Management of the Difficult Airway

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Management of the Difficult Airway

This important topic can be divided into anticipated and unanticipated difficult airway management. Although both situations may require similar techniques, the approach, urgency and risk of adverse outcomes differ considerably between the two settings.

Difficulties arise most commonly at the start or end of anaesthesia, with the former the more common. Difficulty at the end of anaesthesia involves either airway obstruction or aspiration; when the problem is airway obstruction, difficulty may be categorized in the same manner as difficulty after induction. Difficult airway management may involve any of the four main categories of airway management:

Airway management is usually routine and straightforward, but each of the above techniques may fail. Anaesthetists are used to high levels of success at what they do and routine airway management does not usually fail. The frequency of failure of routine airway management is as follows:

CICV is an abbreviation for ‘Can’t intubate, can’t ventilate’.

Failure rates probably vary depending on definitions used, operator experience and the group of patients examined. Novices may have failure rates more than 10-fold higher. Difficulty may arise at least 10 times more often than failure. For example, difficult laryngoscopy (and hence difficult intubation) occurs in about 6% of intubations in unselected patients but in selected groups, e.g. those presenting for cervical spine surgery, this may be as high as 20%. The urgency of a procedure also contributes to ease and success. During emergency intubation (with rapid sequence induction), intubation fails approximately eight times as often as during elective intubation.

About a quarter of major airway emergencies occur in the Intensive Care Unit (ICU) or the emergency department and it is necessary to ensure that the same response to airway difficulty can be provided in these locations as in the operating theatre. In the emergency department, tracheal intubation may be difficult in 1 in 12, fail as often as 1 in 50, and an emergency surgical airway has been reported to be needed as often as 1 in 200 intubation attempts.

Although it is important not to dismiss complications arising during uncomplicated airway management, the vast majority of complications occur during ‘difficult airway management’, however defined.

Airway management difficulties contribute to a large proportion of anaesthesia-related deaths and CICV accounts for over 25% of all anaesthesia-related deaths.

BEFORE MANAGING THE DIFFICULT AIRWAY

Preparedness

The key to safe management of the difficult airway is preparedness.

Organizational Preparedness

Guidelines: Organizational preparedness requires that those events which might reasonably be anticipated to occur can be managed appropriately in the organization. This in turn requires guidelines (or policies) and equipment. As a minimum, the guidelines should cover the following:

Guidelines will also ideally include unexpected failed mask ventilation and unexpected failed insertion of a SAD. Guidelines might also address the indications for fibreoptic intubation and management of extubation of the difficult airway. These guidelines need not be created by every institution and there is much to be said for nationally accepted or published guidelines being adopted as local policy (e.g. the Difficult Airway Society [DAS] guidelines in the UK). There are several advantages to widespread adoption of this approach; for example, practice becomes based on available evidence and employees who move between hospitals will be immediately familiar with emergency protocols.

Equipment: Logic dictates that the equipment needed to satisfy institutional preparedness is that which is needed for all the guidelines to be carried out in their entirety. This equipment should be procured, stored, maintained and checked appropriately to ensure that it is readily available whenever and wherever it is required. Difficult airway equipment (perhaps better described as advanced airway equipment) is usually maintained in an airway trolley (Fig. 22.1). It is advisable for all airway trolleys in an organization to have the same content and layout; this includes areas such as ICU and the emergency department. Organizing the airway trolley so that the layout of the equipment matches the flow of the airway guideline may improve compliance with the guideline and patient care; an example based on the DAS guideline is shown in Figure 22.2.

Communication and Training: The final aspect of institutional preparedness is communication and training. Guidelines are of limited value if they are not understood, accepted and practised by the relevant staff. Many hospitals have access to training in advanced airway management. Guidelines should be distributed widely. Training should involve the use of local guidelines and locally available equipment to ensure relevance. Where possible, those individuals who work together in teams should be trained together so that the chances of the team working well in an emergency are enhanced. The ‘team’ need not be limited to the anaesthetist and anaesthetic assistant, and some training (rather like a trauma team) allocates specific roles to surgeons, scrub nurses and other anaesthetists who attend to help in a crisis. While there is no evidence that such an approach improves outcome in real airway emergencies, it probably enables an organized, systematic approach and has the value of enabling a ‘team leader’ to oversee the management of the crisis, perhaps avoiding ‘task fixation’ and promoting ‘situation awareness’.

Institutional preparedness is a process whereby the organization facilitates good difficult airway management by individuals. Such preparation usually requires that the organization has a nominated airway lead for this role, usually a consultant anaesthetist.

Personal Preparedness

Individual anaesthetists have a clear responsibility to be prepared to manage the difficult airway. At different stages of training and expertise the responsibilities will differ. The elements of individual preparedness are:

Through appropriate education, individual anaesthetists should ensure that they have the appropriate knowledge and skills to deal with anticipated and unanticipated airway difficulties and emergencies which they may reasonably expect to encounter. It is also important that the less experienced know the limitations of their expertise and therefore when to call for assistance.

Individual training requires that each anaesthetist is familiar with local guidelines and is trained to find and use the locally available equipment according to local guidelines. Training should also include an understanding of how the less experienced anaesthetist seeks senior assistance. To the trained anaesthetist, management of the difficult airway should become a part of routine practice.

Appropriate individualized assessment and planning is a vital part of personal preparedness and is discussed below.

Assessment and Planning a Strategy: While it is accepted that not all cases of airway difficulty can be anticipated (perhaps 50% are unanticipated), many can be. Airway assessment is discussed in detail in Chapter 21. Only principles are discussed here.

Airway assessment involves using patient history, previous notes and any other available documentation (e.g. alert bracelets) to identify:

Assessment should include an assessment of the likely ease or difficulty of performing the planned primary airway technique and potential rescue techniques. Assessment should also specifically assess the risk of aspiration. When difficulty with one technique is identified, particular attention is required in assessment of other techniques, first because that rescue technique is more likely to be required and second because in patients in whom one technique fails there is an increased likelihood that other techniques will also fail. Multiple airway problems tend to co-exist in the same patient.

While there are many features that may predict difficult airway management the following should raise particular concerns:

The importance of assessment and planning is underlined by the fact that several large studies examining major airway complications have identified failure to assess, failure to alter technique in the light of findings, and failure to have back-up plans as causes of poor outcomes.

A strategy is a logical sequential series of plans which aim to achieve oxygenation, ventilation and avoidance of aspiration and which are appropriate to the patient’s specific features and condition. Airway management should not rely on the success of plan A and should be based on a clear strategy that is communicated to all. An aphorism that may encapsulate this is ‘in order to succeed, it is necessary to plan for failure’. Guidelines are, in essence, a strategy for unexpected difficulty. The strategy should usefully identify a ‘place of safety’; this is a pre-planned rescue plan when problems arise; for instance, if insertion of a laryngeal mask is known to be successful this may be the place of safety, but alternatively the safest option may be to allow the patient to wake.

Assessment is a pointless ritual unless the chosen technique is adjusted as necessary according to the findings. The strategy should be consistent with the findings at assessment.

MANAGEMENT OF THE DIFFICULT AIRWAY

Training, Teamwork and Human Factors

Many ‘airway disasters’ are associated with poor planning, use of techniques that are unfamiliar to the user (sometimes used incorrectly or sub-optimally), poor team-work and poor communication. Human factors associated with airway management complications include:

Task fixation is the tendency, having started a task (e.g. tracheal intubation), to persevere with attempts to complete that task, even when it is not in the patient’s interest (e.g. repeated attempts risking airway trauma and progression to CICV). Situation awareness should enable the anaesthetist (or someone else in the team) to realise that the task is failing and that another technique or approach is necessary, or perhaps that priorities have changed (e.g. from intubation to oxygenation and waking the patient). When a team works well together and hierarchical boundaries are broken down, communication within the team is enhanced. A level hierarchy should not be confused with lack of leadership; the ability of one person to step aside and observe the team behaviour may have value. Conversely, multiple individuals all pursing their own approach to managing the crisis is unlikely to be constructive or successful.

Good team-work and avoiding the pitfalls of human factors does not happen by accident and requires that a team works together and is trained in human factors and teamwork together.

Before Approaching the Difficult Airway

Several questions can usefully be considered before approaching any anticipated difficult airway. These questions are based on the preamble to the American Society of Anesthesiologists’ (ASA) Difficult Airway algorithm.

Consider the relative merits of:

The ASA also makes the recommendation to ‘actively pursue opportunities to deliver supplemental oxygen throughout the process of difficult airway management’.

