injuries poisoning
Overview of Heat Illness
Prevention of Heat Illness
Physicians should recommend the following measures ( General reference ) to help prevent heat illness: During excessively hot weather, older adults and children should not remain in unventilated residences without air-conditioning. Children and older adults should not be left in automobiles in the hot sun. If possible, strenuous exertion in a very hot environment or an inadequately ventilated space should be avoided, and heavy, insulating clothing should not be worn. Weight loss after exercise or work can be used to monitor dehydration; people who lose 2 to 3% of their body weight should be reminded to drink extra fluids and should be within 1 kg of starting weight before the next day’s exposure. If people lose>4%, activity should be limited for 1 day. If exertion in the heat is unavoidable, fluid should be replaced by drinking frequently, and evaporation should be facilitated by wearing open-mesh clothing or by using fans. Maintaining adequate levels of fluid and sodium helps prevent heat illnesses. Thirst is a poor indicator of dehydration and the need for fluid replacement during exertion because thirst is not stimulated until plasma osmolality rises 1 to 2% above normal. Thus, fluids should be drunk every few hours regardless of thirst. Because maximum net water absorption in the gut is about 20 mL/minute (1200 mL/hour—lower than the maximum sweating rate of 2000 mL/hour), prolonged exertion that causes very high sweat loss requires rest periods that reduce sweating rate and allow time for rehydration. The best hydrating fluid to use depends on the expected loss of water and electrolytes, which depends on the duration and degree of exertion along with environmental factors and whether the person is acclimatized. For maximum fluid absorption, a carbohydrate-containing beverage can be absorbed by the body up to 30% faster than plain water. A beverage containing 6 or 7% carbohydrate concentration is absorbed most rapidly. Higher carbohydrate concentrations should be avoided because they can cause stomach cramps and delay absorption. However, for most situations and activities, plain water is adequate for hydration as long as overhydration is avoided. Significant Hyponatremia has occurred in endurance athletes who drink free water very frequently before, during, and after exercise without replacing sodium losses. Special hydrating solutions (eg, sports drinks) are not required, but their flavoring enhances consumption, and their modest salt content is helpful if fluid requirements are high. Laborers, soldiers, endurance athletes, or others who sweat heavily can lose≥20 g of sodium/day, making heat cramps more likely; such people need to replace the sodium loss with drink and food. In most situations, consuming generously salted foods is adequate; people on low-salt diets should increase salt intake. For more extreme circumstances (eg, prolonged exertion by unacclimatized people) an oral salt solution can be used. The ideal concentration is 0.1%sodium chloride, which can be prepared by dissolving a 1-g salt tablet or one quarter of a teaspoon of table salt in a liter (or quart) of water. People should drink this solution under moderate to extreme circumstances. Undissolved salt tablets should not be ingested. They irritate the stomach, can cause vomiting, and do not treat the underlying dehydration. For prevention of heat illnesses, oral salt solutions are reserved for prolonged exertion in laborers, soldiers, and endurance athletes with heavy sweating, and not recommended for those engaged in routine exercise. Successively and incrementally increasing the level and amount of work done in the heat eventually results in acclimatization, which enables people to work safely at temperatures that were previously intolerable or life threatening. To reach maximum benefit, acclimatization usually requires spending 8 to 11 days in the hot environment with some daily exercise (eg, 1 to 2 hours/day with intensity increased from day to day). Acclimatization markedly increases the amount of sweat (and hence cooling) produced at a given level of exertion and markedly decreases the electrolyte content of sweat and the risk of a heat illness. People who are not acclimatized are more likely to suffer from heat cramps or other heat illness during prolonged exertion and may need to increase their sodium intake. Unacclimatized people are more likely to suffer from heat cramps and heat illnesses during prolonged exertion and may need to increase their sodium intake. When possible, people should adjust their activity level based on the environment and any heat loss-impairing gear (eg, firefighting or chemical protective outfits) that must be worn. Work periods should shorten and rest periods increase when Temperature increases Humidity increases Workload is heavier Sun gets stronger There is no air movement When protective clothing or gear is worn The best indicator of environmental heat stress is the wet bulb globe temperature (WBGT), which is widely used by the military, industry, and sports. In addition to temperature, the WBGT reflects the effects of humidity, wind, and solar radiation. The WBGT can be used as a guide for recommended activity (see table Wet Bulb Globe Temperature and Recommended Activity Levels ). Although the WBGT is complex and may not be available, it can be estimated based on only temperature and relative humidity in sunny conditions and when the wind is light (see figure Wet bulb globe temperature based on temperature and relative humidity ). Values are derived from an approximate formula that depends on temperature and humidity and that is valid for full sunshine and a light wind. Heat stress may be overestimated in other conditions. 1.Lipman GS, Gaudio FG, Eifling KP, et al: Wilderness Medical Society clinical practice guidelines for the prevention and treatment of heat illness: 2019 Update.Wilderness Environ Med. 30(4S):S33-S46, 2019. doi: 10.1016/j.wem.2018.10.004 