Introduction and Causes of Heatstroke
What is Heatstroke
Heatstroke refers to the collective symptoms of impaired thermoregulation, water and electrolyte metabolic disorders, and damage to nervous system function caused by prolonged exposure to high temperatures and thermal radiation. In July 2010, "heatstroke" was added to the national list of statutory occupational diseases.
Heat illness is a disease characterized by dysfunction of the thermoregulatory center, failure of sweat gland function, and excessive loss of water and electrolytes, occurring in hot, humid, and windless environments. Depending on the pathogenesis and clinical manifestations, heatstroke is usually classified into heat cramps, heat exhaustion, and heat (sun) stroke. The three conditions can develop sequentially or overlap. Heatstroke is a fatal disease with a high mortality rate.
Heatstroke refers to the collective symptoms of impaired thermoregulation, water and electrolyte metabolic disorders, and damage to nervous system function caused by prolonged exposure to high temperatures and thermal radiation. Patients with cranial and brain diseases, the elderly, the weak, and postpartum women are particularly susceptible to heatstroke due to poor heat tolerance. Heatstroke is a life-threatening emergency. Without prompt and effective treatment, it can lead to seizures and death, permanent brain damage, or kidney failure. A core temperature of 41°C is a sign of a poor prognosis; a slight further increase in temperature can often be fatal. Old age, debilitation, and alcoholism can worsen the prognosis.
The diagnosis of heatstroke can be made based on elevated body temperature, muscle cramps, and/or syncope occurring during work or life in a high-temperature environment, and other diseases must be ruled out. Diseases that need to be differentiated from heatstroke, especially heatstroke, include encephalitis, organophosphorus pesticide poisoning, toxic pneumonia, bacillary dysentery, and malaria. Heat exhaustion should be differentiated from gastrointestinal bleeding, ectopic pregnancy, and hypoglycemia; heat cramps with abdominal pain should be differentiated from various acute abdominal diseases.
Prevention of heatstroke should fundamentally improve labor and living conditions, isolate heat sources, reduce workshop temperatures, adjust work and rest schedules, and provide cool drinks containing 0.3% salt. Knowledge about the prevention and treatment of heatstroke should be publicized, especially the early symptoms. Individuals with organic cardiovascular diseases, hypertension, organic central nervous system diseases, and obvious respiratory, digestive, or endocrine system diseases, as well as liver and kidney diseases, should be listed as contraindications for employment in high-temperature workshops.
What are the causes of heatstroke?
There are many causes of heatstroke. Working in a high-temperature workshop, especially with poor ventilation, can easily lead to heatstroke. In agriculture and outdoor work, direct exposure to sunlight, combined with the ground being heated by the sun, further increases the ambient temperature, causing congestion of the meninges and ischemia of the cerebral cortex, leading to heatstroke. Increased humidity in the air can also induce heatstroke. In public places or crowded families, heat generation is concentrated while heat dissipation is difficult. In addition to high temperatures and strong sun, excessive mental stress, overcrowding, excessive work intensity, long working hours, lack of sleep, and excessive fatigue are also common contributing factors.
In a normal person, under the control of the hypothalamic thermoregulatory center, heat production and heat dissipation are in a dynamic balance, maintaining body temperature at around 37°C. When a person exercises, the body's metabolism accelerates, increasing heat production. The body uses skin vasodilation, increased blood flow, increased sweat gland secretion, and increased respiration to transfer the heat generated inside the body to the skin surface, dissipating it through radiation, conduction, convection, and evaporation to maintain a normal body temperature. When the ambient temperature exceeds the skin temperature (generally 32-35°C), or there is a heat radiation source in the environment (such as an electric stove, open flame), or the air humidity is too high and ventilation is poor, it is difficult for the body's heat to dissipate through radiation, conduction, evaporation, and convection. The body may even absorb heat from the external environment, leading to heat accumulation in the body and causing heatstroke.
Engaging in labor for a certain period in a high-temperature environment (generally room temperature exceeding 35°C) or under the scorching summer sun, without sufficient heatstroke prevention and cooling measures, often leads to heatstroke. Sometimes, even if the temperature does not reach a high level, heatstroke can still occur due to high humidity and poor ventilation. Factors contributing to the onset of heatstroke include old age, weakness, fatigue, obesity, alcohol consumption, hunger, dehydration, salt loss, wearing tight, non-ventilating clothing, fever, hyperthyroidism, diabetes, cardiovascular diseases, extensive skin damage, congenital absence of sweat glands, and the use of atropine or other anticholinergic drugs that affect sweat gland secretion.
Normal body temperature is generally stable at around 37°C, which is the result of a balance between heat production and heat dissipation achieved through the action of the hypothalamic thermoregulatory center. The main sources of heat production in the human body are the basal heat generated during oxidative metabolism in the body, and heat from muscle contraction. The accumulation of 3.89 J (0.93 cal) of heat per kilogram of body weight is sufficient to raise the body temperature by 1°C. At normal room temperature (15-25°C), the human body's heat dissipation is mainly through radiation (60%), followed by evaporation (25%) and convection (12%), with a small amount through conduction (3%). When the ambient temperature exceeds the skin temperature, the human body's heat dissipation relies solely on sweating and evaporation from the skin and alveolar surfaces. The evaporation of 1g of water can dissipate 2.43 KJ (0.58 kcal) of heat. Heat from deep body tissues is brought to subcutaneous tissues through circulating blood and dissipated through dilated skin blood vessels. Therefore, the more the skin blood vessels dilate and the greater the blood flow through them, the faster the heat dissipation. If heat production in the body exceeds heat dissipation or heat dissipation is obstructed, excessive heat accumulates in the body, causing damage to organ functions and tissues.
The main pathogenesis of heatstroke is due to the effect of heat sources in the external environment on the human body and the inability of the body to dissipate heat through normal physiological means to achieve thermal balance, leading to heat accumulation in the body and an increase in body temperature. Initially, the hypothalamic thermoregulatory center increases cardiac output and respiratory frequency, dilates skin blood vessels, and increases sweating to enhance heat dissipation. Subsequently, as heat further accumulates in the body, the thermoregulatory center loses control, cardiac function decreases, cardiac output reduces, central venous pressure increases, sweat gland function fails, leading to further heat accumulation and a sharp increase in body temperature. A body temperature above 42°C can cause protein denaturation; cells die within minutes if the temperature exceeds 50°C. Autopsies reveal congestion, edema, and scattered petechial hemorrhages in the brain, with degeneration of nerve cells; turbid swelling and hemorrhage in the myocardial interstitium; congestion and edema in the lungs; scattered petechial hemorrhages in the pleura, peritoneum, and small intestine; central necrosis in liver lobules; and ischemia and degenerative changes in renal tubular epithelial cells in the kidneys.
The mechanism of heat cramps is that in a high-temperature environment, the human body's main method of heat dissipation is sweating. It is generally believed that the maximum physiological sweating limit for a workday is 6L, but for people working in high temperatures, the amount of sweat can exceed 10L. Sweat contains about 0.3%-0.5% sodium chloride. Therefore, excessive sweating leads to excessive loss of water and salt, causing muscle cramps and pain.
The pathogenesis of heat exhaustion is mainly due to the body's inability to adapt to the hot environment, causing peripheral vasodilation, insufficient circulating blood volume, and collapse. Heat exhaustion can also be accompanied by excessive sweating, water loss, and salt loss.