Disclaimer

These recommendations seek to reflect the latest published evidence regarding airway management. Where high-quality evidence was lacking, expert opinion and consensus is presented. The recommendations do not represent standards of care and instead are suggestions for optimal practice. They should be applied with specific consideration of the individual patient’s characteristics, the clinical context, the airway manager’s skills, available resources, and local healthcare policies.

Introduction

Significant morbidity related to airway management continues to be reported, with the failure to plan for difficulty a recurrent theme.1,2,3 Most published airway guidelines focus on management of the already-unconscious patient when difficulty with tracheal intubation is encountered. Although less frequently addressed, avoiding having to manage an unexpectedly difficult airway almost certainly has greater potential to prevent patient harm. Airway-related morbidity can be prevented by careful patient evaluation and formulation of an airway management strategy (a co-ordinated series of plans) before proceeding with airway management. Lack of an airway evaluation or the failure to change usual practice based on its findings has been associated with morbidity.1 Airway evaluation includes examination for anatomic predictors of difficulty with tracheal intubation, face-mask ventilation (FMV), supraglottic airway (SGA) use, and emergency front of neck airway access (eFONA). It should also include assessment of physiologic issues (e.g., apnea tolerance, aspiration risk, and altered hemodynamics) and the clinical context (e.g., case urgency, airway manager experience, equipment availability, and access to expert assistance). Airway evaluation should occur before starting airway management as well as before its discontinuation.

Video laryngoscopy (VL) has helped achieve more consistent glottic visualization and has improved first-attempt intubation success rates in the unconscious patient, especially in populations deemed to be at risk for difficult direct laryngoscopy (DL).4 Nevertheless, there remain patients who, based on thorough airway evaluation, would likely be more safely managed with awake tracheal intubation. This article addresses airway evaluation and provides recommendations to help formulate and implement a safe airway management strategy when difficulty is anticipated. In part 1 of these updated two-part recommendations,5 we address management of airway difficulties encountered in the unconscious patient, whether anticipated or not. Recommendations in both articles are meant to be broadly applicable to all specialties that have airway management in their practice mandate.

Methods

The methods presented here are identical to those described in the companion part 1 article5 and are reproduced here for the benefit of the reader. The Canadian Airway Focus Group (CAFG) is comprised of 17 members (see Appendix), with representation from across Canada as well as one member from each of New Zealand and Australia. The CAFG membership includes anesthesiologists, emergency physicians, and critical care physicians. Topics for review were divided among the members, with most assigned to two members. Members reviewed the literature published from 2011 onwards.

A medical librarian helped design and conduct the literature searches. Though not constituting a formal systematic review, databases searched included Medline, EMBASE, Cochrane Central Register of Controlled Trials, and CINAHL. Non-English and non-French, animal, manikin, and cadaver studies were excluded from searches, as were case reports, editorials, and letters. Nevertheless, team members had the discretion to include such material where relevant.

The CAFG met every two weeks by video conference from April 2018 to July 2020 to review findings and arrive at consensus regarding recommendations. Consistent with other recent airway management guidelines,6,7,8,9 we did not assign levels of evidence or strength of recommendation. This follows from a lack of what is considered high-level evidence seen in other medical fields. Randomized controlled trials of airway devices typically address efficacy (often in a population of low-risk elective surgical patients) but when critical events are uncommon (as with airway management), they are unable to evaluate the safety of techniques or decision-making.10 Information gleaned from large database studies is better able to capture uncommon events,10 but analysis is limited to association rather than causation and the population studied may not represent all practice environments. Thus, although evidence-based to the extent possible, some of the recommendations are based largely on expert consensus.

After review by the CAFG, draft documents were sent to several airway experts internationally (see Acknowledgments) for informal review and comment.

Definitions

The following definitions are used throughout the manuscript.

  • Anticipated difficult airway. A difficult airway is predicted when the airway manager anticipates difficulty with any or all of FMV, tracheal intubation, SGA use, or eFONA.

  • Awake tracheal intubation. Awake tracheal intubation (ATI) refers to tracheal intubation of a patient who is sufficiently conscious to maintain a patent airway unassisted, to maintain adequate gas exchange by spontaneous ventilation, and to protect the airway against the aspiration of gastric contents or other foreign material. Awake tracheal intubation can occur via the nasal, oral, or front of neck routes, and is facilitated by topical, regional, or local infiltrative airway anesthesia.

  • At-risk tracheal extubation. The at-risk tracheal extubation is defined by the patient anticipated to be intolerant of tracheal extubation or who might be potentially difficult to re-intubate. Difficult re-intubation might be anticipated based on pre-existing or de novo conditions (e.g., neck fusion or immobilization; upper airway edema).

Prediction of difficulty with airway management

Predicting difficulty underlies the planning for safe airway management. Expert opinion appearing in audits of airway-related morbidity and closed legal claim studies suggest that the “failure to prepare for failure” by omitting, not documenting, or not acting on positive findings of an airway evaluation figures prominently in cases with poor outcomes.1,2,3 Canadian data,3 and that from the USA,2 reveal that most anesthesia airway-related closed claims involved patients presenting for elective surgery (78% and 63%, respectively).

Comprehensive airway evaluation includes physical examination of the patient and review of relevant physiologic and contextual issues, pertinent diagnostic imaging studies, and any available records of previous airway management. A history of previous difficulty is more often correctly predictive of difficulty than the bedside examination.11,12,13,14,15

Alone or in combination, the various bedside screening tests of anatomic features have been criticized for their poor performance in correctly predicting when difficulty will indeed occur with airway management.11,13,16 Nevertheless, the presence of certain anatomic features (Tables 1, 2, 3, 4, 5, 6, 7) should alert the airway manager to carefully consider the safest approach to airway management and which devices to have available; little downside will accrue if airway management turns out to be non-problematic. Conversely, when bedside screening suggests that no difficulty is expected, while more often correctly predictive of the actual outcome,11,16,17 unanticipated difficulty can still occur, such that the airway manager must be ready with a strategy to address difficulty in all patients. Performing and documenting an airway evaluation is standard of care, and furthermore, acts as a cognitive prompt18 to consider the potential for difficulty with every patient. The CAFG recommends that all patients undergo airway evaluation before the initiation of airway management and before the discontinuation of airway support (e.g., tracheal extubation).

Table 1 Published predictors of difficult tracheal intubation using direct laryngoscopy
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Table 2 Published predictors of difficult tracheal intubation using video laryngoscopy
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Table 3 Published predictors of difficult tracheal intubation using other devices
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Table 4 Published predictors of difficulty with face-mask ventilation and difficult face-mask ventilation combined with difficult direct laryngoscopy
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Table 5 Published predictors of difficult supraglottic airway use in the adult patient
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Table 6 Presumptive predictors of difficulty with front of neck airway access
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Table 7 Physiologic and contextual issues that may impact airway management
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Published predictors of difficult airway management

Predictors of difficult tracheal intubation by DL and VL and other devices appear in Tables 1–3. Predictors of difficult FMV and difficult SGA use appear in Tables 4 and 5, respectively. Predictors of difficult eFONA have not been prospectively studied but appear on a presumptive basis in Table 6. The likelihood of actually encountering difficulty with any modality increases in proportion to the number of anatomic predictors of difficulty.

There are currently few published studies looking at predictors of difficulty with tracheal intubation using VL; this is a gap in the literature that should be addressed. Physiologic and contextual factors that may also impact planning and implementation of airway management appear in Table 7.