Securing the Airway Awake

When airway difficulty is anticipated, the point at which the anaesthetist risks loss of control and ‘burning bridges’ is likely when general anaesthesia is induced. At this point, respiratory drive is diminished or obliterated, airway reflexes are largely ablated and the loss of muscle tone of the airway means that the risk of airway obstruction increases dramatically. If general anaesthesia is induced, the time from cessation of administration to patient waking is often up to 10 min, which is more than sufficient to cause profound hypoxaemia, hypoxic tissue injury or even death.

Securing the airway awake should be considered actively whenever significant difficulty in intubation is predicted. The argument for this increases when mask ventilation is predicted to be difficult, when rescue techniques such as direct tracheal access are predicted to be difficult and when there is a high risk of aspiration.

Although awake fibreoptic intubation (AFOI) is generally considered the standard mode of awake intubation, there are several methods of awake intubation reported. These include:

While not all anaesthetists currently have the skills and experience to perform AFOI, such skills must be available in every anaesthetic department at all times and should be deployed whenever indicated.

Administration of Muscle Relaxants in the Patient with a Difficult Airway

When general anaesthesia is administered, neuromuscular blocking drugs can be friend or foe during difficult airway management. It is notable that neuromuscular blockade is not usually necessary for mask ventilation or SAD insertion, but does facilitate tracheal intubation and probably insertion of an emergency surgical airway.

When mask ventilation is problematic, administration of a neuromuscular blocking agent usually makes ventilation easier. This has led some to promote the use of neuromuscular blockade when mask ventilation is difficult in patients with a difficult airway. However, it is important to note that the evidence of easier ventilation is derived from patients who are not particularly difficult in the first place. In contrast, there is no robust evidence that neuromuscular blockade makes ventilation reliably easy when dealing with patients with abnormal anatomy or an anticipated difficult airway. There is also no robust evidence that neuromuscular blockade reliably converts CICV to a situation in which ventilation is possible. The disadvantage of inducing neuromuscular blockade in this situation is that it commits the anaesthetist to securing the airway promptly and eliminates the option of waking the patient. Patients who are difficult or impossible to ventilate using a face mask are also at increased risk of failed intubation. Thus administration of a neuromuscular blocker may be reasonable when difficult mask ventilation occurs and waking the patient is not desirable but the anaesthetist must be prepared to manage a critical airway if it does not improve the situation.

In contrast, when both mask ventilation and intubation have failed, if waking the patient is not possible, there is little to be lost and much to be gained by administering a neuromuscular blocker. If successful, it will avoid an unnecessary emergency surgical airway and may save the patient’s life.

The subject remains controversial but can be summarized as follows:

Selecting an Appropriate Size of Tracheal Tube

A couple of decades ago, the use of tracheal tubes as large as 10 mm internal diameter was routine. While smaller tracheal tubes are used by most anaesthetists, some persist in using tracheal tubes as large as 9 mm internal diameter. In the circumstance of difficult airway management, there is a strong argument for using small tracheal tubes. A smaller tracheal tube:

Spontaneous ventilation is rarely required for prolonged periods after tracheal intubation and all but the most impaired patient can breathe with ease through a tracheal tube of 6 mm internal diameter. Selection of a tracheal tube of 6.0–6.5 mm internal diameter may make airway management easier and use of tubes larger than 7.0 mm is rarely indicated.

DIFFICULT AIRWAYS AND THEIR MANAGEMENT

The ASA and DAS Guidelines

Because problems relating to the management of a difficult airway are the leading cause of death related to anaesthesia, the need for guidelines to formalize and help in the management of the difficult airway has been recognized in many countries. Major complications arising from difficult airway management are relatively rare but they are frequent enough that almost all anaesthetists will encounter them in their careers.

The first guidelines were published in 1993 by the ASA. The introduction of guidelines in the USA has been demonstrated to have led to a reduction in death and brain damage claims (and therefore probably critical incidents) related to airway management, most notably at the time of induction of anaesthesia. Many European countries developed their own guidelines in subsequent years. While all these claim to be evidence-based, the paucity of robust evidence means that most guidelines differ significantly from each other, often reflecting local preferences. The UK guidelines were published by the Difficult Airway Society in 2004. The major differences between the guidelines published by the ASA and DAS are summarized in Table 22.1. Both emphasize the most important principles in airway management:

TABLE 22.1

Comparison between the American Society of Anesthesiologists’ and Difficult Airway Society’s Guidelines Dealing with Management of the Difficult Airway

ASA Guidelines 2012 DAS Guidelines 2004
Breadth of ‘difficult airway’ management covered A clinical situation in which a conventionally trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation or both A Cormack and Lehane grade 3 or 4 view despite optimal direct laryngoscopy, using an alternative laryngoscope and external laryngeal manipulation
Evaluation of the airway 11 non-reassuring findings Not covered
Number of attempts at laryngoscopy allowed before moving to a different technique > 3, multiple attempts Up to 4 during routine intubation and 3 during RSI. A further single attempt if a more experienced anaesthetist arrives.
Techniques recommended for difficult intubation Multiple including AFOI, blind, retrograde, LMA used as conduit and invasive airway access Optimal laryngoscopy with gum elastic bougie (Plan A), then LMA/ILMA as conduit using fibreoptic control (Plan B)* then invasive airway access (Plan D)
Order of techniques None given Clear flow chart
Recommendations for extubation Yes Published separately (2012)
Recommendations on training None given Should form part of all anaesthetist training

RSI, rapid sequence induction; AFOI, awake fibreoptic intubation; LMA, laryngeal mask airway; ILMA, intubating laryngeal mask airway.

*Plan B is omitted during RSI.

The ASA guidelines cover airway assessment and a number of different difficult airway situations. They offer the user a wide choice of options at each point of airway difficulty. They recommend multiple different techniques and it is likely that not all will be within the competence of all anaesthetists. They offer ‘choices’. In contrast, the DAS guidelines are didactic and present a single recommended pathway arranged in plans A to D and differentiating between the patient undergoing routine intubation or rapid sequence induction. They do not prescribe any advanced techniques but recommend simple procedures using equipment that should be familiar to all anaesthetists in training. They also strongly emphasize the need for regular practice of the recommended techniques using simulators and manikins where appropriate. The DAS guidelines are shown in Figures 22.3–22.5.

Difficult Mask Ventilation

The first problem encountered in any difficult airway situation is often difficulty with face-mask ventilation. This is a vital step because it represents the basic and least invasive way of ensuring oxygenation of the patient. For mask ventilation to occur, a clear, sealed and patent airway from face mask to the lower airway is required. Difficulty can be diagnosed when there is inadequate chest movement despite high airway pressures (in the case of obstruction) or very low airway pressures (due to a leak during inspiration). Capnography and spirometry, both of which are available on most modern anaesthetic machines, can also identify poor ventilation before hypoxaemia occurs (Fig. 22.6).

Difficulties with Mask Ventilation can be due to:

Face-mask ventilation requires the combination of: establishing a seal between the mask and the face; maintaining a clear upper airway; and ventilation of the lungs. Flexion of the lower cervical spine, extension of the upper cervical spine and mandibular protrusion are required, ideally with good quality facial soft tissues to enable an adequate seal with the mask. Using a ‘C-grip’, the thumb and first finger are used to hold the mask pushing downwards while the remaining three fingers pull the chin, jaw and soft tissues into the mask while also maintaining head and neck positions (Fig 22.7). Manual ventilation is performed with the anaesthetist’s other hand. Problems with the upper airway can often be predicted by prior airway assessment. Patients for whom obtaining an adequate mask seal is often problematic include the edentulous elderly, bearded patients and those who require high ventilation pressures, such as the morbidly obese.

If there are problems with maintaining patency of the airway, the following simple measures should be employed:

In a two-person (four-handed) technique, the senior anaesthetist holds the mask with two hands, one on either side of the mask, maintaining the airway seal and head and neck position, while a second person performs manual ventilation. In the three-person (six-handed) technique, the third person acts solely to improve airway positioning and seal with jaw thrust. In an alternative technique, one or two people maintain the airway and the reservoir bag is squeezed by a foot, or mechanical ventilation is employed. If ventilation is still not possible and the depth of anaesthesia is adequate an appropriate SAD should be inserted. Ensure adequate depth of anaesthesia and muscle relaxation where appropriate.

MANAGEMENT OF UNPREDICTED DIFFICULT INTUBATION

Every anaesthetist should have a strategy prepared for dealing with problems with intubation, including plans for the more serious situation of CICV. The DAS algorithm is a suitable approach and is shown in Figures 22.3–22.5. This, or another equally valid strategy, should be familiar to all anaesthetists who are practising without direct supervision.

Management is in four parts which should be approached in sequence in the event of deteriorating oxygenation and increasing difficulty with ventilation.

