Hospitals in the United Kingdom and Ireland tracked patients who reported regaining consciousness during surgery. “I thought I was about to die,” said a girl who was having a dental procedure. (Bigstock)

If you’re facing surgery, this may well be your worst nightmare: waking up while under the knife without medical staff realizing.

The biggest-ever study of this phenomenon is shedding light on what such an experience feels like and is causing debate about how best to prevent it.

For a one-year period starting in 2012, an anesthetist at every hospital in the United Kingdom and Ireland recorded every case where a patient told a staff member that he had been awake during surgery. Prompted by these reports, the researchers investigated 300 cases, interviewing the patient and doctors involved.

One of the most striking findings, says the study’s lead author, Jaideep Pandit of Oxford University Hospitals, was that pain was not generally the worst part of the experience: It was paralysis. For some operations, paralyzing drugs are given to relax muscles and stop reflex movements. “Pain was something they understood, but very few of us have experienced what it’s like to be paralyzed,” Pandit says. “They thought they had been buried alive.”

“I thought I was about to die,” says Sandra, who regained consciousness but was unable to move during a dental operation when she was 12 years old. “It felt as though nothing would ever work again — as though the anesthetist had removed everything apart from my soul.”

The audit found that most episodes of awareness were brief and happened before or after the surgery took place. But waking still caused distress in 51 percent of cases. In addition to paralysis, people reported sensations of pain and choking.

The audit found a much lower incidence of waking up than previous studies: one case for every 19,000 operations involving general anesthesia. Smaller studies had suggested the rate could be as high as one in 500.

The latest study tallied only reports that were volunteered by patients; older studies questioned everyone who underwent surgery. This proactive questioning could overestimate the problem, Pandit says.

But John Andrzejowski, an anesthetist at the Royal Hallamshire Hospital in Sheffield, thinks the latest audit probably missed many non-trivial cases. “The true figure is probably somewhere in the middle,” he says.

The audit team is urging anesthetists to use a device called a nerve stimulator to enable them to give the minimum dose. A lower dose should be enough to stop spontaneous movements yet still allow the patient to move if he becomes conscious enough to feel pain, Pandit says.

Sometimes complete paralysis is essential to avoid severing a nerve, points out Andrzejowski, who advocates using monitors that record brain activity through scalp electrodes. But Pandit argues that these give no clear signal of consciousness and are hard to interpret.

— New Scientist