The enhanced airway evaluation

Patients with obstructing airway pathology may have distortions of upper or lower airway anatomy that cannot be identified by regular bedside screening tests. For the patient with known or suspected obstructing glottic or supraglottic airway pathology, awake nasal endoscopy or oral VL performed under local anesthesia immediately before airway management can help clarify the extent and location of the problem.19 Subglottic pathology can be assessed by review of recent imaging studies.20 Point-of-care ultrasound is playing an increasing role in physiologic diagnosis and evaluation of targeted management of resuscitation before, during, or after airway management.21

Another aspect to enhancing the airway exam in patients with significantly altered anatomy is to identify the location of the cricothyroid membrane (CTM).22 If visual inspection or palpation fails to identify the CTM location with certainty, it should be identified using ultrasonography and marked,22,23 with the patient’s neck in an extended position. The patient can subsequently be positioned optimally for the intended airway technique; if eFONA is required, the patient can quickly be returned to the neck-extended position to utilize the previously made marking.24

Decision-making when difficult tracheal intubation is predicted

Few published studies or guidelines specifically address which patients with predictors of difficult tracheal intubation can safely be managed after the induction of general anesthesia. Nevertheless, cues can be taken from the UK’s NAP4 study1 and closed claims analyses.2,3 In NAP4, ATI was judged to have been underutilized in patients with known difficult airways. Eighteen cooperative patients with predictors of both difficult tracheal intubation and difficult FMV underwent intubation attempts after induction of general anesthesia. All suffered complications and two patients died.1

When difficulty is predicted, ATI enables patients to maintain their own airway patency, gas exchange, and protection of the lower airway against aspiration during tracheal intubation; thus, ATI potentially provides a safety benefit. Conversely, despite possessing predictors of difficult laryngoscopy or intubation, some patients might still be safely managed after induction of general anesthesia. When difficult laryngoscopy or intubation is predicted, deliberate consideration of the following four questions can help the airway manager decide whether ATI is indicated or if management might safely occur after induction (Fig. 1).

Fig. 1
figure 1

Flow diagram: Decision-making when difficult tracheal intubation is predicted. ATI = awake tracheal intubation; DL = direct laryngoscopy; FMV = face-mask ventilation; SGA = supraglottic airway; VL = video laryngoscopy.

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A. Does the patient clearly need awake tracheal intubation?

Significant and obvious anatomic deformities or pathologic alterations of the head and neck are often most safely managed with ATI. Examples include (but are not limited to) the patient with very limited mouth opening, a fixed flexion deformity of the head and neck, or a pathologically enlarged tongue. In such patients, there is often no chance that standard techniques such as DL, Macintosh blade video laryngoscopy (Mac-VL) or hyper-angulated blade VL (HA-VL) are feasible. Alternatives to these standard techniques are likely to be less familiar to the airway manager or take longer to use, especially in the context of distorted anatomy. Thus, if managing the airway in apneic conditions after induction of general anesthesia, this could put the patient at risk of significant hypoxemia. In addition, anatomy altered to this extent will often also predict difficulty with fallback modes of ventilation such as FMV or SGA use (see next section). For these reasons, ATI is a safer option.

B. Is difficulty also predicted with fallback ventilation options?

When difficult tracheal intubation is predicted, no matter how effective the primary device chosen to facilitate tracheal intubation may be, all have a failure rate. When this occurs, FMV or SGA ventilation will be needed between attempts. Unfortunately, when difficult or failed tracheal intubation has occurred, difficult FMV is more likely,55,56,57 and vice versa.46,57 Similarly, failed SGA ventilation is associated with a higher incidence of difficult FMV.49,52 This phenomenon has been referred to as the “composite failure of airway management”.55 Tracheal intubation and FMV are reported to have predictors of difficulty common to both modalities44 (Table 4). Thus, when difficulty is predicted with one mode (e.g., tracheal intubation), the airway manager must be especially vigilant in assessing the patient for predicted difficulty with other modes (e.g., FMV, SGA ventilation, or front of neck airway access [FONA]). When significant difficulty is predicted with two or more modes, (e.g., tracheal intubation and FMV), ATI should be strongly considered as a potentially safer option.

C. Is there any physiologic compromise?

Physiologic compromise (Table 7) complicates and distracts from difficult airway management.53,54 It is also accentuated by induction of anesthesia that additionally risks hypoxemia, aspiration, or hemodynamic instability in those at risk. Separation of difficult airway management from induction of anesthesia is therefore of value; thus, ATI is likely the optimal choice for both safety and controlling the cognitive load of the airway manager.

Rarely, physiologic issues might be the sole indication for ATI, without any anatomic predictors of difficulty with airway management, as with a critically ill patient with significant lung parenchymal disease and a high shunt fraction.58

D. Are there any complicating contextual issues?

Contextual issues (Table 7) might also favour ATI when difficult tracheal intubation is predicted. For example, when an airway manager is practicing in a resource-austere setting without access to expert assistance or VL, the use of ATI for the predicted difficult airway patient might improve the margin of safety if patient transfer to a more fully equipped facility is not an option.

As indicated in Fig. 1, if all of the preceding questions are answered in the negative, airway management after induction of general anesthesia may be considered. Nevertheless, it must be emphasized that this decision remains one of clinical judgement and that the algorithm based on these questions has not been validated in a randomized-controlled trial. An airway manager’s individual threshold for performing ATI or other patient or system factors might also impact the decision. Conversely, if the pathway through the Figure 1 flow diagram has suggested that ATI might be a safer option, a fifth question must then be addressed, as follows.

Can the patient cooperate with ATI and is there time?

Proceeding with ATI generally requires both a cooperative patient and time for its completion. If these are lacking, options become more limited. In some critically ill patients, physiologic disturbances or an alteration in sensorium can make compliance with ATI challenging. This may guide the airway manager towards tracheal intubation after the induction of general anesthesia if airway management must proceed at that time (Fig. 1). Under these circumstances, regardless of how the induction of general anesthesia proceeds (e.g., with or without an attempt to maintain spontaneous ventilation), “double set-up” (Table 8) preparations for eFONA are recommended in case of need. This decision must be balanced against the benefit of delaying tracheal intubation in favour of less invasive approaches for ventilation/oxygenation or further medical management, if this is an option.

Table 8 Components of the “double set-up” in airway management
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When difficulty is predicted, tracheal intubation should only proceed after the induction of general anesthesia when the estimated margin of safety is equivalent to an awake technique. In the elective surgical setting, perceived time pressure or airway manager discomfort with performing ATI must not play a role in decision-making for the patient with a difficult airway. Rather, help might be sought from a colleague with more experience in performing ATI.

Implementation of the planned strategy when difficult tracheal intubation is predicted

When difficult tracheal intubation is predicted, the following principles are common to implementing the plan, whether by ATI or after induction of general anesthesia:

  • An additional experienced airway manager should be sourced. For more challenging situations, having this individual standing by in the room is advisable;

  • The airway manager should brief the assembled team on the intended strategy for securing the airway;

  • The briefing should include the planned response to failure of the intended technique;

  • An SGA must be available for use as a rescue technique in the event of failed tracheal intubation;

  • During the briefing, the airway manager should include triggers for declaring failure of one technique and proceeding to the next. At this time, all members of the team should be explicitly empowered to state when they believe a trigger has occurred.

