPAP) or just the nose (for nasal CPAP). Such masks tend to be single-patient use devices made of plastics and soft silicone rubber. They are usually of a higher quality than single-use anaesthesia masks as comfort and tolerability is the key to treatment compliance and success. CPAP masks often incorporate additional ports for valves and airway manometry and have attachments for a retention harness to keep the mask comfortably on the patient’s face.

Specialized face masks

Flexible endoscopic intubation

One manufacturer (VBM, Salz, Germany, Fig. 6.90) makes a facemask that can be used to permit endoscopic intubation.

Figure 6.90 Facemask with perforated silicone membrane allowing fibreoptic intubation on the anaesthetized patient, the tube can be forced through the membrane, which is replaceable. The same effect can be achieved using the Mainz Universal Adapter (pictured alongside) and an ordinary facemask.

Monitoring ventilation

Several manufacturers make facemasks incorporating ports for capnography attachments.

Supraglottic airways

History

Prior to 1988 maintaining a clear airway in a non-intubated, anaesthetized patient, might well have involved elevating and protruding the lower jaw, supporting it in this position with a Guedel airway, placing a facemask over the nose and mouth and securing this with a Clausen’s (head) harness to provide a gas-tight fit: all essentially dextrous tasks requiring practised performance. Although preceded by numerous devices that were designed to control the airway without tracheal intubation, it was not until the advent of the Laryngeal Mask Airway (LMA), first described in 1983,⁵ and introduced commercially in 1988, that such devices achieved success in anaesthesia. It soon became evident that the LMA allowed all the tasks described above to be replaced with a single device requiring minimal training in its use, but with an astonishing success rate in achieving a clear leak-free airway. Within a year of its introduction all UK hospitals had placed orders: the anaesthetic ‘supraglottic revolution’ had begun.

Since that time more than 40 novel, and less novel, supraglottic airway devices (SADs) have been brought to market. Since 2003 numerous manufacturers have produced copies (or near copies) of the LMA, most of them disposable and plastic. Many new supraglottic devices are based on the general design of the LMA and several are based on the Combitube (see below), which, although in origin pre-dates the LMA,^6,⁷ was (and remains) more a device for airway rescue than for routine anaesthetic use. Other novel approaches to SAD design have met with varying degrees of success. No design has so far proven as popular as the LMA, in spite of the occasional publications claiming similar or better performance.^8,⁹

Major advances since the original LMA have been rather few but the recent evolution of devices designed with increased safety in mind, is a significant step.

Features

SADs generally have the following features in common:

• An inflatable cuff that sits over or above the level of the larynx. A minority of devices are cuff-less. Crucially, in all SADs, function relies on an open laryngeal inlet.

• ‘Blind’ insertion is possible, obviating the need for laryngeal visualization.

• They rely, for correct positioning, on a soft distal tip that lodges in or just above the upper oesophagus behind the cricoid ring. A minority sit well above this.

• There is an inability to guarantee tracheal isolation from gastric contents in the event of reflux or vomiting. This issue is increasingly being solved.

• The use of wide bore tubing for the airway tube (as this is not limited by the size of the larynx and trachea), and which can therefore be used as a conduit for other instruments such as a tracheal tube or a flexible endoscope.

• An ISO 15 mm male connector proximally enables connection to an angle piece, catheter mount or breathing system.

Terminology

The term originally coined to describe the generic group of LMAs and other similar devices is supraglottic airway devices (SADs). The term extraglottic has been suggested as more accurate by some authors.¹⁰ The term SAD has the advantage of primacy and widespread use and is adopted here. Several authors have attempted to classify SADs on the basis of patient or device anatomy but the classifications are cumbersome and not widely adopted.¹¹ The author of the previous incarnation of this chapter attempted (to no avail!) to introduce the term ‘augmented supraglottic airway’ to delineate simple oral and nasopharyngeal airways from those supraglottic devices that aim to provide a gas-tight seal to the airway.

This author has coined the phrase first-generation and second-generation SADs to demarcate those devices which are simple airway tubes (first generation), from those which are designed with the intention of reducing the risk of pulmonary aspiration of gastric contents (second generation). The proposed advantage of this classification is that it is simple, is not dependant on patient/device anatomy, but is ‘patient centred’. Second-generation devices may be designed to improve patient safety, but the effectiveness of this design feature is not proven in all cases. Second-generation devices comprise the ProSeal LMA, the Combitube and Easytube, the Laryngeal Tube Suction mark II, the Streamlined Liner of the Pharynx Airway, the i-gel and the Supreme LMA.

Pharyngeal seal and efficacy vs oesophageal seal and safety

Functionality of an SAD depends on several factors including insertion ease and success rate, manipulations required during anaesthesia to maintain airway position and patient tolerance of the device during emergence. During controlled ventilation efficacy is dependent on factors such as whether the device orifice sits over the larynx and the quality of the device seal with the laryngopharynx (pharyngeal seal). The pharyngeal or airway seal pressure is usually assessed by allowing a fresh gas flow of 3–5 l min^-1 into the closed breathing system of an apnoeic non-paralyzed patient and noting the maximal airway pressure generated or the pressure when a leak can be detected.

The safety of a SAD reflects the likelihood and severity of complications occurring at all stages of anaesthesia and afterwards. Complications include failures, displacements, airway obstruction and sequelae such as sore throat, pharyngeal trauma and nerve injuries from pressure effects. The risk of aspiration is a major concern with SADs. Moderation of this risk requires a good-quality seal with the hypopharynx and/or oesophagus (oesophageal seal) to prevent gas leaking into the oesophagus and stomach and also to prevent regurgitant matter passing from the oesophagus into the airway. Ideally oesophageal seal pressures are assessed in terms of hydrostatic pressure needed in the oesophagus to cause liquid regurgitation (hence needing cadaver studies). A correctly functioning drain tube should enable regurgitant matter to bypass the larynx and be vented externally. This protects the airway and gives an early indication of the presence of regurgitation.

Several recent studies indicate that the extent of oesophageal seal varies considerably between different SADs.¹²^–¹⁵ They also demonstrate that under experimental conditions in cadavers, those with a drain tube will usually effectively vent regurgitant fluid provided the drain tube is not occluded. Particulate matter has not been studied. These are important findings, though their clinical correlates are not in all cases confirmed.

First-generation SADs

The laryngeal mask airways

The next section focuses on the classic LMA. Much of what is included also applies to other laryngeal masks and supraglottic airways in general. Several alternatives to the classic LMA are described in more detail below.

The LMA Classic

As its name implies the classic laryngeal mask airway (cLMA) (Intavent Direct, Maidenhead, UK) is designed to act as a mask that fits over the larynx. It consists of an oval soft silicone mask that sits over the larynx with an integrated stem that extends through the oral cavity to allow attachment to the anaesthetic circuit or other appropriate equipment.

The mask (distal) end of the cLMA is made of medical grade silicone and consists of a shallow bowl resembling a small facemask, which is surrounded by an inflatable tubular cuff (Fig. 6.11). The latter, when inflated, fits around the laryngeal inlet and supports it in a position away from the posterior pharyngeal wall. The back of the bowl leads into a semi-flexible tube which passes out of the pharynx and mouth and has a 15 mm ISO male connector so that it can be attached to a breathing system. At the point the tube enters the mask, there are two thick silicone rubber strands (grilles, or bars) designed to prevent the epiglottis falling into it and occluding the lumen. The mask cuff is inflated via a pilot tube that terminates in a small ‘pilot balloon’ giving an indication of cuff inflation/deflation. A self-sealing valve prevents deflation of the cuff.

Figure 6.11 The laryngeal mask airway in sizes 1, 1½, 2, 2½, 3, 4, 5. A size 6 is now also available which is not shown here.

cLMAs are made from silicone rubber so that they can be autoclaved and reused. The manufacturer has designated the cLMA for 40 uses. Experience suggests the cLMA can withstand many more cycles of sterilization, but this is ‘off label’ use and cannot be recommended. Originally produced in four sizes, two mid-range sizes and two further larger sizes were added later (Fig. 6.11).

Experience with sizes 1 and 6 is comparatively limited. It should be noted that, although originally developed from plaster casts of cadaveric adult larynxes, subsequent sizes are simply scaled versions of the originals. As infant and paediatric laryngeal anatomy varies considerably, the smallest sizes may not provide as reliable an airway as adult sizes. The manufacturer’s recommendations are as shown in Table 6.1. Where the predicted size does not fit well, an alternative size may provide a better airway.

Table 6.1 Manufacturers recommendations for LMA selection and cuff inflation

The term LMA is a registered trademark of Intavent Ltd, UK.

cLMA dimensions relevant for its use as a conduit

The size of tracheal tube that can be passed through a given size of cLMA varies as tracheal tubes of the same internal diameter can have different external diameters depending on the model and manufacturer (Table 6.2).

Table 6.2 Size of tracheal tubes that can be passed through a cLMA. The tabulated results are for a lubricated Portex blue line uncuffed tracheal tube* passed without force in a cLMA. If using a cuffed tracheal tube, reduce the size of tube by 0.5 mm. The results do not apply to laryngeal masks other than the LMA Classic. Distances are to the mask grilles: intubation would require longer tracheal tubes. (*External diameter ranges from 1.3 to 2.6 mm greater than internal diameter (ID), increasing as internal diameter rises.)

cLMA SIZE	SIZE OF UNCUFFED TT PASSABLE (mm ID)	DISTANCE FROM CONNECTOR TO MASK GRILLES (mm)
1	3.5	108
1½	4.5	135
2	5.0	140
2½	6.0	170
3	6.5	200
4	6.5	205
5	7.0	230

Inserting the LMA

Because the LMA, when correctly placed,would elicit a gag reflex in the awake patient, it should only be inserted in a patient whose pharyngeal reflexes have been sufficiently depressed by general anaesthesia or adequate local anaesthesia and/or analgesia.

The LMA is correctly placed when it is advanced to lie with its tip at the top of the oesophagus (surrounded by the upper oesophageal sphincter: cricopharyngeus); providing it is facing forwards the orifice of the mask will then lie over the laryngeal inlet.

Pre-use checks

As the device is reusable and subject to wear and tear, before use it should be checked for damage, particularly cuff leaks, eccentric inflation of the cuff or failure of the self-sealing valve on the pilot balloon. The airway tube should also be checked by flexing to ensure it does not occlude when bent. Finally the lumen of the device must be checked to exclude the presence of foreign bodies introduced during the cleaning/sterilization process. Before insertion the concave part of the mask is pressed against a hard surface while deflating it, which causes the cuff to retract backwards behind the bowl. The back of the mask is lubricated with a water-based gel.

Standard insertion

General anaesthesia should be adequate to allow generous mouth opening and jaw thrust without response. Under such circumstances there should be no need to use neuromuscular blockers. The patient’s head and neck are then placed in the ‘sniffing position’. The manufacturer’s recommended insertion technique requires that the cuff is deflated as above and the LMA is grasped like a pen in the dominant hand. The tip of the operator’s gloved index finger is placed at the junction of the tube and mask whilst the non-dominant hand maintains the position of the head and neck by cradling the occiput so that the patient’s mouth falls open. The mask is inserted into the mouth and the bowl is kept pressed against the hard palate as it is advanced in one smooth movement into the hypopharynx. The upward pressure against the palate flattens the cuff of the mask to give a smooth thin leading edge. The hard and then the soft palate and finally posterior pharyngeal wall act as a scoop to guide the mask into place and prevent snagging on the tongue or epiglottis. The mask is advanced until resistance is felt. For many people the index finger is not long enough to fully insert the LMA: the hand in the mouth, guiding the LMA, should remain in place while the hand on the occiput can now be used to push the LMA stem inwards (still guided by the hand in the mouth) until resistance is felt. The LMA is not fully inserted until it reaches resistance, signifying reaching the cricopharyngeal constrictor. Without holding the tube the cuff is then inflated with air. The manufacturer indicates a maximum volume for cuff inflation which must not be exceeded; inflation to an optimal pressure is preferable (see below). Use of the maximum volumes is likely to lead to excessively high intracuff pressures that reduce the device’s efficacy and safety profile. Where inflation to a predetermined volume is used, half the manufacturer’s recommended maximum is a good starting point.

From personal observation, most users do not use the recommended insertion technique and yet find that the device seats well and provides a reliable airway. It is perhaps this feature that accounts for the success of this device.

Alternative methods of insertion

Many users simply grasp the airway near its proximal connector and slide the device down the back of the tongue, relying on the elasticity of the epiglottis to return it to its normal position and not remain down-folded over the larynx. Rotational techniques have been described in which the LMA is inserted either upside down and rotated 180^o on reaching the soft palate (akin to insertion of a Guedel airway) or inserted laterally parallel to the tongue and rotated 90^o inwards and towards the midline as the faucial pillars are reached. All alternative techniques are supported by some, but limited, clinical evidence, and may be particularly useful in children. Some techniques appear to be designed mainly to avoid insertion of the anaesthetist’s hand into the patient’s mouth.

It is reasonable to state that poor LMA insertion technique is common and that good basic technique improves anatomical placement and device function: this in turn is likely to improve device safety. Good basic technique is particularly important when the newer LMAs (flexible LMA, ProSeal LMA) and techniques such as controlled ventilation and tracheal access via the LMA are to be used.

