Theraputic Hypothermia

Hypothermia, defined as a core body temperature less than 95 oF(35oC) occurs

when heat loss exceeds the body's heat production. (Ruffolo p.47) Thermal stability in

humans depends on the body's 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