Doctors David Ghozland and Marc Winter make an incision in the belly button of a 49-year-old woman, Sheryl, who had two fibroids, in preparation for a single-site robotic-assisted hysterectomy at miVIP Surgery Center, in Los Angeles, California April 23, 2014. REUTERS/Lucy Nicholson
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Measuring certain kinds of brain activity may help doctors track and predict how patients will react to anesthesia before going under for surgery, our research has found.

Doctors currently have no perfectly reliable way of ensuring patients are adequately unconscious before an operation begins. Although rare, the uncertainty sometimes results in traumatic experiences of patients "waking up" during surgery.

Using a technique that measures electrical impulses in the brain of those in various states of sedation, we discovered network "signatures" that can indicate when loss of consciousness will occur.


Everyone is different

Every day in Australia, more than 6,000 people are anesthetized for surgery. Doctors need to figure out exactly how much sedative to give them, and keep them unconscious throughout the operation.

Anesthetists estimate the concentration of sedative required using calculations mainly based on a patient's weight. As the patient "goes under", their level of awareness is monitored by observing indirect - and somewhat crude - measures, such as blood pressure, heart rate or physical movement.

This method works well in most cases, but people's susceptibility to anesthesia varies. One to two in every 1,000 people report having some awareness or recall during surgery. This equates to 2,000 to 4,000 such cases each year in Australia.


Naturally, experiences such as these are emotionally traumatic. What's more, many suffer mental distress long after the surgery, resulting in negative memories of their hospital experience. Some have even reported a reduction in their quality of life.

Getty Images/Carsten Koall

Losing consciousness




Brain monitoring such as this is not commonly used in the operating theater today. One reason is that current devices are unable to deal with the considerable variability in how people respond to sedatives. But our study shows that devices calibrated for accurate monitoring based on the latest neuroscientific advances could help reduce the incidence of awareness during surgery.

Our study





We also measured the behavioral responsiveness of the participants with a simple task. They were asked to press one button if they heard a "ping" and a different button if they heard a "pong".


The right measure

We found that the strength of a participant's brain network was clearly linked to their behavioral responsiveness. In other words, as the brain network indicating consciousness weakened, behavioral evidence of awareness also diminished.

Interestingly, while some participants showed behavioral evidence of consciousness at moderate levels of the anaesthetic, others remained responsive.


Our current findings indicate the change in consciousness due to the sedative was clearly correlated with specific patterns of brain network activity. This gives us confidence in making the "reverse inference" that tracking this network activity can be used to infer the true level of consciousness in the absence of behavior.

Further engineering and testing could help advance and adapt current brain monitoring technology for use in the operating theater. It is clear that networks measured by an appropriate EEG can capture and explain why people respond differently to anesthesia.

This monitoring can help doctors optimize the amount of drug needed for someone to become unconscious without increasing risk of complications or awareness during surgery.

Srivas Chennu, Senior Research Associate, University of Cambridge