Additional airway manoeuvres may be used to ‘create pharyngeal space’ while inserting the LMA. These include chin lift/jaw thrust (which can be applied by an assistant or by the operator by placing a thumb into the mouth and pulling on the jaw from behind the front teeth), or traction on the tongue. Any technique that requires the operator to remove their hand from the occiput risks losing the optimal head and neck position.

Confirmation of correct placement

Remarkably, for a device that is inserted blindly, the mask almost always adopts the correct position and provides a patent airway with a success rate above 95%.¹⁶

When the LMA cuff is inflated three observations assist confirmation of correct placement. First as the mask tip inflates the LMA rises 0.5–2 cm before coming to an abrupt halt, second the anterior neck is seen to slightly fill and finally the longitudinal black line running along the dorsal aspect of the tube should remain in the anatomical midline. While none of these ‘tests’ are foolproof, any failures should raise suspicion that the mask is malpositioned. In particular, rotation of the longitudinal line generally indicates rotation or misplacement of the mask portion.

In a spontaneously breathing patient, ventilation should be silent. Airway noise (which may mimic stridor or bronchospasm) suggests misplacement with partial airway obstruction. Airway obstruction may arise from poor positioning or laryngospasm (often associated with an inadequate depth of anaesthesia). The anaesthesia reservoir bag excursion should be normal. Spirometry, available on many modern anaesthetic machines, is a useful monitor and shows a typical non-obstructed loop. In an apnoeic patient, gentle squeezing of the reservoir bag should produce normal chest movements with an applied pressure no greater than 20 cm H₂O. A small leak is permissible; a large leak or a high inflation pressure usually indicates the possibility of misplacement (frequently down-folding of the epiglottis or inadequate depth of insertion of the LMA), or of breath-holding by the patient.

The seal between the pharynx and the LMA is modest, with a median of 16–20 cm H₂O and rarely exceeds 30 cm H₂O. When controlled ventilation is applied to the LMA, airway pressure should not exceed 20 cm H₂O. Increasing airway pressures lead to loss of ventilating volume (risk of hypoventilation) and an increasing likelihood of oesophageal/gastric inflation (risk of regurgitation and aspiration). For this reason, the LMA is arguably not suited to use for controlled ventilation in obese patients and for those in challenging circumstances such as lithotomy position and for laparoscopic surgery. The main reason is that there are better and safer SADs available for such uses.

Indications for using the LMA:

Instead of a facemask and pharyngeal airway, with the added benefit of:

1. releasing the anaesthetist’s hands to deal with other matters, and removing them from proximity to the operative site

2. providing a more reliable airway, particularly in patients placed in positions other than supine or where a facemask does not seal well against the face as in bearded patients.

Instead of a tracheal tube, in certain circumstances, for example:

1. elective procedures involving spontaneous or controlled ventilation, where tracheal intubation would have been used only to enable a ‘hands-free’ and gas-tight airway

2. elective procedures where intubation and the necessary drugs may elicit particularly undesirable cardiovascular or respiratory responses

3. patients in whom difficult intubation (but not difficult airway or mask ventilation) is predicted, as in those with cervical spine problems or moderately limited mouth opening, usually as a prelude to intubation via the LMA

4. as a first choice airway for use in emergencies by non-anaesthetic staff on the basis that success rate at establishing ventilation for non-specialist staff is greater with the LMA than with facemask ventilation or tracheal intubation.⁸

As an aid to extubation:

1. The LMA can be used as an aid to extubation and recovery, even after peroperative tracheal intubation. The LMA is less stimulating than a tracheal tube and less likely to elicit coughing and straining during recovery. It also protects the larynx from blood and secretions arising from the nasopharynx and oropharynx. An example of such use would be insertion of the LMA at the end of a tonsillectomy to facilitate a smooth wake-up. Placement of the LMA is much easier if the tracheal tube is at first left in place to guide insertion of the LMA. The device is advanced over the posterior aspect of the tracheal tube which ensures that the tongue and epiglottis are easily negotiated and the larynx may be held forward allowing the tip of the LMA to seat more easily behind the cricoid. The tracheal tube can then be removed.

For difficult airway management:

1. To provide a conduit to facilitate intubation. The LMA orifice lies directly over the laryngeal inlet in >90% of cases. In theory a gum elastic bougie or narrow long tracheal tube may be passed blindly through the LMA to enter the trachea; however, in practice, success rates are as low as 10–25% and such a ‘blind technique’ also risks trauma to a potentially already compromised airway. Far preferable are flexible endoscopic guided techniques, with use of an Aintree catheter being the best technique (described below).

2. To rescue the airway when intubation and/or facemask ventilation have failed. There is now considerable evidence to support the use of the LMA in these scenarios, some even suggesting that the LMA is more likely to be an effective airway in those in whom intubation has failed than it is in the general population. The device is consequently recommended in all international airway management algorithms.

During resuscitation:

1. There is considerable interest in use of SADs for maintenance of the airway during cardiopulmonary resuscitation. Several SADs are now recommended by the resuscitation councils. The largest bulk of evidence supports the use of the LMA, though several newer SADs that enable a higher pharyngeal seal may offer additional protection against regurgitation/aspiration and have potential benefits. The LMA may be used as a primary airway by those with little or no intubation skills and as a rescue device when tracheal intubation fails or is impractical because of patient entrapment. It may be easier for non-anaesthetists to achieve ventilation with a SAD than with a facemask.¹⁷

Contraindications

Accepted wisdom has it that the LMA does not protect the lungs against aspiration of refluxed or regurgitated gastric contents. In reality it offers some protection in the unconscious patient and therefore is ‘safer’ in this respect than facemask ventilation, with or without simple airway adjuncts.^13,¹⁵ However, the LMA does provide less protection than the tracheal tube. The LMA should, therefore, not be used in patients with a full stomach or risk factors for regurgitation/aspiration (delayed gastric emptying, hiatus hernia, etc.).

The LMA is also contraindicated in patients who are difficult to ventilate by virtue of size, chest disease or surgical positioning, as the mask seal is rarely above 25 cm H₂O.

The LMA is more susceptible to dislodgment than a tracheal tube and because it lies external to the larynx, laryngeal closure (e.g. laryngospasm) will lead to airway obstruction. The LMA should therefore not be used during procedures where access to the airway for repositioning is impractical. It is unwise to use the LMA for prone surgery, especially if the patient cannot be rapidly turned supine. It is widely used for ear, nose and throat surgery and intraoral procedures, such as tonsillectomy but this requires experience in lower risk situations, good communication and co-operation with the surgeon and a high level of surveillance by the anaesthetist to detect and rapidly respond to malpositions or disconnections. Devices other than the classic LMA are likely to be more appropriate: especially the flexible LMA.

LMA Flexible

The reinforced (or flexible) LMA (Intavent Direct, Maidenhead, UK) is an alternative version of the LMA in which the tube is thinner, narrower and longer and is reinforced with a spiral of steel wire to add flexibility and reduce the risk of kinking; it is available in sizes 2–5 (Fig. 6.12). Placement of the flexible LMA (fLMA) requires meticulous technique to prevent rotation leading to mask misplacement: the mask can rotate 180^o about the axis of the airway tube, leaving the mask orifice facing backwards, without this being evident proximally. In performance terms the main difference between the fLMA and the classic LMA is that, once placed, its proximal tube can be moved in any direction without those movements being transmitted to the mask end of the device and leading to displacement. This makes the fLMA very popular for head and neck and intraoral procedures and enables the tube and breathing circuit to be positioned away from the operative site. Because the mask portion of the fLMA isolates the lower airway from above it is suitable for nasal and dental procedures. It may be used without a throat pack (therefore bypassing the risk of throat pack retention) though careful attention is required of both surgeon and anaesthetist to ensure surgical debris is not in the oral cavity during emergence. The fLMA is routinely used by a minority of anaesthetists for tonsillectomy where it can reduce the risk of blood entering the trachea during recovery from anaesthesia.

Figure 6.12 LMA Flexible, (Intavent Direct, Midenhead, UK).

Because of the flexibility of the airway tube, insertion of the fLMA is more difficult. The bowl tends to rotate or the stem buckles if it is simply pushed from above as many do with the classic LMA. Alternative techniques of insertion specific to the fLMA have been described. Most involve use of a rigid or semi-rigid accessory (either placed within the fLMA tube, or attached to the outside of it) to increase the longitudinal rigidity of the device. Many, however, fail to prevent the commonest cause of misplacement of the device which is axial rotation. There is no convincing evidence that any of these techniques have benefit over standard insertion techniques and several introduce the possibility of trauma caused by the ‘stiffener’.

Single-use versions of both the classic and flexible LMA are available. While these are identical in form many are made of PVC and therefore less pliable. Minor performance differences exist between reusable and single-use devices with the reusable devices generally performing better with easier insertion and less airway trauma.

Other ‘laryngeal masks’

The term LMA is a registered trademark and applicable only to those devices manufactured by the company who originally produced the classic LMA. When the patent on many (but not all) aspects of the LMA design lapsed in 2003 several manufacturers introduced designs that are similar, though not identical (for example none had the epiglottic grill which remained under patent until 2008). Since that time there has been an explosion of such devices with more than 20 companies now distributing these products. To distinguish such a device from the LMA it should correctly be referred to as a laryngeal mask (LM). The majority of these devices will differ from the original LMA in some aspect. Mask shapes and sizes vary, as do the profiles of the airway tube (stem) and its connection to the bowl. They may be made of silicone, PVC or other plastics. Some devices have been introduced, withdrawn, redesigned and reintroduced. There has been much marketing but little evaluation of most new LMs. Design and material changes will inevitably alter function somewhat. In many cases this may not be clinically important. Whether these design changes alter the patient experience is largely unevaluated. Whether minor performance differences are important, when LMs are used for indications such as for airway rescue and for difficult airway management, is also generally unknown. What can be said is that most silicone devices have better performance characteristics than PVC ones and several designs do not perform as well as the original LMA design, with none, to date, exceeding its performance. In summary: it must not be assumed that generic and novel laryngeal masks will reproduce experience with the reusable LMA Classic or that they are fully interchangeable.

Cuff pressure monitoring

One novel design feature is an integrated cuff pressure monitor, currently unique to one manufacturer. The ‘Cuff Pilot’ (Ultimate Medical, Victoria, Australia) is a simple pressure indicating device incorporated into the inflation valve to give a constant visual representation of intracuff pressure (Fig. 6.13).

Figure 6.13 A single-use laryngeal mask incorporating Cuff Pilot cuff pressure monitoring device.

Photograph courtesy of Ultimate Medical Pty, Victoria, Australia.

One other manufacturer (Armstrong Medical, Coleraine, UK) produces a pilot balloon that simply and visibly herniates above recommended pressures (Fig. 6.14).

Figure 6.14 A single-use laryngeal mask with herniating pilot balloon to indicate an over-inflated cuff. A positioning aid is also shown which is inserted as a stiffener into the stem of the device. Armstrong Medical, Coleraine, UK.

Intubating LMA

The intubating LMA (ILMA, Intavent Direct, Maidenhead, UK) was designed specifically to enable (blind) tracheal intubation by capitalizing and improving on the LMA’s high success rate at guiding instruments within its lumen into the larynx (Fig. 6.15).^18,¹⁹ It is significantly different from the classic LMA: the bowl of the device is rigid as is the short, wide right-angled (approximately 110°) airway tube, which is constructed of stainless steel. This necessitates a novel insertion technique and a handle is provided to allow manipulation of the position of the bowl. Instead of grills across the mask orifice there is a semi-rigid flap designed to lift the epiglottis as the tracheal tube enters the bowl of the mask and prevent impaction of the tracheal tube. The device is supplied with a dedicated tracheal tube made with a soft rounded silicone ‘bullet-shaped’ tip to better negotiate the curve of the device and which is less traumatic when impacting the larynx. The ILMA tracheal tubes range in size from 6.0 to 8.0 mm ID, with all size tubes passing through all ILMAs.

Figure 6.15 The intubating laryngeal mask airway (Intavent Ltd, UK). The LMA can be used with dedicated tracheal tube and ‘pusher’.

Intubation through the ILMA involves four steps:

1. ILMA insertion

2. reattachment of the breathing circuit and manual ventilation to determine the optimal position (highest compliance, lowest resistance). ILMA position is adjusted as necessary

3. while maintaining the ILMA in the optimal position the ILMA tracheal tube is advanced into the trachea and correct placement confirmed

4. removal of the ILMA over the tracheal tube and reattachment of the tracheal tube to the breathing circuit.

After intubation it is recommended to remove the ILMA for all but the shortest procedures, as the rigid airway tube exerts high pressures on the surrounding mucosa (sore throat and hoarseness though usually mild are more frequent after use of the ILMA than the cLMA). Removal of the ILMA is achieved by using a ‘tube stabilizer’ (or the hub of a 5 ml syringe) to maintain the tracheal tube position, while the ILMA is withdrawn over it.

Although the ILMA lies over the glottis rather less frequently than other LMAs, successful blind intubation is enhanced by features that ensure the tracheal tube exits the mask at the correct angle and in the midline. With good technique first time success rate of 75% is achieved; increasing to 88–95% with two or more attempts.^20,²¹

The ILMA should not be used for those patients with contraindications to laryngeal mask use. Its use should be avoided in patients with oesophageal disease, as blind intubation attempts can result in oesophageal intubation with a risk of injury and perforation.

