Redheads require more anesthetic, study finds

WASHINGTON -- The genetic quirk that makes red hair red may also make carrot-tops harder to knock out -- in the operating room, that is.

A new study suggests people with naturally red hair need about 20 percent more anesthesia than patients with other hair colors.

It's a small study that will need confirmation. But it marks the first time scientists have linked a visible genetic trait to anesthesia doses, said Dr. Daniel Sessler of the University of Louisville, whose study will be presented today at a meeting of the American Society of Anesthesiologists.

Inadequate doses of general anesthesia can allow people to recall surgery, or even wake up during it, problems that occur in 1 percent of cases, Sessler said.

Anesthesiologists have long grumbled that redheads can be harder to put under, but no one had ever studied whether that was real or folklore, said Dr. Andrea Kurz of Washington University in St. Louis. But why would hair color possibly matter? The theory hinges on melanin, a pigment responsible for skin and hair color.

The sun triggers a hormone that in turn triggers the production of melanin to form a tan. Redheads seldom tan easily because they have a defective receptor for that hormone -- a quirk with this "melanocortin-1 receptor" that also leaves their hair red. Without its intended receptor to dock in, the melanin-producing hormone may crossreact with a receptor on brain cells that influences pain sensitivity, Sessler explained.

That's still a theory. Here's what Sessler can say for certain: He and colleagues gave 10 healthy women with naturally red hair and 10 with dark hair the common inhaled anesthetic desflurane. Then they administered electric shocks -- not enough to do damage but enough to cause pain -- and inched the desflurane dose up or down according to the pain response until each patient was judged to be at the optimum anesthetic dose. The redheads required a 20 percent higher dose.

Sessler said his lab first tested a few blondes and found they reacted the same as brunettes.

The study doesn't address whether men would react similarly -- there are gender differences for many drugs -- or whether redheads would be similarly affected by noninhaled anesthesia.

The research "gives us a window into what determines anesthetic requirements," said Sessler, whose lab is beginning more studies.

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