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MEDICAL BIOLOGY: ON HYPOTHERMIA

The following points are made by S. Shapiro et al (MMWR 2004;53:172):

1) Hypothermia, a preventable lowering of the core body temperature to less than 95 deg F (less than 35 deg C), causes approximately 600 deaths each year in the US. Exposure to excessive cold (or excessive exposure to cold) slows enzymatic activity throughout the body, leading to potentially fatal rhabdomyolysis, coagulopathy, renal failure, and dysrhythmias. Alcohol intake, activity level, and type of clothing are among the modifiable factors associated with hypothermia.

2) Understanding the epidemiology and pathophysiology of hypothermia is important to preventing hypothermia-related mortality. This report describes three cases of fatal hypothermia that occurred during 2003 and reviews national statistics on mortality from cold exposure in 2001.

3) Case 1. In the fall of 2003, a man aged 44 years was found dead outdoors in Vermont. He wore a T-shirt, long-sleeved shirt, two sweatshirts, underpants, pants, socks, and boots. His clothes were wet, and an empty vodka bottle was nearby. Local investigators reported that he looked as though he "lay down and went to sleep." Overnight, the temperature had dropped to less than 32 deg F (less than 0 deg C). Autopsy findings were unremarkable except for a fatty liver. A toxicology screen was negative except for an elevated blood alcohol concentration (BAC) of 0.30 g/dL, nearly four times the legal intoxication limit of 0.08 g/dL in Vermont. Cause of death was certified as hypothermia, with alcohol intoxication as a contributing factor.

4) Case 2. In the spring of 2003, a man aged 76 years with Alzheimer's disease was reported missing from his home in Vermont. The next day, a farmer found the man lying in a swampy area where his car had become stuck in the mud. Overnight, the temperature had dropped to less than 32 deg F ( less than 0 deg C). The man was pronounced dead at the scene; cause of death was hypothermia precipitated by a cold, wet environment.

5) Case 3. In the fall of 2003, Alaska state troopers reported that a hiker aged 35 years was found dead alongside a highway. The hiker was not clothed from the waist up and was missing a shoe. The overnight temperature was 44 deg F (6.7 deg C), but conditions were wet and windy. The hiker's BAC was 0.28 g/dL, nearly four times the legal intoxication limit of 0.08 g/dL in Alaska; his toxicology screen was positive for cocaine and marijuana. Cause of death was hypothermia, with drug and alcohol intoxication as contributing factors.

6) In the US, certain populations (e.g., alcoholics; drug users; elderly, homeless, and chronically ill persons; and those with preexisting heart disease) are at increased risk for dying from hypothermia. During 2001, a total of 599 persons in the US died from "exposure to excessive natural cold", as categorized in the International Classification of Diseases, Tenth Revision. Of these victims, 67% were male, and 51% were aged more than 65 years. As persons age, their risk for dying from hypothermia increases. Approximately 71% of the hypothermia-related deaths in 2001 occurred during November-February. The three states with the highest rates of death from hypothermia were Montana (1.44 persons per 100,000 population), Alaska (1.42), and New Mexico (1.04).

Centers for Disease Control and Prevention http://www.cdc.gov

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Related Material:

HYPOTHERMIA AND TREATMENT AFTER CARDIAC ARREST

In general, "ischemia" is a sudden loss of blood supply to a tissue caused by blockage of a blood vessel or by cardiac arrest. The term "ischemia/reperfusion injury" refers to the damage that can occur to a tissue when it is reperfused after a prolonged period of ischemia. The phenomenon is of considerable clinical importance, especially in connection with heart attacks and strokes.

The following points are made by M. Holzer et al (New Engl. J. Med. 2002 346:549):

1) An estimated 375,000 people in Europe undergo sudden cardiac arrest each year, and recovery without residual neurologic damage after cardiac arrest with global cerebral ischemia is rare. After cardiac arrest with no blood flow for more than 5 minutes, the generation of free radicals, together with other mediators, during reperfusion creates chemical cascades that result in cerebral injury. Until recently there was no therapy with documented efficacy in preventing brain damage after cardiac arrest.

2) Several studies have demonstrated that in dogs moderate systemic hypothermia (30 degrees C.) or mild hypothermia (34 degrees C.) markedly mitigate brain damage after cardiac arrest. The exact mechanism for this cerebral resuscitative effect is not clear. A reduction in cerebral oxygen consumption and other multifactorial chemical and physical mechanisms during and after ischemia have been postulated. These mechanisms include retardation of destructive enzymatic reactions, suppression of free-radical reactions, protection of the fluidity of lipoprotein membranes, reduction of oxygen demand in low-flow regions, reduction of intracellular acidosis, and inhibition of the biosynthesis, release, and uptake of excitatory neurotransmitters.

3) The authors report a study comparing mild hypothermia with standard normothermia in human patients who had had cardiac arrest due to ventricular fibrillation. The authors report that in such patients who have been successfully resuscitated, therapeutic mild hypothermia increased the rate of favorable neurologic outcome and reduced mortality. The authors suggest that of the 30,000 cardiac arrest cases in Europe each year who would meet the inclusion criteria for this study, "we can be 95 percent confident that treatment with hypothermia would prevent an unfavorable neurologic outcome in 1200 to 7500 of these patients."

New Engl. J. Med. http://www.nejm.org

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