Airway management equipment

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Chapter 6 Airway management equipment

Standards, techniques (and fashions) in airway management have changed considerably over the last two decades. Although the most basic principle of anaesthesia is the maintenance of a patent airway aimed at providing adequate oxygenation and ventilation, the range of devices and products used has seen major changes especially in the focus of the designs. Of the developments in the last decade several are notable.

The laryngeal mask in its various forms has continued to expand both within and beyond routine airway management. Prior to the introduction of what is now branded as the LMA Classic, there was usually a clear choice between tracheal intubation and facemask application, each with its own distinct advantages and problems. The laryngeal mask is now the commonest device for airway management during anaesthesia in the UK and is used for approximately 56% of cases.

Numerous alternatives to the LMA have since been developed. These devices which sit outside the larynx and aim to provide a gas-tight seal are now generally referred to simply as supraglottic airways or SADs (supraglottic airway devices): the term extraglottic airway is more anatomically accurate but is not widely used.1 The number and variety of SAD designs have expanded dramatically in the last few years with the result that there are numerous products that vary considerably in materials and performance. Many of these are single-patient use laryngeal masks designed to compete for the market share of the original LMA. Nonetheless several newer SADs offer genuine advances in versatility, efficacy and safety.

The use of the flexible fibreoptic endoscope (fibrescope) for intubation continues to increase and to emerge from being the domain of a few to becoming a mainstream activity at which anaesthetic trainees rightly feel they must be adept. Technological developments are apparent here too with an increasing shift towards miniaturized digital video-based devices rather than optical glass-fibre image transmission.

In the last few years, we have also seen the proliferation of a new generation of crossover devices for laryngoscopy which combine features of both fibrescopes and traditional rigid (lighted retractor type) laryngoscopes. These rigid devices with predefined shapes, rely instead on fibreoptics, prisms and mirrors or digital camera technology for image transmission from the tip of the device. The standard technique of direct laryngoscopy for tracheal intubation is being challenged. While some commentators suggest that direct laryngoscopy has a limited future, the precise role of ‘indirect’ laryngoscopy with such devices in elective and emergency procedures, and in cases of airway difficulty is far from established. It is certain that the development and introduction of these devices is currently outstripping the profession’s capacity (or desire) to carefully evaluate their proposed benefits. Unanticipated complications may accompany some techniques, and harm, albeit rare, may be seen with this technology too.

Finally, overlying all the above considerations; concern about the transmission of infective agents, particularly those responsible for variant Creutzfeldt–Jakob disease (vCJD), has been the apparent driving force behind an increasing trend towards reliance on single-use airway devices. This trend, whether based on science or not (of which more later) has meant that the majority of airway devices now being developed are at least in part single-use. Production and material costs and hence price, as well as storage and stocking issues, are ultimately more significant considerations for single-use items and this is already affecting the range and quality of equipment available in many hospitals.

This chapter addresses all these areas: it will be evident that the field of airway management has seen a massive proliferation of devices and techniques. Whereas it was once possible for this book to be a complete and up-to-date inventory of all equipment that anaesthetists were likely to come across in their professional lives, our more modest aim now, particularly in this chapter, is to represent examples and classes of devices that are currently in popular use and to further illustrate important themes in such developments.

Materials used in airway devices

As ever, the choice of material is governed by the ideal characteristics required for the intended function; taking into account patient and environmental safety and attendant legislation, balanced against the costs of the raw material and production costs.

Simple airway adjuncts

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).

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.

Oropharyngeal airways for flexible endoscopic oral intubation

A number of airways have been devised to assist oral intubation. When used to aid flexible endoscopic intubation they serve to deliver the endoscope behind the tongue, and as close to the larynx as possible, ideally having bypassed any secretions. Their shapes are broadly similar to the Guedel airway but often describing a fuller curvature along the length and with a more circular cross-section (Fig. 6.4).

The Berman airway (originally designed to assist blind oral intubation and pharyngeal suction), like the VBM and Ovassapian (not pictured) airways is open along one side. These devices when used for endoscopic intubation are removed before passage of the tracheal tube. The fully enclosed Optosafe airway has a large enough diameter to accommodate a tracheal tube.

The airways also act as a ‘bite block’ preventing damage to expensive fingers or delicate endoscopes (see also: Flexible endoscopes, conduit airways). This purpose is better served by the use of a dedicated bite block such as the BreatheSafe (Fig. 6.5) which more resembles a dental prop and allows full access to the oral cavity while preventing mouth closure.

All the above devices are available in a number of sizes and correct size selection is important for good function.

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.

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.

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.

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.

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 face3 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.

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.

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.

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.1215 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.

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.

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

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.

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 180o on reaching the soft palate (akin to insertion of a Guedel airway) or inserted laterally parallel to the tongue and rotated 90o 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:

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

As an aid to extubation:

For difficult airway management:

During resuscitation:

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 180o 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.

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