The American Society of Anesthesiologists (ASA) difficult airway algorithm recommends that if initial attempts at tracheal intubation after the induction of general anesthesia are unsuccessful, the practitioner should “consider the advisability of awakening the patient”. With respect to the use of muscle relaxants, “awakening” is assumed to mean return to an unparalyzed state that permits life-sustaining spontaneous ventilation (hereafter referred to as functional recovery). The advisability of attempting and the likelihood of achieving functional recovery before life-threatening hemoglobin desaturation occurs depends on the initial alveolar fraction of oxygen (FAO2) and the minute ventilation (V with ringE).

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