Heat Illness At A Glance

Patients with heat exhaustion retain the ability to dissipate heat and have a normal CNS function. With heat stroke, refuse compensation mechanisms for heat dissipation (although sweating may still be present) and the central nervous system function is impaired. Heat stroke should be considered in patients with hyperthermia and clouding of consciousness or other central nervous system dysfunction into account, regardless of sweating.

For heat illness include a number of disorders ranging in severity from muscle cramps to heat exhaustion to heat stroke (which is a life-threatening emergency is). The heat disease, although preventable, affects thousands of people each year in the US and can be fatal; it is the second leading cause of death in young athletes. If heat stroke is not treated quickly and effectively, the mortality reaches 80%. Patients with heat exhaustion retain the ability to dissipate heat and have a normal CNS function. With heat stroke, refuse compensation mechanisms for heat dissipation (although sweating may still be present) and the central nervous system function is impaired. Heat stroke should be considered in patients with hyperthermia and clouding of consciousness or other central nervous system dysfunction into account, regardless of sweating. Pathophysiology action of heat comes from the environment metabolism heat is dissipated through the skin via the following mechanisms. Radiation: The immediate transfer of body heat to a cooler environment by means of infrared radiation, a process that no air motion or direct contact is required evaporation: cooling (by water evaporation z B . welding) convection: transferring heat to cooler air (or liquid) on exposed skin is conduction: transferring heat from a warmer surface to a cooler surface which is in direct contact with the participation of each of these mechanisms varies with the ambient temperature and humidity. When the ambient temperature is lower than the body temperature, radiation provides 65% of the cooling. Evaporation typically provides 30% of the cooling and exhalation of steam and production of urine and feces make up about 5% ready. If the ambient temperature> 35 ° C, making evaporation almost all the heat dissipation, since the other mechanisms only work if the ambient temperature is lower than body temperature. However, the effect of sweating is limited. Sweat, the drips from the skin, not evaporated and does not contribute to cooling. The efficacy of sweating is also limited from the body surface and moisture. If the humidity> 75%, the evaporative cooling decreases significantly. So if both ambient temperature and humidity are high and go all the mechanisms lost for heat removal and there is a clearly growing risk for heat illness. The body can compensate for large differences in heat stress, but a significant or prolonged heat exposure, which expands the capacity for heat dissipation, increases the body’s core temperature. Moderate, transient increases in the core body temperature can be tolerated, but large increases lead (typically increases to> 41 ° C) protein denaturation and, v. a. in hard work in the heat, the release of inflammatory cytokines (e.g., tumor necrosis factor ? example, IL-1?). As a consequence it comes to cellular dysfunction and activation of an inflammatory cascade; it leads to dysfunction of most organs and activating the coagulation cascade. These pathophysiological processes are similar to the multiple organ failure (multiple organ failure (multiple organ dysfunction syndrome, MODS)) that follows an elongated shock. Compensation mechanisms include an acute phase response by other cytokines (e.g. inhibits., By stimulation of the synthesis of proteins, which reduces the production of free radicals and the release of proteolytic enzymes) moderate the inflammatory response. Likewise, an increased core body temperature triggers the expression of heat shock proteins. These proteins increase temporarily the heat tolerance by little explored mechanisms (eg. as possibly by preventing protein denaturation) and the regulation of cardiovascular reactions. On prolonged or extreme increase in the temperature, the compensation mechanisms are overloaded or malfunctioning; this favors the development of inflammation and multiple organ failure. The heat output is modulated by changes in cutaneous blood flow and in the sweat production. The cutaneous blood flow is at 200-250 ml / min at normal temperatures, but increases with heat stress up to 7 or 8 l / min (and facilitates the heat loss due to convective, conductive, radiating and evaporative mechanisms) which requires a significant increase in cardiac output. Heat stress also increases the production of sweat from negligible up to> 2 l / h, although the sweat that drips from the skin, does not contribute to cooling, however, it contributes to dehydration. Significant sweating may be less evident in an extremely hot, dry air quickly evaporates in the sweat, occur. At