Heat related illness is the result of disordered physiology that is a byproduct of thermoregulation. Not all disorders are due to accumulation of body heat; some may be caused by indirect physiologic failures such as salt and water imbalance or circulatory collapse. To attempt to classify these as specific syndromes serves no real purpose, for the basic physiologic mechanisms must be given primary attention. However, heat stroke is one disorder that must be treated as a disease entity resulting from collapse of the temperature regulatory mechanism.
Heat stroke
Heat stroke is an acute and dangerous form of heat disorder. It is characterized by high body temperature of at least 40.6° C., convulsions or coma, and cessation of sweating. These are the result of positive heat storage.
In most cases the onset of symptoms is with sudden delirium or coma. Headache, numbness and tingling, dizziness, restlessness, or mental confusion may be experienced for varying lengths of time before collapse. Cessation of sweating may also be noted as a prodromal symptom.
Most patients are in coma, but the central nervous system features may range from disorientation to involuntary limb motions or coarse tremors. The respiratory rate may be at least double normal, and can lead to respiratory alkalosis and tetany. The pulse rate may be as high as 150, and usually there is an elevated blood pressure. Shock commonly follows. The hallmarks of heat stroke are anhidrosis, hyperpyrexia, and coma.
The treatment of heat stroke must include supportive management as well as establishment of negative heat balance. Speed is essential in lowering body temperature to avoid brain damage. A cold water bath or spray is the most effective and rapid method for body cooling. Wet sheets may be wrapped around the body and evaporative cooling accelerated with fans. Rapid cooling of the skin results in peripheral vasoconstriction and stagnation, which must be corrected by vigorous massage of the extremities. Rest and sedation are useful in reducing metabolic heat production.
Untreated heat stroke is fatal. In about one-third of the uncomplicated treated cases the patients may die, but there seems to be some correlation between the prognosis and the height of fever, as well as its length. Treatment Should be aimed at reducing the temperature to 40° C. within one hour. The temperature will continue to fall after cessation of cooling, but a secondary rise to 40° C. may occur within the first day, and must be corrected with cooling techniques.
As much as a week may be necessary for stabilization of the body temperature and return of sweating. When treatment has been delayed for more than four hours or has not been immediately effective, there may be shock or residual damage such as pulmonary edema, cerebral ataxia, hepatic or renal failure, or myocardial damage.
The prevention of heat stroke is approached through identifying the environments in which the disorder has occurred or is expected to occur, adapting human activity to limits Of safety within the environment, and taking advantage of the acclimatization capability of man.
Circulatory failure may occur in the presence of successful thermoregulation. The cardiovascular system may have accomplished its important function of transferring heat from the core to the periphery, but the blood is a dual-purpose fluid, since it must also transport metabolites for working tissues. When man works at high temperature, the working muscles place greater demands on the circulation, and less blood is available for cooling the body through heat dissipation at the skin. As perspiration becomes profuse, as much as 3 or 4 liters per hour, dehydration develops and further embarrasses the circulation through reduction in blood volume and increase in blood viscosity.
Heat Syncope.
Heat syncope is a disorder ranging in severity from simple light-headedness to severe fatigue and loss of consciousness. Hypotension with some degree of cerebral anoxic results from peripheral venous pooling. Vasomotor tone is decreased, as evidenced by a fall in both systolic and diastolic pressures, but the diastolic falls less so that the pulse pressure is decreased. The pulse rate is increased slightly. Sweating is visible, and the temperature may be elevated to about 39° C., especially if the episode is induced by exercise. Pallor is marked, and the muscles are flaccid. The patient should be removed from the heat and allowed to rest in a recumbent position. Recovery should occur in a few minutes, but if the patient remains in hot surroundings, more than an hour may be necessary for a return to a sense of well-being. The episode is self-limiting.
Heat Exhaustion.
A more serious circulatory disorder is a form of heat exhaustion, which is associated with a depletion of both salt and water. The concentration of body fluids is not altered remarkably, but a decrease in blood volume accounts for the manifestations, which develop insidiously over several days.
You Must Know About Heat Related illness Symptoms
Early symptoms include headache, fatigue, confusion, and drowsiness. Anorexia, visual disturbances, and vomiting follow and, if persistent, lead to circulatory collapse. However, the patient is usually incapacitated in the early stages of the illness, so that treatment is begun early; hence, the illness is rarely fatal. The picture is one of peripheral vascular collapse with pallor, profuse sweating, decrease in blood pressure, and little, if any, elevation of temperature.
Treatment includes removal of the patient to cool surroundings, rest in bed, and replacement of salt and water. Drinking of isotopic saline is useful, but a patient can seldom take more than 20 grams of salt per day orally. At least that amount of salt should be given for several days until the urine chloride content reaches 3 or more grams per liter. Intravenous isotonic saline is necessary when there is coma or severe vomiting.
Heat Cramps.
Heat cramps are the result of electrolyte imbalance alone. This disorder occurs in persons working at high temperature and drinking large quantities of water. The basic pathophysiologic change is a dilution of body fluids, which is really a form of water intoxication. Body fluid volume is relatively well maintained. Without any prodromal, the voluntary muscles begin fibrillar twitching and then proceed to spasm, which may be very painful. The abdominal wall and extremities are most often involved.
The episode usually occurs late in a workday and is accepted by some workers as a non serious occupational hazard. Since the cramps are corrected promptly by salt replacement, workers rarely seek medical care.
Diagnosis is based on a history of an abundant intake of water during sweat- producing work at high temperature followed by characteristic muscle cramps.
Temperature is normal and cardiovascular function is unimpaired. Severe cases may require intravenous isotonic saline. Salted foods or fluids are usually adequate. Prevention is dependent upon a sufficient intake of salt, usually about 3 grams extra per day. This requirement can be met for most persons by the liberal use of the salt shaker at mealtimes. Limitation of water intake during work in hot surroundings will prevent cramps, but may result in the more serious consequences of thermoregulate failure.
