Sleep index, wakefulness can predict patient ability to breathe on their own

Laurent Brochard, MD, PhD, and the co-authors of this study used polysomnography and a novel sleep index. The sleep index was developed by one of the co-authors, Magdy Younes, MD, PhD. The index has an odds ratio product (ORP) that provides a continuous digital score from 0 (very deep sleep) to 2.5 (full wakefulness). The objective was to determine whether the ORP was associated with the likelihood that a patient could be removed from mechanical ventilation.

Dr. Brochard, 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, Canada is the senior study author. He explains that patients who are under mechanical ventilation in intensive care units often suffer from severe sleep deprivation. As a result, they tend to exhibit abnormal patterns of sleep or wakefulness, which could also explain in part, the development of delirium.

Mechanical ventilation is life-saving, but it can also cause lung damage, infections, and other health problems. That is why it is important to take patients off the ventilator as soon as its medically possible. Physicians use a spontaneous breathing trial (SBT) during which a patient breathes on their own without the help of a ventilator. This is done to assess their readiness to breathe on their own. Dr. Brochard points out that in order to successfully separate the patient from the ventilator, it is necessary to get an adequate response from a number of physiological systems, which could potentially be impaired by sleep deprivation. He also notes that previous studies have linked pathological sleep with prolonged difficulties in being separated from the ventilator.

The purpose of this research was to assess whether a period of sleep and wakefulness in the hours before attempting separation from the ventilator could predict a greater level of success. To determine this, the researchers analysed data from 37 patients at three hospitals in Toronto, Canada. These patients were scheduled for an SBT and had already undergone polysomnography for 15 hours before the test. SBT was successful in 19 of the 37 patients while the breathing tube was removed in 11 others. In 8 patients, the breathing tube was not removed despite a successful SBT because other clinical factors suggested that they were not ready for extubation. The SBT was unsuccessful in 18 patients.

Study Findings

Overall, the results of the study show that:

• Classical sleep states determined by conventional sleep scoring guidelines were not associated with the success or failure of the SBT.
• Longer duration of full wakefulness was correlated with successful SBT and extubation.
• Poor correlation between sleep depth in the right and left-brain hemispheres predicts SBT failure.

"Defining wakefulness or sleep classically necessitates detecting short-wave brain activity that typically characterises sleep and a decrease in higher frequencies that characterise wakefulness and comparing these results to clinical behaviour: does the patient look awake or asleep?" Dr. Brochard said.

Sleep deprivation produces a brainwave pattern similar to pathological wakefulness, and while the patient may appear to be clinically awake, they may, in fact, be obtunded or not fully awake. The authors of the study speculate that this state of pathological wakefulness may be the flip side of sleep deprivation.

It is thus important to understand the dissociation between the brain hemispheres. Clinicians in the ICU need to understand the cause of this dissociation, and they need to determine if the cause is sleep deprivation, the influence of sedative drugs or other medical conditions. By answering these questions, it may be possible to better manage mechanically ventilated patients in the ICU.