Awake tracheal intubation in the patient with anticipated difficult tracheal intubation

When performed by experienced airway managers, high success and low complication rates have been reported with ATI.59,60,61 All awake techniques are facilitated by one or more of topical, regional, or local infiltrative anesthesia, often aided by small doses of adjunctive systemic medications. Any discomfort with ATI is typically brief and patients are usually accepting of an airway manager’s recommendation for airway management, especially when its safety aspects are discussed.62

The Difficult Airway Society in the UK has recently published comprehensive guidelines on ATI.63

Topical airway anesthesia for awake tracheal intubation

Topically applied lidocaine provides good conditions for ATI and has a favourable safety profile compared with other agents. Used for ATI, a maximum dosage of 9 mg·kg−1 (lean body weight) of topical lidocaine has been recommended by the DAS ATI guidelines,63 although there have been reports of symptoms and signs of toxicity at this and lower doses in volunteers.64 Thus, the lowest lidocaine dose compatible with adequate conditions for the procedure should be used. There is no published evidence to recommend one topicalization regime over another, nor is there evidence that percutaneous nerve blocks are superior to topical airway anesthesia.

Adjunctive systemic medications during awake tracheal intubation

Systemic medications should complement topical airway anesthesia and should not be used to compensate for its ineffective application. The goal of therapy should be considered in choosing a systemic agent and its dosage. Anxiolysis and sometimes, amnesia, may be achieved with a benzodiazepine or dexmedetomidine65,66; decreasing airway reflexes may be aided by opioids, such as a low-dose remifentanil infusion. Sedation is a secondary and arguably less desirable goal during ATI, as it may impair the patient’s ability to cooperate with application of topical anesthesia.67 The use of systemic medication in the patient undergoing ATI because of obstructing pathology must be carefully considered, recognizing that total loss of airway patency has been reported.68

Reviews on the use of systemic medications during ATI have been published.65,69 No single systemic agent has yet been definitively identified as the best to aid ATI, although dexmedetomidine has been established as an effective sedative for the purpose.66,69 Airway managers’ preferences and familiarity with the various drugs are important factors to help guide their choice of agent.

Choice of device to facilitate awake tracheal intubation

ATI has traditionally been accomplished using a flexible bronchoscope (FB). More recently, HA-VL has also been reported to successfully facilitate ATI via the oral70,71 and nasal72 routes. While each class of device has benefits and limitations when used for ATI (Table 9), they appear to have comparable safety profiles.73,74 If one technique fails, the other may prove successful. Both options require effective topical airway anesthesia for ATI. Note that awake VL will not be an option for some difficult anatomical presentations (Table 9). Nevertheless, it is important for the airway manager to appreciate that for many difficult airway situations, ATI can proceed with a variety of devices.75

Table 9 Benefits of and limitations to the use of VL and FB for facilitating awake tracheal intubation
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Other options to facilitate ATI include optical stylets, the concurrent use of VL and the FB, or awake placement of an SGA under topical anesthesia to provide a conduit for FB-aided intubation.77 The latter is particularly effective in the setting of redundant upper airway tissue, as seen with significant obesity, patients with obstructive sleep apnea, and some children with predicted difficult airways.78,79,80 Blind passage of a tracheal tube through an SGA without being facilitated by a FB is not recommended for ATI.

The CAFG recommends that all airway managers should be competent in ATI. This includes effective application of topical airway anesthesia as well as the use of both the FB and VL for that purpose. Maintaining skills in ATI is important to ensure that airway manager discomfort is not a deterrent for performing an awake technique when clinically indicated.

Failed awake intubation

Awake tracheal intubation may fail59,60,61 for a number of reasons, including inadequate topical anesthesia, excess sedation, adverse anatomy, or a lack of patient cooperation. The airway manager must carefully consider the next steps. Simply proceeding with induction of general anesthesia after failed ATI has resulted in major morbidity and death.1,81 Options include deferral of an elective surgical case, summoning more experienced help, or application of additional topical anesthesia. Simply deepening systemic sedation may be hazardous. For an urgent or emergency situation that cannot be deferred, tracheal intubation after the induction of general anesthesia must sometimes be undertaken, with a “double set-up” preparation for eFONA (please see section 6.2 and Table 8).

Reports of complete airway obstruction occurring during attempted ATI have been published,59,68,82,83 most often in the setting of advanced obstructing airway pathology. Possible causes include excess sedation, or a direct adverse effect of local anesthetic on upper airway patency.84,85 The latter phenomenon does not imply that ATI should be avoided in patients with obstructing airway pathology, but rather, that the airway manager should be ready with an alternate plan, including rapidly proceeding with eFONA if a “cannot ventilate, cannot oxygenate” (CVCO) situation occurs. It should also be noted that if eFONA is anticipated to be difficult and prolonged (e.g., due to a thick neck, previous irradiation or overlying induration or infection), it should not be considered a viable fallback technique. In this situation, awake cricothyrotomy or tracheotomy under local infiltrative anesthesia (next section) may be the more prudent planned approach.

Awake tracheotomy or awake cricothyrotomy

Elective FONA by tracheotomy or cricothyrotomy is a good option as a planned primary technique when great difficulty is predicted with airway management—e.g., with a friable airway cancer and/or severely narrowed airway. Requiring patient cooperation, local infiltrative anesthesia, and most often performed by a surgeon, this option might be chosen in the following situations, among others:

  • For the patient presenting with advanced obstructing upper airway pathology that might cause significant technical difficulties during attempted awake oral or nasal intubation (e.g., a very friable, large base of tongue tumour);

  • When the glottic opening is very small (e.g., because of obstructing tumour burden) and FB-aided awake oral or nasal intubation would transiently completely occlude the patient’s breathing during intubation, possibly causing panic and loss of patient cooperation;

  • When both oral and nasal routes are not available (e.g., because of substantial disruption by trauma or distortion by advanced upper airway pathology);

  • When a surgeon elects to do awake tracheotomy as an alternative to awake oral or nasal intubation if the airway manager is not confident that ATI is a feasible option.

The “impossible airway” and awake institution of extracorporeal membrane oxygenation as a primary technique

An impossible airway might be predicted in clinical situations where all four of FMV, SGA use, tracheal intubation, and FONA are anticipated to fail. Failed FONA might occur with obstructing pathology distal to the thoracic inlet (or planned FONA site), or when anterior neck pathology precludes access to the trachea by cricothyrotomy or tracheotomy. In these circumstances, establishing awake veno-venous or veno-arterial extracorporeal membrane oxygenation (ECMO) prior to or as a replacement for airway intervention might represent a safer option to maintain oxygenation.86 This underlying rationale, together with continually improving technology and expertise in ECMO, supports its use in the context of the impossible airway situation, although the currently supportive evidence appears chiefly as single case reports87,88,89 and case series,90 with the attendant potential for positive publication bias. The decision to initiate ECMO prior to airway intervention should ideally occur by multidisciplinary consultation involving surgeons, anesthesiologists, perfusionists, and critical care staff, considering both diagnostic findings and clinical signs and symptoms such as stridor, dyspnea, and orthopnea.

Even in experienced hands, establishing ECMO may be complicated and is time-consuming. Therefore, it has no role as a rescue technique for a failed airway encountered after the induction of general anesthesia. This is distinct from the use of veno-arterial ECMO in the cardiac arrest scenario, when extracorporeal cardiopulmonary resuscitation is possible when specific criteria are met. In this case, patients are often transitioned to mechanical circulatory support some time after cardiac arrest and, although in a low-flow state, they will have received continuous ventilation and oxygenation throughout.

