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IMPORTANT QUESTIONS ABOUT UNCONSCIOUSNESS:
Why do we process sound when our memory won’t record it? // What lights remain on in the darkened mind? // How do drugs stop pain messages in their tracks? // How can the answers make going under and coming to safer and swifter?

Understanding Anesthesia

By Charles Slack // Portraits by Eric Ogden // Summer 2006
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Emery Brown in the Ether Dome at the Massachusetts General Hospital

Eric Ogden for Proto

One hundred and sixty years after anesthesia first saw the light of day in the Ether Dome at the Massachusetts General Hospital, Emery Brown wants to know what really happens when a patient goes under.

In a surgical suite, a woman in her mid-40s lies motionless, her upper and lower body draped with sterile cloth. She has just had her gallbladder removed, and the surgeon is suturing the last of several small abdominal incisions through which he threaded his laparoscopic instruments. Across the table, an anesthesiologist monitors digital readouts showing the patient’s heart rate, blood pressure and other vital signs. When the surgeon finishes suturing, the anesthesiologist cuts the flow of drugs so the patient can find her way back to consciousness.

The case is routine in every way, one of 50,000 every day in the United States in which patients undergo general anesthesia. From long experience, the anesthesiologist expects the woman’s involuntary functions, such as her ability to breathe, to return first; then, she will slowly awaken, first showing small signs of life—a frown, perhaps a tear—and then gradually become aware of her surroundings. Yet now, precisely the opposite is happening. When he speaks, she opens her eyes. He asks her to squeeze his hand, and her firm grasp confirms she is able to recognize commands and carry out high-level cognitive functions. But her brain still is not performing one of its most basic assignments: instructing her lungs to inhale and exhale.

Because the patient’s breathing tube is still in place, the situation is more intriguing than it is alarming. Indeed, data from the pulse oximeter clipped to her middle finger—the device uses light to measure blood oxygen levels—reveals her blood is 100% saturated. Nor is the patient disconcerted by the unusual sequence of events; within a minute, as the anesthesiologist pumps the balloonlike device that forces air into her lungs, her chest begins to rise and fall. But for the anesthesiologist, Emery Brown, a member of the Massachusetts General Hospital’s Department of Anesthesia and Critical Care and an associate professor of anaesthesia at Harvard Medical School, the episode is a stark reminder of how little anesthesiologists really know about the phenomenon to which they have devoted their careers.

During the 160 years since ether was introduced, anesthesiologists have become better and better technicians. General anesthesia is now so routine that people speak of “going under” as casually as they might refer to a stressful but otherwise unexceptional business trip. The risk of a fatal accident during anesthesia has plunged from one in 10,000 cases 36 years ago to just one in 250,000 today.

Still, only now, after long and steady improvements in the practice of anesthesia, are researchers beginning to piece together what happens in the brain of an anesthetized patient. Advances in imaging technology, information processing, molecular biology and other specialties are enabling scientists to map the functions of various brain regions, study the brain’s electrical waves and analyze communications between individual neurons. In the process, a specialty sometimes regarded as almost a trade in the medical hierarchy—an essential service but hardly a hotbed of research—is becoming an arena of cutting-edge inquiry.

At stake is much more than satisfying intellectual curiosity. Grasping how anesthetics affect specific parts of the brain could help researchers develop better-targeted drugs that shut down only certain functions—those involved with feeling or remembering pain, for example—while leaving others unimpaired. According to Ira Rampil, professor and director of clinical research in anesthesiology at Stony Brook University in New York, the current array of anesthetics are reliable tools for putting patients under and bringing them back, and anesthesiologists tend to use much the same procedure for every patient. But with more specialized choices, physicians could tailor drug and dosage to each case. “We could become fine chefs rather than short-order cooks,” Rampil says.

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Consciousness Unbound

Some researchers say the key to learning how anesthetics work is to examine a much tougher subject: consciousness.

Number Conscious

The bispectral index uses EEG readings to assign a number to a patient's level of consciousness, allowing doctors to administer more precise doses of anesthesia.

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hed-dossier

1.“A Primer for EEG Signal Processing in Anesthesia,” by Ira J. Rampil, Anesthesia, October 1998. A definitive if highly technical account of BIS readings and other uses of EEG in anesthesiology.

2.“The Effects of Anesthetics on Brain Activity and Cognitive Function,” by Wolfgang Heinke and Stefan Koelsch, Current Opinion in Anaesthesiology, December 2005. An excellent overview of recent work, from EEGs to neuroimaging.

3.“Consciousness Unbound,” by George A. Mashour, Anesthesiology, February 2004. A reflection on the various “cognitive binding” theories of consciousness, and their implications for anesthesia.

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