Particularly with the increased availability of flexible endoscopes, the exact role for the ILMA is questionable, given that it cannot be relied upon as a blind technique in the difficult intubation scenario and that for use as a conduit for a flexible endoscope the view may be better through an ordinary LMA.^22,²³ Experience with the device as an airway is limited and it cannot be recommended for routine use;²⁴ this, together with the different insertion technique compared to the classic LMA, compounds problems associated with its use.

Recently a single-use ILMA made of clear plastic and PVC has been introduced by the original manufacturers. The design mimics that of the ILMA and early studies suggest similar if not slightly poorer performance to the reusable device.

Other first-generation SADs

Even excluding single-use versions of devices there are currently more than 10 different varieties of supraglottic airway available in the UK. Several others have been withdrawn from the market but it is likely that even more are under development. This situation reflects the considerable success of the cLMA and other SADs. Not all currently available SADs have clearly demarcated applications and a full analysis of their merits and demerits is beyond the remit of this chapter. Many of the issues touched upon in the section on the LMA are equally pertinent to these other products. The most important of these devices are briefly discussed here.

Laryngeal tube

The Laryngeal Tube (LT) (VBM Medizintechnik GmbH, Salz, Germany) was first made in 1999 and consists of a slim airway tube with a small balloon cuff attached at the tip (distal cuff) and a larger asymmetric balloon cuff at the middle part of the tube (proximal cuff). Both cuffs are inflated through a single pilot tube. After insertion it lies along the length of the tongue with proximal and distal cuffs lying in the oropharynx and oesophageal inlet, respectively (Fig. 6.16). Inflation creates a seal and ventilation occurs through orifices between the cuffs. The device is made of silicone and is reusable up to 50 times. Seven sizes are available for all patient ages and sizes, with colour-coded connectors. Size selection for sizes 0–2 is based on patient weight and for sizes 2.5–5 on height. For adults a size 3 is suitable for patients below 155 cm height, size 4 for patients between 155 cm and 180 cm tall, and a size 5 in patients 181 cm or taller. Adult sizes are supplied with a reusable silicone bite-block.

Figure 6.16 The Laryngeal Tube, VBM Medizintechnik, Germany.

The LT has been modified several times with changes to the tip, balloons, pilot tubes and ventilation orifices.

The device is inserted with the head extended or in the neutral position and the cuffs deflated and lubricated. The tip is placed against the hard palate and advanced in the centre of the mouth until resistance is felt. If no resistance is felt depth indicators on the device indicate optimal and maximal insertion. The cuffs are over-inflated to a pressure of 80 cm H₂O and then deflated to 60–70 cm H₂O. Alternatively, large syringes are provided with suitable volumes for each size of LT indicated on the side of the syringe in colours corresponding to the colour codes of the LT (60–90 ml for sizes 3–5). Gentle hand ventilation is used to confirm a functional position. If ventilation is not ideal the LT may be advanced or withdrawn slightly until ventilation is optimum.

The LT is designed for use during spontaneous breathing, controlled ventilation and for airway rescue.

At the end of anaesthesia the LT is left in place until the patient regains consciousness. The balloons are deflated as the device is removed.

The literature on the LT is somewhat confused by the multiplicity of versions that have been evaluated.²⁵ The slim profile of the LT allows easy insertion with little mouth opening and with the redesigned softer distal tip the device causes minimal airway trauma. Initial evaluations, with the original device, reported variable success rates: in particular spontaneous ventilation success was poor. More recent studies suggest high success rates for insertion (above 95%) and good airway seal pressure (approx. 26 cm H₂O).⁹ It has a steep learning curve and may be suitable for use by non-anaesthetists and out of hospital.

The main limitation of the LT is that its tube-like shape provides little protection against axial rotation and this, combined with small ventilation orifices, tends to lead to a significant incidence of partial or complete airway obstruction. Compared to LMAs the LT is more likely to lead to airway obstruction, and less likely to lie over the larynx.²⁶

Whether the lower cuff protects against aspiration of regurgitated stomach contents has not been determined, but a cadaver study of oesophageal seal demonstrated a high pressure seal, in the range 70–80 cm H₂O.

The poor view of the larynx, the narrow internal lumen and small airway orifices all make the LT rather poorly suited for tracheal access and exchange techniques compared to available alternatives.

A single-use version of the LT (LT-D) in PVC as opposed to silicone is available but has not been extensively evaluated.

CobraPLA

The Cobra Perilaryngeal airway (CobraPLA) (Engineered Medical Systems, Indianapolis, USA) is a relatively new single-use SAD (Fig. 6.17). The distal end (whose shape lends the name to the device) consists of a soft plastic head designed to seat in and seal the hypopharynx, with the anterior surface lying at the laryngeal inlet. The anterior surface of the head consists of a grille of bars soft enough to allow instrumentation of the larynx, but their presence prevents epiglottic obstruction of the device orifice. A proximal inflatable balloon is designed to elevate the tongue base and seal the oropharynx.

Figure 6.17 CobraPLA (Engineered Medical Systems, Indianapolis, USA).

The CobraPLA is supplied in eight sizes designed for use in patients ranging from neonate (size 1) to >140 kg (size 6). The internal diameter of the CobraPLA airway is larger than the corresponding cLMA: for the largest CobraPLA this is 12.5 mm.

Prior to insertion the cuff is deflated along the posterior aspect of the airway tube. The device is inserted until resistance is met as the distal tip reaches cricopharyngeus and it may then be withdrawn 0.5–1 cm. The proximal cuff is inflated until an airtight seal is obtained. The device is removed on return of consciousness with the cuff deflated.

The CobraPLA is designed for spontaneous and controlled ventilation and was modified in 2006. There is limited published experience and none with the largest and smallest sizes. Available evidence indicates 80% first attempt insertion success, airway seal of approximately 25 cm H₂O and minor morbidity of similar frequency LMAs.^27,²⁸ A significant number of cases may require airway manipulation (pull/push) to maintain the airway.

As the CobraPLA is designed to be inserted to full depth and then withdrawn 0.5–1 cm, the tip likely does not obturate the oesophagus, which may be of significance in positive pressure ventilation: raised pharyngeal pressure being fully transmitted against the upper oesophageal sphincter. The pharyngeal cuff may prevent egress of regurgitant matter from the oropharynx, and hence increase the risk of aspiration.^29,³⁰ With the exception of a modest increase in airway seal, there do not appear to be any benefits for use over the cLMA.

Second-generation SADs

Second-generation SADs have been designed to be safer for patients by use of additional features to minimize the risk of regurgitation and or aspiration.

LMA ProSeal

The LMA Pro-Seal (Intavent Direct, Maidenhead, UK) (PLMA), which was introduced in 2000, is an important addition to the family of LMAs.³¹ It was designed with three refinements in mind: (1) improved performance during controlled ventilation, (2) improved safety regarding aspiration, and (3) an ability to diagnose misplacement of the device tip.

The PLMA has a softer, larger and deeper mask bowl than the cLMA (Fig. 6.18). The mask cuff extends over the posterior aspect of the bowl pushing it forward when inflated. A drainage tube passes from the tip of the mask, through the bowl, to run parallel to the airway tube. Proximally these are joined by an integral bite block. The changes to mask shape, size and the posterior cuff increase the median airway seal by >80% to above 30 cm H₂O.³² A full range of sizes is available with paediatric ones lacking the posterior mask cuff.³³

Figure 6.18 The LMA Pro-Seal with introducer attached.

The PLMA may be inserted digitally (like the cLMA), or by attaching a metal introducer (Fig. 6.14) or by railroading the whole device via its drain tube over a bougie placed in the oesophagus.³⁴ The latter technique is the most successful and least likely to lead to misplacement.³⁵ It is the technique of choice when first-time insertion success is critical, such as when managing a difficult airway. A gastric tube can be passed through the drain tube when indicated: this should be well lubricated and not refrigerated. The drainage tube allows such reliable insertion of an orogastric tube that inability to do so indicates the PLMA is misplaced with the posterior of the mask folded backwards. Although maximum volumes for cuff inflation are published by the manufacturers, inflation to an intracuff pressure of 60–70 cm H₂O is preferable.

A series of post-insertion tests are designed to confirm correct device positioning.³² First a small amount of gel occluding the proximal drain tube should not be displaced when a pressure of 20 cm H₂O is applied to the airway; this tests separation of the gastrointestinal and respiratory tracts and fails when the PLMA is not pushed in far enough, allowing gas to pass directly from the airway tube up the drain tube. Second, no more than one-third of the bite block should be visible as this also suggests incomplete insertion. Third, pressing on the chest should not displace the drain tube gel; if it does it suggests the drain tube tip has entered the glottis, though airway obstruction is likely to coexist. Finally, pressure at the suprasternal notch should lead to the drain tube gel bulging outwards; this tests that the drain tube is not folded over as suprasternal notch pressure is transmitted to the oesophagus and then to the drain tube, unless the tip is folded over. If doubt exists, attempting to pass a gastric tube (approximately 30 cm in adults) to the tip of the drain tube, or beyond will identify whether it is folded over. In practice these several tests can be carried out in a matter of seconds to confirm correct positioning and function of the PLMA with further attention only necessary if a test is not ‘passed’.

Compared to other LMAs and LMs the PLMA creates a higher seal with pharynx and oesophagus. It enables more reliable controlled ventilation and increases the patients and indications where a supraglottic airway is appropriate. The PLMA also exerts less pressure against the mucosa than either cLMA or ILMA, so reducing the potential for mucosal trauma and damage. These advantages must be balanced against slightly greater difficulty in insertion of the PLMA. When combining a large number of studies, first-time insertion success with the PLMA is 85% and with the cLMA is 93%.^32,³⁶ In contrast a bougie-guided technique is almost 100% successful. The PLMA has potential roles in difficult airway management and is perhaps the logical choice for rescuing the airway after failed rapid sequence induction.^35,³⁷

There is good theoretical and performance evidence to support the view that compared to the cLMA the PLMA does reduce gastric inflation and increases protection from regurgitated gastric contents. However, this is entirely dependent on correct positioning of the device. The PLMA lies with the drain tube in continuity with the oesophagus and the airway tube in continuity with the trachea. As the pharyngeal and oesophageal seals are both increased this creates functional separation of the gastrointestinal and respiratory tracts. The drain tube vents gas leaking from the mask towards the oesophagus and prevents gastric distension. It also vents regurgitated stomach contents. Design and performance features of the PLMA make it likely that its use reduces the risk of gastric inflation and protects from aspiration if regurgitation occurs. Extensive evidence from bench work, cadaver and clinical studies strongly support this claim, but it is unproven and probably unprovable in clinical use. Cadaver studies show an oesophageal seal of 70–80 cm H₂O and efficacy of the drain tube in venting regurgitated fluid.¹⁴ There are several case reports of regurgitated matter being vented by the drain tube.

There are several studies comparing PLMA performance with other SADs. In all of these to date the PLMA performs as well as or better than alternative devices. Infrequent complications associated with the PLMA include oesophageal breathing, gastric insufflation and airway obstruction.³²

In summary, the PLMA undoubtedly has improved performance characteristics over standard laryngeal masks with these being most marked when controlled ventilation is used. Whether it is safer than standard LMs and the classic LMA is impossible to prove in absolute terms but the evidence supports that view. Considering all the available evidence, the PLMA lessens the risk of aspiration compared to the classic LMA, and there is an argument for its routine use. However, the PLMA must not be used electively for cases of significant aspiration risk. Indications include ‘extended roles’ such as obese patients, laparoscopic surgery and selected open abdominal surgery. Use in such cases mandates good understanding of the device and its limitations, experience in lower risk cases and excellent technique. The limit of applications for the PLMA is not known but like any SAD the benefits and risks of its use, compared to a tracheal tube, should always be carefully considered before selection.

LMA Supreme

The LMA Supreme (Intavent Direct, Maidenhead, UK), the newest of the LMAs introduced in 2009, is a single-use SAD (Fig. 6.19) made of PVC and designed to combine the most useful elements of the PLMA (improved seal, drain tube, integral bite block) with the ease of insertion of the ILMA in a single-use device. The manufacturer’s indications for use are the same as the PLMA. Despite this, it is not simply a ‘a single-use’ version of the PLMA as there are several important differences: the stem and mask are more rigid as is the bite block; the drain tube runs within the airway and divides it into two narrow channels and the bowl of the mask includes patented ‘fins’ that are designed to prevent airway occlusion by the epiglottis.

Figure 6.19 The single-use LMA Supreme (Intavent Direct, Maidenhead, UK).

The SLMA is inserted with the patient in the ‘semi-sniffing position’ and is otherwise the same as ILMA insertion. After insertion, correct depth of insertion (and sizing) is indicated by a tab on the upper surface of the device, which should lie 0.5–2.0 cm from the upper lip. If it abuts the lip a larger size should be chosen. The tab is also designed for fixation of the device using adhesive tape.

