It is currently impossible to predict when a comatose patient might become conscious again. Some patients wake up minutes or days after a brain injury, while a rare few regain partial consciousness after decades. Others, however, remain unconscious for the rest of their lives. New research suggests that sleep patterns in comatose patients could help predict their chances of waking up.
Researchers at Columbia University and New York-Presbyterian Hospital cross-referenced sleep patterns in comatose patients with their recovery rates and discovered a promising link. As detailed in a study published Monday in the journal Nature Medicine, this approach has the potential to transform the care of unresponsive brain-injury patients and provide accurate predictions for worried loved ones.
“Families of my patients ask me all the time, will my mother wake up? How is my mother going to look in three, six, or 12 months? Very often we cannot guide them very precisely, and it’s crucial that we improve our predictions to guide their decision making,” lead author Jan Claassen, a neurologist at Columbia University, said in a university statement.
A study by Claassen and colleagues last year suggests that up to one-fourth of comatose patients with brain injuries may have undetected consciousness, known as cognitive motor dissociation. Claassen developed a technique to detect hidden consciousness by identifying when a comatose patient hears and understands a command, such as a request to move their hand, but is unable to respond.
“We’re at an exciting crossroad in neurocritical care where we know that many patients appear to be unconscious, but some are recovering without our knowledge. We’re starting to lift the lid a little bit and find some signs of recovery as it’s happening,” Claassen explained. He is also chief of critical care and hospitalist neurology at NewYork-Presbyterian/Columbia University Irving Medical Center.
For the recent study, Claassen focused on sleep because the brain processes behind it are also key to consciousness. He and his colleagues analyzed the overnight electrical brain activity of 226 comatose patients who had previously undergone Claassen’s technique to detect hidden consciousness. For simplicity, let’s call this the “complex method.”
“The electrical activity during sleep looks relatively chaotic, and then occasionally in some patients, these very organized, fast frequencies appear,” Claassen said. Those fast frequencies, known as sleep spindles, often appeared before the complex method detected hidden consciousness—and before patients awoke or made a long-term recovery.
“Spindles happen normally during sleep and they’re showing some level of organization in the brain, suggesting circuits between the thalamus and cortex needed for consciousness are intact,” he continued.
Overall, patients with both sleep spindles and hidden consciousness were more likely to wake up from the coma and make a substantial recovery. Specifically, 76% of these patients demonstrated consciousness by the time they left the hospital, and 41% of them recovered enough neurological function to be independent during the day within a year of being discharged. On the other hand, 29% of patients who lacked both sleep spindles and cognitive motor dissociation showed signs of consciousness by the time they left the hospital, and just 7% regained neurological function a year later.
The researchers emphasized that this is correlational data, meaning it does not establish that sleep spindles directly contribute to coma recovery. For example, 19 of the 139 patients without sleep spindles or hidden consciousness still regained consciousness. Additionally, the study only considers comatose states from recent injuries. However, their research suggests that better sleep—indicated by the presence of sleep spindles—could improve a patient’s chances of recovery.
“If you think about the ICU environment, it is rather disruptive for a good night’s sleep. There is noise everywhere, alarms going off, clinicians touching them, 24/7. This is all for a good reason, but it’s hard to sleep in that environment,” Claassen said.
While their approach isn’t “ready for use in clinical practice yet,” it paves the way for a future in which doctors will be able to provide anxious family members more accurate predictions of a comatose patient’s chances of recovery.