Management of the patient with anticipated difficult tracheal intubation after the induction of general anesthesia

If difficulty with management is predicted but the airway manager has elected to proceed with tracheal intubation after the induction of general anesthesia, close attention must be paid to details of implementation. Guiding principles are as follows:

  • Position the patient optimally for the planned technique;

  • Pre-oxygenate;

  • Use apneic oxygenation throughout;

  • Fully prepare equipment for the planned primary intubation approach;

  • Fully prepare equipment for alternate intubation techniques;

  • Prepare an appropriately sized second-generation SGA for rescue ventilation and oxygenation;

  • Brief the team on the planned progression of techniques, with objective triggers for transitioning to the next technique;

  • Review and communicate the exit strategy5 to be used if tracheal intubation fails;

  • Ensure that an additional experienced airway manager has been sourced.

Further details appear below.

Patient positioning

Appropriate patient positioning can help with technical aspects of airway management and by increasing safe apnea time.

  • Positioning for laryngoscopy and intubation. Published literature suggests optimal patient positioning for direct- and Mac-VL is the “sniffing” position.91,92,93,94 This is typically obtained by aligning the patient’s tragus with their sternum in the horizontal plane, by flexing the lower neck and extending the head.95 In the obese patient, similar alignment can be achieved in several ways, including commercial positioning devices, back-of-bed elevation, or by creating a ramp with folded sheets.96,97,98,99,100,101,102,103,104 There is currently insufficient evidence to recommend a specific patient position for the use of hyper-angulated videolaryngoscopes, which can be used in both the sniffing and neutral positions of the head and neck. The patient positioned in the neutral position with cervical spine immobilization is sub-optimally positioned for DL and Mac-VL, so that an experienced airway manager and alternate devices such as an HA-VL should be available.105

  • Positioning for FMV. Although the evidence is sparse, the sniffing position appears to be beneficial for improving upper airway patency106 and facilitating FMV.107

  • Positioning for SGA insertion. Product monographs for SGAs typically espouse a sniffing position for insertion, with head extension and lower neck flexion.108,109 Furthermore, a prospective study has indicated reduced neck mobility to be a risk factor for difficult SGA insertion.52 With respect to ventilation once placed, a systematic review and meta-analysis by Kim and colleagues compared the performance of a variety of SGAs in the flexed, neutral, and extended positions.110 Compared with the neutral position, the flexed position improved device seal but impaired ventilation as well as the view of the glottis obtainable with flexible endoscopy. Conversely, compared with the neutral position, the extended position worsened the device seal but had no effect on ventilation effectiveness or endoscopic view. These findings suggest that after insertion, SGAs should generally be used with the head and neck in the neutral position.

  • Positioning for eFONA. Although published evidence is lacking, full extension of the head and neck is likely the optimal position for eFONA.4 This will be aided by placing a bolster or pillow under the patient’s shoulders. There is some evidence that full neck extension may increase the height of the CTM by as much as 30%.111 Pre-induction landmarking of the CTM (e.g., by ultrasound or palpation) should also occur in a position of full neck extension, as the CTM location may change significantly when re-positioning from a neutral to an extended position.111

Pre-oxygenation

The American Society of Anesthesiologists and Canadian Medical Protective Association closed claims publications revealed that many patients who sustained airway-related morbidity were healthy and presenting for elective surgery.2,3 In some cases, harm might have been prevented or mitigated by closer attention to the use of pre-oxygenation and apneic oxygenation techniques to prolong the safe apnea time. Safe apnea time relates to the volume of the patient’s functional residual capacity (FRC), effective de-nitrogenation of the FRC, and oxygen consumption. Of these, FRC and de-nitrogenation are modifiable. As described by Mosier in a recent editorial, three scenarios might be considered, based on the risk of oxygen desaturation with the onset of apnea58:

  • Low to moderate risk of oxygen desaturation: Describing many elective surgical patients with a predicted ample FRC and low shunt fraction, the FRC should be de-nitrogenated by pre-oxygenation with 100% oxygen for three minutes of tidal volume breathing, eight vital capacity breaths over 60 sec,112,113 or until the measured fraction of exhaled oxygen (FeO2) exceeds 0.9.114 More than one strategy has been described for standard pre-oxygenation: 1) use of a tightly applied cuffed face mask attached to an anesthetic circuit or manual resuscitator with O2 flow ≥ 10 L·min−1, or 2) use of a nonrebreathing face mask with oxygen flow at “flush rate” (i.e., ≥ 40 L·min−1).115 The high flow rate helps match the patient’s peak inspiratory flow rate, thus avoiding dilution by room air during peak demand. There is evidence that safe apnea time can be further extended with efforts to increase FRC, e.g., by patient positioning in the semi-seated (Fowler’s), reverse Trendelenburg, or seated upright position,116,117,118,119,120 if hemodynamics allow. This is particularly applicable to morbidly obese patients and term parturients.121,122,123,124 In addition, gentle FMV between loss of consciousness and beginning laryngoscopy is advocated.

  • Moderate to high risk of oxygen desaturation: For the patient at higher risk of oxygen desaturation with the onset of apnea, such as those with lower FRC and increased shunt fraction, the optimal pre-oxygenation strategy likely involves use of positive end-expiratory pressure or non-invasive positive pressure ventilation (NIV) during pre-oxygenation,125,126,127,128 together with back up or reverse Trendelenburg positioning. The concurrent use of standard nasal cannulae with NIV can augment pre-oxygenation and subsequently provide apneic oxygenation during laryngoscopy and intubation,129 although to avoid hazardous gastric insufflation, airway patency must be assured. Use of high-flow nasal oxygenation (HFNO) devices running high flows under a tightly sealed mask should be avoided, e.g., during FMV, for fear of rapid gastric distention or pulmonary hyperinflation and subsequent barotrauma.

  • High risk of oxygen desaturation due to refractory hypoxemia: The critically ill patient with substantial lung parenchymal disease and high shunt fraction is often refractory to pre-oxygenation and apneic oxygenation techniques, resulting in severely limited safe apnea time. The use of awake intubation and HFNO while maintaining spontaneous ventilation is one option to help address this scenario, if feasible.

The benefit of de-nitrogenation/pre-oxygenation is age dependent. Children have a relatively low FRC and high metabolic demand, which combine to create short apnea times despite pre-oxygenation. They often benefit from apneic oxygenation techniques to help maintain oxygenation during airway management.130

The CAFG recommends universal pre-oxygenation before the induction of general anesthesia/rapid-sequence intubation (RSI), if feasible.

