Airway management and acute upper-airway obstruction

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Chapter 25 Airway management and acute upper-airway obstruction

The primary objective of airway management is to secure unobstructed gas exchange and protect the lungs from soiling. Because of the critical importance of maintaining gas exchange, upper-airway obstruction is a life-threatening emergency. Upper-airway obstruction results from a wide range of pathophysiological processes, and therefore rapid assessment and establishment of a patent airway must take priority, even in the absence of a specific diagnosis. As no single airway management modality is universally applicable, the intensive care unit (ICU) physician must be capable of performing a variety of airway management techniques and instituting them in a logical and systematic way (Figure 25.1).

Figure 25.1 Difficult airway algorithm (see text). LMA, laryngeal mask airway; iLMA, intubating laryngeal mask airway; TTJV, transtracheal jet ventilation.

AIRWAY MANAGEMENT TECHNIQUES

Airway management techniques are generally classified as non-invasive or invasive, depending on whether instrumentation occurs above or below the glottis, surgical or non-surgical, and definitive (Table 25.1). Definitive techniques secure the trachea and provide some protection from macroscopic aspiration and soiling. While bag-and-mask ventilation and direct laryngoscopic tracheal intubation remain the routine methods of airway management in ICU, the use of fibreoptic bronchoscopy is increasingly common, especially in special circumstances. Management of failed intubation and ventilation by various alternative techniques, particularly the use of the intubating laryngeal mask airway (iLMA) and cricothyroidotomy, is well described.^1,²

Table 25.1 Characteristics of airway management techniques

The technique of choice will depend on each individual situation and is determined by the interaction of patient and clinical factors, which partially determine the appropriate technique (Table 25.2), and the clinician’s experience in applying the chosen technique. Other factors include availability of help, levels of training and supervision and accessibility of equipment. A portable storage unit with a wide choice of equipment appropriate for difficult airway management should be available in every ICU (Table 25.3).

Table 25.2 Commonly recommended applications of described airway management techniques. Examples of common alternatives are given in approximate order of choice

	Difficult direct laryngoscopic intubation	With difficult spontaneous/mask ventilation
Awake	Fibreoptic bronchoscopic intubation Direct laryngoscopic intubation* Blind nasal intubation Retrograde intubation	Percutaneous cricothyroidotomy* Surgical tracheostomy*
Anaesthetised or comatose (empty stomach)	Bag-and-mask ventilation Direct laryngoscopic intubation Different blade Fibreoptic bronchoscopic intubation Intubating LMA/LMA Lighted stylet Blind nasal intubation	Laryngeal mask airway (LMA) Transtracheal jet ventilation Rigid ventilating bronchoscope Percutaneous cricothyroidotomy Surgical tracheostomy
(full stomach)	Maintain cricoid pressure with all techniques Intubating LMA/Proseal LMA Combitube	Percutaneous cricothyroidotomy Surgical tracheostomy Combitube

The technique(s) chosen should also depend on the clinician’s knowledge and ability. Cricoid pressure should be applied with a force of approximately 30 N, but applied force can be temporarily reduced to assist airway manoeuvres.

* Under local anaesthesia.

Masks

Face and nasal masks of differing make and size variety

Airways

Oropharyngeal airways

Nasopharyngeal airways

Airway intubator guide for oral endoscopic intubation

Laryngeal mask airway (LMA) and intubating LMA with appropriate endotracheal tubes

Rigid laryngoscope with a variety of designs and sizes

Short handle or variable angle (Patil-Syracuse) laryngoscope

Curved blades: Macintosh, Bizarri-Guiffrida

Straight blades: Miller

Bent blade: Belscope

Articulating-tip blade: McCoy

Fibreoptic stylet laryngoscope or Bullard laryngoscope

Endotracheal tubes of assorted size

Murphy tubes

Microlaryngoscopy tubes

Endotracheal tube stylets

Gum elastic bougie (Eschmann stylet)

Malleable stylet

Tube changer, hollow tube changer (jet stylet)

Lighted stylet (light wand)

Fibreoptic intubation equipment

Patil endoscopic mask, oral airways or blocks to facilitate oral endoscopic intubation

Fibreoptic endoscopes with light source, adult and paediatric-sized

Combitube

Emergency surgical airway access

Percutaneous cricothyroidotomy set

Transtracheal jet ventilation – cannula and high-pressure O₂ source connectors

Regulated central wall O₂ pressure (Sanders-type injector)

Unregulated central wall O₂ pressure device

Exhaled carbon dioxide monitor

Capnometer/capnograph

Chemical indicators

NON-INVASIVE TECHNIQUES

BAG-MASK VENTILATION

Mask ventilation, using a bag-mask resuscitator, is a basic skill that requires time and experience to master. It should be learned using mannekins, simulators and practice in the controlled environment of the operating theatre so that when used in the emergency setting in ICU the skill is already well established. The manually squeezed bag is self-inflating, usually with a simple reservoir bag in series, which, if kept inflated, ensures that a consistent high oxygen concentration can be delivered. The addition of a positive end-expiratory pressure (PEEP) valve may improve arterial oxygenation in patients with lung pathology and help overcome airway obstruction due to laryngospasm. Transparent face masks are recommended as they allow observation of misting during exhalation, assessment of the position of adjunct artifical airways and early observation of gross airway soiling.

Some considerations when performing mask ventilation include the following:

1 Inadequate ventilation. Good airway positioning by head tilt and chin lift, or if necessary the jaw thrust manoeuvre, is essential to maintain an open airway. The seal of the mask against the face is important and technically good hand positioning must be learned and practised. A beard may be covered with a large adhesive plastic dressing with a hole cut out for the mouth, or smeared with petroleum jelly or water-based lubricant. Ventilation of edentulous patients may be aided by improving hand position or special masks. Two operators are recommended if a mask face leak is excessive, one to hold the mask and the other to manipulate the bag-mask resuscitator.

2 Gastric insufflation is common if high tidal volumes are used and increases the risk of vomiting and aspiration (aim for 300–500 ml). Severe distension may occasionally cause cardiovascular compromise. Carefully applied cricoid may prevent gastric gas insufflation.

