Novel index of sleep and wakefulness may help physicians decide when to remove critically ill patients from breathing machines

By Ana Gajic

Critically ill patients are more likely to be weaned off of a mechanical ventilator, or breathing machine, if they have higher levels of wakefulness and both their right and left brains experience the same depth of sleep, suggests a new study.

This new research could play an important role in improving patient care in the intensive care unit (ICU). Though patients in the ICU need ventilators to survive, they also cause damage to the body. Monitoring for wakefulness early may lead physicians change the management of a patient.

The research, led by Dr. Laurent Brochard, scientist at the Keenan Research Centre for Biomedical Sciences (KRCBS), was recently published online in the American Journal of Respiratory and Critical Care Medicine: “Sleep and Pathological Wakefulness at Time of Liberation from Mechanical Ventilation.” We asked Dr. Brochard and his team from the Centre of Excellence in Mechanical Ventilation, about the new findings.

Q. What did you set out to study?

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. This in part explains the frequent development of delirium in the ICU.

In a given patient, successful separation from mechanical ventilation necessitates the adequate response of a number of physiological systems, which could all be impaired by sleep deprivation. 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.

We used polysomnography, or a sleep study, and a novel index developed by one of the co-authors, Dr. Magdy Younes, a researcher at the University of Manitoba, to analyze the data from the study. This index is the odds ratio product (ORP), which provides a continuous digital score from 0 (very deep sleep) to 2.5 (full wakefulness). We wanted to determine whether the ORP was associated with the likelihood that a patient could be successfully removed from mechanical ventilation.

To determine whether a patient is ready to be removed from ventilation, physicians use a spontaneous breathing trial during which a patient breathes with no assistance from the ventilator to assess the patient’s readiness for breathing on his or her own.

Q. Why this topic?

While mechanical ventilation is life-saving, it can cause lung damage, infections and other health problems, so patients should be taken off a ventilator as soon as medically possible.

Sleep deprivation has multiple physiological consequences and is highly prevalent in the ICU. It could play a role in poor short-term and long-term outcomes. Studying sleep in the ICU has been, however, very technically challenging until now.

Q. What were the key findings?

Spontaneous breathing trials were performed in 37 patients from three hospitals in Toronto. Patients had three types of responses: they were successful and their breathing tube was removed; they passed the test but the breathing tube was not removed because other clinical factors indicating they were not ready; or they failed the test.

Our study found:

• Classical sleep stages as determined by conventional sleep scoring guidelines were not associated with success or failure of the test of spontaneous breathing.
• Longer durations of full wakefulness were highly correlated with a successful test and separation from the breathing machine.
• Poor correlation between sleep depth in the right and left brain hemispheres strongly predicted test failure.

The fact that the wakefulness scores as determined by the ORP index were associated with success or failure in being separated from mechanical ventilation while standard sleep scores were not reflects the ORP’s ability to better distinguish different levels of sleep.

Classic sleep analysis is made very difficult by frequent ‘atypical’ or ‘pathological’ tracings in ICU patients. An example is a condition sleep specialists call ‘pathological wakefulness.’ Defining wakefulness or sleep means that we need to detect short-wave brain activity that typically characterizes sleep. We compare these measurements to the patient’s clinical behavior, assessing whether the patient looks awake or asleep.

Sleep deprivation produces a brainwave pattern similar to pathological wakefulness and despite being clinically ‘awake’ patients are numb to sensations. The authors speculate that this pathological wakefulness is the flip side of sleep deprivation.

Q. Why is it important?

Patients who cannot be weaned from mechanical ventilation are at risk of remaining chronically ill and spend long periods in the ICU. Monitoring their brainwave activity throughout their ICU stay to detect pathological wakefulness early may lead to a change in management.

Q. What’s next for this research?

The results, including the impact of the dissociation of the two brain hemispheres, are entirely novel and to some extent unexpected. What exactly causes the dissociation between the two hemispheres observed in these patients and this pathological flip side to sleep deprivation needs to be better understood.

Is it primarily sleep deprivation but is there also an influence of the sedative drugs administered in the first days of ICU care? How and how fast can it be reversed? For the first time, we have a monitoring tool of the brain which can permit to address questions of major importance for the outcome of patients in the ICU.

Disclosures/Conflicts of interest: Dr. Magdy Younes is the inventor of the ORP system.

These papers are an example of how St. Michael’s Hospital is making Ontario Healthier, Wealthier, Smarter.

About St. Michael’s Hospital

St. Michael’s Hospital provides compassionate care to all who enter its doors. The hospital also provides outstanding medical education to future health care professionals in more than 29 academic disciplines. Critical care and trauma, heart disease, neurosurgery, diabetes, cancer care, care of the homeless and global health are among the Hospital’s recognized areas of expertise. Through the Keenan Research Centre and the Li Ka Shing International Healthcare Education Centre, which make up the Li Ka Shing Knowledge Institute, research and education at St. Michael’s Hospital are recognized and make an impact around the world. Founded in 1892, the hospital is fully affiliated with the University of Toronto.

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Unity Health Toronto, comprised of Providence Healthcare, St. Joseph’s Health Centre and St. Michael’s Hospital, works to advance the health of everyone in our urban communities and beyond. Our health network serves patients, residents and clients across the full spectrum of care, spanning primary care, secondary community care, tertiary and quaternary care services to post-acute through rehabilitation, palliative care and long-term care, while investing in world-class research and education. For more information, visit www.unityhealth.to.