High-tech device
dramatically speeds recovery from hypothermia
BY DAVID F. SALISBURY
Stanford researchers have
developed a high-tech solution that dramatically reduces
the recovery time for the mild hypothermia that often
accompanies major surgery. A device called the
Thermo-STAT, which fits over the hand and forearm, also
holds promise for the treatment of more severe cases of
exposure and has a much broader potential application in
manipulating core body temperature to treat a variety of
ailments, including chronic disorders like cystic
fibrosis, brain damage after strokes and tumors.
One of the most unpleasant
and dangerous side-effects of extended surgery is
hypothermia. In response to anesthesia, cool temperatures
and paper-thin hospital gowns, many if not most of the
patients wheeled into the operating room experience a
drop in core body temperature. Anesthetics usually take
several minutes to wear off, but recovery from this
internal cooling can take hours, and patients often
endure chills and shivering during this time. Recent
studies have shown that even such relatively mild
hypothermia increases infection rates and ups the
frequency of post-operative heart problems for those at
risk.
In the November issue of
the Journal of Applied Physiology, Dennis Grahn,
senior research scientist in biological sciences; John G.
Brock-Utne, professor of anesthesia; H. Craig Heller, the
Lorry I. Lokey/Business Wire Professor of Environmental
Biology at Stanford; and Donald E. Watenpaugh, research
associate in integrative physiology at the University of
North Texas Health Science Center in Fort Worth, report
on the successful clinical trial of the rewarming
technology.
The experimental device
consists of an acrylic sleeve and mitt that fits over the
hand and seals around the patient's forearm. It contains
a water-perfusion blanket to supply heat and is hooked to
a vacuum pump to reduce the air pressure inside the
sleeve. Its design has been patented by Stanford and
licensed by Aquarius Medical Corp. of Scottsdale, Ariz.,
which has developed and is marketing a commercial version
of the rewarmer.
The device relies on the
fact that the hand and bottom of the forearm are areas of
the body specialized for the transfer of heat. They
contain an arrangement of blood vessels specially
designed for temperature regulation. Dense networks of
arteries and veins under the skin are linked to allow
blood to flow directly from one to the other so it can
act as a heating or cooling agent.
When the body's internal
temperature drops, its automatic response is to shut down
the blood flow through these heat exchange blood vessels
to prevent more heat from escaping. While this may help a
person to survive in some conditions, it also makes
efforts to speed the warming process slower and more
difficult. The Thermo-STAT reverses this shutdown, called
vasoconstriction, by slightly reducing the air pressure
within the sleeve. The reduced pressure causes the
vessels to open and blood to flow normally.
"This gives us the
equivalent of an open heat-pipe that leads directly to
the body's interior," says Grahn, who invented the
device and serves as a consultant to Aquarius.
The clinical trial
reported in the current paper involved 16 hypothermic
patients. Ten were equipped with the Thermo-STAT. Two
were equipped with the device operating at ambient air
pressure. The remaining four were treated using standard
techniques: Two were wrapped in warm blankets and two had
warm air blown around them. While the standard methods
warmed the patients at a rate of about 1.4 degrees
Celsius per hour, the new rewarming method, using reduced
pressure, produced a rewarming rate of 14 degrees per
hour, a ten-fold increase.
"When we started
these tests, we expected to get maybe double the rate of
rewarming," said Watenpaugh, who worked with Grahn
in the early stages of the concept's development. "A
ten-fold increase is really exciting."
Grahn's concern about the
problem of hypothermia in surgery patients provided the
impetus for inventing the rewarmer. Now that it has been
developed, it has a number of other potential
applications.
One obvious extension is
using it to treat people who suffer from severe
hypothermia due to winter exposure. Hundreds of thousands
of people suffer from hypothermia annually in the United
States. The Thermo-STAT is compact, weighing only three
to four pounds, and can run on a battery, so it is well
suited for use by search-and-rescue teams and paramedics.
In the longer term, Grahn
and his colleagues intend to explore the device's ability
to manipulate body core temperatures and how this ability
can be used to treat other diseases:
- Inducing local
hypothermia may be useful in treating chronic
disorders such as cystic fibrosis. Cystic
fibrosis is caused by a mutation of a protein
found in the lungs that prevents the protein from
being processed to maturity. Tissue culture
studies indicate that the mutated protein
functions normally at decreased temperatures. So
it may be possible to treat cystic fibrosis by
periodically lowering a patient's core body
temperature.
- Much of the brain
damage caused by a stroke occurs after the
initial event. According to animal studies and
limited clinical reports, small decreases in
brain temperatures can protect the nerves from
much of this damage. It may be possible to use
the Thermo-STAT in a cooling mode, along with
muscle relaxants, to decrease brain temperature
rapidly enough to reduce stroke damage.
- Hyperthermia, an
elevated core body temperature, could be useful
in the treatment of cancer. Studies are currently
under way to see if local, regional or whole body
hyperthermia induced with both external and
internal heating devices can help shrink
tumors. Current heating methods are both
uncomfortable and carry considerable risk.
Adapting the Thermo-STAT could deliver the
required heating with less risk to the patient.
Studying the effects of
altering core body temperature is a "hot"
research area right now, Grahn says. So, researchers are
likely to come up with other applications for devices of
this sort. SR
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