I was looking forward to my first experience with anesthesia. I had been laid out on a stretcher, and nurses and doctors were prepping my midsection so they could slice it open and cut out my appendix. After a bout of appendicitis, a short vacation from consciousness seemed like a pleasant way to spend a few hours. I had no idea what anesthesia would actually feel like, though, and suddenly I was seized by skepticism. I tried to hoist myself up, already swabbed in iodine, as I suggested that I ought to pop into the men’s room before the scalpels came out. I wouldn’t want to interrupt the surgery with a bathroom break. “Don’t worry,” one of the nurses replied. “We’ll do that for you.”
I lay back down, puzzling over that. After a nurse put the IV into my hand, I had to interrupt again: The anesthesia flowing into my arm was not working. I just couldn’t believe that anything would keep me asleep while someone was knitting up my intestines. The nurses and doctors nodded in my direction as I tried to explain the problem to them, but I was sure they weren’t taking me seriously. I took a long, slow blink. And then there were no doctors and nurses around me. I was lying alone in a new room, recovering from my surgery.
Ever since that experience, I’ve wondered what exactly happened in my head. It didn’t feel like sleep. It was not a blackout, either. It was as if the surgeons had simply cut a few hours out of my life and joined together the loose ends. So I decided to get more familiar with the science behind anesthesia. To my surprise, I discovered that anesthesiologists are a bit in the dark themselves. “How anesthesia works has been a mystery since the discovery of anesthesia itself,” writes Michael Alkire, an anesthesiologist at the University of California at Irvine School of Medicine, in the new Encyclopedia of Consciousness.
The first public demonstration of anesthesia during surgery took place in 1846 in Boston. A man named Gilbert Abbott took some deep drafts of ether, and surgeons began cutting a tumor off his jaw. The audience was shocked that Abbott did not scream and squirm. One London newspaper expressed the amazement that many must have felt: “Oh, what delight for every feeling heart to find the new year ushered in with the announcement of this noble discovery of the power to still the sense of pain and veil the eye and memory from all the horrors of an operation.”
Today anesthesiologists have a number of drugs to choose from, as well as machines to administer them safely. Every year tens of millions of people get general anesthesia. In 2008 Columbia University epidemiologist Guohua Li reported that each year only one person in a million suffers an anesthesia-related death in the United States. But for all these achievements, anesthesia remains deeply puzzling.
To begin with, anesthesiologists have no precise way to determine when people lose consciousness. In Abbott’s day, doctors would simply ask their patients to respond, perhaps by opening their eyes. A lack of response was taken as a sign of unconsciousness. Many modern anesthesiologists talk to their patients, but judging the response is made more complicated by the muscle relaxants that they also use. Sometimes the anesthesiologist will use a blood pressure cuff on a patient’s arm to block the muscle relaxants in the bloodstream. Then the doctor asks the patient to squeeze a hand.
This sort of test can distinguish between a patient who is awake and one who is out cold. But at the borderline of consciousness, it is not very precise. The inability to raise your hand, for example, doesn’t necessarily mean that you are unconscious. Even a light dose of anesthesia can interfere with your capacity to keep new pieces of information in your brain, so you may not respond to a command because you immediately forgot what you were going to do. On the other hand, squeezing an anesthesiologist’s hand may not mean you’re wide awake. Some patients who can squeeze a hand will later have no memory of being aware.
Seeking a more reliable measuring stick, some researchers have started measuring brain waves. When you are awake, your brain produces fast, small waves of electrical activity. When you are under total anesthesia, your brain waves become deep and slow. If you get enough of certain anesthetics, your brain waves eventually go flat. Most anesthesiologists monitor their patients using a machine known as a bispectral index monitor, which reads brain waves from electrodes on a patient’s scalp and produces a score from 100 to 0. But these machines aren’t precise either. Sometimes patients who register as unconscious can still squeeze a hand on command.
The problem with all these methods is that anesthesiologists don’t really know what it is they are trying to measure. So Alkire and other scientists are using neuroimaging to peer into the anesthetized brain to see what happens when it succumbs. In a typical experiment, a volunteer lies in an fMRI brain scanner, which can measure the amount of oxygen used in different parts of the brain. A researcher gives the volunteer anesthesia and measures how those brain regions respond.