3 Pulmonary aspiration. In the emergency situation with a full stomach, mask ventilation with cricoid pressure is recommended until the airway can be secured. Passage of a nasogastric tube to aspirate gastric contents can be attempted, but with caution as vomiting may be induced.

ORO- AND NASOPHARYNGEAL AIRWAYS

In the unconscious patient, functional obstruction is primarily caused by loss of muscular tone and subsequent inspiratory airway narrowing at the soft palate, epiglottis and tongue base. An oropharyngeal airway can help establish an adequate airway for spontaneous or bag-mask ventilation when proper head positioning is insufficient. It is inserted with the concavity facing the palate and then rotated 180° into the proper position as it is advanced. Complications include mucosal trauma, worsening the obstruction by pressing the epiglottis against the laryngeal outlet if the tongue displaces posteriorly, and occasionally laryngospasm. The following sizes (length from flange to tip) are recommended: large adult: 100 mm (Guedel size 5); medium-sized adult: 90 mm (Guedel size 4); small adult; 80 mm (Guedel size 3).

A nasopharyngeal airway is a soft rubber or plastic tube inserted into the nostril and advanced along the floor of the nose (in the direction of the occiput). Correctly positioned, the tube traverses the posterior pharynx. It is better tolerated by semiconscious patients than the oropharyngeal airway. Complications include epistaxis, aspiration and, rarely, laryngospasm or oesophageal placement.

LARYNGEAL MASK AIRWAY (LMA) AND INTUBATING LMA

The LMA is a reusable device that consists of a silicone rubber tube connected to a distal elliptical spoon-shaped mask with an inflatable rim, which is positioned blindly into the pharynx to form a low-pressure seal against the laryngeal inlet.³ LMAs are useful to achieve non-definitive airway patency in many emergency situations (see Figure 25.1), and can be used to provide positive-pressure ventilation.² Once positioned the LMA has been used to guide the passage of stylets, bougies, the bronchoscope and an endotracheal tube into the trachea, but with difficulty.^2,⁴ The iLMA or FasTrach is a modification of the LMA with several features to facilitate intubation once the iLMA is placed.⁵ There is a guiding ramp and epiglottic elevating bar at the aperture to direct the endotracheal tube to the glottis. It also has an anatomically curved, rigid shaft and handle to allow easy and firm manipulation during placement and when the endotracheal tube is passed.⁶ The iLMA is the laryngeal mask of choice if intubation is required, as is frequently the case in ICU patients.

Although preparation and patient positioning techniques for placement of a LMA and iLMA are similar, the insertion technique is quite different. The mask airway is prepared for insertion by deflating and smoothing out the cuffed rim to be wrinkle-free, and the posterior surface and patient hard palate are lubricated with water soluble jelly. The patient is positioned as for endotracheal intubation, with slight flexion of the neck and extension of the atlanto-occipital joint (sniffing-the-morning-air position). The LMA is inserted with the tip of the cuff continuously applied to the hard palate, and with the right index finger guiding the tube to the back of the tongue until a firm resistance is encountered. The cuff is then inflated with 20–40 ml of air (adult sizes) before attachment of the breathing circuit.

To begin insertion of an iLMA, ensure the curved metal tube is in close proximity to the chin (the metal handle points to the toes) and the mask tip flat against the palate prior to insertion. The mask is inserted and positioned with a circular motion, maintaining contact pressure between the posterior aspect of the mask and the palate and posterior pharynx, until some resistance in the hypopharynx is felt. A laryngoscope can be used to assist placement. Once gas exchange is established, an attempt at intubation can be made. The well-lubricated endotracheal tube is passed down the iLMA tube, rotating gently to distribute the lubricant until the 15-cm marker (or the transverse line on the proprietary LMA Fastrach endotracheal tube). The endotracheal tube tip is now positioned through the epiglottic elevating bar. Gently lift the iLMA about 2–5 cm with the metal handle while the endotracheal tube is advanced into the trachea. Inflate the endotracheal tube cuff and confirm tracheal intubation (see later). Remove the endotracheal tube connector, and position the stabiliser rod on the endotracheal tube opening – this is needed to maintain the tube position in the trachea as the mask is removed. Lastly, gently remove the iLMA over the endotracheal tube/stabiliser assembly. Remove the stabiliser rod, reconfirm tube position and secure.

The successful use of an iLMA requires some familiarity with the equipment and technique, and at least simulated exposure is strongly recommended. Contraindications for using an ILMA or LMA include inability to open the mouth, pharyngeal pathology, airway obstruction at or below the larynx, low pulmonary compliance or high airway resistance. Complications include aspiration, gastric insufflation, partial airway obstruction, coughing, laryngospasm, postextubation stridor and kinking of the shaft of the LMA.

COMBITUBE (OESOPHAGEAL–TRACHEAL DOUBLE-LUMEN AIRWAY)

The oesophageal–tracheal Combitube is a double-lumen tube that is blindly inserted into the oropharynx up to the indicated markings.⁷ The oesophageal lumen is blocked at the distal end and has side perforations at the pharyngeal level whereas the tracheal lumen has a hole at the distal end. It has two balloon cuffs, a distal one and a proximal pharyngeal balloon. The patient is ventilated through the oesophageal lumen initially as the Combitube usually enters the oesophagus,⁷ with the distal cuff sealing the oesophagus and the proximal balloon sealing the proximal pharynx. Gas exits the perforations and enters the pharynx and larynx. In the event of failure of ventilation, tracheal intubation may have occurred and then the tracheal lumen is ventilated while the distal cuff seals the trachea. Although demonstrated to be a useful airway management adjunct, its role in resuscitation and management of the difficult airway in the ICU environment is yet to be established. Barotrauma, especially oesophageal rupture, has been reported.

INVASIVE TECHNIQUES

ENDOTRACHEAL INTUBATION

Endotracheal intubation remains the ‘gold standard’ of definitive airway management, allowing for spontaneous and positive-pressure ventilation, with good macroscopic protection from aspiration. Indications include acute airway obstruction, facilitation of tracheal suctioning, protection of the airway in those without protective reflexes, and respiratory failure requiring ventilatory support with high inspired concentrations of oxygen and PEEP.

