During summer, understanding the cause, effects, pathophysiology and differential diagnosis is essential in treating such life threatening emergencies. But before discussing the heat stroke directly, we should first understand the effects of heat over the body under the heading ‘HEAT SYNDROME’.
There are 4 types of clinical syndromes which are associated with high environmental temperature. These are:
- Heat cramps
- Heat exhaustion
- Exertional heat injury
- Heat stroke
Heat syndromes are prevalent especially during the first few days of a heat wave before effective acclimatization can occur. The basic mechanism of acclimatization phenomenon by which humans accommodate to an excessive temperature is unknown. Sweating is the most effective natural mean of combating the heat stress and can occur with little or no change in the core temperature of the body. As long as the sweating continues, humans can withstand remarkably high temperature provided an adequate sodium chloride and water are replaced.
Dilatation of the peripheral blood vessels in an attempt to dissipate heat is another major way for the body to acclimatize to high temperature. Other alterations include a decrease in the total circulating blood volume, decrease in the renal blood flow, increase in anti-diuretic hormone (ADH) and aldosterone, decrease in urine sodium and increase in respiratory and pulse rate. Normally, acclimatization takes from 4 to 7 days.
Heat cramps are the most benign heat syndrome seen in athletes and are characterized by a brief, intermittent and often an excruciating cramping pain. The external temperature does not usually exceed the body temperature and a direct exposure to sun is not necessary. Heat cramps may even be precipitated by strenuous exercise in the cold environments in untrained and heavily clothed persons. Management consists of taking rest in a cool environment and replacement of sodium, potassium and fluid.
It is also known as heat prostration or heat collapse and is possibly the most common. It represents the failure of cardiovascular response to high temperature and is common in elderly who are receiving diuretics. Weakness, anxiety, fatigue, thirst, vertigo, headache, anorexia, nausea, vomiting, an urge for stool and faintness may precede the collapse. There may be hyperventilation, muscular in-coordination, agitation and impaired judgment. The onset is usually sudden and the duration of collapse is brief. Patient looks ashy gray, pupils dilated and skin is cold and clammy. The blood pressure may be low and pulse is high. Treatment consists of removing the patient to a cooler area and placing him or her in a recumbent position, spontaneous recovery is usual.
Exertional Heat Injury
This syndrome occurs in the individuals who are exerting themselves in a hot ambient temperature of more than 27 degree Celsius, when the relative humidity is high. It is common in the runners who enter races with insufficient acclimatization, inadequate conditioning or improper hydration.
In contrast to the classic heat stroke, individuals with exertional heat injury usually sweat freely and the body temperatures is lower (102-104°F) as opposed to (106°F) and higher in the heat stroke.
Symptoms consist of headache, piloerection, chills, hyperventilation, nausea, vomiting, muscle cramps, ataxia, unsteady gait and incoherent speech. In some cases, a loss of consciousness occurs. Physical examination shows tachycardia and hypotension.
Treatment consists of a prompt action like placing the victim under the wet cloth sheets to lower the core temperature to 100.4o F as quickly as possible, massaging the extremities to improve blood flow from the core to the periphery.
It can be divided into two types:
- Exertional heat stroke
- Classic heat stroke
Exertional heat stroke: It occurs in the healthy and young individuals and is generally sporadic. The patient usually sweats. Disseminated intravascular coagulation (DIC), acute renal failure, rhabdomyolysis and lactic acidosis are the common complications.
Classic heat stroke: It occurs in the older individuals in an epidemic form during the heat waves. Patient does not sweat. Acute renal failure, rhabdomyolysis and lactic acidosis are rare. Most of the persons with classic heat stroke have pre-existing chronic diseases including atherosclerosis, congestive heart failure, diabetes, alcoholism, etc. Direct exposure to sun is not a necessary prerequisite for the development of stroke. There may be few premonitory symptoms and loss of consciousness may be the first sign. Other patients may complain of headache, vertigo, faintness, abdominal stress, confusion or hyperpnoea. Pyrexia and prostration are the significant findings on physical examination. A rectal temperature greater than 106o F is common and the internal body temperature as high as 112-113°F has been recorded. Skin is hot and dry, pulse rate is rapid and respiration is rapid and weak. Blood pressure is usually low. Muscles are flaccid and tendon reflexes may be diminished. Lethargy, stupor or comas, depending on the severity, are present. Shock is common in the fatal cases.