Due to its newness the SLMA has been less completely clinically evaluated than other LMAs.³⁸ It is very easily and reliably inserted, even by novices.¹⁷ Once inserted ventilation is reliable and the pharyngeal seal (approximately 24–28 cm H₂O) is higher than the cLMA but lower than the PLMA. The airway sits over the larynx as frequently as the cLMA or PLMA. An orogastric tube can usually be passed via the drain tube. In a direct comparison between the SLMA and i-gel (see later), performance of the two devices during simulated airway rescue was equivalent.³⁹ While efficacy in low-risk patients is therefore largely established, its further performance is not. The effectiveness of the drain tube is yet to be reported. Further evaluation is awaited before it can be recommended for the same extensive a range of indications as the PLMA but early impressions suggest the SLMA will have indications both in and out of hospitals for a wide range of indications.

i-gel

The i-gel (Intersurgical, Wokingham, UK) is a novel single-use, cuffless SAD made of a medical-grade elastomer gel (styrene ethylene butadiene styrene). Its shape partially resembles the inflated PLMA. It has a short wide-bore airway tube with no grilles, an elliptical shaped stem, an ‘anatomically’ shaped bowl, an integral bite block and a drain tube (Fig. 6.20). These features provide low resistance to gas flow, stability, improved pharyngeal seal, the potential for good access to the airway as a conduit, and possibly decreased risks of airway occlusion or aspiration.

Figure 6.20 i-gel disposable supraglottic airway (Intersurgical, Wokingham, UK).

The i-gel is inserted in the sniffing position and after lubrication of the back, front and sides of the device. Standard insertion mimics cLMA insertion with the passage of the i-gel following the roof of the mouth and posterior pharynx until stopped by cricopharyngeus muscles. A rotational insertion technique is also described.

The i-gel is very easily inserted, by experienced and novice users, due to both low frictional properties and the lack of a cuff needing inflation.^40,⁴¹ The pharyngeal seal is 24–28 cm H₂O in most cases, but in a minority is considerably lower and ventilation is not possible. An alternative size should be tried before abandoning the device. Several authors describe that the elastomer’s ‘thermoplastic’ properties leading to an improving seal over time as the device warms, but this is an inconsistent finding and it is also seen with cuffed devices. It is just as likely due to a combination of adaption of the pharynx to the shape of the device within it, and better relaxation with deeper anaesthesia.

The i-gel offers the potential for improved ease of use, improved ventilation and increased safety compared to the cLMA, in a disposable SAD. Its design and performance characteristics make it an alternative to the cLMA. Cases of airway rescue and use of the i-gel to facilitate fibreoptic-guided intubation are reported.

Although the drain tube is smaller gastric access is as reliable as for the PLMA, but the i-gel has lower pharyngeal (ventilation) and oesophageal (protection from regurgitation) seal pressures than the PLMA.^14,³⁸ Whether this has any clinical importance in practice is not yet clear. The same studies report the drain tube is effective in venting regurgitant fluid, unless it is blocked.^14,⁴² The i-gel was intentionally designed with a truncated tip to reduce compression of the oesophageal sphincter and so reduce dysphagia, which may account for the reduced oesophageal seal. On the available evidence it would seem prudent to remove any orogastric tube after use as the i-gel oesophageal seal may not protect the airway if the drain were to become blocked. Cases of protection from aspiration with the i-gel are reported, as is one case of partial aspiration.⁴³

Complications reported with the i-gel are few. Laryngopharyngeal trauma and pain after use appear infrequent indeed. Transient nerve injuries and lingual congestion have been reported rarely.

Combitube

The Combitube (Covidien, Ireland) originally marketed as the Oesophageal Tracheal Combitube (Fig. 6.21) is a development of the oesophageal obturator airway. It is a single-use device and is conceptually different from other SADs in that it is designed to provide an airway after blind placement in either the trachea or the oesophagus. It has two cuffs (like the Laryngeal Tube) and two tubes. The lumen of one tube opens beyond the distal cuff, whilst the other ends between the two cuffs and has only side openings. There were originally two sizes, 37 Fr and 41 Fr, for small and larger adults. A smaller size 26 Fr was recently introduced along with other modifications aimed at reducing the incidence of trauma.

Figure 6.21 The Oesophageal Tracheal Combitude, Kendall, USA.

With the head and neck flexed or in the neutral position it is inserted blindly into the mouth and advanced until the teeth reach between the depth marks. First the proximal high-volume pharyngeal cuff is inflated with 90–100 ml of air to fix the device in place then the lower cuff is inflated with about 15 ml. When inserted blindly, the Combitube almost invariably enters the oesophagus. The proximally longer tube, marked ‘1’, has the lumen ending between the cuffs and ventilation is first attempted through this lumen. If this fails then the second lumen is tried. If oesophageal insertion is confirmed, tube ‘2’ can be used to insert a gastric drain with the smaller balloon acting as an oesophageal obturator. An oesophageal detector device, such as Wee’s device, can be used to confirm the position of the tube tip before ventilation, thereby preventing inflation of the stomach in those cases where the device enters the trachea. Where ventilation with the Combitube fails, this may be due to obstruction of the larynx by the oropharyngeal balloon; the device should be withdrawn by 1–2 cm and ventilation attempted again.²⁵ The incidence of trauma with the Combitube is higher than other SADs and oesophageal rupture must be considered an inherent risk;^44,⁴⁵ the mechanism may involve raised oesophageal intraluminal pressure as a result of obturation, as well as direct injury by the device.

If tracheal intubation is attempted at any time after insertion, the proximal Combitube cuff is deflated, the tube pushed to the left-hand side of the mouth and conventional laryngoscopy performed. The oesophageal seal provided by the distal cuff should prevent soiling of the pharynx by gastric contents during the procedure.

Due to its cost, trauma associated with insertion and the potential confusion of the dual tubes, the Combitube has been superseded by other SADs and has no role in routine elective anaesthesia. It is targeted primarily now at emergency airway management and non-anaesthetic use. The Combitube may have a role in out-of-hospital airway rescue in those trained in its use. It is part of the ASA difficult airway management algorithm and ILCOR recommendations for airway control during cardiopulmonary resuscitation.⁴⁶

The Rusch Easytube (Teleflex Medical GmbH, Kernen, Germany) is a very similar, but more recently introduced device. Minor modifications, including a less bulky distal tube, suggest levels of trauma associated with its use may be reduced, but there is, to date, limited information.

The Laryngeal Tube Suction mark II

In 2002 the Laryngeal Tube – Suction (LTS) (VBM Medizintechnik, Salz, Germany) was introduced as a modification of the Laryngeal Tube, with a drain tube lying posterior to the airway tube to enable gastric tube placement and prevent gastric inflation during ventilation. While the design aimed to increase device safety (compare cLMA and PLMA) the new device was much more bulky, harder to introduce, and potentially traumatic: thereby losing two of the LT’s principal advantages.⁴⁷ In 2005 the mark II LTS (LTS II) was introduced with a slim profile tip and an asymmetric oesophageal balloon. Size selection, insertion technique and reusability for the LTS-II are identical to the LT.

The LTS-II offers the potential for expansion of the role of the LT. It is easier to insert than the LTS and its pharyngeal seal is similar to the PLMA. Evidence of ease of insertion and incidence of airway obstruction remains inconsistent, but is generally improved.⁴⁸

Like the LT, in cadavers, the LTS-II seals well with the oesophagus to a pressure of 70–80 cm H₂O and the drain tube effectively vents regurgitant fluid.¹⁵

Considerably more evidence is needed before the LTS-II role is fully established.

A single-use version of the LTS-II exists (confusingly) called the LTS-D.

SLIPA

The Streamlined Liner of the Pharynx Airway (SLIPA) (SLIPA Medical, Isle of Man, UK) is an inexpensive single-use SAD of novel design, a blow-moulded airway made of a polyethylene based composite with the shape mimicking a ‘pressurized pharynx’ (Fig. 6.22). It was first launched around 2003, although issues with choice of manufacturer and distributor continue to affect availability in the UK and independent evaluations of the device are so far scarce. The SLIPA slightly resembles a boot. It has no cuff, is hollow and is designed to sit with the toe of the boot in the hypopharynx. Lateral prominences in the mid-portion of the airway are designed to locate in the pyriform fossae and the mask displaces the tongue base anteriorly, with the intention of producing a stable device with an improved airway seal.

Figure 6.22 SLIPA (SLIPA Medical, Isle of Man, UK) disposable supraglottic airway device in a range of adult sizes.

The SLIPA is included in the second-generation SADs on the basis of design only. The inventor reports that the interior of the SLIPA provides a protective reservoir able to accommodate 50–70 ml of fluid (compared to a 5 ml capacity of the cLMA).⁴⁹ There are no clinical data to support the clinical relevance of this claim.

There are six adult sizes (47, 49, 51, 53, 55 and 57) and while size selection is based on height, the aim is to match the maximum diameter of the SLIPA with the maximum diameter of the larynx (measured as the maximum width of the thyroid cartilage in millimetres).

Insertion of the SLIPA is aided by extension of the head and neck and may be improved by lifting the mandible or by use of a laryngoscope or finger placed in the pharynx to increase pharyngeal space. Repeated attempts may be associated with increased minor airway trauma.

Early cohort and comparative trials by the inventor showed satisfactory insertion performance.⁵⁰ A few small independent trials have been performed which are supportive of its use showing adequate insertion success and pharyngeal seal pressures similar to the LMA.^51,⁵² Trauma and bleeding are potential concerns.

There are no data available about oesophageal seal and no clinical trials addressing airway protection.

Sads summary

The topic of SADs is complex with too many devices and variants of each. The LMA Classic is a highly reliable and safe device and remains the SAD against which all others should be benchmarked.⁵³ For many newer SADs there is too little research to perform benchmarking and where appropriate evaluations have been performed several first-generation SADs (airway tubes) appear to offer little, if any, benefit over the classic LMA.

In contrast the second-generation SADs do offer potential benefits, as they are all designed to increase safety over and above that offered by the SAD. Most have a higher pharyngeal seal than the classic LMA. Most also have drain tubes whose efficacy has been demonstrated. Several have increased oesophageal seal compared to the classic LMA, which raises the possibility, but not certainty, of increased safety.

Tracheal tubes

It is often stated that ‘the gold standard’ for securing the airway is tracheal intubation. Improvements in SAD design and technology and increased recognition of the complications of laryngoscopy and tracheal intubation have given pause for thought on the veracity of this statement. However, it remains true that a tracheal tube, once placed, offers both reliability and protection that few, if any, SADs can currently provide.

A cuffed tracheal tube, once placed, provides the greatest likelihood of protection for the lungs from inhalation of foreign material, the tube is the least likely device to be dislodged, glottic reflexes are bypassed and for intra-oral and head and neck surgery, only a tracheostomy can potentially give better surgical access (see section above entitled ‘Indications for using the LMA’, for comparison).

History

Tracheal intubation in the form of tracheostomy pre-dates anaesthesia by a number of centuries.⁵⁴ As early as 1542, Vesalius⁵⁵ recorded intermittently blowing into a reed that was passed into the aspera arteria of an animal whose thorax had been opened. He found that this caused the lungs to expand, and the heart to recover its normal pulsations. In 1667, Robert Hooke, at the Royal Society in London, similarly kept a dog alive for over an hour by ventilating its lungs with a pair of bellows tied into the trachea which had been severed below the epiglottis. Thereafter artificial respiration by intubation of the trachea became fairly common by the end of the eighteenth century, for treatment of asphyxia and drowning.

A number of milestones are notable. In 1871, Friedrich Trendelenburg ⁵⁶ developed a cuffed catheter for insertion through a tracheostomy to prevent soiling of the lungs during operations on the upper airway. This tube with its inflatable rubber cuff would look familiar to any modern day anaesthetist and was widely used for the next 30 years.⁵⁷ In 1878, the Glasgow surgeon William MacEwen⁵⁸ placed a metal tube by manual palpation through the mouth into the trachea of a 55-year-old plasterer and, following the administration of chloroform, packed off the laryngeal opening to successfully resect a tumour at the base of the patient’s tongue. ‘Endotracheal anaesthesia’ was born. Eisenmenger’s tube of 1893 was a wide-bore semi-rigid orotracheal tube carrying an inflatable cuff and a pilot balloon to reflect pressure in the cuff.

The development of tubes and anaesthetic techniques has not been a linear progression, some concepts being ‘rediscovered’ more than once. In spite of Dorrance’s description of the cuffed rubber orotracheal tube in 1910 – Guedel and Waters in 1928 described a similar tube for use with a carbon dioxide absorption technique – it was not until after the polio epidemic of the 1950s that the use of cuffed tracheal tubes became standard anaesthetic practice.

I.W. Magill and E.S. Rowbotham, anaesthetists to the British Army Plastic Unit in Sidcup during and after the Great War of 1914–1918, found that they could provide a superior unimpeded surgical field for the head and neck surgery of Sir Harold Gillies by having the patient breathing to and fro through an uncuffed rubber tube passed blindly through the nose into the trachea. Prior to this, ‘insufflation anaesthesia’ (as opposed to ‘inhalation anaesthesia’), whereby chloroform or ether laden air was pumped into the trachea as advocated by Meltzer and Auer in New York,⁵⁹ had achieved rapid and widespread acceptance, partly owing to the different needs of thoracic surgery. This technique, when used for head and neck surgery, had necessitated a second tube being inserted for egress of gasses in order that the pharynx might be packed to prevent soiling of the trachea. It was this second wide-bore rubber tube (that Ivan Magill and Stanley Rowbotham quite by chance found they could ‘blindly’ insert into the larynx) which subsequently became the singular airway for ‘to and fro’ respiration and spawned the dominant technique in the UK for many years.