Preparation

Prior to proceeding with any attempts at intubation, regardless of the technique chosen, preparation and checking of all relevant equipment are essential. Tracheal intubation should be preceded by adequate preoxygenation, particularly in ICU patients who frequently have pulmonary or cardiac pathology. Difficult airway management equipment (see Table 25.3) should also be accessible within a few minutes. Food, vomitus, blood or sputum may obstruct the airway and therefore suction, able to generate at least 300 mmHg (40 kPa) and a flow rate of 30 l/min, should always be available. Excessively vigorous suctioning should be avoided as it can cause laryngospasm, vagal stimulation, mucosal injury and bleeding.

Direct laryngoscopy

Although an essential skill for all intensivists, direct laryngoscopy and intubation is difficult to master.⁸ It can be learned by simulation, exposure to patients in a controlled environment such as the operating room and subsequently practised under supervision in the ICU setting. A detailed description of the technique is beyond the scope of this chapter; however certain problems and complications commonly encountered in ICU patients should be anticipated and prevented.

Cricoid pressure is usually required as few ICU patients can be adequately starved prior to intubation. ICU patients are at high risk for severe hypotension following the use of hypnotic or sedative agents used to facilitate intubation. Mechanisms include, but are not limited to, direct drug effects causing myocardial depression and decreases in peripheral vascular resistance, a reduction in venous return and preload following the increase in intrathoracic pressure with positive-pressure ventilation and the removal of sympathetic stimulation once anxiety disappears. It is therefore useful to ensure adequate hydration, availability of inotrope and vasopressor drugs, judicial use of positive ventilatory pressures and close haemodynamic monitoring before and during the intubation period.

Because intubation is often more difficult in ICU patients (see later), excellent technique is needed. All first attempts at intubation should incorporate proper head position, the use of techniques such as BURP (backward, upward, rightward pressure) that may be helpful to bring the vocal cords into the field of vision, and, if necessary, the use of a gum elastic bougie or equivalent. A difficult-to-visualise ‘anterior larynx’ can often be more easily intubated if a gum elastic bougie is advanced in the midline and directed anteriorly into the trachea. The endotracheal tube is then advanced over the guide from an initial 90° anticlockwise-rotated position. Clinical signs of correct tracheal placement of the guide include coughing (in incompletely paralysed patients), a resistance felt before the guide is fully advanced (usually at 45 cm or less from the lips because of resistance at the carina or bronchus) and a sensation of clicks from the tracheal rings. A number of alternative intubating guides are available, including the hollow endotracheal tube changer, which can be attached to a side-stream capnometer, or to an oxygen source. The lighted stylet is less commonly used and has a light at the distal end that results in a characteristic midline transillumination appearance when the light enters the larynx.

If multiple intubation attempts are required, the maximum interruption to ventilation should be about 30 s and adequate ventilation and oxygenation must be provided between attempts. Minimum monitoring should consist of continuous-pulse oximetry, electrocardiogram (ECG) and blood pressure. In ICU patients the largest reasonable endotracheal tube should be chosen to facilitate optimal sputum clearance, access for fibreoptic bronchoscopy and to reduce airway resistance in difficult-to-ventilate patients. Sizes of 8.0–9.0 mm in adult males and 7.0–8.0 mm in adult females are generally used.

The route of intubation may be orotracheal or nasotracheal. The orotracheal route is preferred because it has fewer complications. Nasotracheal intubation is contraindicated in the presence of fracture of the base of skull. Other complications include epistaxis, turbinate cartilage and nasal septal damage, and in the long-term an increased risk of nosocomial pneumonia and sinusitis.⁹

Confirmation of tracheal tube placement

Confirming correct intratracheal tube placement is essential. Direct visualisation and measurement of expired CO₂ by capnography are the most reliable methods.¹⁶ Capnography may produce false-positive results with the first few breaths after oesophageal intubation (i.e. detectable end-tidal PCO₂), if gastric insufflation from mask ventilation has occurred. A false-negative (decreased PCO₂, despite correct position) may occur with cardiac arrest and low-cardiac-output states. Position can also be reliably confirmed by fibreoptic confirmation and the use of oesophageal detectors or self-inflating bulbs.¹ Other clinical signs, such as auscultation of breath sounds over both sides of the chest and epigastrium, visualisation of condensed water vapour in the tube and chest wall movement, are less reliable.

Complications of endotracheal intubation

These may be classified into those occurring during intubation (e.g. incorrect tube placement, laryngeal trauma, deleterious cardiovascular response to laryngoscopy and intubation, increase in intracranial pressure, hypoxaemia and aspiration), while the tube is in place (e.g. blockage, dislodgment, tube deformation, damage to larynx and complications of mechanical ventilation), and following extubation (e.g. aspiration and postextubation airway obstruction, laryngeal and tracheal stenosis). Specific techniques should be used to minimise side-effects such as cardiovascular responses and increases in intracranial pressure.

TRANSTRACHEAL JET VENTILATION (TTJV)

Percutaneous TTJV, using a large-bore intravenous (IV) catheter inserted through the cricothyroid membrane, can be used to provide temporary ventilation when other techniques have failed.¹⁷ Ventilation through the cannula with a standard manual resuscitator bag is inadequate, and a jet ventilation system is necessary. A high-pressure (up to 50 psi or 344 kPa) oxygen source is required for adequate ventilation through a 14 FG IV cannula with a manually regulated jet injector. Expiratory gases must be able to escape via the glottis. Appropriate chest movements during expiration must be noted. The consequence of expiratory obstruction is severe and potentially fatal barotrauma.

Complications may be caused by insertion of the IV cannula (e.g. bleeding and oesophageal perforation), use of high-pressure gases (e.g. hyperinflation, barotrauma), catheter kinking or displacement (the latter causing potentially catastrophic subcutaneous emphysema) and failure to protect the airway (i.e. aspiration).

