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Am Fam Physician. 2003;67(7):1439-1440

to the editor: Dr. Wexler's article, “Evaluation and Treatment of Heat-Related Illnesses,1” was a valuable review of the complex problem of heat-related illnesses. I would like to emphasize some additional points.

The thermoregulatory system operates around an apparent “set point” that is thermally determined by a dynamic balance between signals from two types of sensors at skin and body core. These sensors have opposite temperature-response characteristics. This concept provides a conceptual framework, which fits a variety of clinical situations.

Clinical syndromes vary from heat syncope, heat cramps, heat exhaustion, and heat stroke.23 Heat syncope occurs when a person experiences orthostatic dizziness or fainting following exposure to a high environmental temperature. Heat illness is precipitated by long hours of standing, postural changes, or physical activity in hot weather, leading to volume depletion and syncope.

Heat cramps usually occur when the person stops work and is relaxing. They differ from cramps experienced during physical exercise, which tend to last for short periods and resolve spontaneously, and from hyperventilation tetany, which may occur during heat exhaustion.

Heat stroke is a complex clinical disorder characterized by the triad of disturbance of the nervous system, generalized anhydrosis, and rectal temperature above 40.6°C (105.1°F).4

Since the temperature of all organs is elevated, the degree of insult to different organs and tissues is related to the absolute rise in core temperature, its duration, and associated metabolic acidosis and hypoxia. It is postulated that major contributors to morbidity and mortality vary with the level of core temperature. Below 40.0°C (104.0°F), the factors are changes in body fluids, electrolytes, and cardiovascular activity. At 40.0°C to 42.4°C (108.3°F), lipopolysaccharide toxicity and cardiovascular demands are incriminated. Above 42.4°C, thermal damage becomes critical, oxidative phosphorylation becomes uncoupled, and enzyme systems are affected. Eventually temperature mechanisms fail and hyperthermia accelerates, leading to dysfunction and organ system failure. Damage to the central nervous system is a hallmark of heat stroke.

Since heat stroke presents different clinical pictures (neurologic, cardiovascular, respiratory, hematologic, renal, and hepatic complications), physicians may fail to recognize and treat it promptly. Heat stroke should be considered if a patient presents with the triad of hyperpyrexia, altered mental status, and hot dry skin.

Various modalities for cooling the body have been used: ice-water immersion; evaporative cooling using large circulating fans and skin wetting; ice packs; peritoneal, rectal, or gastric lavage; alcohol sponge bath; and cardiopulmonary bypass. An alternative efficient method uses evaporative cooling from the warm skin.5

One article2 cites seven objections to ice-water immersion: (1) intense peripheral vasoconstriction shunting blood away from the skin and perhaps causing a paradoxic increase in core temperature; (2) inducing shivering may increase heat production significantly above basal level; (3) extreme discomfort to patients; (4) discomfort to medical attendants; (5) difficulty performing cardiopulmonary resuscitation; (6) difficulty monitoring vital signs; and (7) unpleasant and unhygienic conditions should vomiting or diarrhea occur.

We strongly advise against immersion in ice water or using ice packs especially when managing children. Other supportive measures should be applied jointly with evaporative cooling.

IN REPLY: Dr. Khogali emphasizes some very important points regarding the physiologic changes the body undergoes during heat-related illness that were not discussed in the article.1 I understand Dr. Khogali's concerns regarding cold-water immersion versus evaporative cooling techniques. The article acknowledges that some literature demonstrates the superiority of evaporative cooling techniques compared with cold-water immersion techniques. In fact, the evaporative cooling technique recommended in the article1 was Dr. Khogali's.

Heat stroke is a serious life-threatening emergency that needs prompt attention. Few institutions in the United States have the capability to provide the type of evaporative technique described by Dr. Khogali and used by those who deal with this problem with greater frequency based on their geographic location. The risks associated with ice water immersion are widely recognized; however, a system without other therapeutic options must take immediate action to reduce core temperature by any means possible, and ice water immersion is one such technique.

The most important thing for the patient is that immediate core body temperature reduction is achieved by whatever technique. If the options are ice water immersion or nothing, then ice water immersion should be utilized. If other techniques are available, then they may be utilized as dictated by the experience of the treating physician and the clinical circumstance.

I thank Dr. Khogali for emphasizing these important points, and his input is much appreciated.

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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