Abstract
When airway management is indicated, to avoid a bad outcome, patient safety will be maximised by careful decision making about and careful implementation of the chosen approach. This chapter addresses planning for the safest approach to securing the airway by assessing the patient for anatomical and physiological predictors of difficulty with airway management. When such difficulty is predicted, awake tracheal intubation will often provide the best margin of safety; indications for the procedure are discussed. Equally, when technical difficulty is predicted, the pre-conditions required to safely proceed with airway management after the induction of general anaesthesia are addressed. Predicted or not, difficulty encountered with tracheal intubation or supraglottic airway use in the unconscious patient must be met with a methodical and stepwise approach. This includes calling for help, maintaining patient oxygenation and methodically proceeding from one device type or technique to another, thus avoiding multiple futile attempts with the same device. Failure of a maximum of three attempts at the intended technique (most often tracheal intubation or use of a supraglottic airway) should be taken as an indication to refrain from further attempts, call for help, maintain patient oxygenation and reassess the plan for next steps. Finally, a ‘cannot intubate, cannot oxygenate’ situation is defined by the failure to successfully oxygenate the patient with all of tracheal intubation, face mask ventilation or a supraglottic airway and requires prompt front of neck airway access (‘surgical airway’).
Introduction
A structured approach to airway management helps optimise patient safety throughout the procedure. With a consistent strategy to assessing the patient, the clinician will be in a position to determine the safest approach to managing the airway and to address whether additional equipment or personnel are needed to implement the chosen approach. During its implementation, should difficulty be encountered, a predetermined, structured approach will help efficiently transition from step to step, thus minimising perseveration and avoiding the morbidity associated with multiple attempts.
Patient Assessment Prior to Airway Management
Important to perform to the extent possible in all patients, airway assessment involves evaluation of the following components:
1. Identification of anatomical predictors of significant technical difficulty in managing the airway. In large measure, this will inform the safest approach to airway management.
2. Identification of significant physiological issues that may exacerbate or pose danger to the patient during airway management. These may impact or alter the otherwise chosen approach.
3. Identification of contextual issues such as the skills and experience of the clinician and team, availability of experienced help or equipment availability. As with physiological issues, contextual factors may also alter the otherwise planned approach.
These are each explored in more detail below.
Anatomical Predictors of Difficulty
The airway exam seeks to determine whether the airway can be successfully managed using normal techniques. It generally begins by seeking predictors of difficulty with the planned primary technique. Thus, for planned tracheal intubation, the patient might be assessed for predicted difficulty with both direct (DL) and videolaryngoscopy (VL). Fallback options such as face mask ventilation (FMV) or supraglottic airway device (SGA) use should also be assessed for potential difficulty. Similarly, for the case planned with use of an SGA, the patient should be assessed for difficulty with SGA use but secondarily for ease of FMV and tracheal intubation. Although often not routinely done, evaluation of the patient for ease of rapid front of neck airway (FONA) access is advisable. Published predictors of difficult DL and VL, FMV, SGA use, and FONA appear in Table 4.1 and are reviewed in more detail in Chapter 5. Information gleaned from the airway examination should be supplemented by history from the patient, review of old anaesthetic records or, if available, difficult airway management databases.
Predictors of difficult direct laryngoscopy
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Predictors of difficult videolaryngoscopy
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Predictors of difficult face mask ventilation
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Predictors of difficult SGA insertion or use
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Predictors of difficult front of neck airway access
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The patient with obstructing airway pathology warrants additional evaluation. Often invisible to the standard examination of externally visible anatomical features, known or suspected obstructing airway pathology at or above the glottis can be evaluated with preoperative nasendoscopy. Known or suspected subglottic pathology requires review of imaging studies such as CT or MRI. Nasendoscopy and virtual imaging are discussed in Chapter 6.
The clinician must remember that conditions present during awake airway evaluation may not be maintained during general anaesthesia.
Physiological Issues
Numerous physiological issues may pose risk to the patient during airway management (Table 4.2). These may alter the planned approach to airway management (e.g. tracheal intubation after general anaesthesia vs. awake); in others, the approach may not change, but the physiological issue may require additional attention (e.g. pre-existing hypoxaemia requiring additional oxygenation techniques and earlier use of rescue techniques). Rarely, severe physiological disturbances may require deferral of airway management pending optimisation of the underlying condition.
Physiological issues
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Contextual Issues
Contextual issues relate to the clinician or assembled team, the environment or the patient (Table 4.3) and may also alter the optimal airway management technique.
Issues related to the primary clinician or team
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Issues related to the environment
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Issues related to the patient
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Bedside screening tools for airway assessment have been criticised for low sensitivity and poor positive predictive value. Most of these studies have only addressed predictors of difficult DL, DL-facilitated intubation and to a lesser extent, FMV. Predicted difficulty with VL, SGA and FONA have less evidence one way or the other. Regardless of sensitivity concerns, airway examination will identify overt anatomical issues (e.g. very limited mouth opening or a fixed flexion deformity) best dealt with by awake airway management. Conversely, another approach is to screen for the easy airway: those predicted easy consist of the truly easy – which is the majority – and a small minority who will be unexpectedly difficult. Nevertheless, this small minority of unexpectedly difficult airways still makes up the majority of all difficult airways.
