Preventing Severe Brain Injuries By Cooling The Body

4.5

A review published in this week’s The Lancet claims
that induced hypothermia is underused in the UK and in the USA. This
practice of deliberately cooling the body is capable of preventing or
limiting permanent injuries if it is employed within the first couple
hours of a clinical event.

Dr Kees Polderman (University Medical Center Utrecht, Netherlands)
first cites evidence that has demonstrated improved outcomes after
ischemic injury (reduction in blood supply) when body temperature is
reduced from 37ºC to between 32- 35ºC – a level of mild hypothermia.
Though positive effects have been shown most clearly for brain
injuries, it is probable that body temperature reduction can positively
benefit injuries to the heart and kidneys, among other organs. The
practice has already been used to treat heart attack and stroke.

“Hypothermia is a highly promising treatment in neurocritical care;
thus, physicians caring for patients with neurological injuries, both
in and outside the intensive care unit, are likely to be confronted
with questions about temperature management more frequently,” says
Polderman.

There are three phases in the process of lowering body temperature.
Induction first cools the body to a specified temperature – usually
through the highly effective and safe method of cold fluid (4ºC)
infusion. The second phase involves maintenance, which can be
for several days if the hypothermia is induced to treat traumatic brain
injuries. The third phase, rewarming, must be slow and
controlled. The rates are usually about 0.2 to 0.5ºC per hour
in cardiac arrest patients and even slower in patients with traumatic
brain injury. Studies on animals have demonstrated that rapid rewarming
leads to adverse outcomes whereas slow rewarming maintains the benefits
of the temperature reduction.

The review discusses several physiological reasons for lower body
temperature’s injury protection capabilities. Since lower temperatures
reduce the permeability of the blood brain barrier (the membrane that
protects the brain from chemicals in the blood), brain injury
patients can limit damage from trauma or blood vessel blockage. Induced
hypothermia can also limit the rate of formation of small blood clots,
or thrombi, which can occur after brain injuries. Additionally, the
immune response is depressed by lower body
temperatures, preventing inflammatory reactions that could
harm the brain or other organs after injury. Fever prevention is also
seen as a practical use, as fever development can further harm patients
with brain injuries.

“Use of mild hypothermia seems to be a major breakthrough in the
treatment of neurological injuries… Studies that establish optimum
depth and duration of cooling are also needed. Increasing evidence
suggests that fever is harmful to the injured brain, and it seems
reasonable to maintain normothermia in most patients with neurological
injuries who have decreased consciousness – especially in those
previously treated with hypothermia – for at least 72 hours after injury.
Hypothermia remains widely underused in many countries, especially in
the USA and, to a lesser extent, the UK and Germany; therefore,
applying the existing evidence and working on implementation strategies
should be a priority,” concludes Polderman.

Induced hypothermia and fever control for prevention and
treatment of neurological injuries

K H Polderman
The Lancet (2008). 371[9628]:
p 1955.
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