Study objectives: To objectively measure sleep in
critically ill patients requiring mechanical ventilation and to define
selection criteria for future studies of sleep continuity in this
Design: Prospective cohort analysis.
Setting: University teaching hospital medical-surgical
Patients: Twenty critically ill (APACHE II[
acute physiology and chronic health evaluation II] acute physiology
score [APS], 10 ± 5), mechanically ventilated adults (male 12,
female 8, age 62 ± 15 years) with mild to moderate acute lung injury
(lung injury score, 1.8 ± 0.9) 10 ± 7 days after admission to the
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 identified 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 proportions of non–rapid eye movement
(NREM) and rapid eye movement (REM) sleep. Nocturnal sleep efficiency
was severely reduced (38 ± 24%) with an increased proportion of
stage 1 NREM sleep (40 ± 28% total sleep time [TST]) and a
reduced proportion of REM sleep (10 ± 14% TST). Severe sleep
fragmentation was reflected by a high frequency of arousals
(20 ± 17/h) and awakenings (22 ± 25/h). Electrophysiologic sleep
was not identifiable in the PSG recordings of the remaining patients.
These were classified either as “atypical sleep” (n = 5),
characterized by transitions from stage 1 NREM to slow 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
activity with (n = 5) and without (n = 2) evidence of EEG
activation either spontaneously or in response to deep painful stimuli.
The combined atypical sleep and coma groups had a higher APS (13 ± 4
vs 6 ± 4) and higher doses of 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
patients for future studies to evaluate potential causes of sleep
disruption in this population.