Essay About Various Studies And Heat Loss

Theraputic Hypothermia
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Hypothermia, defined as a core body temperature less than 95 oF(35oC) occurs
when heat loss exceeds the bodys heat production. (Ruffolo p.47) Thermal stability in
humans depends on the bodys ability to adapt to changes in internal and external
temperatures. Heat is transferred throughout tissues and fat, and is released at a rate
directly related to the temperature of the environment through radiation, conduction,
convection, and evaporation.
Hypothermia is typically seen as a bad thing; however, various studies have been
proving it to be very useful. Traumatic brain injury initiates several metabolic processes
that can exacerbate the injury. There is evidence that hypothermia may limit some of these
deleterious metabolic responses. In a randomized controlled trial researchers compared
the effect of moderate hypothermia and normhypothermia in 82 patients with severe
closed head injuries (score of 3 to 7 on the Glasgow Coma Scale) The patients assigned to
hypothermia were cooled to 33 degrees C an average of 10 hours after injury, kept at 32
degrees to 33 degrees C for 24 hours, and then re-warmed. A specialist in physical
medicine and rehabilitation who was unaware of the treatment assignments evaluated the
patients 3, 6, and 12 months later with the use of the Glasgow Outcome Scale. The
demographic characteristics, causes, and severity of injury were similar in the hypothermia
group and the normothermia groups. At 12 months 62% of the patients in the
hypothermia group and 38% in the normothermia had good outcomes (moderate, mild, or
no disabilities). The researchers concluded that “Treatment with moderate hypothermia for
24hours in patients with severe traumatic brain injury and coma scores of 5 to 7 hastened
neurological recovery and may have improved the outcome. (Marion et all)
Two studies done (one in Australia and the other in Europe) showed the
therapeutic value in survivors cardiac arrest. In the Australian study, which involved 77
patients who remained comatose after the restoration of spontaneous circulation, 49% of
those treated with hypothermia were discharged home or into a rehabilitation facility
compared to the 26% of those not treated with hypothermia. There were no significant
differences between the 2 groups with respect to the frequency of adverse events. The
out come of the European study, which involved 9 center in 5 countries and had a larger
number of patients, were similar. Taken together, the findings in these trials are important,
because in the United States so far, permanent brain damage after cardiopulmonary-
cerebral resuscitation causes many delayed deaths and is seen in about 10to 30 percent of
survivors of out-of hospital cardiac arrest. The fact that 2 studies yielded similar results
makes the important conclusions even more compelling. The rationale for the use of
therapeutic hypothermia is complex. Spontaneous uncontrolled hypothermia start with
potential deleterious shivering, thermo genesis , catecholamine release, and
vasoconstriction, there as controlled hypothermia is potentially beneficial. Therapeutic
hypothermia after cardiac arrest, as used in the 2 stories above, is directed at mitigating
neurological injury. Temperature levels are important; mild hypothermia (33oC to 36oC)
may be most effective, and is simple and safe. Moderate hypothermia (28oC to 32oC) can
cause arrhythmias or even ventricular fibrillation and if prolonged, can lead to
coagulopathy and infection. The timing and duration are important; mild hypothermia
should be initiated as soon as possible after resuscitation, but even when delayed for a few
hours, mild hypothermia has been shown to have some benefits un animal models of
cardiac arrest. Mild hypothermia induced in patients for 12 hours, as in the Australian
study, or 24 hours as in the European study, does not appear to have the putative
complications of moderate hypothermia.(Safar, p.612)
In another study, involving 275 patients(137- hypothermia and 138
normothermia), there was a similar outcome once again in favor of hypothermia. 55% of
the patients in the hypothermia group had favorable neurological outcomes compared to
the 39% in the normothermia group. (Holzer p.552) The hypothermia patients in this
study all received standard intensive care, as did the normothermia group. The
hypothermia