Auditory test predicts coma awakening

A coma patient’s chances of surviving and waking up could be predicted by changes in the brain’s ability to discriminate sounds, new research suggests.

Recovery from coma has been linked to auditory function before, but it wasn’t clear whether function depended on the time of assessment. Whereas previous studies tested patients several days or weeks after comas set in, a new study looks at the critical phase during the first 48 hours. At early stages, comatose brains can still distinguish between different sound patterns,. How this ability progresses over time can predict whether a coma patient will survive and ultimately awaken, researchers report.

“It’s a very promising tool for prognosis,” says neurologist Mélanie Boly of the Belgian National Fund for Scientific Research, who was not involved with the study. “For the family, it’s very important to know if someone will recover or not.”

A team led by neuroscientist Marzia De Lucia of the University of Lausanne in Switzerland studied 30 coma patients who had experienced heart attacks that deprived their brains of oxygen. All the patients underwent therapeutic hypothermia, a standard treatment to minimize brain damage, in which their bodies were cooled to 33° Celsius for 24 hours.

De Lucia and colleagues played sounds for the patients and recorded their brain activity using scalp electrodes — once in hypothermic conditions during the first 24 hours of coma, and again a day later at normal body temperature. The sounds were a series of pure tones interspersed with sounds of different pitch, duration or location. The brain signals revealed how well patients could discriminate the sounds, compared with five healthy subjects.

After three months, the coma patients had either died or awoken. All the patients whose discrimination improved by the second day of testing survived and awoke from their comas. By contrast, many of those whose sound discrimination deteriorated by the second day did not survive. The results were reported online November 12 in Brain.

Psychophysiologist Geert van Boxtel of Tilburg University, in the Netherlands, found it surprising that “irrespective of outcome, at the first recording, all of the patients showed signs of auditory discrimination.” This, De Lucia says, suggests that residual auditory function itself does not predict recovery; rather, it’s the progression of function over time that is predictive.

The study couldn’t distinguish whether auditory function initially was preserved due to the hypothermia treatment or was related merely to the early stage of coma. But the scientists speculate that distracting neural jabber may have been reduced during the hypothermia, making it easier for the patients’ brains to separate sounds.

De Lucia and her colleagues are now running a follow-up study with 120 coma patients, to see whether the results can be replicated in a bigger population. “This test could give information about patients who will survive during the first two days of coma, when doctors can still make decisions about treatment,” De Lucia says.