Elsevier

Sleep Medicine

Volume 13, Issue 1, January 2012, Pages 7-14
Sleep Medicine

Original Article
A new classification for sleep analysis in critically ill patients

https://doi.org/10.1016/j.sleep.2011.07.012Get rights and content

Abstract

Background

Patients in intensive care units (ICUs) experience severe sleep alterations and conventional sleep scoring rules are difficult to use in these patients. In a previous study, we showed that abnormal sleep EEG and wake EEG patterns could predict the outcome of noninvasive ventilation in a group of patients treated for acute respiratory failure. Our aims were to assess the prevalence of these abnormal sleep/wake EEG patterns in a larger group and search for objective parameters to help their identification.

Methods

We reviewed sleep studies previously performed with full polysomnography during 17-h in conscious nonsedated ICU patients receiving invasive ventilation during weaning or noninvasive ventilation for acute respiratory failure.

Results

We included 57 patients. Sleep scoring using conventional rules was not feasible in 16 (28%) patients due to the absence of stage-2 markers. Wake EEG in these 16 patients, although recognizable, showed abnormal features, including decreased reactivity to eye opening and slower peak EEG frequency compared to patients with normal sleep–wake EEGs.

Conclusion

In almost one third of awake mechanically ventilated ICU patients, sleep cannot be classified with standard criteria. Two new states, atypical sleep and pathologic wakefulness, need to be added. We suggest rules for scoring these states. The origin and links with outcomes of these abnormal EEG patterns deserve investigation.

Introduction

Most patients in intensive care units (ICUs) experience severe sleep disruption, such as decreased total sleep time and marked fragmentation [1], [2], [3], [4], [5], [6], [7], that could lead to diurnal sleepiness and may have severe consequences on neurobehavioral function [8], [9].

A major obstacle to sleep studies in ICU patients is that the conventional sleep-scoring rules of Rechtschaffen and Kales [10] are difficult to use [11], [12], [13], as the K complexes and sleep spindles used to identify stage-2 sleep are often absent [1], [2]. Thus, links between sleep disruptions in ICU and clinical consequences are difficult to highlight.

In a previous prospective study we showed that abnormal sleep EEG and wake EEG patterns could predict the outcome of NIV in a group of 27 patients treated for acute respiratory failure [6]. In this study, abnormal sleep and pathological wakefulness were characterized by a rough visual inspection of the EEG and were present in 30% of patients.

The objective of the present study was to search for objective parameters to help the identification of these EEG patterns, using EEG spectral analysis and a dedicated EEG reactivity scale. To this aim, we re-analyzed a large number of sleep recordings coming from mechanically ventilated, nonsedated, conscious ICU patients included in previous [5], [6] and on-going studies.

Section snippets

Patients

We reviewed the PSG recordings from adults who were admitted to the medical ICU of the Henri Mondor Teaching Hospital, Creteil, France, for acute respiratory failure, and treated with NIV during at least two days, and enrolled in a previously published study [6]. We also reviewed the tracings of consecutive conscious patients who had received no sedatives for the past 48 h and who were ventilated in pressure–support mode through an endotracheal tube or tracheostomy. Half of them had been

Patients

A total of 57 patients were included. A group of 27 patients (12 men) was treated intermittently by NIV. Acute respiratory failure was due to chronic obstructive pulmonary disease exacerbation (n = 21) or acute heart failure (n = 6). A second group included 15 patients (11 men) during the weaning period who received pressure–support ventilation through a tracheostomy tube with an Evita 4 ventilator (Drager Medical, Lübeck, Germany). Mechanical ventilation (MV) was required because of acute

Discussion

In our study of non-sedated conscious patients admitted to the ICU for respiratory failure requiring NIV or MV, sleep scoring using Rechtschaffen and Kales criteria was not feasible in 28% of cases, because markers for stage-2 sleep were absent. Other findings in this patient subgroup with atypical sleep consisted of decreased amounts of REM sleep and slow background EEG activity with impaired EEG reactivity during wakefulness. These EEG features in the absence of delirium might indicate brain

Conclusion

Conventional sleep scoring was not feasible in one-third of conscious ICU patients free of delirium and receiving mechanical ventilation. Quantitative assessment of sleep/wake EEG patterns can be used to identify this patient subgroup by showing slow EEG activity during wakefulness and an atypical EEG pattern during sleep. These abnormalities may reflect a subclinical form of brain dysfunction that may be associated with an increased risk of delirium [6]. The underlying mechanisms remain to be

Conflicts of interest

The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: doi:10.1016/j.sleep.2011.07.012.

. ICMJE Form for Disclosure of Potential Conflicts of Interest form.

Acknowledgments

LB, XD and MPO designed the study; FRC, AWT and BC recruited the patients. FRC, BC, FG and LM recorded the data. XD, FRC, AWT and LM analyzed the data; XD wrote the first draft, FRC, AWT, LB and MPO contributed significantly to the paper.

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    This work was performed at APHP, Hopital Henri Mondor. Ferran Roche Campo received a grant from the Société de Réanimation de Langue Française (SRLF) and the Société de Pneumologie de Langue Française (SPLF).

    1

    FRC and AWT contributed equally to this work.

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