Fig. 6.  Based on the available data, we propose the following models for interactions of general anesthesia and sleep homeostasis. (A ) Propofol satisfies both NREM and REM sleep debt as effectively as natural sleep,14,16and sleep deprivation potentiates the effects of propofol,15which suggests a balanced, reciprocal relationship between sleep and anesthesia. By contrast, inhalational agents (B ) have a differential effect on NREM and REM sleep. Based on the observed effects of sevoflurane, the influence on NREM sleep homeostasis appears to be profound, denoted here by the larger arrow. However, REM sleep recovery occurs only after the cessation of anesthetic exposure (lack of effect denoted by the “X”), but selective REM sleep deprivation potentiates anesthetic effects.17REM = rapid eye movement sleep; NREM = nonrapid eye movement sleep.