Chest
Volume 117, Issue 3, March 2000, Pages 809-818
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Clinical Investigations in Critical Care
Sleep in Critically Ill Patients Requiring Mechanical Ventilation

https://doi.org/10.1378/chest.117.3.809Get rights and content

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 population.

Design

Prospective cohort analysis.

Setting

University teaching hospital medical-surgical ICU.

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 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 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.

Section snippets

Patient Recruitment

The study protocol and consent were approved by the Wellesley Central Hospital Research Ethics Committee. Written informed consent was obtained from the patient or, if the patient had evidence of an altered sensorium (inappropriate or absent response to commands), from a family member. Patients admitted to the Ewart Angus ICU between April 21, 1997, and June 30, 1998, were screened for eligibility. Selection criteria were endotracheal intubation and anticipated further mechanical ventilation of

Characteristics of Study Population on Day of ICU Admission

Twenty-six patients were studied from April 1997 to May 1998. We were unable to score six records, owing to technical problems. EEG recordings could not be interpreted because of electrical artifact in four of six and because of severe respiratory artifact in two of six patients. Both patients with severe respiratory artifact were very edematous. Characteristics of the study population on the day of ICU admission are given in Table 1. The majority of our patients were admitted to the ICU for

Discussion

This study is our first investigation of sleep in critically ill patients who are mechanically ventilated. None of the patients we studied demonstrated normal sleep. Furthermore, using standard electrophysiologic criteria,32 sleep as it is usually defined was not present in all critically ill patients. Based on our observations, we propose criteria to select critically ill patients at risk of disrupted sleep; APS < 13, GCS ≥ 10, and sedative medication doses (in the preceding 24 h): lorazepam

ACKNOWLEDGMENT

The authors thank the nursing, respiratory therapy, physical therapy, and support staff of the Ewart Angus ICU, Wellesley Central Hospital, for their special care of the patients involved in this study. Dejan Lukic, Mary Luccisano, and Nicky Grenier of the Wellesley Central Hospital sleep laboratory provided outstanding technical support.

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    Funded, in part, by grants from the Ontario Thoracic Society.

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