Plan A: Primary Intubation Attempt

This involves the first and best attempts at intubation. It requires good pre-oxygenation, optimal positioning, optimal anaesthesia, appropriate neuromuscular blockade and an appropriate laryngoscope blade. Use of external laryngeal manipulation and a (high quality) bougie are appropriate. If there is difficulty, the anaesthetist should call for help, but not send away their primary assistant. Attempts at intubation must be limited to no more than four (preferably fewer) as multiple attempts at laryngoscopy are associated with increased risk of airway trauma, failed rescue techniques, CICV, morbidity and mortality. The major concern is of converting a patient who cannot be intubated but can be ventilated into one who cannot be intubated or ventilated. A final attempt is deemed appropriate if a more experienced anaesthetist arrives and adequate face mask ventilation can be maintained.

There is no necessity to use the same laryngoscope blade for all attempts at intubation. Alternative blades include a long (size 4) Macintosh blade, the McCoy (levering laryngoscope) blade and a number of straight-bladed laryngoscopes (e.g. Miller, Henderson). Arguably, at least one attempt should be with a McCoy blade (Fig. 22.10) because it is recognized to move the fulcrum of the force applied to the airway distally and to improve the view when laryngoscopy is awkward. Use of a straight blade may offer the benefit of using an alternative approach to the laryngoscopy, such as a retromolar approach (Fig. 22.11), and this may be helpful, particularly if there is a small mandibular space.

Rigid videolaryngoscopy is appropriate at this point for those with the appropriate skills and training. This is discussed below.

Plan B: Secondary Intubation Attempt

This is appropriate if adequate ventilation is possible and anaesthesia can be maintained. A classic (cLMA) or intubating (ILMA) laryngeal mask airway is inserted to enable ventilation and is then used as a conduit for intubation. Fibreoptic guidance of intubation is recommended.

Intubation Via a SAD: The cLMA is recommended because it is a device with which all anaesthetists are familiar. The cLMA does have several important limitations for such a use.

In view of these limitations, a microlaryngeal or long flexometallic tube is recommended.

Several of these issues may be overcome by the use of an alternative SAD as a conduit. The ProSeal LMA and i-gel have no aperture bars and may be better rescue devices. Current evidence, published since the publication of the DAS guidelines, supports use of the ProSeal and i-gel for fibreoptic guided intubation. Blind intubation via any standard SAD is extremely unlikely to be successful and cannot be recommended. The use of fibrescope through a SAD has a high success rate, is a relatively low-skill procedure and may be practised both in manikins and in patients in a non-emergency setting, with appropriate consent.

An important modification of this technique, which is not included in the DAS guidelines, is to use an Aintree Intubation Catheter (AIC). The AIC (internal diameter 4.6 mm) is slid over the fibrescope and fibreoptic intubation is then performed via the SAD (Fig. 22.12). The AIC is left in the trachea (close to the carina) while first the fibrescope and then the SAD are removed. If oxygenation is required, a connector is available to enable ventilation via a standard anaesthetic breathing system. A lubricated tracheal tube is then railroaded over the AIC into the trachea and the AIC removed. The AIC has an external diameter of approximately 7.0 mm, requiring a standard tracheal tube of at least this size internal diameter to be inserted, although a 6.5 mm internal diameter ILMA tracheal tube is also accommodated. These techniques require practice and it is strongly recommended that, if such techniques are part of departmental guidance, then an appropriate regular training programme should be in place.

Intubation Via an ILMA: The ILMA is also an option for management of plan B. Unlike the other SADs, it is specifically designed for facilitating tracheal intubation. The ILMA has a mask end which is similar to a cLMA but the grille is replaced by an ‘epiglottic elevating bar’ which is a firm piece of silicone anchored at one end only. The stem of the ILMA is both shorter and wider than other LMAs and is rigid, with a handle attached on the concave side (Fig. 22.13); the stem passes through an angle of approximately 110o. The ILMA is supplied with a specifically designed ILMA tracheal tube (ILMA TT) which is straight, reinforced and has a soft bullet-shaped tip. The ILMA is supplied in three sizes (3–5, for patients of 30–100 kg) and each accommodates all sizes of ILMA TT from 6.0–8.0 mm internal diameter (Fig. 22.13).

The ILMA is inserted with the head in the neutral position by holding the handle, placing the bowl on to the hard palate and then advancing with a rotating movement until the ILMA is fully inserted into the airway.

The position of the ILMA over the airway must then be optimized using several steps.

Once the optimal position is established it is maintained, the circuit is disconnected and a lubricated ILMA TT is inserted with the longitudinal line facing either backwards or forwards (as this places the bevelled tip in the optimal position).

If a blind technique is in use, the ILMA TT is advanced until the horizontal black line on the ILMA TT disappears into the ILMA stem indicating that the tip of the tube is about to exit the ILMA, and push the epiglottic elevating bar anteriorly to displace the epiglottis.

The ILMA TT can then be advanced into the trachea (Fig. 22.14). It should enter the trachea in no more than a further 6–8 cm.

The ILMA TT cuff is inflated and correct position confirmed with capnography and other routine tests.

The success rate of the blind technique is approximately 75% (compared to 10–15% when intubating blindly through other SADs). The success rate can be increased to close to 100% by use of a fibrescope within the ILMA TT to guide its direction; this is the technique advocated in the DAS guidelines. When this technique is used, the ILMA TT may be advanced ahead of the fibrescope so that the epiglottic elevator is moved out of the way (‘tube first technique’) or the scope may be negotiated around the elevator and the larynx intubated before the ILMA TT is advanced (‘scope first technique’).

Although all ILMAs accept an ILMA TT of up to 8.0 mm internal diameter, there is little to be gained by the use of the larger sizes and the use of a size 6.0 mm or 6.5 mm tube is probably easier and is certainly large enough. The re-usable (pink) ILMA TT has a high-volume high-pressure cuff; it is a common mistake to inflate the cuff to standard pressures and for a leak to persist (especially if a small tube is used). The solution is simply to inflate further until the airway is sealed. However, because, even if a fibrescope is used, the TT is not seen entering the trachea, it is important to ensure that the cuff is not placed at the level of the vocal cords; this is easily avoided by fibreoscopy through the tube and positioning the tip in the mid-trachea. The single-use ILMA TT (white-tipped) has a medium-volume medium-pressure cuff.

It is recommended that the ILMA TT is inserted whenever the ILMA is used because it maximizes success rates. A sharp-bevelled rigid PVC tracheal tube risks intubation difficulty, laryngeal trauma and, if intubation fails, oesophageal trauma.

When the trachea has been intubated, the ILMA should usually be removed. If left in place, it may cause minor morbidity because it exerts a moderate pressure against the pharyngeal wall. A ‘tube stabilizer’ is provided to facilitate this. The 15-mm connector of the ILMA TT is removed (ideally having been loosened before intubation) and the stabilizing rod is placed into the proximal end of the tube. The ILMA TT cuff is confirmed as inflated and the ILMA cuff is deflated (Fig. 22.14). The stabilizing rod is then used to maintain the ILMA TT position while the ILMA is withdrawn; at the point at which the ILMA is almost out of the mouth, the stabilizing rod is removed and the anaesthetist’s gloved hand is inserted into the mouth to hold the tube in position. There are two important points: first, the stabilizing rod is not a ‘pusher’ and the ILMA TT should not be advanced during this procedure; second, if the stabilizing rod is not removed before the ILMA is withdrawn completely, the pilot cuff of the ILMA TT is avulsed and the cuff deflates (this is problematic, but can be rescued by inserting an i.v. cannula into the cut end of the pilot tube to enable re-inflation, followed by clamping) (Fig. 22.14).

Most evidence on the efficacy of the ILMA is based on a re-usable device, although a single-use PVC device has recently been developed. Other SADs specifically designed for intubation are the intubating laryngeal airway and the Ambu Aura-i.

Plan C: Failed Intubation, Oxygenation and Waking

If intubation cannot be achieved using the above techniques then ventilation should be maintained using face-mask ventilation. The patient should be woken up. Surgery should then be postponed or the airway established using an awake technique. If neuromuscular blockade has been established, this must be allowed to wear off or be reversed; sugammadex may have an important role if rocuronium (or vecuronium) has been used to induce neuromuscular blockade but will not reverse CICV which has an anatomical or mechanical cause.

