Since its introduction in 1846, anesthesia has allowed for medical miracles. Limbs can be removed, tumors examined, organs replaced—and a patient will feel and remember nothing. Or so we choose to believe. In reality, tens of thousands of patients each year in the United States alone wake up at some point during surgery. Since their eyes are taped shut and their bodies are usually paralyzed, they cannot alert anyone to their condition. In efforts to eradicate this phenomenon, medicine has been forced to confront how little we really know about anesthesia’s effects on the brain. The doctor who may be closest to a solution may also answer a question that has confounded centuries’ worth of scientists and philosophers: What does it mean to be conscious?

In the centuries before EEG and computers, the most-active contemplators of consciousness were not doctors but philosophers. The 17th-century French thinker René Descartes proposed an influential theory that leaned on neuroanatomy as well as philosophical inference. He declared the pineal gland, a pea-size glob just behind the thalamus, the seat of consciousness, “the place in which all our thoughts are formed.” But Descartes was a dualist: he believed that body and mind are separate and distinct. Within the physical matter of the pineal gland, he reasoned, something inexplicable must lie, something intangible—something that he identified as the soul.

This idea has been rejected by reductionist thinkers, who believe that consciousness is a scientific phenomenon that can be explained by the physiology of the brain. In an attempt to understand various sensory functions, a 19th-century cohort of reductionist biologists burned, cut, and excised lumps of the brain in rabbits, dogs, and monkeys, eventually pinpointing centers for hearing, vision, smell, touch, and memory. But even the most-extreme experiments of the period failed to identify a center for consciousness. In 1892, a German scientist named Friedrich Goltz, who rejected this notion of cerebral localization and hypothesized instead that the brain operated as a cohesive unit, cut out the majority of a dog’s cerebral cortex over the course of three operations. The animal managed to survive for 18 months; it even remained active, walking its cage and curling up to sleep, and reacted to noises and light by flipping its ears and shutting its eyes. Yet other things had changed. The dog required assistance with eating, and its memory seemed to have been destroyed. “The condition was that of idiocy but not of unconsciousness,” wrote one scientist.

Today’s neuroscientists, most of whom are reductionists, have offered multiple hypotheses about where consciousness resides, from the anterior cingulate cortex, a region also associated with motivation, to some parts of the visual cortex, to the cytoskeleton structure of neurons. Some theories peg consciousness not to a particular part of the brain but to a particular process, such as the rhythmic activation of neurons between the thalamus and the cortex.

What if Terri Schiavo’s family had been able to ascertain that she was, in fact, completely unconscious, more so than she would have been even under heavy anesthesia?

David Chalmers, an Australian philosopher who has written extensively about consciousness, would refer to this neurobiological hunt as the “easy problem.” With enough time and money, scientists could ostensibly succeed in locating a consciousness center of the brain. But at that point, Chalmers argues, an even bigger mystery would still remain, one that he calls the “hard problem.” Say you and a friend are looking at a sunset. Your body is processing a huge variety of sensory inputs: a spectrum of electromagnetic waves—red, orange, and yellow light—which focus on your retina; the vibrations of your friend’s voice, which bounce along the bones of your inner ear and transform into a series of electrical signals that travel from neuron to neuron; memories of past sunsets, which spark a surge of dopamine in your mesolimbic pathway. These effects coalesce into one cohesive, indivisible experience of the sunset, one that differs from your friend’s. The hard problem, or what the philosopher Joseph Levine called the “explanatory gap,” is determining how physical and biological processes—all of them understood easily enough on their own—translate into the singular mystery of subjective experience. If this gap cannot be bridged, then consciousness must be informed by some sort of inexplicable, intangible element. And all of a sudden we are back to Descartes.

