The core body temperature required for the maintenance of bodily functions is 36.5 to 37.5 C, whilst hyperthermia (a condition in which excessive heat disturbs normal bodily functions) may be defined as a core body temperature of 40.0 to 41.5 C/ +38.3 C.
The recent heat waves experienced in the Cape have given rise to an increase in heat related incidents. These conditions occur when excess environmental heat overwhelms the body's thermoregulatory mechanisms. Thermoregulation is the means by which the body is able to maintain an optimal functioning temperature, despite the ambient temperature of the surrounds and is achieved by mechanisms such as sweating and the dilation of peripheral blood vessels. |
Direct and indirect heat related incidents are poorly reported, and when death rates from other causes such as myocaridal infarction and respiratory compromise increase during a heat wave, it is generally not reflected statistically. In the USA, heat waves account for more deaths than all other natural disasters combined. The elderly, homeless and socially isolated remain more affected by heat waves.
Thermoregulation
The generation and maintenance of body heat may be dictated through metabolism, muscle activity, and the environmental temperature. In order to maintain a functioning temperature, when body heat rises, peripheral blood vessels dilate and cardiac output increases resulting in a shunting of blood flow closer to the surface where it can be cooled. Additionally, sweating aids cooling by providing water on the skins surface, which evaporates and in turn further cools the body. When there is a high environmental temperature and high humidity value, heat dissipation through evaporation may be hindered. |
People who exhibit limited mobility and impaired judgement may not be able to purposefully seek a cooler environment or shade themselves from the sun, reduce their physical activity and consciously replace lost fluids and salts due to sweating and over heating. Even with adequate water and salt intake, homeostatic mechanisms may break down and result in hyponatremia (loss of sodium) and cerebral edema.
After seven to 14 days of continuous heat exposure, the body acclimatizes and adjusts to the environment by increasing the amount of sweat production, retaining salts and increasing cardiac stroke volume.
The risk factors for developing a heat syndrome may include:
- Generalized skin conditions (sunburn)
- Dehydration
- Alcoholism
- Mental illness
- Cardiopulmonary disease
- Age >65 years
- Stimulant abuse including: cocaine, amphetamines, MDMA (ecstasy)
Heat disorders
Heat disorders include Heat Stroke and Heat Exhaustion
Classic heat stroke may be defined as a rise in body temperature due simple exposure to high environmental temperatures which overwhelm thermoregulatory mechanisms.
Exertional heat stroke occurs when the body temperature rises in a healthy person who exercises strenuously in a hot environment.
Exertional heat stroke occurs when the body temperature rises in a healthy person who exercises strenuously in a hot environment.
The onset of heat stoke is generally rapid, with patients presenting with weakness, headaches, chills, ataxia and nausea. Additionally, patients may report chest pain, shortness of breath and abdominal pain. The body temperature rises rapidly, sweating ceases and multiple body system failure occurs. Temperatures may be recorded at 40 C or greater, and the skin is usually hot and dry. The initial confusion, delirium and ataxia may be followed by unconsciousness.
Victims should be immediately transported to hospital, and whilst waiting for the ambulance, patients should be removed from the hot environment if possible, clothing removed and applying tepid (not ice cold) water to the skin and fanning. The initial target temperature should be 38.9 C. Other therapies may include supporting of failing organ systems and the repletion of fluids with the correction of electrolyte abnormalities.
Heat exhaustion may mimic other conditions including hypoglycemia, hyperthyroidism, ingestion of toxic substances, alcohol withdraw, arrhythmias and hypovolemia. Most victims are alert and anxious, and in some cases may be slightly confused. Symptoms may include thirst, malaise, headaches, myalgias, nausea and shortness of breath. Patients present with a normal to slightly elevated temperature.
Patients should lie down in a cool area, with fluid and electrolytes being replaced with frequent small sips of water. Untreated heat exhaustion may lead to heat stoke if sweating stops. Patients should be advised to avoid heat and exertion for at least 24 hours after an episode of heat exhaustion.
Heat Cramps:
Deep and painful spasms within the most actively used muscles and are a direct result of salt depletion. Affect muscles become harden and tender to touch, with spams which can be debilitating.
Deep and painful spasms within the most actively used muscles and are a direct result of salt depletion. Affect muscles become harden and tender to touch, with spams which can be debilitating.
Special considerations
The homeless population remain exposed to all weather conditions and as a result are vulnerable to the changes in weather, including heat waves.
Individual measures and simple community projects based on awareness of keeping cool and drinking plenty of fluids during hot weather can effectively help prevent heat disorders. Shelters and street outreach personnel should be trained to detect the early signs of heat illness and provide prompt assistance. Hydration remains critical during hot weather, and individuals with poorly controlled diabetes ans alcoholism are at high risk of dehydration.
- Weisskopf MG, Anderson HA, Foldy S, et al. Heat wave morbidity and mortality, Milwaukee, Wis, 1999 vs. 1995: an improved response? American Journal of Public Health 2002;92(5):830-833.
- Curriero FC, Heiner KS, Samet JM, et al. Temperature and mortality in 11 cities of the eastern United States. American Journal of Epidemiology 2002;155(1):80-87
- Curriero FC, Heiner KS, Samet JM, et al. Temperature and mortality in 11 cities of the eastern United States. American Journal of Epidemiology 2002;155(1):80-87
An Injury and Prevention Awareness Project brought to you by Christiaan Barnard Memorial Hospital Trauma & Emergency Centre.