Management of Unanticipated Difficult Intubation During RSI: The principal differences in the guidelines for unanticipated difficult intubation during RSI are as follows:

image The patient is always fully pre-oxygenated, which creates more time before oxygen desaturation in the event of difficulties with intubation.

image Cricoid pressure is used to prevent pulmonary aspiration of any regurgitated gastric contents.

image Cricoid pressure should be reduced or briefly removed if it is impeding laryngoscopy. This should be done with ‘sucker in hand’ so that regurgitated material can be removed promptly.

image There is no plan B for secondary attempts at tracheal intubation because the patient is at risk of aspiration, and succinylcholine has a relatively short duration of action. Consequently, in all but life-threatening situations, the safest course of action is to postpone the surgery and allow the patient to wake. If rocuronium is used as part of a modified RSI technique, sugammadex may be used to reverse it, although this can only be achieved in a timely fashion if the drug is immediately available before induction commences.

image If (as is often the case) active airway management is required to maintain oxygenation while the patient wakes, the ProSeal LMA is also advocated as a rescue device.

In either situation, if, despite maximal efforts, adequate ventilation cannot be achieved with bag-mask ventilation or via a SAD and there is worsening oxygenation, plan D should be activated. This is the final common pathway of the DAS guidelines and describes a plan for managing the CICV situation.

Plan D: Management of the CICV Situation

As part of plan D, a laryngeal mask airway (or other SAD) should be re-inserted. This may rescue the airway and if it does not, it still maintains a patent upper airway which is important after narrow-bore cricothyroidotomy to provide a route of egress for gases during high pressure source ventilation (see below).

CICV can arise unexpectedly during routine anaesthesia but is probably more frequent when multiple attempts at laryngoscopy/intubation have changed a ‘can’t intubate, can ventilate’ situation into CICV. Risk factors for difficult mask ventilation overlap with risk factors for difficult laryngoscopy (e.g. Mallampati classes 3–4) and patients who are difficult/impossible to ventilate by mask are more likely than others to be difficult or impossible to intubate.

Obesity is also an important factor when considering CICV. Obesity is certainly a risk factor for impossible mask ventilation but the evidence is less clear-cut as to whether it is a risk factor for failed intubation. The importance lies in the fact that, when airway problems occur in obese patients, the time available to secure the airway before profound hypoxaemia occurs is dramatically reduced and may be as little as 30–60 s, even after full preoxygenation. The presence of obstructive sleep apnoea in addition to obesity increases the risk of airway obstruction and rapid hypoxaemia after induction of anaesthesia.

All organizations should have a guideline (and individuals a plan) for the management of CICV. The DAS guideline is one option (Figs 22.3–22.5).

The principles behind management of CICV are:

Insert an Appropriate SAD: The ideal SAD for rescuing the airway during CICV has several properties:

Based on risk factors and epidemiology, CICV might typically occur in an obese, paralysed patient at risk of aspiration and undergoing emergency surgery. The evidence base supports the use of a second generation SAD with a high seal pressure. The ProSeal LMA, inserted over a gum-elastic bougie placed in the oesophagus, is logically the best choice as this combines high first-time success with the best airway seal of all SADs and increased protection against aspiration (Fig. 22.15). Alternatives include the i-gel, LMA Supreme or laryngeal tube suction II.

Prospective studies suggest that the cLMA will rescue many cases of CICV (> 90%), while studies of poor outcomes from airway complications suggest that failure to rescue the airway with a SAD increases the risk of a poor outcome. Multiple attempts at laryngoscopy will probably lead to laryngeal trauma and reduce the success rate of airway rescue with a SAD. Obesity may also be a risk factor.

CICV should not be allowed to progress to a stage where the patient’s life is at risk without attempted rescue with an appropriate SAD.

Wake the Patient if this is Feasible: If the airway cannot be rescued, the default option should be to seek a ‘place of safety’ which in most cases involves waking the patient up. As a rule of thumb, this should be considered actively in all cases of airway difficulty and, if it is feasible, it is the safest option. In cases where difficulty may be anticipated it is particularly useful to adopt a ‘wake up trigger’ as part of the airway strategy and communicate it to all around before commencing anaesthesia. The airway can subsequently be secured awake. This option is equally valid when the airway has been secured with a SAD.

However, waking the patient up is not practical in many emergencies, most commonly because either the patient has received a neuromuscular blocking drug or because of profound progressive hypoxaemia. Less commonly, the urgency of the surgery demands that it must proceed and the airway must be secured ‘come what may’.

If Waking is not Feasible and CICV Persists, Administer a Neuromuscular Blocking Drug if not Already Administered: This may be considered by some to be controversial but we believe it is not; rather, it is entirely logical. It is well recognized that neuromuscular blockade may assist ventilation. The only strong argument for not administering a neuromuscular blocker when ventilation is difficult is the concern about how to manage the airway if ventilation is not improved. In the circumstance of CICV, where waking is not feasible, it is not possible for the situation to get worse and the realistic possibility that neuromuscular blockade may improve the airway means that it is entirely logical because it may prevent the need to provide an emergency surgical airway. Even if it does not enable ventilation, it is likely that performance of an emergency surgical airway will be easier after neuromuscular blockade.

EMERGENCY SURGICAL AIRWAY TECHNIQUES

Devices

Narrow-Bore Cannula with High Pressure Source Ventilation: A narrow-bore cannula (most are approximately 2 mm internal diameter) is usually inserted as a cannula-over-needle technique through the cricothyroid membrane. Once inserted, ventilation is based on two important principles: first, a high driving pressure is required to inflate the lungs due to the enormous resistance to flow through the cannula; second, expiration must take place though the patient’s upper airway. It is appropriate to use specifically designed devices (e.g. Ravussin cannula; Fig. 22.16A) which sit against the neck correctly (Fig. 22.16B) and are less likely to kink. Similarly, a specifically designed ventilating device (e.g. Manujet injector; Fig. 22.17) is strongly recommended. Use of intravenous cannulae (which cannot be fixed securely and tend to kink) and ‘Heath-Robinson’ assemblies for ventilation are difficult to justify in settings such as operating theatres where it can be predicted that such a technique will be required from time to time: avoiding the need for such ad hoc devices is part of institutional and personal preparedness.

Wide-Bore Cannula (≥ 4 mm): Wide-bore cannulae may be cannula-over-needle devices (e.g. QuickTrach) or those requiring a Seldinger insertion technique (e.g. Melker cricothyroidotomy devices; Fig. 22.18). Cannula-over-needle devices require a large sharp needle which risks significant tissue trauma if misplaced and such devices may be too short to reach the trachea in patients with an obese neck. Seldinger-type devices take somewhat longer to insert but the technique is familiar (and generally favoured) by anaesthetists.

The Melker 5.0 mm internal diameter cuffed cricothyroidotomy device is a Seldinger-type device which is generally inserted with ease, using a technique similar to a percutaneous tracheostomy. One option for rescuing the airway is to insert a Ravussin cannula and to ventilate the lungs with a Manujet to re-oxygenate, and then change this to a large bore cannula inserting the Seldinger wire from the Melker kit through the Ravussin cannula as the first step.

Surgical Airway: A surgical airway technique comprises four steps.

Numerous variations are described and include the use of tracheostomy dilators instead of the cricoid hook or insertion of a bougie into the trachea instead of a tube. The important feature is to ensure that, once the trachea has been entered, something stays in it, keeping the tracheostomy tract open at all times.

Various simulation studies suggest that a surgical technique can be performed as rapidly as a Seldinger cannula technique, although these are typically performed in bloodless fields. However, studies from America, where the technique is probably used most commonly, suggest that the likelihood of saving a life with a surgical airway is considerably higher than mortality from the bleeding complications of an attempt.

In a recent study of major complications of airway management, more than 60% of cannula cricothyroidotomies inserted by anaesthetists to rescue the airway in an emergency failed. The causes were numerous and included use of inappropriate equipment, misuse of appropriate devices, device failure, poor technique and inappropriate ventilation via a correctly placed narrow-bore device. The chances of success are increased greatly if the correct equipment is used skilfully and correctly. This requires training. Training in such techniques fades after approximately three months and requires regular updating. Training should include both cannula and surgical techniques.