Apneic oxygenation

The use of apneic oxygenation can be beneficial in prolonging the safe apnea time during airway management. Apneic oxygenation is most often accomplished with the use of standard nasal cannulae at flows of 5–15 L·min−1 or devices that provide heated and humidified oxygen at higher flows (40–70 L·min−1 in adults—i.e., HFNO). Apneic oxygenation is thought to work by a number of synergistic mechanisms, including mass flow of oxygen along a pressure gradient from the pharynx to the alveoli, turbulent supraglottic flow vortices and dead space flushing, as well as the effect of cardiac oscillations on intrathoracic pressure.131,132,133,134 Nevertheless, the airway manager must recognize that while oxygenation might be maintained, carbon dioxide clearance will be diminished during apneic oxygenation. Thus, caution and monitoring are required when allowing prolonged apnea in all patients, but especially those with increased intracranial pressure, metabolic acidosis, or pulmonary hypertension.132

Apneic oxygenation by both standard nasal cannulae and HFNO has been studied in operating room (OR), emergency department (ED), and intensive care unit (ICU) settings. In general, compared with no apneic oxygenation, use of apneic oxygenation is effective in reducing oxygen desaturation during laryngoscopy in both adult and pediatric surgical patients.132,135,136,137,138,139,140,141 Results are mixed in out-of-OR settings such as the ED or ICU, possibly relating to factors such as patient population (e.g., shunt physiology precluding oxygen uptake) or study design (e.g., a non-patent airway during apnea before laryngoscopy).132,142,143,144,145,146,147,148,149,150

The CAFG recommends that at a minimum, apneic oxygenation should be used for patients with anticipated difficult or prolonged laryngoscopy/tracheal intubation and/or for the patient with anticipated intolerance of apnea. It is essential to note that apneic oxygenation relies on a patent upper airway and will have no effect if the airway is obstructed.

Maintenance or ablation of spontaneous ventilation?

General anesthesia with maintenance of spontaneous ventilation has been suggested to facilitate tracheal intubation when difficulty is anticipated. Nevertheless, despite the theoretical safety advantage afforded by the maintenance of inspiratory effort,151 functional upper airway obstruction can occur with loss of consciousness, to a greater degree than occurs during natural sleep.152 This follows from attenuation of upper airway dilator muscle activity, which makes the pharynx vulnerable to collapse.153,154 The tendency of an airway to collapse with loss of consciousness is compounded by the negative intraluminal pressures generated during spontaneous inspiration within a narrowed airway.153 Although inhalational induction is commonly used in pediatric patients, in adults it can take considerable time to reach a plane of general anesthesia sufficiently deep to allow for airway instrumentation without provoking reflex glottic closure. The NAP4 report highlighted the hazards of using inhalational induction in the adult patient with obstructing airway pathology.1 The CAFG does not endorse use of inhalational induction of general anesthesia as a sole strategy for the adult patient with anticipated difficult laryngoscopy or tracheal intubation.

Assessing for FMV efficacy prior to administration of a neuromuscular blocking agent

After the induction of general anesthesia, a trial of FMV prior to administering neuromuscular blocking agents (NMBAs) has been advocated,155 with a view to potentially allowing the patient to awaken if FMV is unsuccessful. Nevertheless, in this situation, the effect of sedative-hypnotics may not dissipate or be reversible in sufficient time for the patient to resume spontaneous ventilation before significant hypoxemia occurs.156 Thus, the more appropriate action when impossible FMV occurs would be to proceed with tracheal intubation or SGA insertion, both of which will be facilitated by neuromuscular blockade.157,158,159 Studies of pharmacologic paralysis (albeit almost always having been performed in patients without difficult airways) generally conclude that pharmacologic paralysis facilitates FMV, and virtually never makes it worse.160,161,162,163,164,165,166,167 With or without anticipated difficulty, if electing to proceed with tracheal intubation after the induction of general anesthesia, the CAFG did not find sufficient evidence to support a recommendation for a trial of FMV prior to NMBA administration.

Use of short or intermediate-acting neuromuscular blockade

When difficulty with tracheal intubation is anticipated, the CAFG could not find evidence of an outcome benefit to justify recommending use of succinylcholine over an intermediate-acting non-depolarizing NMBA. Considerations in choosing a NMBA include the following:

  • Pharmacologic modelling studies have indicated that succinylcholine may not necessarily wear off in time to allow resumption of spontaneous ventilation before hypoxemia occurs in the CVCO situation.168,169 In addition, the residual effects of the sedative/induction agent may persist, also impairing a return to adequate spontaneous ventilation.

  • Similarly, a proportion of patients given sugammadex for reversal of rocuronium or vecuronium would also critically desaturate during the time required to draw up and administer the drug and for it to work, particularly if apnea intolerant.169 In one simulation study of a CVCO situation,170 a substantial time passed from a decision to use the drug, obtaining it, and its administration to the patient. Therefore, the immediate availability of sugammadex is recommended in all airway management locations. It should be noted that sugammadex will not necessarily reverse CVCO situations related to obstructing airway pathology.171,172

  • In critically ill patients where airway management is being performed as part of a resuscitation, expectations of a return to effective spontaneous ventilation is unrealistic when the clinical trajectory is rapidly deteriorating. Use of succinylcholine or a plan to reverse rocuronium if difficulty occurs is not a reliable plan if it is the only difficult airway strategy being deployed.

  • Use of an intermediate-acting NMBA to facilitate tracheal intubation will optimize conditions for the duration of airway management should more than one attempt be required, including change of device or operator.

Choice of equipment

Resources allowing, the CAFG advocates for the routine use of VL (with appropriately selected blade type) for tracheal intubation, with or without anticipated difficulty.5 Regardless of the chosen technique, the airway manager must attain and maintain competence with its use in lower acuity clinical or simulation settings.173,174

Difficulty encountered with a first attempt at tracheal intubation

Difficulty with tracheal intubation after the induction of general anesthesia will inevitably occur from time to time, whether predicted or not. The reader is referred to the accompanying part 1 article5 for recommendations on management of this situation.

Difficult tracheal intubation predicted—other options

When difficult tracheal intubation is predicted, most patients will be intubated either awake or after the induction of general anesthesia with additional preparation and precautions. Nevertheless, in some circumstances, the following options may be considered:

Avoiding predicted difficult tracheal intubation—use of regional or local anesthesia for a surgical case

When difficult tracheal intubation is predicted, some surgical cases may be amenable to regional or local anesthesia, with the following caveats:

  • As complications from the surgical procedure itself, administered local anesthetic or sedative medications could all present the need for airway management despite the use of a regional technique, a complete airway evaluation must still occur, and a management strategy determined.

  • The surgical procedure must be of a predictable duration, and the block must be shown to be effective before proceeding.

  • Ideally, there should be easy access to the patient’s airway intraoperatively.

  • Before proceeding, the team should be briefed on the patient’s difficult airway status, together with the plan for intraoperative airway management if needed.

Deferring management of the patient with predicted difficult tracheal intubation

Occasionally, it might be appropriate to defer airway management when difficult tracheal intubation is predicted. Examples of this include:

  • Transferring an elective surgical patient to a more fully equipped hospital;

  • Transferring a pediatric surgical patient with known facial dysmorphism to a specialized pediatric hospital for management;

  • Rescheduling a semi-urgent surgical procedure from overnight hours until daytime staff have arrived;

  • Deferring tracheal intubation of a critically ill patient by temporizing with the use of non-invasive ventilation or HFNO while additional expertise and equipment is sourced, or until the patient is transferred to a different location (e.g., the OR) for the intubation.

Use of an SGA in the patient with known or predicted difficult tracheal intubation

For the patient with predictors or a history of difficult tracheal intubation, the use of an SGA requires careful consideration. Three scenarios that might be considered include:

  • For the case normally undertaken with tracheal intubation, electively choosing to proceed with an SGA simply to avoid a difficult tracheal intubation situation has been shown to be hazardous.1 The CAFG recommends against this practice. Rather, the difficult intubation situation should be safely dealt with “up front”.

  • For a case where an SGA would normally be used, using an SGA in a patient with anticipated difficult tracheal intubation is often successful, although the airway manager must recognize that the fallback option of defaulting to tracheal intubation should the SGA fail may not easily succeed. This might suggest consideration of initial tracheal intubation as the safer plan when general anesthesia is required. If using an SGA regardless, at the very least, there should be a pre-determined plan for airway management should SGA ventilation fail.