Of note, throughout this time the technique of laryngoscopy was still in its infancy. In 1941, Gillespie, writing in Endotracheal Anaesthesia,⁵⁴ stated: ‘An experienced worker should be able to intubate all but the most difficult cases in ten minutes. The beginner will often require thirty. ’

Design

An orotracheal tube (Fig. 6.23) usually has a preformed curve that approximately matches the anatomical curve of the airway. This aids insertion and ensures that when the tube is further flexed in situ, it is unlikely to kink. The distal end is cut obliquely (bevelled) so that when held in the right hand the aperture faces to the left. The bevel facilitates insertion and allows the tip of the tube to be seen passing between the vocal cords. There may be a hole (a Murphy eye) in the wall opposite the bevel. This is designed to provide a secondary port for gas movement in and out of the tube should the bevel become blocked or wedged against the tracheal wall (Fig. 6.24). Cuffed tubes, by definition, have an inflatable cuff a short distance proximal to the tube tip, which, when inflated, seals the space between the tube and the tracheal wall.

Figure 6.23 An uncut orotracheal tube. A. Bevel; B. Murphy eye; C. tracheal cuff; D. self-sealing valve which keeps gas in the cuff; E. marking to show the internal diameter of the tube in millimetres; F. marking (I.T.Z 79) to show that the plastic has been tested for tissue toxicity; G. the length of the tube in millimetres; H. longitudinal line of radio-opaque material; J. 15 mm connector.

Figure 6.24 If there is marked deviation of the trachea, the distal orifice may become obstructed, a second orifice or ‘Murphy eye’ is then valuable.

Modern tracheal tubes carry several markings, one of which is a longitudinal line of radio-opaque material so that the correct placement can be verified from an X-ray if required. A transverse black mark on some tubes, made several centimetres proximal to the cuff, is designed to indicate the distance that the tube should be placed beyond the vocal cords; the mark should remain just visible above the larynx, indicating that the tube has not been inserted too far. The distance from the tip of the bevel is also marked in centimetres on the tube wall, along with the internal diameter (ID). Markings describing Implant Testing and CE markings are discussed below.

Construction materials

Although traditional red rubber tracheal tubes are now largely consigned to history, much of the design and conventions of modern tracheal tubes derives from their attributes, they therefore continue to be included here.

Tracheal tubes were previously made of red rubber or natural latex, which can be cleaned and sterilized for reuse. The material generally provides a combination of adequate rigidity and minimal mechanical tissue trauma, but it also has several disadvantages. As it is opaque, inadequate cleaning and foreign bodies within the lumen of the tube might be overlooked. Repeated sterilization causes degradation, with the potential for weakening leading to kinking or rupture. The materials themselves are potentially allergenic and irritant when used for long periods, being implicated in the development of laryngeal granulomata.

Currently, plastics (polyvinyl chloride (PVC) and more recently polyurethane) and to a lesser extent, silicone rubber, have replaced red rubber and natural latex as primary materials for the following reasons:

• They are non-irritant and are now inexpensive enough to allow single-patient use and hence sterilization at manufacture.

• As the material is usually clear, foreign bodies and blockages may be seen more easily.

• Manufacturing tolerances are much better with plastics, so that there is much less variation in the size of the lumen (most important in neonatal tracheal tubes).

• Cuffs of rubber tubes are usually thick and require high intracuff pressures to inflate them; inadvertent over-distension of the cuff may result in this pressure being transmitted to the tracheal mucosa with a risk of mucosal ischaemia or necrosis during prolonged use.

In contrast, plastic tubes do not have the elasticity (springiness) of rubber and may be less easy to insert in difficult situations. Their relative rigidity at room temperature, compared with rubber tubes, tends to increase trauma particularly when they are inserted via the nasal route. Strategies to minimize trauma include use of the smallest tube necessary, warming the tube in warm water before use or selection of a tube made of a softer compound (e.g. the Portex Ivory range).

The softness of plastic tubes is dependant on several factors. Polyurethane compounds tend to be softer and more springy than PVC, but are more expensive to manufacture. Chemicals called plasticizers may be added to PVC during manufacture to produce a softer product. The most widely used plasticizers are a group of chemicals called phthalates (particularly dioctyl phthalate in medical products). In recent years concern has been raised at governmental levels in both Europe and America about the effects of phthalates which may leech out of the plastic and some consider to be potentially “carcinogenic, mutagenic and reprotoxic”.² While the level of risk posed by these additives is likely to be very low, several organizations seek their complete removal from manufacturing processes. More expensive plasticizers without such risk are available and in some countries are increasingly used. Silicone rubber (polymethylsiloxane) is an entirely synthetic material containing no latex derivatives, it is both soft and has the advantage that it will withstand autoclaving and therefore can be reused. It is, however, significantly more expensive and is not generally used for disposable airway products. Siliconized plastic refers to a PVC material incorporating a very small amount of silicone oil to form a surface monolayer, with the aim of altering the surface characteristics of the product, for example, to decrease surface adhesion. These tubes tend to be pearlescent or opaque. Siliconized plastic has been used in several single-use LMs to improve performance characteristics.

The type of plastic used in the construction of tracheal tubes is tested to make sure that it is non-irritant. Tubes were at one stage marked with a test number (Z79-IT), which denoted Implant Testing according to the Z79 Toxicity Subcommittee of the American National Standards Institute set up in 1968 in the USA, which established the test method (Fig. 6.23). The test consisted of implanting four samples of the plastic, under sterile conditions, into the paravertebral muscle of anaesthetized rabbits along with two samples of Reference Standard Negative Control plastic for 70–144 h. The implant sites were then examined for signs of inflammation. CE marking now denotes compliance with the essential requirements of the Medical Devices Directive (see Chapter 28).

Size

Adults

Previously, conventional wisdom dictated that the widest diameter tracheal tube, that would pass easily through the narrowest part of the airway, was the correct size. This was in order to reduce the resistance to gas flow and so minimize the extra work of breathing associated with the tracheal tube. In adults, the narrowest part of the airway is at the glottis; the rima glottidis is more ovoid in shape and to achieve a seal, a subglottic cuff is needed. Again conventionally, the tube should be as short as possible so as to further reduce the work of breathing and to prevent the tube from entering a main bronchus (usually the right) and ventilating only one lung. In adults, selection of the largest tube was also a consequence of early cuff design in seeking to avoid excess distension of the cuffs. More recent approaches, however, particularly in adult anaesthetic practice, consider a number of other factors and as a result there is a trend towards use of much smaller diameter tubes:

• When controlled ventilation is used the ventilator, rather than the patient, does the work of breathing. The diameter of the tube does not determine airway pressures distal to it unless the tube is so narrow as not to allow sufficient time for passive exhalation. Tube sizes of 6.5 and 6.0 mm ID do not cause a rise in end-expiratory pressures when used for ventilating adult males and females.^60,⁶¹

• Small tubes are easier to insert and reduce the trauma of intubation.

• The larger the tube, the greater the area of contact between it and the vocal cords and the greater the likelihood of injury. Hoarseness and the incidence of sore throat is increased dramatically with tubes of greater than 7.0 mm ID.⁶² Abnormalities on CT scans of the larynx are visible at 6 months in a high proportion of patients after even short periods of intubation.⁶³ Patients extubated following the use of small soft tubes are immediately able to phonate.

• Even in spontaneously breathing patients, the use of now mandatory continuous capnography, by virtue of being able to demonstrate failing ventilation, allows greater latitude in the selection of tube size. The work of breathing through 6.0 mm ID tubes is not greatly increased ⁶⁴ and ventilation is only marginally reduced with no change in functional residual capacity.⁶⁵

• In the event of difficult laryngoscopy a small tube has further advantages. Smaller tubes fit more closely on a bougie or introducer with reduced likelihood of impaction of the bevel on the structures of the rima glottidis, resulting in less trauma and easier passage of the tube.

Although shorter tracheal tubes are less likely to migrate into a main bronchus, this must be tempered by the knowledge that a tube placed with great difficulty may turn out to be too short or that as the patient’s condition changes (e.g. in burns patients following the development of massive oedema) the tube may become too short.

Three decades ago use of tracheal tubes of internal diameter of 10 mm and even 12 mm was not unheard of. Although such large sizes are rightly now only of historical (or veterinary) interest it is likely that the majority of anaesthetists are still using tracheal tubes larger than is necessary. The move towards smaller tubes is somewhat limited, particularly where fixed length or preformed tracheal tubes (e.g. armoured tubes, RAE tube or Polar tubes (see below)) are used. This is due to the fact that these tubes continue to be designed according to the ‘largest size’ maxim and as a result when smaller diameter tubes are chosen the tube may be too short and the cuff too small.

Table 6.3 gives the classical view of tubes and lengths.

Table 6.3 The classical view of the relative dimensions of tracheal tubes

Children

In pre-pubescent children, the narrowest part of the airway is the cricoid ring. As this is nearly circular it may form a partial seal with the tracheal tube. A small degree of oedema in the paediatric airway will reduce the lumen of the trachea considerably (1 mm of circumferential swelling reduces the diameter of the adult airway by less than 10% and that of an infant by as much as 30%) and may lead to respiratory compromise. Because of these considerations paediatric tracheal tubes have traditionally been uncuffed and use of a tube small enough to leave an audible leak is still standard. Use of uncuffed tubes leads to an unpredictable leak so children have routinely been ventilated with pressure-control ventilation (ensuring ventilation despite a variable leak), while volume-controlled ventilation has been favoured in adults (delivering an assured minute volume despite changes in lung compliance).

While use of uncuffed trachea tubes in paediatrics remains the norm, technology and changing circumstance has led to an increase in the use of cuffed tubes (see below).

Tracheal tube cuffs

High-pressure cuffs

In the era of red rubber tracheal tubes the requirement to sterilize the tubes by autoclaving for reuse necessitated construction that was strong and resilient. As a result tracheal tube cuffs were made of a relatively low compliance thick rubber. Repeated cleaning and reuse could lead to either hardening of the cuff making it ever more rigid or, occasionally, the development of weaknesses which if overinflated could ‘herniate’ over the tip of the tube and occlude it (Fig. 6.25). These cuffs required a high pressure to distend them and were relatively low volume (high-pressure low-volume cuffs). Thick-walled cuffs also tend to inflate in a circular shape rather than conforming to the shape of the (non-circular) trachea within which they lie. In order to achieve enough contact with the tracheal wall and a good seal relative over-inflation was required, with the result that the high pressure within the cuff was transmitted to the tracheal wall. This readily led to a reduction of mucosal pressure to critical levels (capillary perfusion pressure is usually about 35 mmHg) and if prolonged could lead to mucosal ischaemia which in turn in a proportion of patients caused the development of tracheal scarring and tracheal stenosis.

Figure 6.25 Herniated cuff.

Medium-pressure cuffs

These are made from a much thinner elastic material such as latex rubber which fits snugly to the tube in its deflated state without appearing too bulky. The Intubating LMA tracheal tube is an example. An intermediate amount of pressure is required for inflation, but because of the lower intra-cuff pressure and the material’s greater deformability it adapts better to the shape of the tube it lies within (the trachea) and seals without interfering with tracheal mucosal perfusion. Due to the greater compliance of the cuff material, over-inflation is also less likely to lead to dramatic pressure rises and subsequent harm.

Low-pressure or high-volume cuffs

These are made from a thin inelastic material (PVC) which when fully inflated would have a larger volume than that required to effect a seal (Fig 6.26). In situ there is a large area of contact between the cuff and tracheal wall before full inflation of the cuff. The pressure within the cuff can therefore be kept much lower and can achieve a seal with minimal risk of occluding mucosal blood flow. Both medium- and low-pressure cuffs are made of very thin materials which may be ruptured by over-distension or more often damaged by snagging on teeth, instruments or passage through the nose. Low-pressure designs now predominate. This is particularly so in tubes such as tracheostomy tubes used for long-term ventilation on intensive care units.

Figure 6.26 High- and low-pressure tracheal cuffs. Medium-pressure cuffs have a profile between these extremes.

One drawback of the low pressure cuff is that because the cuff material is not fully unfolded when a seal is achieved, a number of small folds (micro-folds) can create small channels (micro-channels) running the length of the cuff. These channels may contribute to the causation of ventilator-associated pneumonia (VAP) by allowing transmission of potentially infective pharyngeal contents past the cuff. It is readily demonstrated in vitro (Fig 6.27) that these micro-folds are not waterproof and despite the mantra of the tracheal tube ‘protecting’ the airway it must be acknowledged that this protection is incomplete. There is increasing interest in the role of micro-aspiration in VAP amongst patients on intensive care.

Figure 6.27 Large-volume cuff inflated in a model trachea shows formation of numerous folds and channels. After Latto 1997.⁶⁶

Polyurethane cuffs may be made that are even thinner than PVC cuffs and recently this has contributed to renewed interest in the use of cuffed tracheal tubes for children. The technology now exists to make cuffs thin enough to not interfere with the insertion of neonatal size tracheal tubes, yet strong enough for routine use. While such use is relatively uncommon it has its proponents, citing both increased reliability of ventilation, and increased protection of the lower respiratory tract, together with the facility for using smaller tubes which exert their seal pressure below the narrowest part of the paediatric airway.

