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Attempts to wean intubated, critically ill patients off mechanical ventilators were less successful when the patients exhibited atypical sleep or pathological wakefulness, researchers reported.

The findings suggest that sleep deprivation may be a risk factor for weaning-failure, and that monitoring sleep patterns prior to weaning attempts could be a successful strategy for identifying mechanically ventilated patients who are not ready to breathe on their own, reported Laurent Brochard, MD, PhD, of the University of Toronto and St Michael's Hospital in Toronto, and colleagues, in the

To measure sleep in critically ill patients, researchers combined standard polysomnography with a novel sleep index, developed by co-author Magdy Younes, MD, PhD, of Sleep Disorders Centre in Winnipeg, Canada, which utilized a portable sleep diagnostic device rating deep sleep (score of 0) to full wakefulness (score of 2.5).

Brochard explained to 番茄社区 that disordered sleep and sleep deprivation are common among ICU patients on mechanical ventilation.

"A number of studies have shown that sleep architecture is very abnormal in these patients," he said. "Most lose the circadian rhythm, and experiencing no REM sleep is also common."

He said these sleep issues could play a role in delirium, which is also common among patients on mechanical ventilation, and in neurocognitive dysfunction after an extended ICU stay.

Brochard noted that while several earlier studies have linked disordered sleep to more difficulties weaning patients off mechanical ventilators, the impact of ICU stays and sleep deprivation on liberation from ventilation is poorly understood.

"Successful separation from mechanical ventilation necessitates an adequate response from a number of physiological systems, all of which could be impaired by sleep deprivation," he said, adding that the current study was conducted to determine whether assessment of periods of sleep and wakefulness in the hours before attempted ventilator weaning would predict success or failure.

Electroencephalogram (EEG) data recorded during a 15-hour period preceding the spontaneous breathing trial (SBT) was analyzed to assess patient ability to breathe without mechanical ventilation.

The researchers hypothesized that patients with atypical sleep or pathological wakefulness were more likely to fail an SBT. In addition to conventional scoring, they used a digital scoring system that produces a number of EEG markers -- odds ratio product (ORP) and spindle characteristics -- that are relevant to identify pathological wakefulness and atypical sleep, as well as possible cerebral pathology.

"ORP is highly correlated with arousability and is therefore a valid index of sleep depth. One of its advantages is that it can distinguish between different levels of wakefulness since the awake range extends from 2.5 (full wakefulness) to 1.8 (epochs still scored wake but contain some sleep features). This would make it particularly useful for identifying Pathological Wakefulness in which wake EEG contains some sleep features," the researchers wrote.

They analyzed data from 37 mechanically ventilated patients treated at three Toronto-area hospitals, scheduled for a SBT, to assess their readiness for breathing on their own.

All patients had undergone polysomnography for 15 hours prior to the SBT test, and 31 had the ORP analysis.

The SBT test was successful in 19 of the patients, but eight did not have their breathing tubes removed due to other clinical issues. SBT was unsuccessful in 18 patients.

Classical sleep stages determined solely by conventional sleep scoring guidelines were not associated with success or failure of SBT.

"The high prevalence of stages referred to as pathological wakefulness or atypical sleep made the classical scoring of sleep of limited value and the distribution of sleep stages did not differ," the researchers wrote.

Longer duration of full wakefulness (ORP score >2.2) was highly correlated with successful SBT and extubation and the degree of wakefulness was clearly lower in patients who failed SBT based on ORP assessment.

In addition, poor correlation between sleep depth in the right and left brain hemispheres was also highly predictive of SBT failure.

"The lack of synchronicity between the two parts of the brain seen in some patients was a complete surprise to us," Brochard said.

He noted that correlation of sleep depth between the left and right brain hemispheres is a characteristic of sleep studies in normal participants and those with chronic sleep disorders.

The finding that nearly half the patients in the ICU study exhibited discordant sleep depth between the two brain hemispheres was characterized as "remarkable and highly significant" by the researchers, and highly predictive of SBT failure.

"Although it is not possible at present to determine why SBT failure and poor right/left correlation are associated, the finding that a poor correlation is associated with severe pathological wakefulness suggests a possible link," they wrote.

They added that this phenomenon of regional differences in sleep -- some parts of the brain are asleep while others are awake, and often called uni-hemispheric sleep -- is seen in dolphins and related mammals, as well as in birds that must go for long periods without sleep.

"It is possible that this primitive adaptive mechanism is reactivated in humans under conditions where natural sleep is deemed by the individual to be unsafe," the authors wrote.

Study limitations included those "intrinsic" to the classical sleep scoring process, they noted. Also, "Assessment of hemispheric EEG correlation with the [right/left] ORP was not correlated with specific neurological investigation but there were no clinical grounds to suspect the presence of primary brain disease," the authors stated.

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