Pathophysiology of Heat Stroke
Despite of wide variations in the ambient temperatures, humans and other mammals can maintain a constant body temperature by balancing heat gain with heat loss. When heat gain overwhelms the body’s mechanisms of heat loss, the body temperature rises and a major heat illness ensues. Excessive heat denatures proteins, destabilizes phospholipids and lipoproteins and liquefies membrane lipids leading to cardiovascular collapse, multi organ failure and ultimately death.
Full recovery has been observed in the patients with temperature as high as 46°C and death has occurred in the patients with much lower temperatures. Temperatures exceeding 106°F or 41.1°C are generally are catastrophic and require immediate aggressive therapy.
Heatstroke is a very complicated process. Acute physiological alterations, such as arterial hypotension, intracranial hypertension, cerebral hypoperfusion, cerebral ischemia and increased intracellular metabolism occur while exposed to a high ambient temperature. Hyperpyrexia causes cytotoxity, results in degradation and aggregation of extensive intracellular proteins, influences the change of membrane stability and fluidity, damages the transmembrane transport of protein and function of the surface receptor and induces different cytoskeletal changes.
Heatstroke resembles sepsis in many aspects and endotoxemia and cytokines may be implicated in its pathogenesis. The excessive accumulation of cytotoxic free radicals and oxidative damage may occur in the brain tissues during genesis and development of the heatstroke.
Direct thermal toxicity causes cell death, cerebral oedema and local haemorrhage. Myocardial damage and frank infarction are frequent even in the patients with normal coronaries due to the effect of heat on myocytes and coronary hypoperfusion secondary to hypovolaemia.
Hemoconcentration is common. Leucocytosis is characteristic as are proteinuria, cylindruria and an elevation of BUN. Lactic acidosis is common in classic stroke. Prolonged BT and CT and prothrombin time are common. Liver damage is common; it appears 24 to 36 hours after the admission. Renal failure is a common complication of exertional heat stroke.
Patients with heat stroke may die within a few hours after being discovered, or may die of complications such as acute renal failure. However a number of patients die several weeks after the acute episode, usually of myocardial infarction, heart failure, renal failure, bronchopneumonia or complicating bacteremia.
Temperature: Typically, the patient’s body temperature exceeds 41°C, but, in the presence of sweating, evaporating mechanisms and initiation of cooling methods, body temperatures lower than 41°C are common.
Pulse: Tachycardia or rate exceeding 130 beats per minute is common.
Blood pressure: Patients are commonly normotensive with a wide pulse pressure; however, hypotension is common and is due to a number of factors including vasodilatation of the cutaneous vessels, pooling of the blood in the venous system and dehydration. Hypotension may also be due to myocardial damage and may signal cardiovascular collapse. This usually corrects with normalization of the body temperature.
Central Nervous System
Symptoms of CNS dysfunction are present universally in the persons with heatstroke. Symptoms may range from irritability to coma. Patients may present with delirium, confusion, delusions, convulsions, hallucinations, ataxia, tremors, dysarthria and other cerebellar findings, as well as cranial nerve abnormalities and tonic and dystonic contractions of the muscles. Patients also may exhibit decerebrate posturing, decorticate posturing or may limp. Coma may also be caused by electrolyte abnormalities, hypoglycemia, hepatic encephalopathy, uremic encephalopathy and acute structural abnormalities such as intracerebral hemorrhage due to trauma or coagulation disorders. Cerebral oedema and herniation may also occur during the course of heatstroke.
Examination of the eyes may reveal nystagmus and oculogyric episodes due to cerebellar injury. Pupils may be fixed, dilated, pinpoint or normal.
Heat stress places a tremendous burden on the heart. Patients with a pre-existing myocardial dysfunction cannot tolerate heat stress for prolonged periods. Patients commonly exhibit a hyperdynamic state with tachycardia, low systemic vascular resistance and a high cardiac index. A hypodynamic state with a high systemic vascular resistance and a low cardiac index may occur in the patients with pre-existing cardiovascular diseases and low intravascular volume. A hypodynamic state may also signal cardiovascular collapse. The central venous pressure is generally within the reference range or elevated unless the patient is severely volume depleted. High-output cardiac failure and low-output cardiac failure may occur.
