Normal sleep in comparison with altered consciousness under sedation

peer reviewedNaturally occurring sleep and altered consciousness related to the infusion of sedative medications are sometimes mistakenly thought of as being equivalent. While similarities between these two states do exist, differences are considerable and clinically important. Normal sleep is characterized by a cyclic, organized series of brain activities with clearly defined stages that is governed by circadian and homeostatic forces and responsive to external stimuli where arousal leads to almost immediate patient awareness. Consciousness altered by sedative medications has few, if any, of these characteristics. The unique effects of sleep and altered consciousness related to sedative use on brain activity can be described by both phenomenological and physiological parameters. This chapter will review the similarities and differences between natural sleep and sedative-associated alterations in consciousness to determine whether the essential physiologic functions of sleep, some of which may be important to recovery from critical illness, also occur during sedative infusion administration