By Jessica Duke, MD
Humans require a narrow range of body temperature to function properly. To maintain a normal body temperature (36.5-37.5°C or 97.7-99.5°F), there must be a balance between the heat produced by the body and the heat gained or lost to the environment. When the body gains or produces more heat than is lost, body temperature rises and heat illnesses occur.
Although there are a variety of heat illnesses, the most important distinction is between heat stroke and all the other less severe forms of heat illness. Heat stroke is a severe, life-threatening emergency that requires immediate, rapid cooling and evacuation. On the other hand, heat cramps, edema, syncope, and exhaustion are not immediately life threatening and usually improve with rest and rehydration.
Heat cramps are painful, involuntary muscle contractions that occur during or after exercise in hot conditions. The exact cause of these cramps is unclear, but victims typically have muscle fatigue combined with significant salt and water losses that are replaced with non-electrolyte containing solutions, such as water. Heat cramps often resolve with gentle stretching and oral electrolyte replacement with either a sports drink or simply by adding ¼-½ teaspoon of table salt to 1 liter of water. If heat cramps do not respond to these treatments, the patient may require intravenous fluids and should be evacuated.
Heat edema is swelling in the extremities, usually the feet and ankles, as a result of increased pressure, leaky blood vessels, and vasodilation in hot conditions. It is a benign, self-limiting condition that is reversed by extremity elevation or wearing of compression stockings.
Heat syncope is fainting that occurs when the body, in an effort to cool itself, dilates blood vessels to such an extent that blood flow to the brain is reduced. Before fainting, patients may experience lightheadedness, vertigo, tunnel vision, and nausea. The first steps in managing heat syncope are to consider other medical causes of syncope and to evaluate the patient for trauma from the fall. If the patient is determined to have fainted from the heat and does not have any significant trauma, then treatment consists of rest in a cool environment along with water and electrolyte replacement.
Heat exhaustion is a combination of significant dehydration and rise in body temperature as a result from strenuous exercise in hot conditions. Victims may present with weakness, fatigue, headache, lightheadedness or dizziness, thirst, nausea, and vomiting. In mild cases, treatment consists of rest in a cool environment along with oral water and electrolyte replacement. More severe exhaustion may require active cooling, intravenous fluids, and should be evacuated.
Heat stroke is a severe heat-related illness characterized by a core temperature >40°C or 104°F and central nervous system abnormalities, such as altered mental status, ataxia, seizure, or coma as a result of either exposure to environmental heat alone (classic heat stroke) or strenuous exercise in hot conditions (exertional heat stroke). Patients with heat stroke require immediate cooling, intravenous fluids, and evacuation. If available and safe to do so, the patient should be immersed in cold water. Special care must be taken to protect the patient’s airway and to prevent the patient from becoming hypothermic. If immersion is unavailable or unsafe, evaporative cooling measures should be initiated by removing the victim’s clothing then dousing them in cool water and fanning them.
To prevent these heat-related illnesses from happening to you in the wilderness, consider the following tips:
- Acclimatize. Prepare yourself for exercise in hot, humid conditions and do not overexert yourself until you have had 10-14 days to acclimatize to a hot environment.
- Know the diseases and drugs that may contribute to heat-related illness. These include alcohol, antihistamines, laxatives, blood pressure medications, burns, and certain heart conditions.
- Avoid strenuous activity during the hottest part of the day, usually between 10 AM and 4 PM.
- Wear the proper clothing. Full-brim hats minimize heat gain by providing shade and loose-fitting clothes maximize heat loss by allowing air circulation and evaporation to occur.
- Drink to thirst. It is important to stay hydrated, but do not force yourself to consume a certain volume of water as this may lead to other serious problems, such as hyponatremia.
- Consume salt-containing foods or add salt to water (¼-½ teaspoon of table salt to 1 liter of water) if exposed to hot conditions for more than a few hours, especially if you are only using water for hydration.
- Take shade breaks. Rest in the shade at regular intervals to allow yourself to cool down. Do not wait until you feel sick to take a break.
- Understand the warning signs and symptoms of heat illness so that you can recognize and treat them early on.