Ventilation and Expiration Via Cricothyroidotomy Devices

Narrow-Bore Cannula: When ventilating through a narrow-bore cannula, a high pressure source is needed to overcome the resistance of the cannula. However, the pressure changes in the trachea during this type of ventilation are similar to those during conventional ventilation. The technique should not be confused with ‘jet ventilation’ or ‘oscillation’; what is achieved is ‘high pressure source conventional ventilation’. Appropriate sources of the high pressure for such ventilation are either wall oxygen or an oxygen cylinder, both approximately 400 kPa (4 bar, 4000 cmH2O, 58 psi). If wall oxygen is used, the flow rate should be set at greater than 15 L min −1. When using an anaesthetic machine, pressure regulators and ‘blow-off’ valves reduce the pressure available; an attached anaesthetic breathing system with a conventional anaesthetic reservoir bag limits pressure to 6 kPa (60 cmH2O), which is totally inadequate for ventilating through a narrow cannula. If the anaesthetic flush is deployed continuously, a pressure of 30–60 kPa (300–600 cmH2O) can be achieved and this may be just sufficient to ventilate the lungs. Maximum flow rates from an anaesthetic machine are 15 L min −1 via a flowmeter and 30–60 L min −1 when the oxygen flush button is depressed. An anaesthetic machine cannot provide a reliably high pressure source unless a connection is made to a high pressure source outlet at the back of the machine, usually a ‘mini-Schrader’ connector which can then be used to drive an injector or similar device (Fig. 22.19). An oxygen ‘injector’ such as a Sanders or Manujet injector can deliver a high pressure source ranging from 0.5–4 bar (500–4000 kPa) at a flow rate of up to 1000 mL s −1. Wall oxygen or the use of an injector may inflate the chest by 500 mL within 0.5 s. Using a Manujet, a driving pressure of 1 bar may be adequate to ventilate most slim patients, and reduces the risk of barotrauma. Neuromuscular blockade, and inserting a SAD to maximize the expiratory route, also increase the success of the technique.

However, when ventilating the lungs using a cricothyroid cannula in the presence of complete upper airway obstruction, the critical aspect is not lung inflation (inspiration) but lung deflation (exhalation). This is critical both to generating adequate minute ventilation and preventing complications. Exhalation of 500 mL via a 14-gauge cannula takes at least 30 s and therefore is of no practical use. There is a myth that a second cannula should be inserted into the airway to enable exhalation; to enable exhalation in 4 s would require 32–64 cannulae! Delivering further breaths through a misplaced cannula or without allowing full expiration leads inevitably to barotrauma, which can rapidly be life-threatening. However, even in CICV, exhalation through the upper airway is usually effective. During ventilation via the patient’s normal airway, the upper airway is drawn inwards in inspiration and tends to collapse. In expiration, positive intraluminal pressure tends to expand and open the upper airway. As a result, inspiratory airway obstruction is more common than expiratory. Even in CICV situations, the airway is sufficiently patent during expiration to allow exhalation in up to 90% of patients. As a ‘rule of thumb’ during high pressure source ventilation via a small cannula, the operator should ensure that the chest falls completely before the next inspiration. A hand placed on the chest during ventilation can confirm that the chest is rising and falling, and detect early surgical emphysema if it develops. If exhalation is slow because of upper airway obstruction, the frequency of ventilation must be decreased appropriately. Ventilation can continue safely, albeit at a slower rate and with a reduced minute volume. Manually compressing the chest during expiration to augment exhalation may be of benefit. If expiration cannot be achieved, the gas flow should be reduced to basal flow (0.25–0.5 L min −1) in an attempt to provide apnoeic oxygenation, without ventilation.

A device (Ventrain) has recently been developed which uses a driving gas that bypasses a cricothyroid/tracheal cannula during the expiratory phase and entrains gas from the cannula to achieve ‘assisted exhalation’ using the Venturi effect. It is not yet in widespread use but may solve some of the problems and confusion surrounding this mode of ventilation.

Wide-Bore Cannula and Surgical Techniques: Wide-bore cannulae are defined as those with an internal diameter of at least 4 mm because this is the minimum calibre through which an adult can exhale with adequate speed to maintain a normal minute volume. This applies whether inspiration is mechanical or spontaneous, because expiration is a passive process.

After the device has been inserted, ventilation can be achieved with a low pressure gas source (e.g. a standard anaesthetic machine). In contrast to narrow bore cannulae, large bore cannulae require that the upper airway is obstructed during inspiration to avoid the ventilating gas being vented via the upper airway. This may be achieved by actively obstructing the upper airway (e.g. a SAD is inserted and the proximal end obstructed) or, preferably, by the use of a cuffed cannula. Spontaneous ventilation via a wide bore cannula is also possible.

To summarize, this is a complex and often confused topic. There are three methods of achieving oxygenation and ventilation via a cricothyroidotomy.

MANAGEMENT OF THE PREDICTED DIFFICULT AIRWAY

The main difference between management of the unanticipated and the predicted difficult airway is that the latter enables the anaesthetic team to plan and prepare more thoroughly and to fit a strategy to the specific needs of the patient rather than following a guideline designed to ‘fit all situations’. Due to the limitations of airway assessment, many patients with a ‘predicted difficult airway’ will not prove to be difficult, but this is not a reason to ignore preoperative findings or history of difficulty. Many airway disasters are preceded by anaesthetists ignoring the history or signs of difficulty and then getting into avoidable trouble.

When airway management is predicted to be difficult, the strategy can be based around achieving:

Ensuring the right place may require that the patient is transferred to a location where appropriate monitoring, equipment and skills are available to manage the airway safely. However, transfer of a patient with a critical airway is fraught with danger and an assessment of specific risks should be made, including a plan for management of deterioration during transfer. In the operating theatre setting, patients in whom airway difficulty is anticipated should usually be managed in the operating theatre rather than the anaesthetic room for reasons of space, visibility, monitoring, communication and teamwork.

The right time implies patients with anticipated difficulty should be managed at the time that is safest for the patient. Urgent and emergency patients must be managed with appropriate promptness but elective procedures should be managed with enough time for assessment, collecting all necessary information (e.g. retrieving notes and scans as necessary) and gathering the equipment and personnel needed for optimal management.

The right plan has been discussed earlier in the chapter in the section describing strategy. In patients with a predicted difficult airway, careful assessment is vital to determine which specific routes of access and techniques are likely to be problematic or successful, so that a logical individualized strategy can be constructed.

The right person may not be the anaesthetist to whom the patient presents. The right person may also not be one individual but a number of individuals with the skills to carry out specialized parts of the airway strategy. If possible, the right personnel should be present from the start of airway management. Most airway difficulties provide ample opportunity for teaching and these opportunities should be seized.

Although the detail may differ, the principles of managing the patient with predicted airway difficulty are no different to managing unanticipated problems (e.g. strategy, oxygenation, rescue techniques, good teamwork).

MANAGEMENT OF THE OBSTRUCTED AIRWAY

The management of the obstructed airway represents a very dangerous, although rare, situation. Obstruction may occur from the pharynx to any point distally and may be due to many causes including infection or trauma, but the most common cause is malignancy. The patient may present late or occasionally be referred incorrectly to the ICU team with a diagnosis of worsening asthma/COPD, having failed to respond to treatment and perhaps in extremis. To manage these patients safely and achieve a successful outcome requires careful preparation, planning and good communication between anaesthetists, ENT specialists, the operating theatre team and, in some situations, cardiothoracic surgeons.

Optimal management of the obstructed airway is controversial but it is generally the case that airway obstruction becomes worse during anaesthesia because of supine positioning and loss of airway tone and reflexes. All approaches may lead to life-threatening complications (e.g. complete obstruction after induction of anaesthesia, haemorrhage or swelling in the airway). Involvement of anaesthetists and surgeons with appropriate experience is essential and back-up plans should be established and communicated to all.

Precise management depends on the level and cause of the obstruction, the urgency for intervention and several other factors. Assessment should determine the following factors.

image What is the level of the obstruction?

image What is the degree of obstruction?

image Is it fixed or variable?

image What is its cause (e.g. tumour, haematoma, infection)?

image Is it friable or likely to bleed?

image Has there been previous airway or neck surgery, or radiotherapy? All place the patient in a higher risk category.

image Can the patient’s airway be improved? If time allows, nebulized adrenaline (epinephrine) or steroids may improve the airway for short periods of time. Heliox (a mixture of helium and oxygen) may be beneficial before anaesthesia in critical cases. Radiotherapy may improve the airway, although often this is impractical.

image Is there any important co-morbidity?

image What is the surgical plan and preferred route for anaesthetic access? These patients illustrate the complexity of a ‘shared airway’ and there is no point in planning an anaesthetic approach which is not compatible with an agreed surgical plan.

image What is the urgency of the intervention? It is important to differentiate patients in whom anaesthesia is planned to achieve surgery to improve the airway from those in whom anaesthesia is necessary to secure the airway in order to preserve life.

Important features of the history and clinical examination are noisy breathing and waking up in the middle of the night fighting for breath (having a panic attack), or having to sleep in an upright position. These features enable the anaesthetist to determine the patient’s ‘best breathing position’ to be used during induction of anaesthesia. If a patient cannot tolerate lying flat when awake, that position is likely to be dangerous after induction of anaesthesia. Stridor (inspiratory noise) is a concerning sign as it represents significant upper airway narrowing; however, it is not always present and patients with chronic obstruction may can present with a very narrow airway and no stridor. Expiratory noise (wheeze) may indicate a lower level of obstruction.