a welding production of> 2 l / h, a dehydration can develop very quickly. As the sweat contains electrolytes, the electrolyte loss can be significant. However, a prolonged exposure triggers physiological changes from that used to the body at the heat load (acclimatization); z. For example, the sodium concentration is 40- 100 mEq / l at nichtakklimatisierten people sweat, but decreases with acclimated persons 10-70 mEq / l. Etiology heat diseases are caused by a combination of increased heat and vermindeter heat causes Common factors that contribute to heat illness. Excessive heat usually results from excessive exertion, high ambient temperatures or both. Medical conditions and the use of stimulants increase the generation of heat. A limited cooling effect may be due to obesity, high humidity, high temperatures in the area or warm clothing and of all that affects sweating or evaporation of sweat. Clinical effects of heat illness are amplified by the following conditions: inability to tolerate increased cardiovascular demands (for example, due to aging, heart failure, chronic kidney disease, respiratory disease, liver failure.). Dehydration electrolyte imbalance taking certain medications (Common factors that contribute to heat illness) the elderly and the very young are also at increased risk. Ätere people have a high risk because they often use medications that can increase the risk, have higher rates of dehydration and heart failure, and have an age-related loss of heat shock proteins. Children have a high risk due to their greater surface area to body mass ratio (resulting in a larger heat gain from the environment on a hot day) and slower sweat production. Children are slow to acclimatize and respond less thirst. Both the elderly and infants can be relatively immobile and therefore find it difficult to leave a hot environment. Common factors that contribute to heat illness condition Examples Excessive heat exposure Certain diseases hyperthyroidism infections Malignant hyperthermia Neuroleptic malignant syndrome severity Salicylatvergiftungen seizures Serotonin syndrome High ambient temperature – Physical exertion training Physical work Stimulants amphetamines (stimulants) cocaine Methylendioxymethamphetamine (MDMA or Ecstasy) monoamine oxidase inhibitors Phencyclidine (PCP) discontinuation of certain medications alcohol opioids Limited cooling Warm clothing protective clothing for workers and athletes (eg. B. upholstered in football) High humidity – obesity and / or low cardiovascular fitness – High ambient temperature – Impaired sweating * Skin burn scars, extensive Extensive eczema heat rash Severe Psoriasis Systemic sclerosis On ticholinergika antihistamines antiparkinsonian drug atropine Scopolamine phenothiazines Cystic Fibrosis – * Impaired sweating is a cause of the limited cooling. Prevention Common sense is the best prevention. Doctors should recommend the following measures: excessively hot weather, older and young people should not stop in unventilated homes without air conditioning. Children should not be left in vehicles that are in the sun. If possible, strenuous exercises in a very hot environment or in poorly ventilated spaces should be avoided, and it should not thick, insulating gear. The weight loss after exercise or work can be used to monitor the dehydration; People who lose 2-3% of their body weight should be reminded to take extra fluids, and their weight should be different from exposure the next day not more than 1 kg of initial weight. When a person loses> 4% (by weight), the activity should be limited to one day. If an effort in the heat can not be avoided, the liquid should (often lost imperceptibly in very hot and dry air) replaced by frequent drinking and evaporation should be facilitated by wearing wide-meshed clothes or by the use of subjects. Sufficient hydration fluid and Na can prevent heat illness. Thirst is a poor indicator of dehydration and the need for fluid replacement during exercise because thirst is not stimulated until the plasma osmolality to 1 to 2% above normal increases. Liquid to be drunk – so should every few hours – regardless of thirst. Since the maximum net water absorption in the intestine is about 20 ml / min (1200 ml / h lower than the maximum sweat rate of 2000 ml / h), requires a prolonged effort, which causes very high sweat loss, rest periods, reduce the sweat rate and time allow rehydration. Which hydration is best to use depends water and electrolyte loss from the expected, which in turn depends on the duration and degree of effort along with environmental factors, and whether the person is acclimatized. For maximum liquid receiving a carbohydrate-containing beverage can be absorbed by the body up to 30% faster than pure water. A beverage having a carbohydrate concentration of 6 or 7% can be determined quickly absorbed. Higher carbohydrate concentrations should be avoided because they cause stomach cramps and delay absorption. However, water alone is sufficient as hydration for most situations and activities, as long as fluid overload is avoided. Significant hyponatremia (hyponatremia) is in endurance athletes who drink free water, very often before, during and after training occurred without replacing sodium losses. Special Hydratisierungslösungen (z. B. sports drinks) are not required, but their taste increases consumption, and its moderate salinity is helpful if the fluid requirement is high. Workers, soldiers, endurance athletes or other people who sweat a strong, able ? 