CRICOTHYROIDOTOMY

Cricothyroidotomy, by surgery or percutaneously, is a reliable, relatively safe and easy way of providing an emergency airway.¹⁸ It is the method of choice if severe or complete upper-airway obstruction exists. The simplest, fastest and most proven method uses a horizontal incision through the cricothyroid membrane with the space held wide open by the scalpel handle or forceps. This is followed by insertion of a small tracheostomy or endotracheal tube (Figure 25.2). If available, a small surgical hook is useful to hold down the inferior margin of the incision to facilitate cannulation. Commercial cricothyroidotomy sets, using the Seldinger technique, are available. A tube with internal diameter of 3.0 mm will allow adequate gas flow for self-inflating bag ventilation provided supplemental oxygen is used. Since the diameter of the cricothyroid space is 9 × 30 mm, tubes of 8.5 mm outer diameter or less should avoid laryngeal and vocal cord damage. Commercially available percutaneous tracheostomy sets that meet the above requirements are available. Complications such as subglottic stenosis (1.6%), thyroid fracture, haemorrhage and pneumothorax are acceptably low. Cricothyroidotomy is generally contraindicated in complete laryngotracheal disruption and age < 12 years.

Figure 25.2 Cricothyroidotomy performed with a scalpel. (a) Thyroid cartilage; (b) cricoid cartilage; (c) thyroid gland; (d) cricoid membrane, usually easily palpable subcutaneously.

TRACHEOSTOMY

There is little agreement on the indications, best technique or optimal timing of tracheostomy in ICU patients. Suggested indications for tracheostomy include bypass of glottic and supraglottic obstruction, access for tracheal toilet, provision of a more comfortable airway for prolonged ventilatory support and protection of the airways from aspiration.¹⁹ In uncomplicated patients, percutaneous tracheostomy performed by an intensivist at the bedside is at least as safe as surgical tracheostomy performed in the operating room, and is probably associated with a lower incidence of infectious complications.^20,²¹ The added convenience and cost savings have made percutaneous tracheostomy the procedure of choice in many institutions. However, the percutaneous technique is best avoided in the presence of coagulapathy – an international normalised ratio (INR) > 2 or platelet count < 40 × 10⁹/l; significant anatomical abnormality in the anterior neck in the region of the trachea, vessels or thyroid gland; previous tracheostomy scar; or a cervical spinal injury that is considered unstable.

Ciaglia’s percutaneous technique was described in 1985.²² After making an adequate skin incision and using blunt dissection with forceps the trachea is gently exposed. The endotracheal tube is then withdrawn so that its cuff lies just above the vocal cords. The operator confirms tube position to be above the stoma site by palpation of the trachea. A J-wire is placed in the trachea through a needle inserted through the membrane above or below the second tracheal ring. A series of curved dilators is used to enlarge the stoma progressively. A tracheostomy tube is then inserted into the trachea and the endotracheal tube removed. Ciaglia later introduced a modified tapered dilator to avoid the use of multiple dilators. Although quicker, the single dilator may cause more tracheal wall injuries and ring fractures.²² The Griggs technique utilises a Kelly forceps, modified to allow it to be guided by the J-wire, to dilate the tract before insertion of tracheostomy tube.²³ Although the Griggs technique is marginally faster (by 2–3 minutes) than the Ciaglia technique, most, but not all, prospective studies have suggested that the Griggs technique may cause marginally more bleeding and functional complications, and cannula insertion may be somewhat more difficult.^24,²⁵ Fibreoptic bronchoscopy during percutaneous tracheostomy may help to prevent incorrect guidewire placement and tracheal ring rupture or herniation, but definitive evidence supporting its routine use is lacking. Definitive identification of the best technique still requires further investigation and long-term follow-up.

Minitracheostomy describes the percutaneous insertion of a small 4-mm non-cuffed tracheostomy tube through the cricothyroid membrane or trachea, mainly to facilitate suctioning in patients with poor cough ability.

Complications of tracheostomy are listed in Table 25.4.

Table 25.4 Complications of tracheostomy

Immediate

Procedural complications

Haemorrhage

Surgical emphysema, pneumothorax, air embolism

Cricoid cartilage damage

Misplacement in pretracheal tissues or right main bronchus

Compression of tube lumen by cuff herniation

Occlusion of the tip against the carina or tracheal wall

Delayed

Blockage with secretions

Infection of the tracheostomy site, tracheobronchial tree and larynx

Pressure on tracheal wall from the tracheostomy tube or cuff

Mucosal ulceration and perforation

Deep erosion into the innominate artery

Tracheo-oesophageal fistula

Late

Granulomata of the trachea

Tracheal and laryngeal stenosis

Persistent sinus at tracheostomy site

Tracheomalacia and tracheal dilatation

LOCAL ANAESTHESIA

Instrumentation of the upper airway in awake patients requires good local anaesthesia to increase comfort, improve cooperation, attenuate cardiovascular responses and reduce the risk of laryngospasm. Rapid transcricoid injection and either sprayed or nebulised lidocaine to the nares, posterior pharynx and tongue are effective (Table 25.5).²⁶ Nerve block techniques may improve analgesia but are not essential. Cocaine has been a popular choice for its vasoconstrictor properties, but it is toxic and its supply is regulated. Systemic absorption of topically applied lidocaine (maximum dose 4 mg/kg) is variable, and the clinician should be alert for signs and symptoms of toxicity.

Table 25.5 Local anaesthesia of the upper airway in adults

Technique	Drug dosage
Nerve block
Internal branch of superior laryngeal nerve	Lidocaine 1–2% (2 ml/side)
Glossopharyngeal nerve	Lidocaine 1–2% (3 ml/side)
Topical anaesthesia of the tongue and oropharynx
Gargle	Lidocaine viscous 4% (5 ml)
Spray	Lidocaine 10% (5–10 sprays = 50–100 mg)
Nebulised	Lidocaine 4%
Topical anaesthesia of the nasal mucosa
Cocaine spray or paste	Cocaine 4–5% (0.5–2 ml)
Gel	Lidocaine 2% gel (5 ml)
Lidocaine spray	Lidocaine 10% (10 sprays = 100 mg)
Lidocaine + phenylephrine spray	Lidocaine 3% + phenylephrine 0.25% (0.5 ml)
Topical anaesthesia of glottis and trachea
Spray-as-you-go through bronchoscope	Lidocaine 1–4% (3 mg/kg)
Cricothyroid membrane puncture	Lidocaine 2% (5 ml)
Nebulised	Lidocaine 4% (4 ml) ± phenylephrine 1% (1 ml)

THE DIFFICULT AIRWAY

The difficult airway has been described as one in which a conventionally trained anaesthesiologist experiences difficulty with mask ventilation, tracheal intubation or both. Difficult intubations may be expected in 1–3% of patients presenting for general anaesthesia, and the incidence is likely to be considerably higher in ICU patients.

