Heat Stroke vs Heat Exhaustion
What is Heat Stroke?
Heat stroke is a form of heat illness also known as classic Non Exertional Heatstroke (NEHS). It commonly occurs in infants, elderly people and chronically ill individuals. It is characterized by elevated body temperature above 41o °C, lack of sweating and altered sensory perceptions. A core temperature above 41o °C is considered diagnostic of heatstroke although heatstroke can occur at lower body temperatures. In addition to this classic triad, various neurological features such as irritability, irrational behavior, hallucinations, delusions, cranial nerve palsies, and cerebellar dysfunction are associated with heatstroke. Heatstroke commonly occurs after sustained episodes of elevated ambient temperature. Individuals who cannot control the heat balance such as individuals with low cardiac reserve capacity (Elderly, post ischemic heart disease, heart failure, congenital cardiac abnormalities) poor control of water intake and loss (infants, patients having skin diseases, diabetes mellitus) are susceptible to have a heatstroke. Muscle degeneration (rhabdomyolysis) resulting in hyperkalemia, hypocalcemia and hyperphosphatemia, acute liver damage resulting in clotting disorders and hypoglycemia, acute renal failure and pulmonary edema. Clinical conditions such as thyrotoxicosis, sepsis, convulsions, tetanus and drugs such as sympathomimetics cause an elevated heat production. Burns, skin diseases and drugs like barbiturates, neuroleptics, antihistamines cause a reduced heat loss. Lack of behavioral responses like switching on a fan, drinking a cold drink which would help the thermoregulation also affects the heat balance. Either a pathological rise in heat production or a reduction of heat loss can result in elevated core body temperature. As the regulatory mechanisms are impaired the recovery phase is inefficient. Therefore, heatstroke is considered a medical emergency.
What is Heat Exhaustion?
Heat exhaustion is a form of heat illness also known as Exertional Heatstroke. It commonly occurs in individuals who engage in vigorous physical exercise in a humid and hot environment. The classic symptoms are elevated core body temperature above 41o °C, excessive sweating and altered sensory perception. Non specific symptoms such as headache, dizziness, weakness, abdominal pain, muscle cramps, nausea, vomiting and diarrhea can occur with heat exhaustion. Sometime there can be blackout and loss of consciousness preceding heat exhaustion. Patients presenting with heat exhaustion are commonly healthy young adults such as athletes, military personnel. These individual’s ability to sweat is not affected; therefore, when they present to a doctor the core body temperature is commonly well below the diagnostic 41o °C. Because the heat loss mechanisms are intact, the rate of complications is less than in heatstroke. Poor physical fitness, obesity, fatigue and lack of sleep are a few of the identified risk factors for heatstroke. Heat production during strenuous exercise can be as high as ten times the basal metabolic rate. In heat exhaustion the production of heat overwhelms the heat loss mechanisms resulting in a net elevation of core body temperature. When the strenuous exercise is stopped, the heat is dissipated via the intact heat loss mechanisms and the individual recovers.
What is the difference between Heat Stroke and Heat Exhaustion?
Heat stroke and heat exhaustion are at the extreme end of the heat illness spectrum. While heat exhaustion occurs in the presence of intact regulatory mechanisms, heatstroke occurs due to altered regulatory mechanisms. While heat exhaustion is caused by vigorous exercise, heatstroke is caused by impaired heat regulation. In both situations rapid cooling, treatment of the cause and complications are essential.