20 g losing day, which increases the likelihood of heat cramps Na /; Such people need to replace the sodium loss with drinks and food. In most situations, it is to consume sufficient generously salted foods; People who follow a diet with low salt content should increase the salt intake. In extreme circumstances (eg. As prolonged exposure in non-acclimatized persons) can be used oral saline. The ideal concentration is 0.1% NaCl, the sodium chloride by dissolving a 1 g tablet or salt of a teaspoon quarter in one liter (or quart) of water can be produced. This solution should be drunk under moderate to extreme circumstances. Unresolved salt tablets should not be included. They irritate the stomach, can cause vomiting and do not treat the underlying drainage. Tips and risks Salt tablets should not be swallowed because they cause stomach irritation. Instead, they are dissolved in water to be drunk. Acclimatization if the severity and duration gradually increases the work done in the heat of work, finally enters a recovery time, enabling the people of the ability to operate safely at temperatures that would previously have been intolerable or life-threatening. To achieve the maximum benefit, a recovery time usually requires a stay 8-11 days in hot environments with some training every day (for example 1 to 2 hours / day from day to day increased intensity). The acclimatization increases the amount of sweat (and hence the cooling) at a given effort significantly and reduces the electrolyte content of perspiration. Acclimation reduces the risk of heat illness nachhaltig.Mäßigung level of activity if possible, people should adjust their level of exercise, based on the environment and accessories that affect heat loss (z. B. firefighting or chemical protective clothing) and must be worn. Working hours should be shortened and rest periods increased when the temperature rises, the humidity increases the workload heavier the sun gets stronger There is no air movement protective clothing or equipment worn are the best indicator of environmental heat stress is the “wet bulb globe temperature” (WBGT), the is commonly used by military, industry and sports. In addition to the temperature of the WBGT index reflects the effects of humidity, wind and solar radiation. The WBGT can be used as a guide to recommended activity ( “Wet Bulb Globe Temperature” and recommended activity levels). Although the WBGT is complex and may not be available, it can be solely on temperature and relative humidity, estimated based under sunny conditions and when the wind is light (see table: “Wet bulb globe temperature” based on temperature and relative humidity. ). “Wet bulb globe temperature” based on temperature and relative humidity. The values ??are derived from an approximate formula which depends on temperature and humidity, and which is valid for full sunshine and a light wind. Heat stress can be overestimated among other conditions. “Wet Bulb Globe Temperature” and recommended activity level Temperature ° C (° F) recommendations ?15,6 (?60) No Precautions> 15.6 to 21.1 (> 60-70) No precautions if adequate hydration is maintained > 21.1 to 23.9 (> 70-75) Not acclimatized: stop or limited activity acclimatized: activity with caution; Rest periods and water breaks every 20 to 30 minutes> 23.9 to 26.7 (> 75-80) Not acclimatized: Avoid Acclimatized hiking, sports and sunlight: Severe to moderate activity with caution permitted> 26.7 to 31.1 ( > 80-88) Not acclimatized: Avoid activity acclimatized: Limited short activity permitted only if fit ?31.1 (> 88) Avoid activities and sun exposure Important points When the ambient temperature of> 35 C, the cooling is largely based on evaporation, but when the humidity> 75%, the evaporation decreases significantly so that a high risk for heat illness is, when both the temperature and the humidity are high. Among the many risk factors for heat illness, certain medications and disorders (including those that disturb the electrolyte balance and reduce the cardiovascular reserves) and extreme old age. Prevention includes measures which commands common sense as well as maintenance and replacement of fluids and sodium. Acclimatization, which requires daily training for 8 to 11 days, reduces the risk of heat illness lasting. Activity levels should be limited with increasing temperature, humidity, solar radiation and the amount of clothing or equipment, and if the air movement is reduced.

Health Life Media Team

Leave a Reply