More than 85% of difficult intubations can be managed successfully by experienced clinicians without resorting to a surgical solution. The experience of the operator is probably the most important factor determining success or failure. Experience implies greater manual skills, better anticipation of problems, use of pre-prepared strategies, and familiarity with multiple techniques. Thus, training of intensivists must specifically include a variety of airway management strategies and skills.

ASSISTANCE AND ENVIRONMENT

Because the patient’s condition may rapidly deteriorate as a consequence of a poorly managed airway emergency, the most senior help available should be immediately summoned. If the situation allows, the patient should be moved to the best location for emergency airway interventions, usually the operating theatre or ICU, and difficult airway equipment requested (see Table 25.3). A senior assistant can help in gaining IV access, administering drugs, setting up equipment and managing the airway. A skilled intensivist or ear, nose and throat surgeon (gowned and standing by) can help to provide a surgical airway or perform rigid bronchoscopy to remove foreign bodies.

ANTICIPATING AND GRADING A DIFFICULT AIRWAY

Intubation difficulty can be anticipated or predicted by the following (although the sensitivity and specificity of individual features and classifications tend to be low, a combination of features will significantly raise the risk of a difficult airway):

1 Anatomical or pathological features of difficult intubation in subjects who otherwise appear normal:

a short neck, especially if obese or muscular (a thyromental distance < 6 cm)

b limited neck and jaw movements (e.g. as a result of trismus, osteoarthritis, ankylosing spondylitis, rheumatoid arthritis or perioral scarring)

c protruding teeth, small mouth (interincisor distance < 3 cm), long high curved palate or receding lower jaw

d space-occupying lesions of the oropharynx and larynx

e congenital conditions with any of the above features (e.g. Marfan’s syndrome)

2 Mallampatti classification ²⁷ of visualising the oropharyngeal structures (a cooperative sitting patient is required for this assessment, and class > 2 predicts possible difficulty):

a class 1: visible soft palate, uvula, fauces and pillars

b class 2: visible soft palate, uvula and fauces

c class 3: visible soft palate and base of uvula

d class 4: soft palate is not visible

3 The degree of difficulty experienced visualising the larynx by direct laryngoscopy should be recorded and is commonly graded by the classification of Cormack and Lehane.²⁸ Recently grade III has been devided into IIIa (epiglottis is mobile) and IIIb (epiglottis is not mobile) subgrades:

a grade I: complete glottis is visible

b grade II: anterior glottis is not visible

c grade III: epiglottis but not glottis is visible

d grade IV: epiglottis is not visible

FAILED INTUBATION AND VENTILATION ALGORITHMS

A pre-prepared plan in the event of failed intubation and/or ventilation is essential and a number have been described in the form of single or multiple algorithms.^1,² The algorithm shown here is an example of a single algorithm applicable to some anticipated airway difficulty scenarios in ICU patients (see Figure 25.1). Although not comprehensive, the algorithm is complex and only one or two pathways are applicable to an individual clinical scenario. The relevant pathway should be identified as early as possible in each individual case and then applied. Ultimately effective implementation depends on the skill of the operator and the appropriate use of the airway techniques described above.

If the initial attempt at intubation fails, call for help immediately. Repeated attempts at direct laryngoscopy should be avoided unless a more experienced operator intervenes, or a potentially helpful manoeuvre has been carried out (e.g. significant repositioning, externally applied laryngeal pressure or change of laryngoscope blade). Hypoxia will quickly result if the patient is inade-quately ventilated between attempts (see above). In addition, oedema and bleeding caused by repeated laryngoscopy attempts may impair both mask ventilation and the use of alternative techniques such as fibreoptic intubation. When indicated to prevent hypoxia a surgical airway should not be delayed (see Figures 25.1 and 25.2).

UPPER-AIRWAY OBSTRUCTION

ANATOMY AND PATHOPHYSIOLOGY

The upper airway begins at the nose and mouth, and ends at the carina. Obstruction is likely to occur at sites of anatomical narrowing, such as the hypopharynx at the base of the tongue, and the false and true vocal cords at the laryngeal opening. Sites of airway obstruction are classified as supraglottic (above the true cords), glottic (involving the true vocal cords) or infraglottic (below the true cords and above the carina).

The upper airway can also be divided into intrathoracic and extrathoracic portions, which behave differently during inspiration and expiration. The intrathoracic airway dilates during inspiration because it is ‘pulled outwards’ by negative intrapleural pressure. Positive intrapleural pressure during expiration causes compression and narrowing. Conversely the compliant extrathoracic airway, unexposed to intrapleural pressure, collapses during inspiration and expands during expiration. Recalling this phenomenon helps the understanding of typical clinical signs, radiographs and flow–volume loops.

AETIOLOGY

Acute upper-airway obstruction may result from functional or mechanical causes (Table 25.6). Functional causes include central nervous system and neuromuscular dysfunction. Mechanical causes may occur within the lumen, in the wall or extrinsic to the airway.