Other than in the most urgent cases or if the patient’s condition makes it impossible, full investigation is warranted. This usually involves CT or MRI, nasendoscopy and lung function tests. Imaging is vital to planning both the surgical and anaesthetic approaches and should be viewed together. Imaging is performed supine and is a static image; it does not necessarily reflect the airway in the sitting position or the dynamic nature of the obstruction. It is also important to note the date of any imaging; lesions may progress rapidly.

Nasendoscopy is underused by anaesthetists and, although discussion of the surgical findings may be useful, it is often sensible for the anaesthetist to perform awake nasendoscopy, even when a fibreoptic approach is not planned. Lung function tests including flow volume loops may help in assessing the extent of physiological compromise and the level of the obstruction. If these tests are not possible, a ‘walk test’ may be of value because it enables the accompanying anaesthetist to assess exercise tolerance and respiratory pattern, and may elicit signs such as noisy breathing which add information not acquired at the bedside.

Patients with an obstructed airway can be considered according to the level of obstruction.

Upper Airway Obstruction

In patients with upper airway obstruction, the cause is usually malignancy, trauma or infection affecting the larynx and other supraglottic structures such as the tonsils and tongue. Many approaches to the airway are possible. The management depends on whether or not it is judged that intubation from above the vocal cords is going to be possible. Usually an informed decision can be made after nasendoscopy and imaging.

If it is clear before surgery that intubation will not be possible due to excessive tumour reducing the laryngeal opening, no recognizable structures visible at nasendoscopy or any other reason that might make direct laryngoscopy difficult, the safest approach is to perform a tracheostomy under local anaesthesia. Lesions of the base of the tongue and floor of the mouth often interfere with laryngoscopy, particularly if there has been previous surgery or radiotherapy. Where there is doubt, awake fibreoptic intubation is a safe method for trying to secure the airway. Laryngeal lesions may interfere with all forms of tracheal intubation. Awake fibreoptic intubation may be an option but surgical technique may require unrestricted access to the larynx. Supraglottic (from above), transglottic (via a narrow 2–3 mm catheter placed through the cords) or transtracheal (via a catheter placed in the trachea) ventilation may all be options or necessities and each requires attention and good communication between the anaesthetist and surgeon.

Inevitably, some patients require general anaesthesia for airway management. The choices between intravenous and inhalational induction, and between spontaneous and controlled ventilation, are controversial. Whichever method is chosen, a clear plan for airway management and back-up is needed, with all relevant equipment and personnel present. Airway interventions should not be performed before the patient is adequately anaesthetized. A senior ENT surgeon should be in the operating theatre and prepared to carry out immediate surgical cricothyroidotomy or tracheostomy if the airway is lost. If intubation proves impossible but the airway is patent and the patient is stable, the patient may be woken or a tracheostomy undertaken, depending on the patient’s needs.

Mid-Tracheal Obstruction

This presents an entirely different problem and is often caused by a retrosternal thyroid mass, although malignancies and infections may be the cause (Fig. 22.20). In the presence of a thyroid mass, the onset of airway compromise is usually slow and further radiological assessment is possible. A CT scan is vital to show the level and extent of the obstruction. Lesions below the larynx do not interfere with laryngoscopy (although the larynx and trachea may be displaced; Fig. 22.21) or the ability to use a face mask or SAD but they may interfere with ventilation after induction of anaesthesia and the ability to insert a tracheal tube.

There are several key issues which must be clarified before anaesthesia.

If laryngoscopy is predicted to be straightforward, if there is no tracheal invasion and if there is a clear distance below the obstruction and above the carina, a standard anaesthetic induction technique followed by administration of a muscle relaxant can be considered. Otherwise, the safest way of securing the airway is likely to be awake fibreoptic intubation, although the problem of obstructing the airway while the obstruction is passed (‘cork in a bottle’) remains and may be distressing to the patient. Airway stimulation and coughing may lead to complete obstruction; an experienced operator is essential. Plan B in the situation in which a rapid tracheostomy would not be possible is the use of a rigid bronchoscope by a skilled operator.

Lower Tracheal or Bronchial Obstruction

This is a very difficult clinical problem and life-threatening complications may occur. The cause is usually a malignant mediastinal mass and obstruction of the superior vena cava often co-exists. Sudden and total obstruction to ventilation can occur at any time, particularly if the patient becomes apnoeic or a muscle relaxant is used. Subatmospheric intrapleural pressure during inspiration may contribute to holding the airways open; if lost, the pressure from any mass external to the airway can cause airway collapse and complete obstruction. A tissue diagnosis should be obtained under local anaesthesia if possible and an emergency course of chemo/radiotherapy should be considered; stenting or laser resection may be surgical options. Management is complex and, if possible, the patient should be transferred to a cardiothoracic centre where rapid induction of anaesthesia and skilled rigid bronchoscopy may be the technique of choice. Extracorporeal oxygenation may be required.

SPECIFIC TECHNIQUES

Supraglottic Airway Devices for Airway Rescue

SADs are an important group of devices for airway rescue, in particular for failed mask ventilation or for CICV. Neuromuscular blockade is not required for insertion (unlike tracheal intubation) and success rates are high. Success rates for airway rescue are reported to be as high as 95% for the classic laryngeal mask airway. Whether rates are as high for PVC and other single-use laryngeal masks is not known.

Despite this high rate of success, there is a strong argument for selecting an alternative SAD as first choice. Patients who require airway rescue are often obese, male, scheduled to undergo emergency surgery and likely to have received a neuromuscular blocker either before or during the airway emergency. Many are at a significantly increased risk of regurgitation and aspiration of gastric fluid because of obesity, urgency of surgery and possible gastric inflation during attempts to ventilate by face mask. These are not the type of patients whom most anaesthetists would choose to manage with a standard laryngeal mask. In this circumstance, the requirements for a SAD to rescue the airway are:

There is therefore a good argument for choosing a second generation SAD for airway rescue. Suitable devices include the ProSeal LMA (probably inserted over a bougie to increase success), i-gel. The Supreme LMA and Laryngeal Tube Suction II enable airway rescue but are less suited as conduits to intubation.

‘Videolaryngoscopes’, Rigid Indirect Laryngoscopes, Optical Stilettes and Advanced Intubation Aids: (see also Chapter 15)

Numerous devices aimed at improving management of difficult direct laryngoscopy have been developed and marketed in the last decade. The main principle behind these devices is an intent to convert intubation that would previously have been blind (e.g. blind nasal, bougie-guided, light-wand guided) into a visualized technique. The devices can be described as videolaryngoscopes, rigid fibrescopes or indirect laryngoscopes, although none of these descriptions includes all devices. They can be divided into three major groups:

Bladed indirect laryngoscopes form the largest group. Older versions include the Bullard and Upsherscope and newer devices include the Glidescope, McGrath 5 and C-MAC. These devices move the viewing point beyond the curve of the laryngoscope blade, making it possible, effectively, to ‘see round corners’. A much wider angle of view is achieved because the viewing point is distal.

Conduited intubation guides include several rigid fibreoptic laryngoscopes (Pentax AWscope, AP Advance laryngoscope) and the Airtraq (Fig. 22.22), which uses optical prisms rather than fibreoptics to illuminate the object and transmit an image.

Optical stilettes are metal rods with an internal fibreoptic or video system which enables the user to view the image from the distal end directly from the viewing port or on a remote screen. Most stilettes are rigid with a fixed angle (e.g. Bonfils, Levitan). The Shikani stilette (Fig. 22.23) is semi-malleable and the Sensascope has a flexible fibreoptic tip which allows some manipulation. Optical stilettes are placed within the lumen of the tracheal tube and then directed into the larynx before the tracheal tube is advanced into the airway. The main advantage of the stilettes is that they require minimal mouth opening (as little as 1 cm) and can be advanced with negligible tissue disruption. Their main disadvantage is the inability to manipulate and displace airway structures in the manner that a bladed instrument can.

The potential advantages of these devices include:

Despite their obvious appeal, the benefits of these devices are less well proven than might be expected. Most research undertaken has been on patients with a normal airway and some is of poor quality. As a result, their efficacy in patients with a difficult airway is uncertain. The ability to move the viewing point distally in the airway is an obvious advantage but the fact the tracheal tube is not introduced under direct vision means that its insertion may be more difficult. The devices may improve the view of the larynx without making intubation easier and in easy intubations, these devices often prolong the time to intubation. To overcome this problem, many manufacturers advise the use of a rigid or semi-rigid stilette to pre-form the shape of the tracheal tube before insertion. There is a risk of damage to other tissues in the airway as the tracheal tube/stilette assembly is introduced (blindly). Conduited devices and stilettes have a potential advantage over bladed indirect laryngoscopes because the device guides the tracheal tube directly to the area being viewed through the device and there is no need for blind introduction of a tracheal tube/stilette assembly. There is no consensus on which device or group of devices performs best.

