Slow brain waves reveal precisely when a patient loses awareness while under anesthesia, and could prevent the small percentage of cases in which patients are “awake” during surgery.
Being aware of what’s happening during surgery and even feeling the pain seems like an unthinkable nightmare. Isn’t that what anesthesia is for?
But it does happen in up to one percent of surgeries involving high-risk patients, according to research published in 2011, and affects between 20,000 and 40,000 patients annually in the U.S. alone. Now, scientists from the University of Oxford in the U.K. believe they’ve found a way to put an end to this disturbing statistic.
Using EEG brain monitoring and MRI imaging scans, the researchers discovered that people lost awareness when low-frequency electrical waves, also called “slow waves,” enveloped the brain. When the waves reached a plateau, sensory signals no longer reached the thalamocortical regions, which are the parts of the brain linked to conscious awareness.
“Awareness in anesthesia is a ‘never event’—it isn’t good enough for it to be rare,” Roisin Ní Mhuircheartaigh, one of the researchers, told Healthline. “Our goal is to allow anesthesiologists to look at a patient’s brain activity and know with confidence that [he or she] is safely asleep.”
The researchers have applied for a patent on their findings and are looking into developing better monitoring equipment for patients under anesthesia. They are the second group of scientists this year to do so. Earlier this year, researchers from the Massachusetts Institute of Technology and Boston University published their findings on slow waves and unconsciousness.
“They looked at EEG, too, but have focused on the relationship between slow waves and alpha activity,” Catherine Warnaby, another Oxford researcher, told Healthline. “A key difference is that we have looked at slow wave saturation and have the FMRI evidence to support that this state represents a state of perception loss.”
Warnaby stressed that anesthesia is very safe, but little is known about how it works in the brain. In patients with severe health problems, too much anesthesia can adversely affect their heart or lungs. Elderly patients may experience severe confusion after an operation if given too much anesthesia.
“We think that this has great potential to become an individualized marker for delivering anesthesia during surgery,” Warnaby said. “If we can prove further that this saturation relates to the point where people lose awareness of the outside world, it may change the way that anesthetics are delivered worldwide. Anesthesiologists would be able to give anesthetics to achieve this saturation level and know that they were giving each individual just the right amount of the drug.”
The research could also help resolve other riddles of the brain, Warnaby added. “Our findings could have implications for all sorts of altered states and disorders of consciousness, such as locked-in syndrome or persistent vegetative state.”
In both the Oxford and U.S. research, scientists experimented with the common anesthetic, propofol.
There are EEG monitors available to assess the depth of anesthesia, although there isn’t much evidence that these methods are better than traditional monitoring at reducing awareness during surgery, Warnaby said.
The next step is to perform further experiments to recreate a surgical setting. Researchers will look at how other drugs used during surgery—such as painkillers—affect slow waves during anesthesia.
“Depending on the operation, anesthesiologists have to give drugs that block muscle function, ‘paralyzing drugs,’” Mhuircheartaigh said. “If inadequate anesthetic drugs are given while the patient can’t move to let us know they’re awake, awareness can occur.”
Like Warnaby, Mhuircheartaigh stressed the rarity of these cases, especially in healthy people. “However, rare isn’t good enough,” she told Healthline. “We hope that by looking at this key process in the brain we can be sure that the patient can’t perceive any surgery.”