Table 25.6 Clinical conditions associated with acute upper-airway obstruction

Functional causes

Central nervous system depression

Head injury, cerebrovascular accident, cardiorespiratory arrest, shock, hypoxia, drug overdose, metabolic encephalopathies

Peripheral nervous system and neuromuscular abnormalities

Recurrent laryngeal nerve palsy (postoperative, inflammatory or tumour infiltration), obstructive sleep apnoea, laryngospasm, myasthenia gravis, Guillain–Barré polyneuritis, hypocalcaemic vocal cord spasm

Mechanical causes

Foreign-body aspiration

Infections

Epiglottitis, retropharyngeal cellulitis or abscess, Ludwig’s angina, diphtheria and tetanus, bacterial tracheitis, laryngotracheobronchitis

Laryngeal oedema

Allergic laryngeal oedema, angiotensin-converting enzyme inhibitor-associated, hereditary angioedema, acquired C1 esterase deficiency

Haemorrhage and haematoma

Postoperative, anticoagulation therapy, inherited or acquired coagulation factor deficiency

Trauma

Burns

Inhalational thermal injury, ingestion of toxic chemical and caustic agents

Neoplasm

Pharyngeal, laryngeal and tracheobronchial carcinoma, vocal cord polyposis

Congenital

Vascular rings, laryngeal webs, laryngocele

Miscellaneous

Cricoarytenoid arthritis, achalasia of the oesophagus, hysterical stridor, myxoedema

CLINICAL PRESENTATION

The signs of partial airway obstruction are often progressive and begin with hoarseness, other voice changes or coughing, with more severe obstruction being markedby drooling, gagging, choking, inspiratory stridor or noisy respiration. Paradoxical chest wall movements and intercostal and supraclavicular retractions may be marked in severe obstruction. Powerful respiratory efforts may produce dermal ecchymoses and subcutaneous emphysema. Respiratory decompensation may be rapid in onset, and progress to complete obstruction. Lethargy, diminishing respiratory efforts and loss of consciousness are late signs of hypoxaemia and hypercarbia. Bradycardia and hypotension herald impending cardiac arrest.

Signs of sudden complete upper-airway obstruction are characteristic and progress rapidly. The victim cannot breathe, speak or cough, and may hold the throat between the thumb and index finger – the universal choking sign.²⁹ Agitation, panic and vigorous breathing efforts are rapidly followed by cyanosis. Respiratory efforts diminish as consciousness is lost, and death results within 2–5 min if obstruction is not relieved.

SPECIAL EVALUATION OR INVESTIGATIONS

If the patient remains stable, specific diagnostic evaluation may be undertaken, provided advanced airway management facilities and skilled personnel are immediately available.

LARYNGOSCOPY AND BRONCHOSCOPY

Indirect laryngoscopy in a stable, cooperative patient is useful to diagnose foreign bodies, retropharyngeal or laryngeal masses and other glottic pathology.³⁰

Assessment with a flexible fibreoptic bronchoscope or laryngoscope is the evaluation method of choice in ICU patients and enables direct visualisation of upper-airway anatomy and function. The procedure can be performed at most sites without transporting the patient and risking complete obstruction. It can be applied to an awake, spontaneously breathing patient and, with care, should not worsen the obstruction. If indicated, definitive airway control by intubation can usually be achieved, by advancing an endotracheal tube over the bronchoscope into the trachea. Disadvantages are the need for a skilled operator and a cooperative patient, and the poor visual field reduces effectiveness if blood and secretions are copious.

Direct laryngoscopy enables forceps removal of foreign bodies and high-volume suctioning of blood, vomitus and secretions. Endotracheal intubation can rapidly be achieved under direct vision. Disadvantages are the need for general anaesthesia or good local analgesia (often difficult in the emergency setting). Direct laryngoscopy can be traumatic, and may worsen soft-tissue bleeding and oedema.

RADIOGRAPHIC IMAGING

Patients with potentially unstable airways should not be transported from a ‘safe’ environment like the emergency room, operating theatre or ICU for radiological investigation until the airway is secure. Anteroposterior and lateral plain neck X-rays are useful to detect radiopaque foreign bodies. The lateral view in the upright position in inspiration with the neck fully extended may reveal swelling of the epiglottis and supraglottic tissues. Ballooning of the hypopharynx is a classical signs of epiglottitis, but is not always present. Soft tissues and the extent of space-occupying lesions are best visualised by computed tomography (CT) scan, which can also assess the thyroid, cricoid and arytenoid cartilages and the airway lumen in stable patients, or in those in whom the airway has been secured.³¹ Although magnetic resonance imaging (MRI) has been used to image the upper airway, its use in acute airway obstruction is unproven.

GAS FLOW MEASUREMENT

Flow–volume loop measurement reveals characteristic patterns corresponding to different types and position of pathological lesions (Figure 25.3).³²

Figure 25.3 Flow–volume loops. Patterns resulting from different pathological lesions: (a) lower-airway obstruction (e.g. chronic obstructive pulmonary disease or asthma); (b) fixed, non-variable upper-airway obstruction (e.g. fibrous ring in trachea); (c) variable upper-airway obstruction, intrathoracic (e.g. tumour in the lower trachea); (d) variable upper-airway obstruction, extrathoracic (e.g. vocal cord tumour or paralysis).

MANAGEMENT

PREPARATION

Simplified algorithms to assist the management of partial and complete upper-airway obstruction are shown in Figures 25.4 and 25.5 and an appropriate management path should be chosen. Improvisation may be required for certain difficult problems. Special techniques in patients with suspected cervical spine instability are discussed elsewhere in this volume. Initial management follows:

1 Supplemental oxygen (100%) is immediately administered.

2 A choice of equipment for definitive airway control must be available and ready for use (see Table 25.3).

3 In adults IV access should be secured.

4 Initiate continuous monitoring of vital signs and pulse oximetry.

5 Patient transport before securing the airway must be carefully considered as it is difficult to provide safe conditions during transport.³⁰

Figure 25.4 Management of partial upper-airway obstruction (UAO). i.v., intravenous; CT, computed tomography; MRI, magnetic resonance imaging; LA, local anaesthesia; GA, general anaesthesia.

Figure 25.5 Management of complete upper-airway obstruction (UAO). Attempts at orotracheal intubation should not take longer than 10–20 s. FB, foreign body; TTJV, transtracheal jet ventilation.