There is increasing evidence, for some of these devices, that videolaryngoscopy does offer a useful alternative to direct laryngoscopy in patients known, or found unexpectedly, to be difficult to intubate. In addition, they can be used awake after topical administration of local anaesthetic to the airway because less tissue distortion is needed in comparison to a conventional laryngoscope. It is likely that their use will become much more prevalent. All the devices are expensive and have a learning curve. If such a device is to be used, it is logical to acquire skills in the use of one device; if skills in the use of more than one device are needed, it is logical to select one device from each of the three groups.

EXTUBATION AND RECOVERY

Airway problems at extubation and in the recovery room account for approximately one-third of major airway complications of anaesthesia. Most involve airway obstruction, some with secondary aspiration of fluid into the lungs. At the time of extubation, there is a change from a controlled situation, with airway protection, suppressed airway reflexes and the ability to deliver 100% oxygen, to one of absent airway protection, partial recovery of airway reflexes and an ability to reliably deliver only much lower oxygen concentrations. In this respect, it contrasts markedly with intubation. Airway obstruction which occurs during emergence and recovery needs to be rapidly recognized and resolved to prevent hypoxaemia and post-obstructive pulmonary oedema (POPO), which considerably worsen the situation.

Factors which increase the risk of problems at the time of extubation/emergence and recovery include:

Management of at-risk extubation requires recognition of the potential problem, planning, preparation, preoxygenation and, sometimes, special procedures. Communication with the operating theatre team is important because there is a natural tendency for the surgical and nursing team members to relax and attend to other tasks at the end of surgery.

Planning involves creating a strategy for extubation (plan A and back-up plans), communicating this to assistants and colleagues and ensuring that the right equipment is immediately available and that personnel with the necessary skills are present. This may require the difficult airway trolley, summoning senior anaesthetic assistance or requiring the surgeon to remain in the event that an emergency surgical airway is required. Planning also includes making a clear decision as to whether the airway will be removed with the patient ‘deep’ or awake.

Pre-oxygenation is part of preparation but is separated for emphasis: it is the single most important preparatory step before extubation.

Preparation involves optimizing the patient for extubation. This includes (but is not limited to) ensuring full reversal of neuromuscular blockade, adequate offset of anaesthetic and opioid medication (choice of appropriate drugs at an early stage in the anaesthetic makes this easier), pharyngeal and bronchial suction as necessary and emptying the stomach if there is a risk of aspiration. Dexamethasone may be administered to minimize airway swelling although its effect is delayed and its administration does not influence the immediate consequences of extubation. Direct inspection of the airway may be necessary to assess oedema and is specifically indicated when there has been blood in the airway to ensure that there is no risk of aspiration of blood after extubation. A leak-test may be performed, in which the tracheal tube cuff is deflated and positive pressure applied while listening for an audible leak around the trachea. The test assesses only laryngeal swelling and is very dependent on the size of tracheal tube used and the pressure applied, so its efficacy in predicting safe extubation is limited.

Special procedures are non-routine actions at extubation performed to improve the safety of extubation and to facilitate re-intubation if that is necessary. Examples include insertion of a cricothyroid needle or airway exchange catheter (AEC) prior to extubation, exchange of the tracheal tube for a SAD immediately before or after extubation, or extubation followed immediately by CPAP. If an AEC is left in place it should be placed in strict accordance with manufacturer’s instructions and the tip should not lie beyond the mid-trachea (i.e. no more than 26 cm from the lips in adults). Administration of oxygen through the AEC risks significant barotrauma if the catheter migrates distally and is unnecessary other than in exceptional circumstances. If it is considered that there is very high risk at extubation, an elective tracheostomy may be appropriate. Alternatively, extubation may be delayed and the patient transferred to ICU. In these circumstances, extubation on ICU will probably need the same processes of planning through to special procedures and it may be appropriate to return to the operating theatre specifically for safe extubation.

Problems occurring in the recovery room are particularly dangerous because the care of the patient’s airway is delegated to a nurse and there may be limited access to equipment, personnel with advanced airway skills and capnography. The anaesthetist usually returns to the operating theatre and is involved in anaesthetizing the next patient within a few minutes. If the airway is at risk after surgery, the anaesthetist must either recover the patient in the operating theatre or remain with the patient until the airway is safe. A diagnosis of hypoventilation and airway obstruction in recovery may be masked by administration of oxygen because oxygen desaturation may not occur until the situation is advanced. Recovery staff should be skilled in the recognition of signs of airway obstruction and its early management. Capnography should be available and can be used with a SAD or face mask in place: its use is increasingly recommended during recovery. Where it is used the recovery room staff need to be trained in its interpretation.

Aspiration of blood and blood clots is a specific risk after intraoral surgery (e.g. maxillofacial, tonsillectomy, adenoidectomy). Good surgical technique and good surgical and anaesthetic communication are important in preventing problems. At the end of surgery, the surgeon and the anaesthetist together must ensure there is no blood, blood clots (including in the post nasal space) or bleeding before airway removal. If a throat pack has been used, recommended methods of communicating its presence and ensuring its removal are important. Positioning for extubation and transfer are important; extubation and transfer with the patient in the lateral position is recommended until consciousness and airway reflexes have returned. Aspiration of blood or blood clot can cause laryngospasm or tracheal obstruction. If tracheal obstruction occurs, the diagnosis may be missed unless it is actively considered; the clinical picture of hypoxaemia, inability to ventilate and high airway pressures may be mistaken for asthma, anaphylaxis or even oesophageal intubation. A flat capnograph trace in an intubated patient (even during CPR) indicates absence of ventilation; the tracheal tube or trachea may be obstructed or the tube is not in the trachea. Management may require bronchial suction, reintubation or rigid bronchoscopy.

Deaths still occur from aspiration of blood in the recovery period and all anaesthetists must be aware of the clinical signs and management.

Guidelines on Management of Extubation

There has been a steady increase in interest in the topic of extubation. In 2012, DAS published the first national guidance on extubation of adult patients (Fig. 22.24). This guidance divides extubation into four phases: plan, prepare, perform and post-extubation care. It recommends that an early assessment is made to determine whether extubation is low (fasted, uncomplicated airway, no other risk factors) or high risk (others). After taking the precautions described above, low risk extubation can usually be managed awake or ‘deep’ according to the anaesthetist’s preference and judgement, though making clear that the default method is awake. For patients requiring high risk extubation a number of options are offered: awake extubation, advanced techniques, delayed extubation and tracheostomy. Advanced techniques are conversion to a laryngeal mask with the tracheal tube in situ before extubation, a ‘remifentanil extubation’ or use of an AEC. Deep extubation in the high risk setting is not advocated. All the advanced techniques are described in detail but require expertise and practice before use in an acute situation.

THE DIFFICULT AIRWAY IN OTHER LOCATIONS

A difficult airway is encountered most commonly in the operating theatre suite around the time of surgery, but most deaths from airway management difficulty occur elsewhere. At least a quarter of major airway events occur outside theatres, with ICU and the emergency department being particularly important areas. When such events occur in these sites, the risk of injury is increased compared to the risk in the operating theatre environment.

The reasons for this are complicated. Patients on ICU are critically ill, with markedly reduced physiological reserve. Approximately 8% have a difficult airway. Most have pre-existing respiratory compromise and increased intrapulmonary shunt and therefore tolerate airway obstruction or apnoea very poorly. Initial tracheal intubation is often performed as an extreme emergency and allowing the patient to wake if difficulty occurs is often not an option. While intubation in the ICU is accepted to be very high risk, a large proportion of critical airway events in this setting occur at a time well after intubation. Dislodgement of tracheal tubes and particularly tracheostomies, followed by airway difficulty, especially in the obese, is a notable cause of morbidity and mortality. The airway is often oedematous for a considerable period after prolonged intubation and re-intubation may be more difficult.

In the emergency department, patients often have reduced physiological reserves as a result of the pathophysiological problem that led to admission. Trauma is a specific condition in the emergency department which often increases the difficulty of airway management. The combination of an at-risk cervical spine requiring immobilization of the neck, blood in the airway and multiple trauma with pulmonary injury and hypovolaemia is a major challenge.

There are also extrinsic factors which may lead to an increased likelihood of difficulty and to poor management of the difficult airway outside the operating theatre suite.

