Little is known about sleep/wake abnormalities in intensive care and less is known about the mechanisms responsible for these abnormalities. We studied 22 (20 mechanically ventilated) medical intensive care unit (ICU) patients with continuous polysomnography (PSG) and environmental noise measurements for 24-48 h to characterize sleep-wake patterns and objectively determine the effect of environmental noise on sleep disruption. All 22 patients demonstrated sleep-wake cycle abnormalities. There were large variations in total sleep time (TST) with the mean total sleep time per 24-h study period of 8.8 +/- 5.0 h. Sleep-wake cycles were fragmented and nonconsolidated with a mean of 57 +/- 18% and 43 +/- 18% of the TST occurring during the day and night, respectively. Environmental noise was responsible for 11.5 and 17% of the overall arousals and awakenings from sleep, respectively. The mean noise arousal index was 1.9 +/- 2.1 arousals/h sleep.
Conclusions: (1) ICU patients are qualitatively, but not necessarily quantitatively, sleep deprived; and (2) although environmental noise is in part responsible for sleep-wake abnormalities, it is not responsible for the majority of the sleep fragmentation and may therefore not be as disruptive to sleep as the previous literature suggests.