AIRWAY MANAGEMENT TECHNIQUES IN AIRWAY OBSTRUCTION

THE UNCONSCIOUS PATIENT

If the upper airway is obstructed by the tongue and retropharyngeal tissues in an unconscious patient, airway patency is initially achieved by using standard airway manoeuvres ³³ and oropharyngeal and nasopharyngeal airways. Definitive airway control should follow if consciousness does not immediately return.

ENDOTRACHEAL INTUBATION

1 Direct laryngoscopic intubation is the method of choice for the unconscious, apnoeic patient as it allows rapid evaluation of any supraglottic problem and immediate airway security. It can also be attempted in an awake patient after careful application of local anaesthesia. Although there is some risk of loss of the airway after local anaesthesia, complete loss of the airway under general anaesthesia is common and may be catastrophic.

2 Awake fibreoptic intubation in a spontaneously breathing patient is usually safe, but requires a skilled operator. The procedure will take 2–10 minutes or longer,³⁴ and urgency of the case must be assessed beforehand with this time frame in mind. Alternatives should be initiated if the obstruction progresses or if intubation fails after a reasonable time. The following points may assist visualisation in acute upper-airway obstruction:

a The procedure is clearly explained to the patient.

b Good local anaesthesia and mucosal vasoconstrictors are important. Failure is most commonly due to excessive secretions and bleeding.

c If desired, the suction port of the fibrescope can be used to insufflate 100% oxygen or apply local anaesthetic. This also clears the fibrescope tip of secretions. Additional large-bore suction catheters may help.

3 Blind nasotracheal intubation provides a patent nasopharyngeal airway during the procedure, but is less useful when fibreoptic laryngoscopy is available.

Once endotracheal intubation is safely accomplished and confirmed, secure fixation of the endotracheal tube is mandatory. The patient’s upper limbs may need to be restrained to avoid self-extubation.

SURGICAL AIRWAYS

A surgical airway is indicated when endotracheal intubation is not possible, or when an unstable cervical spine is threatened by available airway techniques. It is the last line of defence against hypoxia. In airway obstruction options include the following:

1 Cricothyroidotomy is the method of choice if severe or complete upper-airway obstruction exists.

2 Percutaneous transtracheal jet ventilation. The technique must not be used in complete upper-airway obstruction because expiratory obstruction can cause severe and potentially fatal barotrauma.

3 Tracheostomy in the emergency setting is rarely required, although surgical tracheostomy under local anaesthesia may be reasonable under some controlled conditions (see Figure 25.4).

COMMON CLINICAL CONDITIONS AND THEIR MANAGEMENT

FOREIGN-BODY OBSTRUCTION

Foreign-body obstruction is the most common cause of acute airway obstruction. The elderly, especially those in institutions, are at risk. The use of dentures, alcohol and depressant drugs increases risk. Fatal food asphyxiation or ‘café coronary’ should be considered in any acute respiratory arrest where the victim cannot be ventilated.³⁵

Patients who are still able to cough or speak clearly should be given the opportunity to expel the foreign body spontaneously. If not, expulsion of the foreign body can be attempted with one or a combination of chest thrusts, abdominal thrusts (Heimlich manoeuvre ²⁹) or back blows applied in rapid sequence in the most convenient order.³³ The abdominal thrust is performed from behind: the rescuer encircles his or her arms around the victim, placing the thumb of one fist between the umbilicus and xiphisternum. The fist is gripped by the other hand, and an inward, upward thrust is applied. Chest thrusts are similar (rescuer’s arms should encircle the chest, and a fist placed over midsternum) and are convenient for use in pregnancy and obesity. Unwanted effects, such as vomiting, aspiration, fractured ribs, barotrauma and ruptured organs, have been reported. Extract visible solid material with a finger sweep only in unconscious patients.³³ If these manoeuvres fail, management immediately proceeds as shown in Figures 25.4 and 25.5. If cardiac arrest occurs, proceed with cardiopulmonary resuscitation.

EXTRINSIC AIRWAY COMPRESSION

Extrinsic space-occupying lesions can cause upper-airway obstruction. Compression from haematomas may be associated with trauma, neck surgery, central venous catheterisation, anticoagulants and congenital or acquired coagulopathies. Haematomas following surgery should immediately be evacuated by removing skin and subcutaneous sutures. If this fails, an artificial airway must be secured immediately. In patients with coagulation abnormalities, intubation is preferred over a surgical airway. Most haematomas secondary to coagulopathy do not require surgical intervention, and resolve with conservative therapy (i.e. vitamin K and blood component therapy).

Partial airway obstruction caused by retropharyngeal abscess is best managed by drainage under local anaesthesia. Gentle fibreoptic examination and intubation or direct laryngoscopy and intubation in the lateral, head-down position are favored by some.³⁰ Risks are related to inadvertent rupture of the abscess, with subsequent flooding of the airway.

Ludwig’s angina is a mixed infection of the floor of the mouth resulting in an inflammatory mass in the space between the tongue and the muscles and anterior neck fascia. The supraglottic airway is compressed and becomes narrowed.³⁶ Direct laryngoscopy is difficult, as the tongue cannot be anteriorly displaced. Awake fibreoptic-guided intubation or a surgical airway, along with antibiotic therapy, is required.

INTRINSIC AIRWAY COMPRESSION

Burn inhalation and ingestion injury

Patients with large burn area (more than 40%), or with severe facial burns or inhalation injury (soot in the nostrils, burns of the tongue and pharynx, stridor or hoarseness) are at risk pf developing progressive supraglottic oedema, usually within 24–48 hours. Such patients usually require early prophylactic tracheal intubation. If not prophylactically intubated, subsequent need for tracheal intubation can best be decided by frequent (2–4-hourly), repeated awake fibreoptic laryngoscopy as well as regular charting of known signs and symptoms of obstruction.³⁷ Careful inspection by direct laryngoscopy is an alternative to fibreoptic laryngoscopy. Ingestion of hot fluids or corrosive agents can also cause delayed oedema and airway swelling and should be managed similarly.³⁸

Adult epiglottitis

Epiglottitis is an uncommon but increasingly recognised infectious disease in adults.³⁹ It involves the epiglottis and supraglottic larynx, causing swelling with consequent airway obstruction. Haemophilus influenzae, H. parainfluenzae, Streptococcus pneumoniae, haemolytic streptococci and Staphylococcus aureus are common causative organisms. Reported mortality varies in adults (0%–7%), due to difficult diagnosis and non-standardised treatment.⁴⁰ Clinical features are sudden onset of sore throat (pain often greater than suggested by clinical findings), muffled voice, dysphagia, stridor, dyspnoea and respiratory distress. Systemic toxaemia is common. Gentle indirect laryngoscopy, fibreoptic laryngoscopy or lateral neck X-ray confirms the diagnosis.