Tracheal tube (and SAD) cuffs are inflated via a small-bore inflation tube (pilot tube) either welded onto the outside of the tracheal tube or more commonly now integrated into its wall. The inflation tube is connected, at its proximal end to a small ‘pilot balloon’ to give an indication of the distension of the cuff. Accessing the pilot balloon by a one-way valve allows inflation of the device’s cuff.

All cuff types should only be inflated to the pressure necessary to achieve sufficient seal to prevent gas leak at the airway pressures generated by positive pressure ventilation. This has the added advantage that it permits leakage (often audibly) if there is overpressure in the breathing system. During prolonged use of a tracheal tube intermittent use of a manometer attached to the pilot balloon allows maintenance of an intra-cuff pressure below 30 cm H₂O. Only one manufacturer currently makes integrated pilot pressure monitors (Cuff Pilot; see above, ‘Other Laryngeal Masks’) for tracheal tubes, though further development is likely.

Nitrous oxide and tracheal tube cuffs

Nitrous oxide (N₂O) diffuses into tracheal tube cuffs filled with air. This applies also to cuffs on supraglottic airways. The rate at which diffusion occurs depends on:

• the permeability of the material from which the cuff is constructed (rubber being more permeable than plastic)

• the surface area of the cuff exposed to N₂O

• the partial pressure of N₂O in the respiratory gas.

The rise in intra-cuff pressure caused by this diffusion into the cuff depends on the compliance of the cuff. Low-volume high-pressure cuffs suffer the greatest pressure rise and may well transmit this pressure rise to the tracheal mucosa. High-volume low-pressure cuffs expand with only a slight increase in pressure until full inflation; at this point, owing to the inelasticity of the material, the pressure may rise rapidly to up to 12 kPa (90 mmHg). This can damage the tracheal mucosa.⁶⁷ In practice equilibration takes place over approximately 20 minutes, so checking the cuff pressure after 20 minutes will minimize problems. Should the anaesthetic gas mixture be changed at a later time to increase (or decrease) the fractional concentration of nitrous oxide, further diffusion into (or out of) the cuff will occur.

This phenomenon can be avoided if the cuff is filled with either a liquid, or a gas mixture identical to that of the inspired gas, or else by regular monitoring of the cuff pressure and volume. Alternatively, there are several devices that limit the pressure rise:

• The Mallinckrodt Brandt device has a large pilot balloon made from a material that allows nitrous oxide which has diffused into the cuff to escape (Fig. 6.28).

• The Mallinckrodt Lanz (Fig. 6.29) device consists of a special control valve and pilot balloon arrangement. A compliant latex balloon, protected within a larger open plastic covering, connects to the cuff via a flow restrictor. Insertion of a syringe into the valve bypasses this restriction allowing rapid inflation of the cuff. Thereafter, gradual volume changes in the cuff are buffered by the pilot balloon. When filled with a preset volume the device regulates the cuff pressure to between 20 and 25 mmHg.

• Portex Soft Seal cuffs are made of a PVC material using a higher molecular weight plasticizer, which results in a five-fold lower permeability to nitrous oxide. Fig. 6.30 compares rises in intracuff pressure between a Soft Seal and two other cuffs during 1 hour of anaesthesia using 66% nitrous oxide.

• The Bivona ‘Fome-Cuf’ uses a piece of shaped foam to replace the air within the cuff. Prior to insertion the cuff is evacuated to collapse the foam and after insertion the pilot tube is opened to the atmosphere to allow the foam to expand, to ‘inflate’ the cuff (Fig. 6.31). Because the pilot tube is left open, diffusion of nitrous oxide does not further inflate the cuff. The pilot tube may also be connected to the ventilation circuit to equilibrate intracuff pressure with proximal airway pressure during positive-pressure ventilation.

Figure 6.28 The Mallinckrodt Brandt device on a size 8 tracheal tube.

Figure 6.29 The Mallinckrodt Lanz device on a size 9 tracheal tube.

Figure 6.30 Mean changes in intracuff pressure every 5 min in three groups: group I, Mallinckrodt Lo-Contour tube; group II, Portex Profile tube; group III, Portex Soft Seal tube.

From Al-Shaikh et al 1999,⁶⁸ with permission of Oxford University Press.

Figure 6.31 Bivona ‘Fome Cuf’ tracheal tube. The pilot tube for deflating the cuff can be connected into the ventilation circuit to equilibrate intracuff pressure during IPPV.

Nasotracheal intubation

The diameter of tubes inserted through the nose is clearly limited by the size of the nares and the air passages of the nasal cavity. The position of the nasal septum and turbinates may result in a fairly convoluted passageway for intubation. Smaller diameter, softer and thinner-walled tubes are therefore needed for ease of insertion and to diminish the risk of bleeding. Similarly, a streamlined cuff made of material that is not easily torn is preferable. The pilot tube is incorporated as far as possible in the body of the tube.

The flexible LMA has removed the need for nasal intubation for many cases in which it has been traditionally used. In some centres uncuffed nasal tubes remain popular for use in adults using spontaneously breathing techniques, such as for short dental cases. The larynx is packed to protect the lungs for the period of the surgical procedure, and afterwards the small soft tubes cause minimal irritation and can be removed once the patient has woken. The necessity to use the highly error prone throat pack is a potential disadvantage. They increase the incidence of sore throat but, more importantly, in spite of many years of use anaesthetists and surgeons still contrive to devise seemingly new and exotic circumstances and procedures for forgetting to remove them in order to cause postoperative airway obstruction.⁶⁹

Specially designed nasal tubes which are made of soft plastic, are preformed and incorporate an appropriate cuff are probably best suited for such techniques. Designs such as the north-facing Portex polar tube (see below) enable safe fixation and removal of the anaesthetic circuit from the face.

The design of the bevel is also important; sharp long bevels have tended to be replaced by short bevels with rounded tips (Fig. 6.32) which are less likely to snag on obstructions. Some manufacturers even use a different softer compound for the leading edge of the tracheal tube.

Figure 6.32 A blunt cupped tracheal tube bevel, compared with a standard bevel.

Common problems with the use of tracheal tubes

Many of the problems, particularly relating to tube kinking or obstruction by external compression, are now rarely seen with the use of PVC tubes. These soften with warming when in use, appearing more often to remould rather than kink abruptly: so much so that specially designed non-kinking tubes, such as the Oxford tube and even the ‘armoured tube’ are now largely obsolete (see below). Some of the common problems are:

• Disconnection of the tube from the 15 mm ISO connector or of the connector from the catheter mount is common. This is most likely during shared airway or head and neck surgery. With the patient’s head often positioned away from the anaesthetist and hidden by drapes and surgeons, vigilance and appropriate monitoring (which includes alarm-enabled capnography) is vital.

• Leak. In uncuffed tubes excessive leak indicates a larger tube is required. With cuffed tubes a leak may arise if the cuff is at the cords. It may also indicate inadequate cuff inflation or deflation caused by cuff damage, over-inflation or a fault in manufacture.

• Kinking external to the patient. Tubes are prone to being kinked by the position of the breathing system, e.g. an uncut tube emerging from the mouth or as in Fig. 6.33, due to rotational forces being applied by a breathing system. Paediatric tubes, which have thinner walls and are connected to relatively heavy attachments, are particularly prone to this, especially when softened by warm respiratory gasses.

• Kinking inside the patient (Fig. 6.34). Modern PVC tubes are fairly resistant to this form of obstruction. If a tracheal tube must be bent acutely when in situ, a reinforced tube or one that is specially shaped should be used (see below, Tubes for special purposes). When the airway is shared with the surgeon, tube kinking and extubation or disconnection are increased problems. The Boyle-Davis gag used for tonsillectomy, if used without care or experience or with the incorrect blade size, frequently causes kinking (and/or inadvertent extubation on removal, and can advance an overly long tube into the bronchus). Obstruction by biting is a risk as a patient emerges from anaesthesia. Red rubber tubes were prone, especially after repeated autoclaving, to obstruction by a tightly inserted throat pack or even by inward herniation of the tube wall underneath the high-pressure cuff.

• Foreign bodies. All manner of foreign bodies have been found within airway devices causing blockage. Tracheal tubes (and other airways) should not be placed in the same dish as Luer-Lock caps, needles and ampoules etc., even after use. Diaphragms of dried mucus and even K-Y jelly, which may be virtually invisible, have also been found blocking tubes. In single-use devices, this danger has been superseded by diaphragms of clear plastic being formed across the openings of tubes when, for unwrapping, they are pushed through their plastic packaging. The invisible film is then kept firmly in place by the connector when the next item in the sequence is attached. Rarely manufacturing defects may lead to devices with similar occlusions. Standard checking of the breathing system will detect obstructions only as far as the final patient interface. There is often a presumption that tracheal tubes (or SADs) are patent; visual inspection of all such devices before use, and a high index of suspicion during use, is mandatory to prevent rare but potentially fatal problems.

• Distal obstruction can occur in several ways. The opening may be occluded if the larynx or trachea is deviated to one side by pathology (e.g. Fig. 6.24) or by surgical displacement (e.g. during thyroidectomy). It is also seen if the tube is advanced too far into the right main bronchus (Fig. 6.35). This pattern of obstruction may be more evident in expiration than inspiration. The presence of a Murphy eye may counteract such problems.

• (Endo) bronchial placement. A tube may be passed too far down the trachea and enter a main bronchus (usually, but not always, the right). This can occur after correct placement when the head and neck is repositioned; extension of the head and neck tends to advance the tube. It is a particular problem when using tubes of pre-formed length (e.g. RAE tubes) and in children. During laparoscopy, bronchial intubation may also occur as the carina rises upwards with diaphragmatic displacement caused by pneumoperitoneum.

• Extubation. Short, uncuffed and preshaped tubes (a combination of which is commonly used in children) are particularly prone to inadvertent extubation. Head and neck movement and surgical interference are additional triggers.

Figure 6.33 Occlusion of the tracheal tube due to rotational forces by the breathing system.

Figure 6.34 A. Kinking of an tracheal tube inside the mouth following neck flexion and softening of the tube during anaesthesia. B. Head in correct position.

Figure 6.35 Occlusion of the tip of a long tracheal tube is more likely with more flexible smaller diameter tubes.

ISO connectors, angle pieces and catheter mounts

ISO connectors

The tracheal tube is attached to the other components of the breathing system by a male 15 mm ISO (International Organization for Standardization) tapered connector (Fig. 6.23J). This connector itself fits into the tracheal tube via a tapered cone producing a secure connection. In PVC tubes with nylon/PVC connectors, because of the surface characteristics of the materials (stiction), the seal often can only be broken by cutting the tube. Tubes are therefore supplied from the manufacturer with the connector only lightly inserted so that the tube may be cut to length.

Either the breathing system or the ‘catheter mount’ (see below) houses a matching female 15 mm tapered connector. This two-part design permits a rapid disconnection and reconnection. However, the connection should be made secure with a ‘push and twist’ movement.

Connectors and angle pieces

Connectors join the airway device forming the patient interface (i.e. facemask, SAD or tracheal tube) to the anaesthetic breathing system. The term catheter mount originates from the days of ‘insufflation anaeasthesia’ and is not recognized in international standards. The early pioneers in anaesthesia produced connectors in a variety of shapes and sizes with any of a number of goals in mind, for example:

• streamlining the fit in order to improve surgical access around the head and neck of a patient

• minimizing resistance to gas flow

• allowing insertion of suction catheters.

Many of these functions have been incorporated into the design of specialist tubes and a more limited range is now available, although the Magill nasal connectors retained a loyal following until becoming difficult to source.

The connector with the female counterpart to the 15 mm ISO connector at the proximal end of the tracheal tube may be a simple angle piece designed to also fit the 22 mm female taper of a facemask, or it may allow other functionality (Fig. 6.36).

Figure 6.36 Angle pieces: A. older version with 22 mm tapers; B. newer design (here single-use) with proximal 15 mm external taper and distal dual mode taper (external 22 mm male and internal 15 mm female); C. combined angle pieces and catheter mount arrangement (see text).

These connectors may serve a variety of functions (Fig. 6.37), for example:

Figure 6.37 A variety of tracheal tube connectors. Clockwise from top left: intersurgical flexible corrugated models for gas sampling, and with ‘Seal-Around’ cap on swivel mount for bronchoscopy or suction; Mainz Universal Adaptor (blue-coloured) for endoscopy/intubation via tracheal tube or facemask; plain angle piece; swivel mount.

• swivel connectors to reduce torsion on the tube

• suction ports

• sealed ports enabling introduction of a flexible fibreoptic scope through a gas-tight seal.

A smaller standard of 8.5 mm is available for paediatric tubes to reduce component weight (see Chapter 12).

Catheter mounts

The term ‘catheter mount’ does not appear in BS EN ISO 4135:2001, which is the current official glossary of the terms used in anaesthesiology. Its modern equivalent, ‘tracheal tube adaptor’, is yet to gain common usage. Some historical explanation of the term is appropriate.

