Being aware of what's going on during an operation under general anesthesia sounds scary. The good news is a new study suggests it happens less often than had been thought.

Previous research has found that about 1 in 500 patients is aware or awake under general anaesthesia. The new report, from the U.K.'s Royal College of Anaesthetists, finds it is far less common, about 1 case in 15,000.

Researchers also found that even where brain monitoring equipment is available, fewer than 2% of anesthesiologists routinely use it to check the effectiveness of the anesthetic.

Anaesthesia Study

The findings come from the biggest study of its kind. It surveyed 7,125 anesthesiologists and coordinators at 329 hospitals across the U.K.

There were 153 cases of "accidental awareness" reported in 2011:

• 30% happened during surgery.
• 23% happened after surgery but before the full recovery time.
• 47% happened after anesthesia has begun but before surgery had started.

Awareness during surgery was more likely to lead to pain or distress.

"Waking up during surgery is a fear," says researcher Jaideep Pandit, DPhil, a consultant anaesthetist at Oxford University Hospitals in the U.K. "It's a legitimate fear."

He hopes the study will calm some concerns: "Anything to use data to be reassuring is always a good thing."

He admits some under-reporting is possible in the study. Anesthesiologists may have forgotten how many awareness cases they'd seen. Since anesthesiologists don't routinely see patients after operations, they may not always learn about the awareness report. Sometimes patients may forget the incident or think it is too trivial to mention.

From Terrified to Interested

How do patients describe the experience of being aware during an operation? These vary greatly, from "the very, very severe adverse experiences of a combination of pain, paralysis, terror," Pandit says, to anecdotal reports of patients almost being fascinated by what's happening around them: "Completely unconcerned and untroubled and almost interested in the proceedings."

He and colleagues are planning more research to focus on patient experiences. "Even for someone who reports they are not particularly bothered by it, at the very least it must be surprising for them."

Brain Monitors

Brain monitoring systems have been in use the U.K. for about 10 years. The monitors help check that a patient really is under the anesthetic. Pandit says these are available in about two-thirds of hospitals, but even where they are supplied, most anesthesiologists don’t use them. "One would have hoped that if the profession is doing what it wants to do, which is keep people asleep, and there is a monitor that they believe in, that they would of course use it."

There's a debate over how useful the monitors are, and some research suggests they don't appear to help lessen the numbers of people being awake during surgery.

Different Responses to Anesthetic

Pandit says it isn’t clear why some people wake up during a procedure while others don't, although it is possible the drugs used for anesthesia have a different effect on different people. "We know that's true of other drugs. Be it antidepressants or cardiovascular drugs or cancer drugs. They don’t all have the same effect in people," he says. "Some people get side effects and some people don't."

SOURCES: Pandit, J. Anaesthesia, published online March 12, 2013.Jaideep Pandit, DPhil, consultant anaesthetist, Oxford University Hospitals, U.K.

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