Anticipated difficult tracheal intubation: Canadian Guidelines.



    The following discussion and accompanying flow diagram attempt to identify the relevant factors that must be weighed when creating a patient-specific airway strategy. Neither discussion nor flow diagram is meant to be prescriptive. Many factors impact the decision, including patient cooperation, consent, and the clinician’s expertise.


SGD = supraglottic device; IV = intravenous; RSI = rapid sequence induction/intubation.

Two primary questions should be addressed:
If general anesthesia is induced, is tracheal intubation predicted to succeed with the chosen technique(s)? Guidance to help answer this question comes from the published studies on predictors of difficult tracheal intubation. Most of these studies relate to direct laryngoscopy (Table 1). Fewer studies have been published on the predictors of difficulty using alternative techniques such as video laryngoscopy (Table 2). Thus, if the intended “Plan A” or “Plan B” intubation technique includes the use of an alternative to direct laryngoscopy, the clinician must estimate the probability of success in his or her hands under the prevailing conditions.
Data from within- and outside the operating room (OR)- point to increasing morbidity with multiple intubation attempts. Any doubt about whether tracheal intubation will succeed in the anesthetized patient in a maximum of three attempts using direct laryngoscopy or an alternative to direct laryngoscopy would favour an awake approach.

If tracheal intubation fails, will oxygenation by face mask or SGD succeed? When difficult tracheal intubation is predicted, evaluation of the probable success of fallback oxygenation by face mask or SGD ventilation is especially warranted. Predictors of difficult face mask (Table 3) and SGD (Table 4) ventilation have been studied and published. In most situations, significant predicted difficulty with both tracheal intubation and face mask or SGD ventilation should be taken as a strong signal to consider awake intubation, particularly in the cooperative elective surgical patient (Strong recommendation for, level of evidence C).
It should be emphasized that overlap exists between some predictors of difficult direct and video laryngoscopy and those of difficult face mask ventilation. As such, when difficult laryngoscopy is predicted, a careful and deliberate assessment of predicted ease of face mask ventilation should occur. Consideration should also be given to the probability that successful ventilation by face mask or SGD may diminish with repeated intubation attempts.
Other patient or contextual issues may impact the decision of whether to proceed with tracheal intubation before or after induction of general anesthesia, and these issues should be considered (Strong recommendation for, level of evidence C). Although not an exhaustive list, if any of the following issues coincide with predicted difficult intubation, an awake approach may be most prudent:
Anticipated short safe apnea time: With the onset of apnea, rapid oxygen desaturation can be anticipated in the patient with decreased functional residual capacity, increased oxygen consumption, or low starting oxygen saturation. This will shorten the available time for intubation attempts before oxygen desaturation supervenes. Patients with respiratory or metabolic acidosis may also be less tolerant of apnea.
Significant risk of aspiration: When practical, awake intubation should be considered for the patient with predicted difficult tracheal intubation who is also at increased risk of regurgitation and aspiration of gastric contents.
Presence of obstructing airway pathology: Significant intrinsic, extrinsic, or incipient obstructing airway pathology should prompt consideration of awake management. In the NAP4 study, a number of cases were documented where attempted post-induction tracheal intubation resulted in serious patient morbidity in the presence of obstructing airway pathology.
Additional skilled help not available: Skilled assistance during the management of a difficult airway is of considerable importance. Its absence should elevate the option of awake management (although this too may necessitate additional assistance).
Clinician inexperienced with planned technique or device not available: The clinician must be competent and experienced with the planned intubation technique(s) when a post-induction approach is contemplated, and the preferred device(s) must be readily available.
Thus, for the patient with anticipated difficult tracheal intubation, a post-induction approach may be considered if successful intubation is anticipated with the chosen technique(s) within three attempts, successful fallback oxygenation by face mask or SGD ventilation is predicted, and other patient and contextual issues are favourable.
Conversely, if there is a significant risk that tracheal intubation may require more than three attempts despite optimized conditions, face mask ventilation or SGD ventilation is also predicted to be difficult, or other patient and contextual issues are unfavourable (e.g., lack of additional skilled help), the risk of failed oxygenation is elevated and an awake approach is prudent (Figure).

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