  • Despite the above, SGA use is often (appropriately) recommended as a fallback option after failed tracheal intubation in the induced patient.5,6 The SGA can be used to maintain oxygenation and temporize the situation pending the patient’s awakening, while obtaining more equipment or expertise, or it might be used as a conduit to facilitate FB-aided intubation. In an urgent situation (e.g., failed tracheal intubation during emergency Cesarean delivery under general anesthesia), a risk to benefit analysis might justify continuing with the SGA.

Special situations

The patient with a known or suspected highly infectious respiratory pathogen

Airway management guidelines for patients with known or suspected highly transmissible infections should follow core principles, with some modification. The contemporary experience of the COVID-19 pandemic caused by SARS-CoV-2 infection is but one example that may lead to respiratory failure requiring tracheal intubation.175

  • Team safety. The risk of transmission of a highly infectious pathogen such as SARS-CoV-2 to a healthcare worker in the immediate peri-intubation period depends on the pathogen and precautions taken.176,177 Spread for most pathogens is assumed to occur by direct contact with droplet containing viral particles, and/or from aerosols generated during a patient cough or an airway procedure (i.e., aerosol-generating medical procedure [AGMP]). Whether it is an elective surgical patient who has tested positive for a highly infectious pathogen, a critically ill patient with unknown status, or a patient requiring tracheal intubation because of primary respiratory disease caused by a highly infectious pathogen, airway manager and team safety is paramount. Hastening to manage one of these patients without considering team safety may result in healthcare worker infections. The number of people in the room should be kept to a minimum, with a pre-assigned primary airway manager, an airway assistant, and ideally a third clinical support practitioner.

  • Personal protective equipment (PPE). While there has been significant controversy surrounding what defines “safe” PPE for practitioners caring for patients infected by a highly infectious pathogen, it remains possible that airway management poses a significant potential risk for clinicians.178 During airway management involving AGMPs, an important risk period occurs while removing (doffing) PPE. Incorrectly donning PPE or using inadequate PPE also poses a risk to the airway manager. Airborne, contact, and droplet precaution PPE for practitioners directly performing or assisting in airway management includes an N95 respirator, eye shield, Association for the Advancement of Medical Instrumentation level 3 gown, neck cover, and gloves.176,178 Training in donning and doffing PPE should be performed regularly and practitioners should be checked to ensure adequate PPE coverage before entering the patient care room.

The CAFG recommendations for airway management of the patient with a known or suspected respiratory infectious disease spread by droplet or airborne mechanism reflect other published consensus statements on the topic179,180,181,182,183,184 and are summarized in Table 10.

Table 10 Airway management considerations for the patient with known or suspected respiratory infectious disease spread by droplet or aerosol
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The patient with obstructing airway pathology or a traumatized airway

The patient with known or suspected obstructing airway pathology, or with airway trauma, requires careful and skilled evaluation and planning. Obstructing pathology can occur from tumour, infection, edema, foreign body, or stenosis. Trauma can distort the expected anatomy and might involve a breach of integrity of the airway, sometimes in more than one location. If general anesthesia has been induced and the patient is apneic, patients in both categories may present significant technical difficulties with some or all of DL or VL, FMV and SGA use. When tracheal intubation is indicated and time and resources permit, enhancing the standard airway evaluation is advised. Patient cooperation allowing, nasal endoscopic evaluation of the pharynx and larynx will help clarify the nature and extent of glottic and supraglottic pathology or injury.19 Any available computed tomography or magnetic resonance imaging scans should also be reviewed, especially for patients with pathology below the glottis, recognizing that for dynamic pathology, any imaging occurs at an unknown point in the patient’s respiratory cycle.20

Planning a safe approach to tracheal intubation of these patients should occur according to the principles described in Section 6 above, in consultation with all involved team members, including the surgical team. If difficulty is anticipated with two or more of tracheal intubation, FMV, and SGA ventilation, an awake approach (via a nasal, oral, or front of neck route) is advised.

The trauma patient with a blunt or penetrating injury to the airway must be assessed for how best to approach airway management, as well as for the potential for vascular or other injury. Patient cooperation and time allowing, securing the airway awake during spontaneous ventilation (e.g., by awake tracheotomy or awake oral or nasal intubation) enables avoidance of positive pressure ventilation above the level of a known or suspected airway breach, and its attendant risk of causing or exacerbating pneumothorax, pneumomediastinum or subcutaneous emphysema. There is also the potential for entering a tear, creating a false passage, or converting a partial tracheal disruption to a complete disruption during tracheal intubation. Thus, indirect visualization of the anatomy (e.g., using a FB until distal to the suspected or known level of breach) is recommended. Management of the traumatized airway has recently been well reviewed.187

Successful use of an SGA as a primary technique has been described under combat conditions,188 as well as in surgical patients with obstructing pathologies.189 Such reports are limited to observational case series or single case reports; randomized-controlled trials are lacking. Thus, while an SGA might successfully rescue a failed intubation, the CAFG recommends securing the obstructed or traumatized airway by tracheal intubation or FONA, when resources allow. As indicated in section 7.1.6, some severe cases of obstructing pathology below the thoracic inlet might be most safely managed with institution of ECMO before the airway is managed. Multidisciplinary planning and management are required.

The morbidly obese patient

The obese patient is at elevated risk during airway management. The NAP4 audit reported that patients with a body mass index (BMI) > 30 kg·m−2 were twice as likely to suffer a severe airway complication, and those with BMI > 40 kg·m−2 (morbidly obese) were four times as likely.1 Patients were obese in 68% of difficult intubation claims in a recent analysis of the Anesthesia Closed Claims Project database.2

A higher BMI is associated with difficult FMV.25,28,40,45,46,47,48 A co-existing thick neck40,41,42 (e.g., circumference > 40–50 cm), obstructive sleep apnea (OSA),25,40,43,46,167 and/or a history of snoring39,45,47,48 are also associated with difficult FMV. A thick neck15,28,190,191,192 and OSA167 are associated with difficult DL or intubation. Whether obesity alone predicts difficult laryngoscopy/intubation continues to be controversial, with some studies reporting an association,15,29,31,39,192,193,194,195 and others not.11,25,191,196,197,198 No studies have yet reported obesity to be a risk factor for difficult or failed VL-facilitated tracheal intubation, although one study has reported a thick neck to be associated with failed HA-VL-facilitated tracheal intubation.33 In another study, a higher neck skinfold thickness was associated with longer times to successful intubation with a FB in anesthetized patients.38 Obesity or a thick neck also predicts difficulty with SGA use in some,49,50,51 but not all199 studies, and may predict difficulty with palpation of landmarks for eFONA.

Even more significant are physiologic challenges during airway management of the obese patient.53 With reduced FRC, apnea is poorly tolerated, so that if difficulty is encountered in establishing ventilation, rapid oxygen desaturation must be anticipated.

Canadian Airway Focus Group recommendations for airway management of the obese and morbidly obese patient are as follows:

  • The potential for technical difficulty with both tracheal intubation and other modes of ventilation, coinciding with likely apnea intolerance, suggests that the airway manager should carefully consider whether ATI might confer a safety benefit (Fig. 1).

