Just imagine that the whirring noise—from drills and saws cutting into your skull—is the gentle engine-hum of a motorboat, gliding past your canoe as you float in a tranquil lake.

Those may be some of the instructions a cancer patient might hear while in a hypnotic trance during brain surgery.

The technique, which replaces general anesthetics, was used on 37 patients undergoing surgery to remove brain tumors, researchers report in the journal Neurosurgery. Though there's been little science to back up hypnotherapy, the authors conclude that their small study's success suggests hypnosis could be a viable tool to help sedate patients during delicate brain surgery.

Such surgeries are particularly tricky because they often require a patient to be awake to respond to questions or perform certain mental tasks, the authors note. Surgeons use those responses and interactions to help avoid damaging critical brain areas as they carefully extract tumors.

Typically, anesthesiologists put patients to sleep for the start of such a surgery—while the skull is opened—rouse them in the middle, then put them back to sleep for the surgical wrap-up. The technique is referred to simply as the asleep-awake-asleep (AAA) procedure. But, it has two main drawbacks: doctors have to monitor and manage the patient’s breathing during the already-involved surgery; and, it can take some patients (particularly older ones) a while to fully wake up from anesthesia, which lengthens surgery time.

To see if hypnosis could be a viable alternative, researchers led by Ilyess Zemmoura of the Centre Hospitalier Universitaire de Tours, France, pitched the method to brain cancer patients. These patients all needed an awake surgery to remove a certain type of brain tumor that arises in glial cells (support cells in the brain), called glioma. For the hypnosis sedation to work, patients had to meet with a hypnotist a few weeks before the surgery and practice getting into a "trance" state.

Researchers explained the stupor-based surgery to 48 patients. Of those, 11 patients went with AAA—two because they preferred the standard method, three had emergency surgery and couldn’t prepare for hypnosis, and the remaining six patients wanted to try hypnosis but couldn’t get into a trance at the time of surgery and switched to the AAA procedure at the last minute.

The other 37 patients went through surgery with a combination of hypnosis, pain relievers, and local anesthetics, or “hypnosedation." Some of the patients required multiple surgeries for recurring tumors. In all, the researchers conducted 43 surgeries with patients under hypnosis. Below is a video of one of them, but please note that it includes graphic images that may not be suitable for everyone.

During hypnosedation, the patient is asked to visualize a happy, safe space, plus imagine separating mind from body and “maintain[ing] a distance of 2 cm between them” (PDF). At various points in the surgery, the hypnotist will prompt the patient to hold body and mind farther apart. The hypnotist also instructs patients to visualize different things when sounds and movements arise during the operation. For instance, drill motors could be from a boat engine, vibrations from surgical cutting may be from riding a bicycle with triangular wheels.

For the 37 patients, hypnotists tailored each trance experience to the habits, likings, and personality of the patient, which was worked out in the training session prior to surgery. Thus, hypnosis is not a trivial or easy swap from the standard method, the authors conclude. “It requires intense involvement and long training of the whole team, including the patient,” the authors wrote. “Therefore, the method we describe is limited by the necessity to work with an anesthetic team experienced in both neuro-anesthesiology and hypnotherapy.”

The study also has a big flaw: it didn't include a control group. This makes it impossible to compare the pros and cons of hypnosedation to AAA. The authors acknowledge this and conclude that AAA is still the gold standard and, overall, hypnosedation is not optimal.

But, it may be a useful alternative for some patients, they note. In questionnaires and assessments taken after the surgeries, most patients reported positive experiences and little to no psychological impacts from the generally tough operation. Only two of the 37 patients said they wouldn’t use hypnosis again.

The study isn’t the first to explore hypnosis for surgeries and other medical treatments. The method has been knocked around the medical community for years as a way to focus attention and concentration. It has been considered a way to combat chronic pain, labor pains, and change behaviors such as smoking and overeating. While anecdotes and small studies report success, there is not enough data to support effectiveness and reliability, and researchers have struggled to even define a "trance state," let alone standard methods for inducing one. Overall, strong skepticism has lingered within the medical community, as hypnosis advocates have called for more research.

Neurosurgery, 2015. DOI: 10.1227/NEU.0000000000000993 (About DOIs).