patients experience a small initial decrease in core temperature after
induction of general anesthesia, they all recover so that they're nor-
mothermic by the end of surgery, he says — so long as you do your
part: Actively warm patients during surgery.
An additional strategy is prewarming, actively warming patients for
about 30 minutes before induction of anesthesia. "This increases heat
content in the body, specifically the tissue temperature in the peripher-
al thermal compartment," says Dr. Sessler. "Heat can only flow down a
temperature gradient. That's how prewarming works. This reduces the
gradient, and thus the amount of redistribution.
"People assume that you get more hypothermia with long cases
than with short cases," he adds. "In fact the opposite is true. In a
short case, you have this redistribution and you don't have time to
recover. In longer cases, you have more time to recover and become
normothermic. Without active warming, however, a patient's temper-
ature will just go down and down."
4. Is prewarming more important
for shorter cases than for longer ones?
Yes, prewarming is most indicated and effective for shorter cases
(less than 60 minutes, induction to emergence). And it's simply a mat-
ter of how much time patients' bodies have to warm up. After induc-
tion of anesthesia, most patients have an internal redistribution of
body heat that slightly reduces their core temperature, explains Dr.
Sessler. "This large flow of heat overwhelms even forced air," he says.
"But after redistribution is complete, the forced-air warming gradually
increases core temperature. The longer the operation, the more time
is available for forced air to transfer heat." Put another way: Because
core temperature progressively increases after the initial hour of anes-
thesia, patients having longer operations are more likely to be nor-
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