Awareness Under Anesthesia

Abstract

You begin to hear distant rock music playing, people conversing about their weekend. Then the scalpel is requested-incision. Pain sends you reeling and you attempt to muster a scream. No one seems to hear you and you are unable to lift a finger. The scenario is so rare that numerous movies have been made about awareness under anesthesia. Awareness under anesthesia is a rare event, however, it is a complication that no one ever desires to occur. We will explore how frequent awareness is during surgery, what risk factors are involved, and what tools anesthesia providers utilize to ensure everyone undergoing surgery is adequately anesthetized.

Figure 1

Oksana Tevis, A. A. with BIS monitor. St. Louis, MO, Feb 2022. Used with permission.

Figure 1

Continuum of Depth of Sedation: Definition of General Anesthesia and Levels of Sedation Analgesia Minimal Sedation (Anxiolysis) is a drug-induced state during which patients respond normally to verbal commands. Although cognitive function and physical coordination may be impaired, airway reflexes, and ventilatory and cardiovascular functions are unaffected. Moderate Sedation/Analgesia (“Conscious Sedation”) is a drug-induced depression of consciousness during which patients respond purposefully** to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained. * Monitored Anesthesia Care (“MAC”) does not describe the continuum of depth of sedation, rather it describes “a specific anesthesia service performed by a qualified anesthesia provider, for a diagnostic or therapeutic procedure.” Indications for monitored anesthesia care include “the need for deeper levels of analgesia and sedation than can be provided by moderate sedation (including potential conversion to a general or regional anesthetic.”1 ** Reflex withdrawal from a painful stimulus is NOT considered a purposeful response. Deep Sedation/Analgesia is a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully** following repeated or painful stimulation. The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway, and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained. General Anesthesia is a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation. The ability to independently maintain ventilatory function is often impaired. Patients often require assistance in maintaining a patent airway, and positive pressure ventilation may be required because of depressed spontaneous ventilation or drug-induced depression of neuromuscular function. Cardiovascular function may be impaired. Because sedation is a continuum, it is not always possible to predict how an individual patient will respond. Hence, practitioners intending to produce a given level of sedation should be able to rescue*** patients whose level of sedation becomes deeper than initially intended. Individuals administering Moderate Sedation/Analgesia (“Conscious Sedation”) should be able to rescue*** patients who enter a state of Deep Sedation/Analgesia, while those administering Deep Sedation/Analgesia should be able to rescue*** patients who enter a state of General Anesthesia. ** Reflex withdrawal from a painful stimulus is NOT considered a purposeful response. *** Rescue of a patient from a deeper level of sedation than intended is an intervention by a practitioner proficient in airway management and advanced life support. The qualified practitioner corrects adverse physiologic consequences of the deeper-than-intended level of sedation (such as hypoventilation, hypoxia and hypotension) and returns the patient to the originally intended level of sedation. It is not appropriate to continue the procedure at an unintended level of sedation. Source: American Society of Anesthesiologists. Position on Monitored Anesthesia Care. Last amended on October 17, 2019. Used with permission.