  • Regardless of the chosen approach, close attention to patient positioning is recommended, with ramping to ensure the patient’s tragus is aligned with the sternum.96,98 “Back up” or reverse Trendelenburg positioning will help delay oxygen desaturation.116,117,118,119,120,121,122,123,124 If general anesthesia is elected, careful pre-oxygenation must occur, with a goal of achieving FeO2 ≥ 0.9.

  • Apneic oxygenation is recommended during laryngoscopy and intubation of all morbidly obese patients when managed after the induction of general anesthesia.

  • Given the anticipated short apnea time and potential for difficulty with fallback ventilation options, primary use of VL (with appropriately selected blade type) is recommended for tracheal intubation to help maximize first-pass success.

  • Careful planning and documentation should occur before embarking on airway management of the obese patient. The team should be briefed on the strategy in the event that difficulty is encountered; this should include the triggers for moving to the next step in the plan. Given the potential for rapid oxygen desaturation, the airway manager should consider having a second experienced airway manager stand by for assistance if required.

The patient with an increased risk of aspiration

In the NAP4 audit, aspiration was the most common cause of airway management-related death and brain damage.1 In an incident-reporting study from Australia and New Zealand, aspiration was associated with significant harm, with many of the cases occurring in fasted patients.200 In the difficult airway patient, the risk of aspiration increases in conjunction with the potential for longer or multiple intubation attempts and/or gastric insufflation with FMV between attempts.201,202,203

Tracheal intubation is indicated when general anesthesia is required in the at-risk patient. Although second-generation SGAs with integrated drainage ports may confer some protection against aspiration,204 neither an SGA or FMV would typically be used as an intended primary technique in this scenario. Nevertheless, these modalities can and should be used as needed to maintain oxygenation between intubation attempts.

Although better referred to as “cricoid force”, cricoid pressure (CP) applied with a force of 10 N (i.e., 1 kg) before induction and 30 N (i.e., 3 kg) after loss of consciousness may reduce the risk of regurgitation and hence aspiration during RSI by occluding the hypopharynx behind the cricoid cartilage.205 Nevertheless, especially if poorly applied, CP can also make tracheal intubation more challenging,206 and it can also complicate SGA insertion. Evidence on the effectiveness of CP has been conflicting207 and controversial, creating equipoise around its use. Birenbaum et al. recently published a large randomized non-inferiority trial (n = 3,472 at-risk patients) on the use of CP.208 The primary outcome of aspiration did not differ between the actively applied CP (ten cases; 0.6%) and sham CP (nine cases; 0.5%) groups (relative risk of aspiration for the sham CP group compared with the actual CP group 0.9; 90% confidence interval, 0.39 to 1.99). In addition, glottic visualization and duration of intubation favoured the sham CP group. Despite the clinically equivalent occurrence of aspiration between groups, methodologically, the authors were unable to declare non-inferiority of sham CP because of a lower-than-expected aspiration event rate. Other study limitations included the non-inclusion of obstetric, critical care, and ED patients, and there were few (< 1% of the total) subjects with an anticipated difficult airway. Nevertheless, given that the original Sellick communication on CP was a small, non-randomized, unblinded, uncontrolled case series of 26 patients,209 having the very large Birenbaum et al. study suggest no clinically important difference in the incidence of aspiration in an at-risk population is very helpful in advancing our understanding of CP.

Canadian Airway Focus Group recommendations for airway management of the patient with an anticipated difficult airway and an increased risk of aspiration are as follows:

  • There may still be a role for correctly applied CP in some settings (e.g., obstetrics). Given the limited data available, the ultimate decision to use CP is at the discretion of the airway manager;

  • When a significantly elevated risk of aspiration coincides with an anticipated difficult airway, performing ATI with minimal sedation may confer a safety benefit;

  • If the airway manager decides to intubate the at-risk patient after the induction of general anesthesia, practical advice includes suctioning a nasogastric tube if already present (consider inserting one if not) before induction, placing the patient in the back up or reverse Trendelenburg position, and having two suction devices immediately available for oropharyngeal suctioning. Before induction, an in situ nasogastric tube should be attached to continuous low-pressure suction to prevent intra-gastric pressure accumulation following induction210;

  • Use of VL allows airway team members to assess the laryngeal view, the impact of CP (if used) on the view of the glottis, and provides heightened situational awareness during a critical time. Nevertheless, should massive regurgitation occur, the camera may be obscured. Thus, unless difficulty in glottic visualization is anticipated, use of Mac-VL is preferable in the patient at high risk of regurgitation, to allow direct, eye-to-glottis visualization if necessary;

  • If CP is deemed to be impeding either laryngoscopy or tracheal intubation, it should be removed;

  • The use of FMV with low inspiratory pressure during RSI, before or between attempts at tracheal intubation, can extend safe apnea time without oxygen desaturation;

  • If the planned tracheal intubation attempts fail, a second-generation SGA should be inserted, and the integrated drainage port used to drain the esophagus. If CP had been applied, it should be removed for insertion of the SGA and not reapplied.

The patient with a bleeding upper airway

Bleeding in the upper airway and subsequent problems with airway management are important causes of airway-related morbidity and death.211,212,213 Bleeding in the upper airway is fundamentally different from other challenging airway situations in that flexible bronchoscopic and videolaryngoscopic intubation are often more difficult or impossible because of soiling with blood. In addition, because the stomach may be filled with blood, the use of an SGA is only suitable as a temporary measure, or as a guide to intubation.213,214

Initial therapeutic measures include compression of the bleeding site, patient positioning (the patient will often only tolerate the sitting position), suctioning, oxygen delivery, and fluid resuscitation. Concomitantly, the airway should be evaluated for predictors of difficult or impossible DL, and the location of the CTM should be established. If laryngoscopy and intubation is predicted to be otherwise technically easy and the CTM is identified with certainty, then RSI can be employed, with two large bore rigid suction catheters ready. Otherwise, preparations should be made for an ATI with alternative techniques that can be used even if visibility of the airway is obscured by blood.213 Such techniques include awake FONA, awake FB-guided intubation via an SGA as well as awake DL or Mac-VL, awake retrograde-, blind nasal-, oral digital-, lighted stylet-, and ultrasound-guided intubation.213 Awake intubation with a FB or VL can still be attempted in this situation, but might fail, so the airway manager should be prepared to use one of the alternatives mentioned above. In addition, a “double set-up” to allow for eFONA should be prepared (Table 8) in case the airway is lost during attempted management.

Management of the bleeding airway has recently been reviewed in detail.213,215

Tracheal extubation

Published audits and closed legal claims continue to document the risks associated with tracheal extubation. Re-intubation in the ICU after failed extubation and tracheal tube exchange in the patient with a difficult airway have also caused patient morbidity.1,2,3,216,217 Although such cases consistently account for up to 25% of total airway management-related morbidity, a substantially smaller proportion of all published articles on airway management relate to tracheal extubation, rather than intubation.2 Fortunately, excellent guidelines218 and narrative reviews219,220 on tracheal extubation have been published. Intentional extubation is elective and thus allows for careful planning to occur (Fig. 2), including identification of at-risk patients after tracheal extubation.

Fig. 2
figure 2

Considerations for planning for safe tracheal extubation.

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The at-risk tracheal extubation

The patient may be deemed at risk at the time of tracheal extubation in one or both of two ways: 1) failure to tolerate tracheal extubation, where the patient is at risk of failing to maintain gas exchange, airway patency, or airway protection after extubation; and 2) if tracheal re-intubation might be difficult, either because the patient was originally difficult to intubate, or because of an interval event (Table 11).

