Device Doesn’t Help Prevent Patients From Waking During Surgery

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About one in 1,000 surgery patients experience the trauma of awareness during anesthesia, and later remember feeling pain and distress during their operation. Many go on to develop symptoms of posttraumatic stress. So hospitals are always trying to develop better methods to prevent “intraoperative awareness.”

A new study compared the effectiveness of two methods of monitoring patients during surgery: one involves measuring the concentration of anesthetic drugs in patients’ exhaled breath — a cheap and effective method.

The other uses a device called the bispectral index or BIS monitor. BIS monitors track patients’ brain activity to determine whether they are awake or asleep — a method that’s also effective, but more expensive than measuring patients’ breath.

The question is, Is BIS more or less effective than the alternate approach? “[F]or many years anesthesiologists have monitored the cardio-respiratory system very vigilantly, but we haven’t rigorously tried to monitor the nervous system, which is the site of action for anesthetic agents,” senior author Dr. Michael S. Avidan, professor of anesthesiology at Washington University School of Medicine, said in a statement. “That’s what the bispectral index attempted to do.”

Anesthesiologists from three major teaching hospitals (Washington University School of Medicine in St. Louis, the University of Chicago and the University of Manitoba in Winnipeg) examined more than 6,000 surgery patients, who were considered at high risk of awareness during anesthesia — those undergoing cardiac surgery; those who regularly consumed a lot of alcohol, sedatives or painkillers; and those who had previous experiences of awareness.

The researchers found that among the 2,861 patients in the BIS monitor group, 19 experienced awareness, compared with eight of the 2,852 in the group who was being monitored by breath.

“Our study does not show that the BIS monitor is ineffective,” said co-author and anesthesiologist Dr. Alex S. Evers at the Washington University School of Medicine. “It’s just that it’s not superior to the protocol based on measuring the concentration of anesthetic a patient actually has received, which is a simpler and less expensive approach.”

The research was published in the New England Journal of Medicine.

Correction [August 27, 2011]: An earlier version of this article reported that the rate of patients who are aware during surgery was one in 100, when in fact it was one in 1,000. That’s a big discrepancy and we regret the error.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.

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