Post-operative trembling endured by millions of people who undergo surgery each year results from the use of anesthetics--and not from decreased body temperature, as had been assumed, a new study says.
The finding could lead to improved treatments to prevent the unpleasant and uncontrollable tremors that in some cases resemble a seizure and can be dangerous to patients, researchers said.
"We now know that a very dramatic side effect of surgery has been misinterpreted for more than 35 years," said Daniel I. Sessler, assistant professor of anesthesia at UC San Francisco and head of the study.
Sessler, with researchers at UCLA and the University of Minnesota, compared electrical signals produced in muscles during normal shivering to those in nine women recovering from anesthesia after surgery. They found that the post-surgical tremors were not related to body temperature, but matched tremors produced in people with severed spinal cords.
Anesthetics, they found, wear off in the spine while the brain remains asleep, essentially disconnecting the spine from the brain's chemical messages. If the patient's skin gets cold, triggering shaking, the brain cannot signal the muscle reflex to stop, Sessler said. After about 15 minutes, when the brain wakes up, the tremor stops.
"People have been trying to do something for years about post-surgical tremors, but generally without success because they have been treating it as a thermo-regulatory problem," he said. The findings are to be published later this year in the journal Anesthesiology.
Sessler said such tremors can be prevented by warming the skin with infrared heating lamps and perhaps even by something as simple as a hair dryer while the patient is still asleep.