SyncVib

Uncontrollable, even violent, shaking happens to about half of the

25 million people who undergo surgery each year as they are waking up,

but the apparent shivering is not because the patient is cold, as has

been thought for decades, University of California at San Francisco

researchers report.

Instead, it now appears that the general anesthetics used to make the

patient unconscious wear off at different rates in the spine and the

brain. The spinal cord "wakes up" faster than the brain, creating "a

condition where the spine is chemically disconnected from the brain, and

leading to abnormal reflexes," according to a statement released by the

researchers.

The researchers discovered that the tremors resembled a condition

called clonus, an abnormal spinal reflex action that causes shaking in

people with severed spinal cords. The cord initiates a reflex muscle

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action that becomes a continual shaking because the brain cannot shut it

Doctors have had a hard time figuring out what's going on because

surgery patients are cold, too. During surgery, the patient's body

temperature frequently drops, sometimes as much as 6 degrees Fahrenheit,

because he is only partly covered, he receives cold intravenous fluids,

and cold air is pumped into his lungs.

"These people are cold. They have a tremor that looks like a shiver,"

said Dr. Daniel I. Sessler, an anesthesiologist who led the study. "That

is why everyone thought it was shivering."

Anesthetics, however, upset the body's ability to regulate its

internal temperatures. The drugs, in essence, prevent the body from

shivering from cold.

To make matters even more confusing, the treatment for clonus

shivering is heating the skin with a sun lamp. Sessler's group

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discovered that any skin stimulus -- quickly bending an arm or a leg,

coldness -- can stimulate the shaking.

"Warming the skin stops the tremor immediately, even while the core

temperatue is very low," Slesser said.

Post-surgical shaking -- which can last 15 to 30 minutes -- can have

severe consequences: It increases the metabolic rate, as much as

twofold, straining the heart; it also pulls apart incisions, damages

delicate surgical repairs and even breaks teeth.

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