Heat-related illnesses can affect people of any age who are subjected to extreme heat and humidity regardless of physical fitness level or baseline health status. The most serious of the heat-related illnesses is heat stroke. Prompt identification, early initiation of cooling measures (including cold-water immersion [CWI]), and transport to a higher level of care, when appropriate, are imperative. This article reviews heat-related illness identification, as well as management strategies.
Heat-related illnesses: From the benign to the severe
Some of the less severe forms of heat-related illness include heat cramps (which are due to dehydration and salt loss), heat rash, and heat edema. Heat rash and heat edema are benign. Heat rash typically resolves with cooler clothing and a cooler environment. Heat edema tends to improve after sleeping in a cooler environment with legs elevated. Heat syncope is the result of decreased cerebral perfusion due to fluid loss and vasodilation that results in a distributive hypovolemia. It commonly occurs after vigorous exercise when the athlete is standing still.
Heat exhaustion requires a more careful clinical assessment. It is the inability to continue activity in the heat, often with weakness and collapse. Also due to salt and water losses, it results in cardiovascular output that is insufficient to meet the circulatory and metabolic demands of the body. The body temperature is often elevated but <40° C (104° F), vomiting can occur, and mild central nervous system (CNS) dysfunction may be present.
Heat stroke is the most severe form of heat-related illness and can be life-threatening.1
It is important to understand that these heat-related illnesses do not progress along a continuum. Patients develop heat stroke without having had milder forms of heat illness, and patients with a milder type of heat illness usually do not progress to heat stroke.
Heat stroke: Definition, types, risk factors
Heat stroke is defined as a core body temperature ≥40° C (104° F) with CNS dysfunction in the setting of environmental heat stress. The mortality rate can reach over 50%.2-6
There are 2 main types of heat stroke: exertional heat stroke and nonexertional (classic) heat stroke. Exertional heat stroke more commonly affects healthy, young people, such as athletes or military personnel. Classic (nonexertional) heat stroke patients are typically elderly and/or have a chronic illness, although occasionally it involves children who are unable to escape from a hot environment.5,7 While exertional heat stroke typically develops over a period of a few hours in participants of prolonged activities, such as marathons, classic heat stroke in the elderly typically develops over a period of days in the setting of high environmental temperatures. In both conditions, there is an inability to maintain a normal body temperature leading to CNS dysregulation with altered mental status and often multisystem organ dysfunction.7
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