Before the introduction of the Boyle’s machine – the forerunner of the current anaesthetic workstation – and the Magill breathing attachment (the first Mapleson A system) the mixed gasses, with added vapour of volatile agents, were fed via a narrow bore tube (catheter mount) to the patient, with no reservoir bag or expiratory valve in the positions in which we now find them. The end of the tube could be attached to an airway device, such as the Boyle-Davis gag or to a catheter that was passed through the larynx into the trachea. In the latter case, the gasses and/or vapours were blown constantly down the catheter and were exhausted to the atmosphere by passing back through the trachea but outside the catheter (see above, under History).

Currently, a catheter mount usually consists of a short piece of flexible kink-resistant 15 mm tubing with a 15 mm ISO female tapered connector for attachment to the tracheal tube (Fig. 6.38). The other end of the catheter mount may have either a 15 mm ISO male taper or a 22 mm ISO female taper connector for coupling with the breathing system. Although the device increases the apparatus dead space of the breathing system, the flexibility it imparts makes this an insignificant consideration except in the very young.

Figure 6.38 A selection of catheter mounts, showing the 15 and 22 mm ISO connections described in the text.

Tracheal tubes for special purposes

Many ‘special’ tracheal tubes have been devised of which only a few examples are described below. Manufacturers’ designs of the same type of tube may vary considerably with even small variations having significant effects on the practicality of devices; the ‘same tube’ provided by different manufacturers may vary in a number of features, be it tip design (e.g. Murphy or Magill type), cuff and pilot balloon design, or even construction material or additional lumens. Some designs, however, are ‘branded’ and available only from one company, although others may have a similar design under a generic description. For a full range of tubes or for particular requirements, it is necessary to consult the manufacturers directly.

RAE preformed tubes

There are two separate versions of these tubes, named after their inventors: Ring, Adair and Elwin (Fig. 6.39). The tube for oral intubation has a preformed bend on the part of the tube where it exits the mouth, so that proximal tube passes down the chin and away from the face, thus improving surgical access to the mouth, nose and head of the patient. The nasal version is bent where it exits the nose so that the part housing the ISO connector passes upwards to the forehead. It is used to improve surgical access for intra-oral procedures.

Figure 6.39 RAE design tracheal tubes for orotracheal intubation (top) and nasotracheal intubation.

The main disadvantage of both designs is that the bend in the tube determines the length of tube that lies within the patient. As patients inevitably vary in size the tube may be too long for a given patient leading to the tip entering the bronchus; this is a particular problem with small children. Conversely, and much more commonly, with the trend towards using smaller calibre tubes, because tube dimensions have not been reformulated, a chosen RAE tube may be too short to reach comfortably below the glottis, increasing the risk of inadvertent extubation (see above: Tracheal tubes, Size). This is a particular problem with the newer cuffed paediatric tubes where manufacturers appear to have simply added a cuff to existing tubes rather than reformulating the proportions.

Reinforced tubes

Most tracheal tubes will kink if bent into an acute enough angle or if compressed by an external force such as from a surgical instrument. Both can occur during the course of an operation. Tubes may be made kink-resistant (but not kink-proof!) by embedding a reinforcing spiral of steel or nylon wire into the wall of the tube, which can then be made of a more elastic material than usual (i.e. silicone rubber, latex rubber or soft plastic). The tubes are consequently very flexible with little preformed shape. This can make insertion into the trachea more difficult, often requiring either a bougie, which has first been passed into the trachea, or a malleable stylet held in the lumen to shape the tube. Reinforced tubes have a thicker wall and therefore a smaller internal diameter (ID) for a given outer diameter.

These tubes are usually supplied at a length of 30 cm or greater for an ID of 5.0 mm and above. The reinforcing spiral will not stretch to accommodate a connector so the tubes cannot be cut to a shorter length than supplied. The ISO connectors are therefore usually bonded at production to a non-reinforced part of the tube. Special care must be taken not to insert these tubes too far. Reusable latex versions were particularly prone to kinking at the ‘soft spot’ between the end of the connector and the start of the spiral reinforcement (Fig. 6.40).

Figure 6.40 Obstruction at the ‘soft spot’ between the connector and the spiral of an armoured tube. A. With the connector placed correctly; B. with incorrect placement leaving an unarmoured segment of tube.

The greater kink resistance of PVC tubes and the availability of polar tubes has diminished the need for using reinforced tubes. Furthermore, the metal wire spiral may obscure radiolological imaging in some cervical spine surgery.

Polar tubes

Portex (Smiths Medical), in their Ivory range of tubes, manufacture a tube for nasotracheal intubation in a soft PVC material (see Tracheal tubes, Materials) with a preformed curve that takes the proximal end of the tube snugly along the nose and over the forehead (Fig. 6.41). These tubes are well-suited to maxillofacial surgery as they impinge relatively little on the surgical field. If access is also needed to the forehead, as in some cosmetic or reconstructive plastic procedures, the proximal end can be swung down without the tube kinking, to descend over the cheek or chin. The soft plastic of the Ivory range is relatively atraumatic in the nose, which in combination with the springiness of these tubes makes them ideal for ‘blind nasal intubation’. Interestingly, the material, originally called ‘Vinyl Portex Tubing’, was actually first developed in 1944⁶⁶ as a substitute for the red rubber tubes whose primary materials were in short supply.

Figure 6.41 Portex Ivory tracheal tubes. Upper: north facing directional (polar) tube. Lower: microlaryngeal tube with greater length and cuff size relative to the tube diameter.

These tubes, in sizes 6.0 and 6.5 mm ID, are a good choice for nasal fibreoptic intubation, in spite of the reservations previously mentioned regarding cuff sizes and small tubes (the length and cuff size in this case is usually adequate, even for the largest adults).

Microlaryngeal tube

This tube (Fig. 6.41, lower) has a small internal diameter (ID usually around 4.5–5.5 mm) but an adult-sized high-volume low-pressure cuff. The tubes are designed to be unobtrusive in the larynx so as to allow surgery around the vocal cords and are long enough for nasal intubation. The high resistance to gas flow in these tubes virtually obligates controlled ventilation and a long expiratory phase should be used to allow complete expiration. Due to their flexibility they can be difficult to insert unless Magill intubating forceps are used. Standard adult-sized bougies and stylets are usually too large to pass through these tubes. Despite their suitability for laryngeal surgery they tend to lodge in the anterior of the laryngeal inlet so do not provide surgical access for all laryngeal lesions. As they are not laser resistant they are unsuitable for such surgery.

Carden tube

This tube was developed to facilitate microsurgery of the larynx. It is rarely used now but may perhaps enjoy a resurgence for jet ventilation. It comprises a shortened cuffed tracheal tube that sits wholly below the glottis attached to a long catheter for insufflation of gas and a long pilot tube for the cuff (Fig. 6.42). It may be inserted by grasping the tube with Magill’s forceps and placing it under direct vision. Alternatively the Carden tube and an uncut plain tube, just wide enough to fit inside it, are threaded onto a stylet. This assembly is introduced through the larynx so that the Carden tube and a centimetre or so of the plain tube pass into the trachea. The cuff of the Carden tube is inflated, the stylet is withdrawn and anaesthesia is maintained in the usual manner through the plain tube. For laryngoscopy, the plain tube is removed as is the breathing system, and gasses are delivered directly to the Carden tube through a feed mount. The expired gasses escape via the lumen of the Carden tube.

Figure 6.42 Carden tube for laryngeal surgery.

Photo courtesy of Portex UK Ltd.

Tubes for laser surgery

Conventional tracheal tubes of either plastic, silicone or rubber may be damaged by the carbon dioxide, KTP or Nd-YAG laser beam. These materials burn more fiercely in the presence of oxygen or nitrous oxide than in air and are easily ignited by a direct or indirect strike from the laser beam. The resultant fire can produce serious upper airway burns and severe distal inhalation injury; injuries may be fatal. Some examples of tubes that can be used in the presence of a laser beam are described below. They must not be assumed to be laser proof and are only indicated for CO₂ and KTP lasers. Figures are provided by manufacturers for maximum power and duration of energy before ignition for different lasers according to standardized tests (e.g. 1 s at 55 watts or 7 s at 30 watts from a CO₂ laser for the Laser-Flex).

Mallinckrodt ‘Laser-Flex’ tracheal tubes

These single-use tubes for oral intubation are made from a gas-tight metal helix with the pilot tubes for the double cuff carried within the lumen of the airway (Fig. 6.43). It is advised that the cuffs, which are not laser resistant, are inflated with saline, ideally dyed with some methylene blue, to prevent ignition of the cuff and so that puncture is obvious. The function of the proximal cuff is to protect the distal cuff and the tube must be replaced if either cuff is defective. The surface of the tube shaft reflects a defocused laser beam with a lower potential for causing tissue destruction. The tip of the tube is made of a soft plastic for a more atraumatic insertion. The tubes have a markedly reduced inner diameter when compared to PVC tubes of the same outer diameter and care must be taken to allow adequate expiratory time in ventilated patients.

Figure 6.43 Mallinckrodt ‘Laser-Flex’ tracheal tubes. Uncuffed and cuffed showing water-filled double cuff arrangement.

Foil wrapped

An alternative approach used by some manufacturers is to spirally wrap a suitably small rubber tube with a narrow strip of silver or copper foil (this may be stippled or corrugated to disperse an incident beam) (Fig. 6.44). The tube is then overwrapped to give a smooth outer coating. The Rusch Lasertubus is covered in Merocel foam (a porous sponge), which is soaked in saline to help absorb laser energy. This tube is provided with a double cuff arrangement.

Figure 6.44 The Rusch Lasertubus (above) and Sheridan Laser-Trach (below, photo courtesy of Hudson RCI) laser resistant single-use tracheal tubes. The embossed copper foil of the Sheridan tube is just visible under the outer covering.

Jet ventilation

This provides a further approach to airway management for laser surgery and is described separately below.

Tubes and catheters for ‘jet ventilation’ (high-pressure source ventilation)

Supraglottic ventilation

If surgical access is significantly impaired by a laser resistant tube, the surgical laryngoscope that is used to suspend the larynx for surgery can be fitted with a metal cannula (Fig. 6.45) that ends above the glottis and can be used for ‘jetting’ with high-pressure gas (supraglottic ventilation). Anaesthesia must be maintained intravenously. The quality of ventilation depends on the surgeon placing the tip of the ventilating catheter above and in line with the trachea and requires careful co-operation between anaesthetist and surgeon (Fig. 6.46). Alternatively, high-pressure source ventilation may be delivered by a small laser-resistant catheter passed through the glottis (transglottic ventilation).

Figure 6.45 Different patterns of laryngoscopes for suspension surgery and examination of the larynx, and alongside, jet ventilation cannulae for use with these devices.

Figure 6.46 Supraglottic jet ventilation with cannula correctly aligned for effective ventilation.

Transglottic ventilation – Hunsaker tube

The Hunsaker Mon-Jet Ventilation tube (Fig. 6.47) (Medtronic Xomed, USA) is a narrow-bore dual lumen tube designed for transglottic high-pressure source ventilation that allows concomitant airway pressure monitoring or gas sampling from the narrower second lumen. The 33-cm-long device (4.5 mm at its widest diameter) is made of a laser-resistant fluoroplastic and ends in a moulded plastic cage which aims to centralize the discharged jet stream and prevent direct impingement on the tracheal wall mucosa. In combination with a dedicated jet ventilator, such as the Accutronic Medical Systems Monsoon or Mistral models (see Chapter 9), this device offers improved surgical access for unhurried instrumentation and laser surgery of the major airways. Unlike the microlaryngeal tube the Hunsaker tube can be easily positioned to allow the surgeon access to any part of the larynx. Because the above ventilators check that airway (pause) pressure is below a pre-set limit before each inspiratory phase even at high cycle rates, jet ventilation can comfortably and safely continue up to and beyond patient arousal at the end of surgery.

Figure 6.47 The Hunsaker Mon-Jet Ventilation tube.

Although the material will not melt and drip or produce a self-sustaining flame, protracted impact of sufficient laser energy will penetrate the tube. An internal stainless steel wire is designed to retain the distal fragment in the event of the tube being severed. Other manufacturers produce similar designs.

Subglottic ventilation: transtracheal catheters

A cannula placed percutaneously into the trachea via the cricothyroid membrane enables subglottic ventilation while allowing the surgeon full access to the larynx. The Ravussin catheter ideally designed for this purpose is described below under Subglottic Devices.

The use of small tubes requires a high pressure gas source for ventilation. This may be a manually operated, fixed-pressure ventilator (Sanders injector, 4 bar); a manually operated, variable-pressure ventilator (Manujet, 0.5–4 bar; see below) or an automatic ventilator. Mechanical ventilators may be of a variety of degrees of sophistication and may provide conventional ventilation, high-frequency ventilation or a combination of the two. The use of a high-pressure source introduces a significant risk of barotrauma (particularly with manual techniques) and this risk increases if the larynx closes or if expiration (which occurs passively through the native airway) is not scrupulously confirmed before each inspiration.^70,⁷¹ Ventilators with airway pause pressure monitoring linked to ventilator cut-outs (see above) are safer and their use is recommended.⁷²

Laryngectomy tube

Conventional tracheal tubes placed through a tracheostomy in patients undergoing or with previous laryngectomy are difficult to fix in place and prone to kinking or slipping down into a bronchus. The ‘U’ shape of the laryngectomy tube (Fig. 6.48) means it sits unobtrusively on the chest wall with the long straight proximal portion allowing direct connection to a breathing system distant from the operative site. The internal portion of the tube is short and the tip is usually cut close to the cuff to minimize the risk of bronchial intubation.