Airway management is controversial.³⁹^–⁴¹ Some experts recommend securing a definitive airway on presentation while others suggest close observation in ICU. There are, however, reports of sudden obstruction and death with the latter approach.⁴⁰ Onset of dyspnoea is an important sign predicting the need for intubation. Both tracheal intubation and tracheostomy are acceptable, but tracheal intubation may result in better long-term outcome. Prior to securing the airway, patient positioning is important, and changing from a sitting to supine position may induce complete obstruction. In more stable patients, awake fibreoptic intubation is preferable if a skilled operator is available. Endotracheal intubation following gaseous induction is recommended by some authorities, but complete obstruction can occur, even when this procedure is undertaken by a skilled anaesthetist.⁴¹ A skilled assistant, scrubbed and ready to secure a surgical airway, may prevent disaster. Rapid-sequence induction using muscle relaxants is dangerous and should be avoided. Tracheostomy under local anaesthesia is a safe alternative.

Antibiotics are administered as soon as the diagnosis is established. Cefotaxime 2 g IV 6-hourly or ampicillin 1–2 g IV 6-hourly plus chloramphenicol 50 mg/kg per day are empiric regimens; however, patient factors, local bacterial sensitivities and cultures of epiglottal swabs and blood may influence the antibiotic choice. Supportive care includes adequate sedation and tracheobronchial toilet. Abscesses should be surgically drained. There is no good evidence supporting the use of steroids.

Angioedema

Allergic responses involving the upper airway may be localised or part of a systemic anaphylactic reaction. Angioedema is characterised by subepithelial swelling. Angioedema of the lips, supraglottis, glottis and infraglottis may result in airway obstruction. The systemic reaction consists of variable combinations of urticaria (79%), bronchospasm (70%), shock, cardiovascular collapse and abdominal pain.⁴² Common causative agents are Hymenoptera stings, shellfish ingestion and drugs. Treatment consists of immediately ensuring an adequate airway (see Figures 25.4 and 25.5), and administration of oxygen, adrenaline (epinephrine) and steroids. As it is likely to recur, the patient should be kept under close supervision and fully investigated.

Hereditary angioedema is a rare, inherited disorder of the complement system, caused by functionless or low levels of C1 esterase inhibitor.⁴³ Non-pruritic, non-painful angioedema involving skin and subcutaneous tissue occurs in various locations, including the upper airway.⁴⁴ Precipitating causes include stress, physical exertion and localised trauma (including dental or maxillofacial surgery and laryngoscopy). Acute attacks do not respond to adrenaline, antihistamines or corticosteroids. Management consists of establishing a secure airway and infusion of C1 esterase inhibitor concentrate (25 U/kg) which has an onset of action of 30–120 minutes.^44,⁴⁵ If not available, fresh frozen plasma (2–4 units) may be considered. Stanozolol 1–4 mg daily or danazol 50–600 mg/day has been shown to be effective in decreasing frequency and severity of attacks.⁴⁶ Antifibrinolytic agents (e.g. tranexamic acid) are less effective. Danazol, C1 esterase inhibitor and fresh frozen plasma (2–4 units) can be used as preoperative prophylaxis.⁴⁵

Angiotensin-converting enzyme inhibitor-related angioedema is increasingly seen and is possibly the result of reduced bradykinin metabolism.⁴⁷ Treatment focuses on airway support.

Postextubation laryngeal oedema

Laryngeal oedema following extubation occurs in about 20% of adults, but is not usually severe enough to precipitate reintubation.⁴⁸ Risk of severe oedema is increased after excessive airway manipulation, traumatic or prolonged tracheal intubation and if high cuff pressures are used. Treatment in adults is conservative, with close observation and humidified oxygen therapy. Nebulised plain epinephrine (1–2 ml 1:1000 solution diluted with 2 ml saline or undiluted 1:1000 solution 4–5 ml) or racemic epinephrine (0.25–0.5 ml 2.25% solution in 2–4 ml saline) has been used. Nebulisation may need to be repeated every 30–60 minutes. The prophylactic use of steroids to reduce post extubation laryngeal oedema remains controversial. Optimal dose, duration and target groups for prophylaxis have not yet been clearly defined. A recent study demonstrated that methylprednisolone 20 mg IV four-hourly started 12 hours prior to extubation (80 mg total dose) reduced the incidence of early re-intubation in patients intubated for more than 36 hours.⁴⁸

POSTOBSTRUCTION PULMONARY OEDEMA

Postobstruction pulmonary oedema may occur in up to 11% of cases of airway obstruction.⁴⁹ Oedema appears to be caused by the markedly decreased intrathoracic and interstitial tissue pressure resulting from forced inspiration against a closed upper airway. The resulting increased hydrostatic gradient causes transudation of fluid from pulmonary capillaries to the interstitium. In addition, increased venous return may increase pulmonary blood flow and pressure, further worsening oedema. Hypoxia and the hyperadrenergic stress state may also affect capillary hydrostatic pressure, although pulmonary capillary occlusion pressure is often normal. The oedema usually occurs within minutes after the relief of the obstruction, but may be delayed up to 2.5 hours.⁵⁰ Management includes maintenance of airway patency, oxygen therapy, diuretics, morphine and fluid restriction. Application of continuous positive airways pressure or ventilation with PEEP may be necessary in severe cases. Pulmonary artery catheterisation need only be used for complicated cases.

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11 Giudice JC, Komansky H, Gordon R, et al. Acute upper airway obstruction – fibreoptic bronchoscopy in diagnosis and therapy. Crit Care Med. 1981;9:878-879.