Sleep in critically ill patients requiring mechanical ventilation

Study objectives: To objectively measure sleep in critically ill patients r equiring mechanical ventilation and to define selection criteria for future studies of sleep continuity in this population. Design: Prospective cohort analysis. Setting: University teaching hospital medical-surgical ICU. Patients: Twenty critically ill (APACHE II [acute physiology and chronic he alth evaluation II] acute physiology store [APS], 10 +/- 5), mechanically, ventilated adults (male 12, female 8, age 62 +/- 15 years) with mild to mod erate acute lung injury (lung injury score, 1.8 +/- 0.9) 10 +/- 7 days afte r admission to the ICU. Measurements and results: Patients were divided into three groups based on 24-h polysomnography (PSG) findings. No patient demonstrated normal sleep. In the "disrupted sleep" group (n = 8), electrophysiologic sleep was identi fied and was distributed throughout the day (6:00 AM to 10:00 PM; 4.0 +/- 2 .9 h) and night (10:00 PM to 6:00 AM; 3.0 +/- 1.9 h) with equivalent propor tions of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, Nocturnal sleep efficiency was severely reduced (38 +/- 24%) with an increa sed proportion of stage 1 NREM sleep (40 +/- 28% total sleep time [TST]) an d a reduced proportion of REM sleep (10 +/- 14% TST), Severe sleep fragment ation was reflected by a high frequency of arousals (20 +/- 17/h) and awake nings (22 +/- 25/h), Electrophysiologic sleep was not identifiable in the P SG recordings of the remaining patients. These were classified either as "a typical sleep" (n = 5), characterized bu transitions from stage 1 NREM to s low wave sleep with a virtual absence of stage 2 NREM and reduced stage REM sleep, or "coma" (n = 7), characterized by > 50% delta or theta EEG activi ty with (n = 5) and without (n = 2) evidence of EEG activation either spont aneously or in response to deep painful stimuli, The combined atypical slee p and coma groups had a higher APS (13 +/- 4 vs 6 +/- 4) and higher doses o f sedative medications than the disrupted sleep group. Conclusion: Sleep, as it is conventionally measured, was identified only in a subgroup of critically ill patients requiring mechanical ventilation and was severely disrupted. We have proposed specific criteria to select patie nts for future studies to evaluate potential causes of sleep disruption in this; population.