Sleep and Anesthesia

While sleep and anesthesia are different states, they have shared characteristics, and clinical and experimental observations in one state can have implications for behavior in the other. Sleep is a natural state of unconsciousness, the propensity for which is governed by homeostatic drive and circadian variability. It is influenced by psychological and environmental factors, is inhomogeneous (being composed of distinct stages), and is readily reversed by environmental disturbances or once the sleep need is met. In contrast, general anesthesia is a drug-induced state of unconsciousness that can be induced independent of homeostatic, circadian, psychological, or environmental factors. Once established, it is a relatively homogeneous state. Its reversal requires drug elimination. The unconsciousness of either state appears to require activation of similar neurological pathways, and understanding the neurobiology of sleep is a key to a better understanding of mechanisms of anesthesia. There are similarities between the states in the changes in muscle tone and ventilatory drive that accompany conscious state change and, indeed, those vulnerable to upper airway obstruction in one state tend to be vulnerable to it in the other. Obstructive sleep apnea is a risk factor for a 'difficult airway' during anesthesia, including problems with tracheal intubation or with airway maintenance. The reverse is also true, suggesting that observations of airway behavior in one state can have implications for it in the other. While the ability to arouse or awaken protects the sleeping individual, anesthetized patients are at particular disadvantage because of drug-induced suppression of arousal responses, necessitating close perioperative monitoring until consciousness and the ability to readily arouse are restored.