Figure 6.48 A laryngectomy tube.

Tubes for thoracic surgery (including bronchial blockers)

Operations within the thoracic cavity may require the collapse of a lung to improve access to other organs, to isolate that lung for its removal or repair, or to prevent contamination from a diseased lung spreading to the other side. This may be achieved in one of three ways.

(Endo) bronchial tubes

Firstly a long tube may be passed, often under endoscopic control, beyond the carina and into the unaffected lung so that the cuff can be inflated within a main bronchus. The other lung is not ventilated and collapses, especially when the pleura is opened. This technique is normally applicable only to intubating the left main bronchus (for surgery on the right lung). This is because the right upper lobe bronchus enters its main bronchus very close to the carina and its lumen would be obstructed by the cuff of the tube described. The bronchial tube may be placed in the trachea initially so as to ventilate both lungs for as long as possible and then advanced when required to isolate the appropriate lung.

Tubes with bronchial blockers

The second method of isolating a lung is to use a tracheal tube through which a fine balloon catheter can be passed either via the lumen of the tube or through a channel in its wall. The balloon tip is then passed, usually with the aid of a flexible endoscope, into the intended main bronchus, which becomes isolated when the balloon is inflated (Fig. 6.49). A central channel which opens beyond the balloon allows suction to deflate the lung and may also be used to augment oxygenation by ‘insufflation’ into the collapsed lung. In the past Foley catheters and Fogarty embolectomy catheters have been used in place of bronchial blockers but improved construction of bronchial catheters obviates this need.

Figure 6.49 Univent tracheal tubes with endobronchial blockers. The lower device allows access to the lung distal to the blocker.

Photo courtesy of Fuji Systems Corporation.

Bronchial blockers have a variety of designs to assist placement; these include fixed angulations, loops for attachment to an endoscope and a novel design with dual balloons either side of a self-deploying ‘V’ (Fig. 6.50). In this latter design the blocker is introduced within a sheath to the carina then advanced beyond the sheath, so the ‘V’ opens up and inevitably straddles the carina, with the dual balloons enabling deflation of either lung as required.

Figure 6.50 EZ-Blocker (AnaesthetIQ BV, The Netherlands) for lung isolation, deployed through a conventional tracheal tube.

Image courtesy of Fannin UK.

Blocker technology has improved considerably in recent years and, as evidence suggests their use is less injurious to the patient than use of a double lumen tube, popularity of blockers has increased, while that of double lumen tubes has waned. Blockers are now available for use even through infant-size tracheal tubes.

Double lumen tubes

The third method is to use a combination or double lumen tube (DLT) (Fig. 6.51). These are formed by bonding together two tubes of similar diameters but different lengths. The shorter tube ends in the trachea and seals this with one cuff, whilst the longer tube is designed to fit a main bronchus and seal this with a separate cuff. The cuffs are supplied by separate inflation tubes and pilot balloons, which are marked and colour-coded to aid identification. DLTs are produced in left- and right-sided versions. Some designs have a small soft carinal hook to prevent over-insertion of the tube but this is uncommon in modern single-use versions. Because the opening of the right upper lobe bronchus is so close to the origin of the main bronchus, the bronchial lumen on right-sided versions also has a side hole and a cuff that is designed so that it does not occlude this (Fig. 6.52). The bronchial cuff and inflation tube are blue by convention.

Figure 6.51 Double lumen tubes (both with malleable tracheal introducers in place). Portex right-sided tube (above) and Mallinckrodt Broncocath left-sided tube (below). The scalloping of the distal cuff is just visible on the right-sided tube (see text).

Figure 6.52 A. The endobronchial section of the tube in the left main bronchus with the carinal hook limiting the depth of insertion. B. The endobronchial section of the tube in the right main bronchus with the carinal hook limiting the depth of insertion and the side hole opposite the right upper lobe bronchus surrounded by the adapted bronchial cuff.

Sizes

The combined size of the two lumens makes the device bulky and prevents its use in children. Because the external shape of the device is circular in cross-section, the lumens of the two tubes are each ‘D’-shaped and the size cannot be quoted in terms of an internal diameter. Sizes are quoted in French gauge (Fr). This scale is constructed from the external diameter of the widest part of the device, measured in millimetres, multiplied by a factor of 3 (corresponding roughly to the circumference). Usual sizes are 28, 35, 37, 39 and 41 Fr; many designs offer only one or two sizes.

Insertion

DLTs are more difficult to insert than conventional tubes due to their bulk and double angulations: left-sided are somewhat easier to insert than right-sided tubes. Also, because the left upper lobe bronchus is not as close to the carina as on the right, depth of insertion is far less critical. Wherever possible the largest possible left-sided DLT is selected and the cuffs are checked for leaks. Left-sided tubes are appropriate for most procedures except for left pneumonectomy. The device is held so that the bronchial tube curves forwards, resembling the Magill curve of a tracheal tube. It is inserted under direct laryngoscopy and once through the larynx it is rotated counter-clockwise so that the tip enters the left main bronchus. Carinal hooks, if present, may snag on the glottis but should ultimately rest on the carina, confirming that full insertion has been achieved. The two connectors are then joined on to those on a twin tube adapter (catheter mount), which links the tubes to the breathing system. The tracheal cuff is then inflated and manual ventilation is commenced via both lumens. This should produce visible equal bilateral chest movement which should be confirmed by auscultation. The tracheal adapter on the catheter mount is then occluded with a hose clamp so that all ventilation is directed down the bronchial lumen. The left bronchial cuff is then slowly inflated whilst auscultating the right lung until a seal is achieved, at which point gas entry to the right lung stops. The tracheal lumen is then released so that the tube can be used as intended.

Insertion of right-sided tubes involves clockwise rotation of the DLT and similar checking of left lung inflation with the added proviso that gas entry should also be confirmed over the right upper zone when the bronchial cuff is inflated.

Both versions may be temporarily reshaped for laryngeal insertion by the insertion of a stiff stylet into the bronchial lumen. This must be removed once the bronchial section has passed through the larynx.

Visual confirmation with a fibreoptic scope is the most accurate method of determining the true position of these tubes and in many centres is now standard procedure. The bronchial cuff should be visible (when the fibreoptic scope is advanced beyond the end of the tracheal lumen) at or just beyond the carina, and with right-sided tubes the origin of the right upper lobe bronchus must be confirmed to lie adjacent to the side hole of the bronchial tube. Large bronchoscopes will not pass into a DLT and a fibrescope of <5 mm diameter is needed. An alternative intubation technique passes the fibrescope through the bronchial lumen and into the correct bronchus before railroading the DLT into place.

If the patient poses a difficult laryngoscopy placement of a DLT may be impossible. Use of DLTs by infrequent users may lead to confusion due to their complexity. In addition, like all tracheal tubes their position may change with patient movement. As DLTs are usually placed when the patient is supine, but surgery is performed in the lateral position (with the table ‘broken’ to open the rib cage), it is vital to ensure that the tube still allows isolation and ventilation of the lungs as intended after the patient is re-positioned for surgery. Finally, the large size of the DLT and the distance it is inserted makes laryngeal and tracheal injury more likely than conventional tracheal tubes.

Tubes to assist intubation

Tracheal tubes have been designed to assist intubation both during conventional and unconventional intubations.

The Mallinckrodt Endotrol tracheal tube (Covidien, Ireland) has a control wire connected to the distal tip that runs in the wall of the tube on the inner aspect of the curvature. Traction on this wire increases the curvature at the tip of the tube to facilitate intubation. This device is no longer available in Europe.

In another design ETView tracheal tube (ETView Ltd, Misgav, Israel) a video camera is incorporated in the tip of the tracheal tube allowing visual confirmation of the passage of the tube tip during insertion and constant observation of the tracheal lumen after placement.

The Intubating LMA tracheal tube (Intavent Direct, Maidenhead, UK) (Fig. 6.15), which is produced both in reusable and single-use versions, is a valuable tube for use in difficult intubations. It is a reinforced silicone tube with a soft bullet-shaped silicone tip. This tip dramatically reduces the likelihood of impingement on the arytenoids (a common problem with conventional tracheal tubes) and largely eliminates ‘hold-up’ of the tracheal tube during insertion. This reduces failure, speeds insertion and minimizes the likelihood of laryngeal trauma. Although it was designed for use with the ILMA its performance characteristics make it also suitable for use with catheter exchange techniques and with a flexible endoscope.

Flexible endoscopic intubation does not allow visualization of the glottis as the tracheal tube is advanced. Many rigid optical laryngoscopes and various other devices which guide the tube into the larynx similarly will not permit visualization or easy realignment of tube passage. When conventional tracheal tubes are used with such devices there is a high incidence of difficult insertion and impaction. Many manufacturers now produce their own branded designs aimed at eliminating hold up of tracheal tubes passed using systems that do not permit concomitant direct visualization of the glottis as the tube is advanced. None should be assumed to outperform other designs or more particularly to function in other scenarios.

‘Hold up’, where the tip of the bevel of a conventional tube is not placed centrally in the glottis and snags usually on the right arytenoid or cord, is a more common problem wherever intubation is carried out without a direct view of the larynx. ‘Hold up’ is thus also possible whenever the tube is advanced unseen over an introducer of any type, be it a gum elastic bougie or a flexible endoscope. As the tube is advanced, the bevel tip is rarely central and impinges on the right cord, arytenoid or posterior rim of the glottis. The conventional solution is to rotate the tube through 90° or more. (See also above: Tracheal Tubes, Size.)

Tubes with additional ports/lumens

Tracheal tubes may have an additional narrow-bore tube fitted to the wall for sampling, pressure monitoring or drug instillation. Sheridan (Hudson RCI, USA) produce a full range of sizes including uncuffed paediatric tubes with an extra lumen ending at the tracheal tip for airway gas sampling or drug instillation.

LITA tube

The extra lumen in this tube has ten small side holes, eight above and two below the cuff for the ‘Laryngotracheal Instillation of Topical Anaesthetic’. There is evidence demonstrating better tolerance of intubation in sedated patients ⁷³ and conflicting evidence regarding suppression of response to extubation^73,⁷⁴ (Fig. 6.53).

Figure 6.53 Sheridan LITA (Laryngotracheal Instillation of Topical Anaesthetic) tube. A black horizontal line indicates uppermost opening.

Photo courtesy of Hudson RCI.

Tubes for non-operative jet ventilation (e.g. intensive care)

Two additional smaller tubes may be incorporated into the tracheal tube lumen to allow jet ventilation and simultaneous monitoring of tracheal pressure. The much wider main lumen of the tracheal tube then permits entrainment of gasses and passive exhalation at low pressures. Such tubes are available in cuffed and uncuffed versions depending on the need for airway protection and control of entrained gasses.

Developments in tracheal tube and cuff technology for intensive care

The humble tracheal tube cuff is perhaps a neglected item of medical technology. Awareness of both chronic complications of prolonged intubation (subglottic/tracheal stenosis) and incomplete protection (micro-aspiration and ventilator associated pneumonia) have led to renewed interest in improving its performance characteristics.

Cuffs made of silicone or polyurethane are available that eliminate microfolds without the need for high intracuff pressures. Use of continuous electronic cuff pressure measurement and ‘servo’ technology enables a user-defined intra-cuff pressure to be maintained continuously, even during patient movements: a common cause of cuff leaks (e.g. Venner PneuX P.Y., Intavent Direct, Maidenhead, UK). A tapered (conical) shape to the inflatable tracheal tube cuff may be effective in preventing it developing folds and microchannels across the full contact surface with the tracheal wall (Mallinckrodt TaperGuard tracheal tubes, Covidien, Ireland).

Addition of appropriately designed small channels opening just above the cuff enables both subglottic suction and lavage.

Finally antimicrobial agents (such as silver nitrate or elutable agents) may be incorporated onto the surface of into the fabric of the tracheal tube.^75,⁷⁶

While the benefit of these innovations is largely unproven, each (or perhaps combinations of them) may in the future lead to distinctly different tracheal tubes designed for prolonged use, such as in intensive care or when special protection is required.

Subglottic devices

Tracheostomy tubes

The distance between the tracheal stoma and the carina is short and variable. Tubes placed in the trachea via a tracheostomy are, therefore, designed to be non-bevelled, short in length and with the cuff bonded closer to the tip of the tube to prevent accidental bronchial intubation. They may be evenly curved along the length or angulated more sharply to describe a near right angle bend.

There are many varieties of tracheostomy tubes (Fig. 6.54) and only some of the features are detailed below. At least one manufacturer, Rüsch, will tailor single tubes for individual requirements. For intensive care and theatre use simple tubes are appropriate. It has become conventional when tracheostomies are used outside critical care areas and in the community to insert a tube with a liner. A liner is a usually plastic tube that lies within the main tube: as it reduces the internal diameter of the tracheostomy it is not suitable for patients with very limited respiratory reserve. The advantage of a liner is that it can be easily removed for claning of secretions without having to remove the tracheostomy tube itself. When a liner is not used humidification and nursing care must be of a high standard to prevent the build up of secretions.