DISORDERS CAUSED BY HEAT Dr Majid Golabadi Occupational Medicine specialist

MEDICAL DISORDERS COUSED BY EXCESSIVE EXPOSURE TO HOT ENVIRONMENTS heat stroke, heat exhaustion, heat cramps, heat syncope, skin disorders

T HE TRANSFER OF HEAT BETWEEN SKIN AND ENVIRONMENT Convection Conduction Radiation Evaporation

ACCLIMATIZATION The scheduled and regulated exposure to heated environments of increasing intensity and duration allows the body to adjust to heat Beginning to sweat at lower body temperatures, Increasing the quantity of sweat produced, Reducing the salt content of sweat, Increasing the plasma volume, cardiac output, and stroke volume while the heart rate decreases.

H EAT S TROKE Life-threatening medical emergency Thermal regulatory failure Cerebral dysfunction with altered mental status Core (rectal) temperature approaches 4l.l°C (106°F) Hyperventilation, respiratory alkalosis and compensatory metabolic acidosis Abnormal bleeding, renal failure, or arrhythmias

Heat CrampsHeat ExhaustionHeatstroke PathophysiologySalt deficiencyVolume/electrolyte depletionThermoregulatory failure Symptoms Painful muscle cramps/ spasm Weakness Nausea Vomiting Weakness Headache Syncope Nausea Vomiting Intense thirst (water depletion) Fatigue Muscle cramps (salt depletion) Malaise Irritability Confusion Prodromal heat exhaustion Collapse Severe/sustained physical exertion (exer­tional heat stroke) Psychotic behavior Objective findings Euthermia Core temperature < 38°C (100.4°F) Profuse sweating Orthostatic vital signs Tachycardia Hyperventilation Tetany Core temperature >40°C(104°F) Altered mental status—bizarre behavior Hot dry skin (classic heat stroke) Moist skin (exertional heat stroke) Coma Hypotension/shock Seizure Tachycardia Cyanosis Rales Laboratory Elevated creatine phospho-kinase (CPK), creatinuria Oliguria Hyperuricemia CPK elevation Dissemination intravascular coagulation Respiratory alkalosis Hypokalemia Thrombocytopenia Myoglobinuria Hypoglycemia Transaminase elevation

THRESHOLD LIMIT VALUES FOR EXPOSURE TO HEAT IN OCCUPATIONAL SETTINGS wet-bulb globe temperature (WBGT) Heat-index guidelines

I N OCCUPATIONS IN WHICH WORKERS ARE EXPOSED TO EXCESSIVE HEAT Medical evaluation to identify at risk individuals for heat disorders Training early signs and symptoms of heat disorders Advising of the importance of proper nutrition and fluid intake. Providing cool drinking water or electrolyte- carbohydrate solutions and shaded rest areas for workers

MANAGEMENT Monitoring for hypovolemic and cardiogenic shock, Maintaining a patent air­way, providing oxygen Correcting fluid and electrolyte imbalances, Supporting vital processes. If hypovolemic shock is suspected, mL of 5% dextrose in 1% or 0.5% normal saline solution may be given intravenously without overloading the circulation. Fluid output should be monitored Monitored for complications, including renal failure (caused by dehydration and rhabdomyolysis), hepatic failure, or cardiac failure, respiratory distress, hypotension, electrolyte imbalance (hypokalemia), and coagulopathy.

PROGNOSIS Elevated creatine phosphokinase (CPK) Elevated liver enzymes, Metabolic acidosis are predictors of multiorgan dysfunction

Because hypersensitivity to heat continues in some patients for prolonged periods following heat stroke, they should be advised to avoid reexposure to heat for at least 4 weeks.

H EAT E XHAUSTION Etiology: prolonged exposure to heat and insufficient salt and water intake can cause heat exhaustion, dehydration, and sodium depletion Symptoms and signs: weakness, nausea, fatigue, headache, con­fusion, a core (rectal) temperature exceeding 38°C (100.4°F), increased pulse rate, and moist skin, Hyperventilation and respiratory alkalosis

H EAT E XHAUSTION Treatment Placing the patient in a cool and shaded environment and providing hydration (1-2 L over 2-4 hours) and salt replenishment—orally if the patient is able to swallow. Physiologic saline or isotonic glucose solution should be administered intravenously in more severe cases. At least 24 hours' rest is recommended.

H EAT C RAMPS Etiology Result from dilutional hyponatremia caused by replacement of sweat losses with water alone Symptoms and signs: Slow and painful muscle contractions and severe muscle spasms that last from 1-3 minutes and involve the muscles employed in strenuous work. The temperature may be normal or slightly increased

H EAT C RAMPS Treatment The patient should be moved to a cool environment and given a balanced salt solution or an oral saline solution. Salt tablets are not recommended. Rest for 1-3 days with continued salt supplementation in the diet may be necessary before returning to work.

H EAT S YNCOPE Etiology In heat syncope, sudden unconsciousness results from volume depletion and cutaneous vasodilatation with consequent systemic and cerebral hypotension. Episodes occur commonly following strenuous work for at least 2 hours. Symptoms and signs: The skin is cool and moist and the pulse weak. Systolic blood pressure is usually under 100 mmHg

H EAT S YNCOPE Treatment Recumbency, cooling, and rehydration. Preexisting medical conditions should be monitored and treated if necessary

S KIN D ISORDERS C AUSED BY H EAT Miliaria (heat rash) is caused by sweat retention resulting from obstruction of the sweat gland duct. Erythema abigne ("from fire") is characterized by the appearance of hyperkeratotic nodules following direct contact with heat that is insufficient to cause a burn. Intertrigo results from excessive sweating and often is seen in obese individuals. Skin in the body folds (e.g., the groin and axillas) is erythematous and macerated Heat urticaria (cholinergic urticaria) can be localized or generalized and is characterized by the presence of wheals with surrounding erythema ("hives").