Atypical sleep in ventilated patients: empirical electroencephalography findings and the path toward revised ICU sleep scoring criteria

Abstract

Objectives: Standard sleep scoring criteria may be unreliable when applied to critically ill patients. We sought to quantify typical and atypical polysomnographic findings in critically ill patients and to begin development and reliability testing of methodology to characterize the atypical polysomnographic tracings that confound standard sleep scoring criteria.

Design: Prospective convenience sample.

Setting: Two academic, tertiary care medical centers.

Patients: Thirty-seven critically ill, mechanically ventilated, medical ICU patients.

Interventions: None.

Measurements and main results: Mechanically ventilated subjects were monitored by continuous polysomnography. After noting frequent atypical polysomnographic findings (i.e., lack of stage N2 markers, the presence of polymorphic delta, burst suppression, or isoelectric electroencephalography), attempts to use standard sleep scoring criteria alone were abandoned. Atypical polysomnographic findings were characterized and used to develop a modified scoring system. Polysomnographic data were scored manually via this revised scoring scheme. Of 37 medical ICU patients enrolled, 36 experienced atypical sleep, which accounted for 85% of all recorded data, with 5.1% normal sleep and 9.4% wake. Coupling observed patient arousal levels with polysomnographic characteristics revealed that standard polysomnographic staging criteria did not reliably determine the presence or absence of sleep. Rapid eye movement occurred in only five patients (14%). The revised scoring system incorporating frequently seen atypical characteristics yielded very high interrater reliability (weighted κ = 0.80; bootstrapped 95% CI, [0.48, 0.89]).

Conclusions: Analysis of polysomnographic data revealed profound deficiencies in standard scoring criteria due to a predominance of atypical polysomnographic findings in ventilated patients. The revised scoring scheme proved reliable in sleep staging and may serve as a building block in future work.

Figure 1

Electroencephalography (EEG) examples of the six proposed atypical sleep stages. Refer to Table 1 for full written descriptions for each of the proposed atypical stages shown in this figure. A_t1 (atypical stage 1), characterized by having at least 10% alpha and/or theta activity (indicated by arrow) but may also include delta activity (indicated by circle). A_t2 (atypical stage 2), characterized by the presence of polymorphic delta but with the presence of background beta, alpha, or theta activity (indicated by arrow). A_t3 (atypical stage 3), characterized by a polymorphic delta activity without the presence of background beta, alpha, or theta activity. A_t4 (atypical stage 4), defined by a burst-suppression pattern, intermittent EEG activity alternating with periods of isoelectric EEG activity. A_t5 (atypical stage 5), defined by a suppression pattern EEG, a very low-voltage EEG activity (< 20 µV amplitude). A_t6 (atypical stage 6), characterized by a complete lack of EEG/cortical activity as shown.

Figure 2

Dissociation between observed wakefulness or level of consciousness and electroencephalography (EEG) patterns. A, EEG demonstrating delta waves (indicated by circle) suggestive of slow wave sleep in a patient with evidence of wakefulness by following simple commands. This epoch would be scored as pathologic wakefulness by the proposed scoring criteria. B, EEG demonstrating theta frequency EEG activity, normally seen in light (stage N1) sleep, in a patient who was unresponsive. Short periods of isoelectric activity can be seen (indicated by arrow) in this example, which can alert the polysomnography reader that this is not normal stage N1. This epoch would be scored as A_t4 by the proposed scoring criteria..

Figure 3

Variability in electroencephalography (EEG) characteristics in comatose patients. A, Polysomnography (PSG) from a patient who had a Richmond Agitation-Sedation Scale (RASS) score of −5 (unresponsive to verbal and physical stimulus) but with theta activity resembling N1 sleep with frequent arousals. B, PSG from a patient who had a RASS score of −5 demonstrating isoelectric EEG activity. This epoch would be scored as A_t6 by the proposed scoring criteria..

Figure 4

Examples of atypical electroencephalography (EEG) findings which if scored using standard sleep staging criteria would cause misleading results. A, Polysomnography (PSG) demonstrating burst suppression, which if standard scoring criteria were used, would be misleadingly scored as stage N1 sleep. This epoch would be scored as stage A_t4 by the proposed scoring criteria. B, PSG demonstrating EEG waveforms with lack of background activity are only seen in pathologic states. This epoch would be scored as A_t3 by the proposed criteria. C, PSG demonstrating onset of rhythmic delta activity after stimulations of patient (suctioning), which would be misleadingly scored as stage N3 sleep if standard scoring criteria were used. Using the proposed criteria, this epoch would be scored as A_t2.

Figure 5

Cumulative sleep stage analysis of all patient data. This pie chart demonstrates the percentage of time that the population spent in each sleep stage as determined by the analysis of 1,945.7 hr of polysomnographic data in all 37 patients. The majority of the collected data (85%) was atypical in character and could not be scored using standard scoring criteria. REM = rapid eye movement, NREM = non-REM.

Figure 6

Proposed approach to scoring sleep in critically ill patients, which can be incorporated into future investigations. EEG = electroencephalography.