In 2004, 60-year-old man checked in for open gastric-bypass surgery and a gall-bladder removal at Virginia Mason Medical Center in Seattle. Simon, as I’ll call him, stood 5 feet 9 inches tall and weighed approximately 300 pounds. In an open gastric bypass, the surgeon penetrates mounds of flesh and fat before finding the peritoneum, the glossy membrane that holds the abdominal cavity intact. Many surgeons use a space-age device called a Harmonic Scalpel, which cuts tissue while simultaneously blasting it with ultrasound waves to stop the bleeding. Once the surgeon uncovers the stomach and yards of folded, tubular intestines, she uses metal retractors to pull the skin apart and clear away slippery membranes, juicy organs, and fatty layers of tissue. Then, to business: cut, suture, cut, suture, cauterize, cut.

No surgeon could have imagined a procedure of this magnitude 167 years ago, in the days before anesthesia. It would have been impossible to endure, both for the patient and the surgeon. Simon’s anesthesiologist, Michael Mulroy, was particularly worried about him because of his hypotension and reliance on painkillers, both of which increased his risk of awareness. To make sure that Simon didn’t drift into consciousness, Mulroy decided to use a BIS monitor.

Surgery records show that throughout the three-hour procedure, Simon’s BIS value hovered between 37 and 51, well below the threshold for sedation. Mulroy had given Simon a relatively light dosage, reluctant to risk further deflating his patient’s dangerously low blood pressure, but he took comfort in the fact that the BIS told him that Simon was unconscious and unaware.

After the surgery, in the postoperative recovery room, nurses asked Simon whether he was in pain. “Not now,” he said, “but I was during surgery.” Simon reported memories that began after intubation, including “unimaginable pain” and “the sensation that people were tearing at me.” According to a clinical report, he heard voices around him and “wished he were dead,” but when he tried to alert the surgical team, his body did not respond to his brain’s commands.

The news of Simon’s experience devastated Mulroy. He explained to his patient that he had used the BIS monitor and that it had confirmed Simon’s unconscious state throughout the procedure. In the end, Mulroy says, all he could do was apologize and arrange for a psychiatrist. He hasn’t seen Simon since, but he published the case in a 2005 issue of the journal Anesthesia & Analgesia. Mulroy felt that the BIS monitor had betrayed him; he might have done more to deepen Simon’s sedation if the BIS had not reassured him that everything was fine.

Mulroy was one of the first to question the BIS, but his concern was soon echoed in other corners of the medical community. In 2008, The New England Journal of Medicine published a study comparing nearly 2,000 surgery patients at high risk of awareness: 967 patients were monitored by the BIS, and 974 via attention to changes in the amount of anesthetic gas they exhaled throughout a procedure. The author, a researcher at the Washington University School of Medicine in St. Louis named Michael Avidan, found that both groups of patients experienced awareness at similar rates. In other words, the BIS was no more effective than a much cheaper and more standard method. After questions were raised about his methodology, Avidan repeated the experiment with a broader sample and found the same thing. Chamoun’s window to the brain, it turned out, was not especially enlightening.

Avidan, who seems to have a singular zeal for highlighting the BIS monitor’s weaknesses, has also published a study showing that in many cases, two monitors on the same patient display different values. In a YouTube video, he applies BIS electrodes to a volunteer’s forehead, cuts them with scissors, and waits a full 40 seconds for the device’s value to change. Today, the BIS monitor has become the most controversial medical device in anesthesiology, if not all of surgery. Aspect’s stock plummeted and the board of directors sold the company in 2009. Chamoun temporarily accepted a high-paying position at the new parent company, Covidien, but resigned not long after. His heart wasn’t in it anymore.

The BIS monitor is not obsolete: it may still be clinically useful, may still prevent some cases of awareness. “It’s important to take into consideration the collective scientific evidence and clinical experience of millions of patients,” says Chamoun. “The BIS can help reduce the risk of awareness, but it will not completely eliminate that risk.”

Even after the Avidan studies, many anesthesiologists around the world still choose to rely on the BIS to guide them through surgery. But guarantee that a patient is unconscious? That, it cannot do. Chamoun is an engineer: he was never interested in providing a holistic assessment of what it means to be conscious. For that, medicine had to hold out for someone who could see beyond the data—someone whose fascination with the mind was as much humanistic as scientific.

Presented by

Joshua Lang is a medical student at the UC Berkeley–UCSF Joint Medical Program.

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