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Understanding Anesthesia

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Anesthesia accidents

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One in 250,000 patients succumbs to an anesthesia accident—a death rate researchers aim to reduce.

As early as 1800, physicians in Europe and the United States knew that compounds such as nitrous oxide, or laughing gas, had pain-deadening properties. But it wasn’t until 1842 that a physician from Georgia, Crawford W. Long, used ether to anesthetize a patient who was having a tumor removed from his neck. Four years later, in the first clinical demonstration of anesthesia, a packed gallery at the Massachusetts General Hospital watched William T. G. Morton, a Boston dentist who had used ether to make tooth extractions less painful, administer ether vapors to a 20-year-old printer named Edward Gilbert Abbott. John Collins Warren, the hospital’s chief surgeon, then removed a vascular malformation from Abbott’s neck. When he finished, Warren proclaimed, “Gentlemen, this is no humbug.” Word of the procedure, which the physician and poet Oliver Wendell Holmes dubbed “anesthesia,” quickly spread across America and Europe.

The advance was sorely needed. Before anesthesia, even minor surgery was nightmarish, and patients who survived often carried psychological scars for the rest of their days. Moreover, many procedures that are now routine, such as appendectomies, were all but impossible to perform, because there was no way to keep a patient from writhing in agony when the knife cut into the body, and chances were high that he would die from shock.

As anesthesia became widely used, a few facts emerged. It turned out that, appearances to the contrary, going under has little to do with sleep. In even the deepest sleep, we toss and turn, feel pain and can be roused by a noise or a shake. An anesthetized patient is in a sort of suspended animation, insensible to noise or any other disturbance. Though the heart continues to beat, the patient has no awareness of a scalpel slicing into flesh, an organ being pushed aside, a tumor being excised. Somehow, propofol and other widely used anesthetic drugs interfere with the brain’s ability to send and receive messages.

“You can’t be aroused from anesthesia under even the most noxious stimulations, because the cognitive ability of the brain has been turned off,” says Steven Shafer, professor of anesthesiology at Stanford University. “There’s nothing else in pharmacology that’s quite like this. We don’t have drugs that turn off the liver or other organs, and yet we are able to turn off the cognitive ability of the brain—and then turn it on again.”

During much of the twentieth century, it was thought that anesthetics shut down the entire brain, akin to turning out a light and leaving a room in total darkness. But recently that theory has given way to a more complex picture of a room divided into cubicles, some of which remain lit while others go dark. Even now, though, nothing is known for certain.

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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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