While some of these factors are unavoidable many are not. All staff who manage the airway in ICU, the emergency department and in remote hospital locations should recognize that both patient factors and extrinsic factors interact to increase the likelihood of difficult airway management. Preparation for such difficulty is vital.

MANAGEMENT OF THE DIFFICULT AIRWAY IN CHILDREN

The unexpected difficult airway in paediatric practice is rare in comparison with the adult population. Many difficulties are relatively easy to predict prior to induction and are associated classically with craniofacial problems such as those which occur in Pierre Robin, Treacher Collins and Goldenhar syndromes. Other types of craniofacial abnormality may also lead to difficult airway management. Congenital subglottic stenosis or tracheal abnormalities such as webs or haemangiomas are encountered occasionally. In most of these children, the small calibre of the airway and limited oxygen reserves mean that most airway difficulty occurs while the child is an infant. In contrast, the airway of a child with mucopolysaccharide storage diseases (Hunter and Hurler syndromes) becomes increasingly difficult to manage as the child grows and the soft tissues become infiltrated, leading to a risk of airway obstruction and difficulty in manipulation of the tissues. Other airway challenges in children may arise in the acute situations encountered with trauma, infections (e.g. epiglottitis, croup) or burns involving the airway. However, unexpected difficulties can also occur during routine surgery.

These were published in 2013 and are available on http://www.das.uk.com/content/paediatric-difficult-airway-guidelines and http://www.apagbi.org.uk/publications/apa-guidelines. The basic principles of difficult airway management described above apply equally in children but the airway management options are more limited.

Recent developments have increased the options for difficult airway management in children. These include second generation SADs, videolaryngoscopes and cuffed tracheal tubes that are appropriate for children. The focus of care for children and infants with airway difficulty is, as in adults, to take all steps to ensure adequate oxygenation (rather than becoming fixated on tracheal intubation) and all anaesthetists involved in the care of children must have a strategy which includes a plan and back-up plans. They should be familiar with the equipment which may be required and have practised using it. If a difficult airway is predicted, it is good practice to have a minimum of two experienced anaesthetists with appropriate paediatric experience present in the operating theatre.

The techniques used in adults are entirely appropriate for the older child (above 30 kg), using smaller equipment. The intubating LMA has a size 3 version and a number of SADs are available in small sizes; classic LMA, ProSeal LMA, Supreme LMA and i-gel now all have size ranges that include size 1.5 (suitable for infants 5–10 kg) and some even size 1 (for < 5 kg). These devices have been shown to be effective in elective paediatric patients but are unproven for difficult airway management and are generally less easy to use and perhaps less reliable in comparison to those used in adult practice.

Inhalational induction is used widely in paediatric practice and is particularly favoured for management of the difficult airway. Gastric distension is a special problem in children and infants and is more likely if there has been respiratory distress before anaesthesia and if positive pressure is applied to the airway. It is sensible to decompress the stomach when an adequate depth of anaesthesia has been achieved. Anaesthesia can be maintained using a tracheal tube inserted partially into the nasopharynx but SADs are increasingly used to maintain the airway and provide a conduit for fibreoptic techniques (even in small babies). The ProSeal LMA and i-gel probably have the best features for this role. Specialized paediatric bronchoscopes are available with an external diameter as small as 2.2 mm (accommodating a 2.5 mm tracheal tube) but they are very fragile, have no facility for suction, can be harder to use than larger fibrescopes and are not available in most institutions. The absence of a suction channel is important because it prevents both clearance of the airway and delivery of local anaesthesia to suppress airway reflexes. Larger adult bronchoscopes with an external diameter of 3.5–4 mm can still be used in children. For larger children, the fibrescope can be used in the standard manner to insert an appropriately sized tracheal tube. However, it may be difficult to remove the SAD safely because the tracheal tube is shorter than the length of the SAD; this is overcome by mounting two tracheal tubes (joined together) onto the fibrescope and removing the SAD over these before detaching the proximal tracheal tube. In smaller children, the fibrescope may be inserted into the trachea and a wire passed into the trachea via the working channel of the fibrescope. If the fibrescope is too large even to enter the trachea, it can be positioned above the larynx and a wire deployed under direct vision. The wire can then be ‘stiffened’ using an airway exchange catheter (or stiff fine-bore nasogastric tube) and then, when tracheal intubation has been confirmed using capnography, an appropriate tracheal tube can be railroaded into place.

Alternative devices available to facilitate intubation in children include:

Management of the Child with an Inhaled Foreign Body

Although this is not necessarily a difficult airway problem, the need to maintain an airway compromised by an inhaled foreign body while sharing it with the surgeon makes it a considerable challenge. The procedure may be semi-elective or occasionally a critical emergency with the child in extremis from airway obstruction. Heliox may be beneficial before anaesthesia in critical situations.

Discussion of surgical plans is always necessary. Traditional anaesthetic priorities are to establish a deep plane of anaesthesia while maintaining spontaneous ventilation and avoiding complications that may require positive pressure ventilation. A calm inhalational induction is the usual technique and may be followed by surgical instrumentation of the pharynx and larynx (high foreign bodies) or use of a rigid bronchoscope (lower airway foreign bodies). Topical anaesthesia to the airway (under deep anaesthesia) may be beneficial. Because the procedure may be prolonged, it is important to use a rigid bronchoscope which enables continuous delivery of oxygen and anaesthetic gases. More recently the necessity of absolute avoidance of controlled ventilation has been questioned.

Airway swelling may occur after removal of the foreign body and infection may be present distally. Careful postoperative monitoring, dexamethasone, nebulized adrenaline and supplemental oxygen may all be needed.

AFTER DIFFICULT AIRWAY MANAGEMENT

Although there is often considerable focus on securing a safe airway in patients with a predicted or known difficult airway, it is equally important to establish a strategy for immediate management at the end of the procedure, and in the longer term if there is a need for further anaesthesia.

Long-Term Management

When the patient has recovered fully and before discharge from hospital, the senior anaesthetist involved should inform the patient of the relevant facts and the ways in which the difficulties experienced may affect airway management in future anaesthetics. It is probably appropriate that any patient whose airway is likely to prove difficult to manage during RSI by a junior anaesthetist is given written information to that effect. The anaesthetic record should contain a clear record of the problem, what was done, what did and did not work, and a judgement as to the likely problems and solutions in the future. This information should be given to the patient, sent to the patient’s general practitioner and filed in the hospital records. An example of a proforma is shown in Figure 22.25. The general practitioner should be asked to include the information in any future referrals. The Read code for difficult intubation can usefully be included in such letters and is SP2y3. It may be appropriate for the patient to wear a medical alert bracelet.

FURTHER READING

Cook, T.M., Nolan, J.P., Cranshaw, J., Magee, P. Needle cricothyroidotomy. Anaesthesia. 2007;62:289–290.

Cook, T.M., Woodall, N., Frerk, C. Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 1 Anaesthesia. Br. J. Anaesth. 2011;106:617–631.

Cook, T.M., Woodall, N., Harper, J., Benger, J. Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 2 Intensive Care and Emergency Department. Br. J. Anaesth. 2011;106:632–642.

Cook, T.M., McDougall-Davis, S.R. Complications and failure of airway management. Br. J. Anaesth. 2012;109:i68–i85. (Suppl 1),

Harmer, M. Independent Review on the care given to Mrs Elaine Bromiley on 29 March 2005. Clinical Human Factors Group. http://www.chfg.org/resources/07_qrt04/Anonymous_Report_Verdict_and_Corrected_Timeline_Oct_07.pdf, 2005.

Hawthorne, L., Wilson, R., Lyons, G., Dresner, M. Failed intubation revisited: 17-yr experience in a teaching maternity unit. Br. J. Anaesth. 1996;76:680–684.

Mihai, R., Blair, E., Kay, H., Cook, T.M. A quantitative review and meta-analysis of performance of non standard laryngoscopes and rigid fibreoptic intubation aids. Anaesthesia. 2008;63:745–760.

Peterson, G.N., Domino, K.B., Caplan, R.A., et al. Management of the difficult airway: a closed claims analysis. Anesthesiology. 2005;103:33–39.

Rose, D.K., Cohen, M.M. The incidence of airway problems depends on the definition used. Can. J. Anaesth. 1996;43:30–34.

Samsoon, G.L.T., Young, J.R.B. Difficult tracheal intubation: a retrospective study. Anaesthesia. 1987;42:487–490.

Sheriffdom of Glasgow and Strathkelvin, 2010. Determination of sheriff Linda Margaret Ruxton in fatal accident inquiry into the death of Gordon Ewing. http://www.scotcourts.gov.uk/opinions/2010FAI15.html

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