Patients with heatstroke commonly exhibit tachypnoea and hyperventilation caused by direct stimulation of central nervous system, acidosis or hypoxia. Hypoxia and cyanosis may be due to a number of processes including atelectasis, pulmonary infarction, aspiration pneumonia and pulmonary oedema.
Gastrointestinal hemorrhage occurs frequently in the patients with heatstroke.
Patients commonly exhibit evidence of hepatic injury including jaundice and elevated liver enzymes. Rarely, fulminant hepatic failure occurs accompanied by encephalopathy, hypoglycemia, disseminated intravascular coagulation (DIC) and bleeding.
Muscle tenderness and cramping are common; rhabdomyolysis is a common complication of EHS. The patient’s muscles may be rigid or limp.
Acute renal failure (ARF) is a common complication of heatstroke and may be due to hypovolemia, low cardiac output and myoglobinuria (due to rhabdomyolysis). Patients may exhibit oliguria and a change in the colour of urine.
These includes Delirium, Meningitis, Delirium Tremens, Neuroleptic Malignant Syndrome, Diabetic Ketoacidosis, Tetanus, Encephalopathy, Hepatic Toxicity, Cocaine Encephalopathy, Uremic Toxicity, Hyperthyroidism, Cerebral malaria and Cerebral hemorrhage
Management of Heat Stroke
Heat stroke is a medical emergency and immediate heroic measures are required. The patient should be wheeled into a shower. A successful protocol consists of vigorous massage of the patient, particularly the torso and the neck to decrease peripheral vasoconstriction. Removal of restrictive clothing and spraying water on the body, covering the patient with ice water soaked sheets or placing ice packs in the axillae and groin may reduce the patient’s temperature significantly and fan should be directed on the patient to accelerate the heat convection. These measures along with the establishment of proper airway, avoidance of aspiration, treating coma and convulsions lead to the survival of most of the patients, particularly if they are young and were previously well. Unfortunately, the poor, ill and elderly, who are often not diagnosed until heat hyperpyrexia has been present for some hours, have a much less favorable outcome.
- Gelsemium: It is an important remedy for heatstroke. It covers all the symptoms of sun stroke. Head full, throbbing of arteries, sensitive to sound, double or partial vision. It is especially indicated in hot, damp and shifting weather, the exact meteorological condition of sunstroke. This is also a drug for prevention of stroke.
- Amylenum Nitrosum: Anxiety, longing for fresh air, dull, confusion of head, giddy, intoxicated feeling, head feels full of bursting, eyes protruded, staring, conjunctiva bloodshot, intense surging of blood to the face. Crampy epigastric pain. Burning and pressure in the stomach, dyspnoea and constriction of the chest and the heart.
- Glonoine: Is the most important drug for heat stroke. Violent headache, vertigo, does not know the street or her house, loosing sense and sinking down. Feels strokes of the pulse in the head with heat. Pain and throbbing in the pit of the stomach with a sense of sinking. Oppressed breathing, sighing, constriction and anxiety. A great remedy for heat prostration.
- Belladonna: It is similar to Glonoine. Drowsiness, dullness of mind, congestion towards head, loss of consciousness, headache, vertigo, anguish, flashes before the eyes and whizzing in the ears.
- Opium: Unconsciousness, deep coma, eyes glassy and half closed.
- Camphor: It is indicated particularly at the commencement of the attack; the patient experiences a violent distress in the head, complains of vertigo, or is suddenly deprived of his consciousness with great depression of the pulse, paleness of the face; these symptoms may be speedily followed by opposite signs of reaction, flushed face, glistening eyes, hot and dry skin and a full, strong and somewhat accelerated pulse.
- Veratrum Viride: Intense cerebral congestion, rapid pulse, tendency for convulsions followed by prostration. A red streak down the centre of the tongue. Increased sensitiveness to sound. Dimness of vision with dilated pupils. Meningitis following sun stroke.
- Aconitum napellus: It is a medicine for cerebral congestion from lying with head exposed to the direct rays of the sun; especially when asleep. It may be due to the paralyzing effect on the circulation. Great thirst and a hot and dry skin.