Importantly, even if it predicts no difficulty (or fails to predict difficulty) performing an airway examination is a cognitive forcing strategy that makes the clinician decide how they might approach unanticipated difficulty if encountered. Pragmatically, performing an airway assessment remains a standard of care.
Deciding How to Manage the Anticipated Difficult Airway
Difficulty Predicted: Management Choices
When patient assessment indicates the potential for difficulty, the clinician must decide how best to proceed. In broad terms, the choices are as follows:
1. Despite predicted difficulty, airway management proceeds after induction of general anaesthesia, with extra preparation. This may occur during spontaneous ventilation or apnoea.
2. Awake airway management, facilitated by airway local anaesthesia, with or without sedation. This can occur via nasal, oral or front of neck routes.
3. Avoidance or deferral of airway management.
Decision Making on How to Proceed When Difficulty Is Predicted
Many published airway management guidelines emphasise management of the unconscious patient in whom difficulty has been encountered. Whilst a recipe for successful management of the patient with predicted difficulty is difficult to provide, what follows at least represents a thought process.
When no technical difficulty is predicted, airway management generally occurs after induction of general anaesthesia. This is more comfortable for the patient (arguably, also the clinician) and delivers optimal conditions, particularly when facilitated by neuromuscular blockade. Although in many cases an SGA is the planned technique, the following discussion chiefly addresses predicted difficult laryngoscopy and tracheal intubation.
General Anaesthesia despite Predicted Difficult Laryngoscopy or Tracheal Intubation
Pragmatically, many patients are managed during general anaesthesia despite having anatomical predictors of difficult laryngoscopy and intubation. There are two general scenarios:
1. General anaesthesia is chosen when moderately difficult DL or VL and intubation is predicted but airway management during general anaesthesia is deemed safe. This should only occur after deliberately considering whether the following conditions are met:
while laryngoscopy/tracheal intubation is predicted to be moderately difficult, it is not predicted to be impossible with the clinician’s usual laryngoscopy/intubation techniques – e.g. there must be a reasonable probability that use of DL and a bougie, or VL (often with a hyperangulated blade) will facilitate successful tracheal intubation
fallback options (e.g. FMV, SGA and FONA) to maintain oxygenation between attempts, or as final rescue, are predicted to succeed
there are no significant physiological or contextual predictors of hazard to the patient, e.g. a full stomach or likely intolerance of apnoea
success is predicted within an acceptable number of attempts – e.g. within three attempts. If predicted difficulty suggests that multiple devices, personnel or attempts will be needed, this suggests the need for an awake approach.
the clinician has a strategy for difficulty if or when encountered and all team members have been briefed on the plan before induction of general anaesthesia
appropriate help is readily available if needed
extra attention is paid to the details of implementation of the chosen approach, especially with pre-oxygenation and apnoeic oxygenation during airway management
2. General anaesthesia is unavoidable despite predicted difficulty due to lack of patient cooperation with a preferred awake technique or because of urgency, such as resuscitation. Although the former scenario is not uncommon in the paediatric patient, in the adult patient, this should only proceed when:
the benefit of proceeding at that time exceeds the risk of deferral
informed consent has been obtained from the patient or surrogate, if feasible
detailed attention to planning has occurred, including plans for failed tracheal intubation and failed oxygenation
help is physically present
a briefing has been performed
a ‘double set-up’ for emergency FONA (eFONA) is prepared, with identification of the location of the cricothyroid membrane (by palpation or ultrasound), together with the presence of the necessary equipment and personnel to proceed rapidly with the procedure, if needed
In either scenario, induction of general anaesthesia may proceed with ablation or maintenance of spontaneous ventilation. Although each may have theoretical advantages, neither has a proven outcome benefit compared with the other:
General anaesthesia with ablation of spontaneous ventilation. Intravenous induction of general anaesthesia combined with neuromuscular blockade generally optimises airway management conditions. However, in the apnoeic patient the clinician must control gas exchange and airway patency during efforts to secure the airway.
General anaesthesia with maintenance of spontaneous ventilation. This is usually achieved with volatile anaesthetics but can be achieved with a total intravenous anaesthetic technique or dissociative anaesthesia with ketamine. The theoretical advantage is that the patient will maintain ventilatory efforts and reasonable gas exchange. However, all volatile anaesthetics impair spontaneous breathing in a dose-dependent fashion and neither maintenance of airway patency nor protection against aspiration of gastric contents or blood are guaranteed. Furthermore, airway reflexes are not necessarily suppressed, so that airway instrumentation or secretions may stimulate responses such as regurgitation and laryngospasm, especially during lighter planes of anaesthesia.
Related posts:
Chapter 6 – Pre-anaesthetic Airway Endoscopy, Real and Virtual
Chapter 7 – Ultrasonography for Airway Management
Chapter 15 – Tracheal Tube Introducers (Bougies), Stylets and Airway Exchange Catheters
Chapter 22 – The Airway in Obstetrics
Chapter 31 – Airway Management during CPR
Chapter 26 – Ear, Nose and Throat Surgery: Airway Management
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