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Sleep quality, wakefulness may predict successful weaning from mechanical ventilation

Critically ill patients who have higher levels of wakefulness and the same depth of sleep in both the left and right hemispheres of their brains are more likely to experience successful weaning from mechanical ventilation, according to a study published in the American Journal of Respiratory and Critical Care Medicine.

“Patients under mechanical ventilation in intensive care units frequently suffer from severe sleep deprivation and, as a consequence, exhibit abnormal patterns of sleep or wakefulness, which explain in part the frequent development of delirium,” Laurent Brochard, MD, PhD, director of the critical care medicine division at the University of Toronto and clinician-scientist at the Keenan Research Centre for Biomedical Science at St. Michael’s Hospital in Toronto, said in a press release.

“Successful separation from mechanical ventilation necessitates an adequate response from a number of physiological systems, all of which could be impaired by sleep deprivation,” Brochard said, adding that studies have associated pathological sleep with difficulties in being separated from the ventilator. “We wondered whether assessing a period of sleep and wakefulness in the hours before attempting a separation from the ventilator could predict the success of this process.”

Abnormal sleep, spontaneous breathing trial outcomes

For the SLEEWE study, Brochard and colleagues evaluated 37 patients at three sites in Toronto who were on mechanical ventilators and had a spontaneous breathing trial planned for the next day. The researchers sought to determine whether abnormal sleep or wakefulness is associated with the outcome of these spontaneous breathing trials by examining polysomnographic indexes and the odds ratio product (ORP), which is a continuous index for evaluating sleep depth. The ORP ranges from 2.5, indicating full wakefulness, to 0, indicating deep sleep.

At enrollment, patients had been ventilated for 6 days and had a sequential organ failure assessment (SOFA) score of 8. On the day of polysomnography, Richmond Agitation Sedation Scale (RASS) score was 0 and five patients (14%) had delirium.

Results showed that patients who failed the spontaneous breathing trial had a shorter ICU stay, compared with those who passed the trial. Delirium was slightly more common in patients who passed the trial, but the finding was not significant. RASS scores were similar across all groups and clinical variables did not differ at the time.

EEGs were recorded using a portable sleep diagnostic device 15 hours before the spontaneous breathing trial and the ORP was calculated from the power of four EEG frequency bands relative to each other.

Nineteen patients (51%) had successful spontaneous breathing trials and 18 patients (49%) failed. Of those who had successful trials, 11 were extubated and eight were considered not ready for extubation due to other clinical factors.

Based on conventional and alternative assessments of polysomnographic recordings, pathological wakefulness occurred in 9% of patients who failed the spontaneous breathing trial, 50% of patients who passed the trial but were not extubated and 27% of the patients who passed the trial.

Atypical sleep was also common, occurring in 55% of patients who failed the spontaneous breathing trial, 50% of patients who passed but were not extubated and 27% of patients who passed the trial.

“As a consequence, only 61% of the patients could be scored according to classical stages,” the researchers wrote.

The researchers noted that total sleep time based on this analysis was shorter in patients who failed the spontaneous breathing trial, and the distribution of stage 4, REM sleep and fragmentation index did not differ between groups when it was scorable.

ORP analysis of sleep, wakefulness

ORP analysis was possible for 31 of the 37 patients, with the researchers noting significant differences among patient groups. On average, patients who were successfully extubated had higher ORP during total recording time and spent more time with ORP greater than 2 and greater than 2.2 compared with patients who passed the spontaneous breathing trial but were not extubated and those who passed the spontaneous breathing trial.

The correlation between right and left hemispheres’ ORP (R/L ORP) ranged from 0 to 0.97, with significantly lower R/L ORP in patients who failed spontaneous breathing trials vs. all patients who had successful spontaneous breathing trials (0.54 vs. 0.8; P = .006). The area under the receiver operating curve of the R/L ORP to predict failure of a spontaneous breathing trial was 0.91 (95% CI, 0.75-0.98). Additionally, the sensitivity and specificity of an R/L ORP greater than 0.7 predicting a successful spontaneous breathing trial were 85% and 88%, respectively.

The reason that ORP was associated with success or failure in extubation, whereas standard sleep scores were not, is likely due to ORP’s ability to better distinguish levels of sleep, which can be difficult in critically ill patients in whom abnormal sleep or pathological wakefulness appears to be common, according to Brochard.

“Defining wakefulness or sleep classically necessitates detecting short-wave brain activity that typically characterizes sleep and a decrease in higher frequencies that characterize wakefulness and comparing these results to clinical behavior: does the patient look awake or asleep?” he said in the press release.

“We now have a monitoring tool of the brain that can help us address questions of major importance for the outcome of patients in the ICU,” Brochard said.

Interpretation

In an accompanying editorial, Dimitris Georgopoulos, MD, PhD, and Katerina Vaporidi, MD, PhD, from University Hospital of Heraklion and University of Crete in Greece, commented on these findings.

“Dres and colleagues found that the vast majority of studied patients exhibited some degree of obtundation or pathological or incomplete wakefulness (ORP, > 1 to < 2) and assumed that this pattern is likely due to sleep deprivation. However, brain dysfunction linked to critical illness could be a possibility, despite the fact that the patients were deemed ready for termination of ventilation. Critical illness (particularly sepsis) may cause long-term central nervous system dysfunction. Impaired memory and executive function are common findings in ICU survivors, whereas sleep abnormalities have been observed even 6 months after hospital discharge. Could ORP-derived indices be used as a monitoring tool during the acute and long-term recovery phases of critical illness? Studies are urgently needed to better clarify the pathophysiology of abnormal EEG patterns in the critically ill,” they wrote. – by Melissa Foster

Disclosures: Brochard reports he has received nonfinancial support from Air Liquide, Fisher Paykel, Philips and Sentec; personal fees from Baxter; and received grants from Covidien and Medtronic. Please see the study for a full list of all other authors’ relevant financial disclosures. Georgopoulos reports no relevant financial disclosures.