Table 11 Potential causes of an at-risk extubation
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In some cases, more objective risk stratification can occur before planned tracheal extubation. For example, the patient considered at risk of supraglottic or glottic airway edema might be assessed with a cuff leak test.221,226,227,228 In a recent systematic review, the authors concluded that the absence of a cuff leak in an at-risk patient is associated with post-extubation stridor or need for re-intubation, but the presence of a leak does not necessarily rule out the occurrence of stridor or need for re-intubation.228 Further assessment of the at-risk patient can occur by indirect visual evaluation of the glottis and supraglottic area using a VL229 or FB before emergence from anesthesia or sedation begins.

Strategies to manage the at-risk patient upon tracheal extubation are presented in Table 12.

Table 12 Strategies to address the at-risk patient upon tracheal extubation
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Lower risk (“routine”) tracheal extubation

Even for the patient not identified as being at risk of morbidity, care must be taken with tracheal extubation. Routine extubation measures such as gas exchange and hemodynamics should be adequate and level of consciousness sufficient to enable airway patency and protection. The patient’s neuromuscular function, temperature, and acid-base status should be near normal. Prior to extubation, the patient should be pre-oxygenated and the pharynx should be suctioned, especially if at risk of pooled pharyngeal blood, to avoid the potential of aspirated blood forming an occluding clot in the trachea.2 Extubation at end-inspiration will help avoid immediate aspiration of blood or residual secretions. Additional CAFG recommendations for tracheal extubation are as follows:

  • As extubation of the surgical patient is often accompanied by airway manager fatigue and team distraction, a “sterile cockpit” concept of minimizing non-essential conversation during emergence and extubation of the surgical patient is advocated.

  • Supplemental oxygen delivery should occur during transportation of all recently extubated patients to high-dependency nursing units including postanesthesia care units. Pulse oximetry monitoring should also be used. Handover should routinely detail the type and ease of airway management.

  • In critical care or ED settings, if a consulting service has recommended tracheal extubation of an intubated patient, direct communication should occur between that service and critical care/ED attending staff about the rationale and timing of extubation. Documentation of intubating conditions/difficulty should be clearly available to consulting services to help guide the extubation plan.

Extubation over an airway exchange catheter (AEC)

If tracheal intubation was or might now be challenging, short-term use of an AEC can be considered at extubation to assist re-intubation should it be required. Appropriately positioned and secured above the carina (e.g., at around 23 cm at the teeth in the adult patient), 11- or 14-French airway exchange catheters are reasonably well tolerated236 and permit spontaneous ventilation, coughing, and talking. Although AECs can support oxygen insufflation and even jet ventilation, barotrauma and fatalities have been reported in these scenarios.237,238,239 Conventional methods of oxygen delivery such as face mask, nasal cannula, or HFNO237 can still be used when an AEC is present; the CAFG recommends against any routine oxygen administration through an AEC. If unavoidable during an emergency, oxygen insufflation through an AEC should be limited to 2 L·min−1, only as a temporizing measure until oxygenation is re-established by a conventional mode of delivery,237 and close attention must be paid to ensuring that gas egress can occur.240

An AEC can be left in situ after extubation of the difficult airway patient until the need for tracheal re-intubation becomes unlikely. Although case specific, in one published ICU series, most patients requiring tracheal re-intubation over an AEC underwent the procedure within two to ten hours after extubation.236 The surgical patient will almost always have the AEC removed before leaving the post-anesthetic care unit. Although infrequently required, tracheal re-intubation over an AEC will be facilitated by the use of VL to both retract the tongue and enable monitoring of tracheal tube passage through the glottis.241 In addition, prior passage of an intermediate catheter (e.g., the Aintree catheter; Cook Group Incorporated, Bloomington, IN, USA) over an 11- or 14-French AEC will facilitate passage of a tracheal tube through the adult larynx by reducing the size discrepancy between the outer diameter of the catheter and the inner diameter of the tracheal tube.242

Of note, the Cook AECs (Cook Group Incorporated, Bloomington, IN, USA) are only licensed for immediate tracheal tube exchange in most countries. Therefore, leaving an AEC in situ for retaining airway access following extubation, though widely practiced, is technically an off-label application.

Human factors and the anticipated difficult airway

The NAP4 study1 and published closed legal claims2,3 have indicated that airway management misadventure was often associated with inadequate evaluation and lack of a pre-determined airway strategy. That is, airway managers simply did not anticipate difficulty or failed to modify their strategy appropriately despite predicted difficulty. The airway manager must be self-aware of potential human factor pitfalls to avoid. Table 13 presents some issues together with suggested mitigating strategies.

Table 13 Potential human factor issues during patient evaluation and airway management decision-making, with suggested mitigation strategies
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Summary and key recommendations

Informed by publications of airway-related morbidity,1,2,3 guidelines should not only address management techniques for the difficult airway when encountered in the unconscious patient but also emphasize the need for detailed patient evaluation, planning, and communication. In this way, safe airway management decision-making and implementation can occur. Briefly summarized, our guiding principles and recommendations are as follows:

  • Airway evaluation of the patient should always occur before embarking on airway management;

  • Airway evaluation includes bedside examination seeking predictors of technical difficulty with FMV, SGA use, tracheal intubation, and eFONA. Patient physiology and contextual issues should also be assessed. Review of previous airway management records, databases, and imaging studies will contribute to a complete evaluation. Nasopharyngoscopy or VL under local anesthesia can add useful information about the patient with known or suspected glottic or supraglottic pathology;

  • Information gleaned from the airway evaluation must be synthesized into the safest decision on how to proceed with airway management. The use of ATI may provide an extra margin of safety when significant difficulty is predicted with VL or DL. It is also useful if difficulty is predicted with more than one mode of airway management (e.g., tracheal intubation and FMV), or predicted difficulty coincides with significant physiologic (e.g., apnea intolerance or aspiration risk) or contextual issues;

  • Awake tracheal intubation can proceed via oral, nasal, or front of neck routes. In some cases, oral or nasal ATI can be facilitated by a variety of devices (e.g., flexible bronchoscopy or VL);

  • If a lack of patient cooperation or time precludes ATI, and airway management after the induction of general anesthesia must proceed, it should proceed with “double set-up” preparation allowing for immediate eFONA;

  • Management of the anticipated difficult airway after the induction of general anesthesia should only occur with an appropriate pre-determined strategy for difficulty if/when encountered. A second airway manager should be sourced, the team briefed, and the required equipment brought to the room. Attention should be paid to patient positioning, pre-oxygenation, and apneic oxygenation;

  • Regardless of the chosen approach when difficulty is predicted, the airway manager must clearly communicate the planned management strategy to the team, including the triggers for moving from one technique to the next;

  • Extra care should be used in the planning and implementation of care for the patient with head and neck pathology, obesity, or increased aspiration risk;

  • Tracheal extubation of the at-risk patient must be carefully planned in terms of assessing whether the patient can tolerate extubation and whether re-intubation might be difficult;

  • As unanticipated difficulty with airway management can occur despite none being predicted, the airway manager must be ready with a strategy for difficulty occurring in every patient, and the institution must make difficult airway equipment readily available and easily accessible;

  • As pandemic conditions add complexity to both routine and difficult airway decision-making and management, individual and institutional preparedness should be mandated.

Management of difficulty with airway management occurring in the already-unconscious patient is addressed in the part 1 companion article.5