Hyperthermia is the phenomenon of elevated body temperature due to failed thermoregulation that occurs when a body produces or absorbs more heat than it dissipates. The human body usually can regulate its temperature. When the body gets too hot, it uses several strategies to cool down, including sweating. But if a person spends too much time in the heat without taking in enough fluids, the body's cooling processes can't work properly. When the body becomes dehydrated, it can no longer cool itself by sweating. When this happens, body temperature can raise high enough to make the person sick. Extreme temperature elevation then becomes a medical emergency requiring immediate treatment to prevent disability or death.
The most common causes include heat stroke and adverse reactions to drugs. The former is an acute temperature elevation caused by exposure to excessive heat, or combination of heat and humidity, that overwhelms the heat-regulating mechanisms. The latter is a relatively rare side effect of many drugs, particularly those that affect the central nervous system. Malignant hyperthermia is a rare complication of some types of general anesthesia.
Hyperthermia differs from fever in that the body's temperature set point remains unchanged. The opposite is hypothermia, which occurs when the temperature drops below that required to maintain normal metabolism. Symptoms of hyperthermia, or heat-related illness, vary according to the specific type of illness. The most severe form of hyperthermia is heat stroke. This happens when the body is no longer able to regulate its internal temperature; this is a medical emergency. The body temperature may be over 105 F, a level that damages the brain and other organs.
Other symptoms include muscle cramps, fatigue, dizziness, headache, nausea, vomiting, and weakness. The heart rate may be elevated, and the skin is reddened. The skin may be moist if sweating is still occurring, or it may be dry if sweating has stopped. Confusion and mental changes may develop, and seizures can occur with brain damage. Ultimately, coma and death may ensue. Heat exhaustion is a less severe form of hyperthermia. People with heat exhaustion typically experience weakness, nausea, vomiting, headache, muscle cramps, and profuse sweating. Other forms of heat illness include heat cramps, which are involuntary spasms of large muscle groups, and heat syncope, which is fainting or lightheadedness. Heat rash is characterized by a prickly or itchy feeling of the skin coupled with red bumps on the skin.
Mild hyperthemia caused by exertion on a hot day may be adequately treated through self-care measures, such as increased water consumption and resting in a cool place. Hyperthermia that results from drug exposure requires prompt cessation of that drug, and occasionally the use of other drugs as counter measures. When body temperature is significantly elevated, mechanical cooling methods are used to remove heat and to restore the body's ability to regulate its own temperatures. Passive cooling techniques, such as resting in a cool, shady area and removing clothing can be applied immediately. Active cooling methods, such as sponging the body with cool water. Drinking water and turning a fan or dehumidifying air conditioning unit on the affected person may improve the effectiveness of the body's evaporative cooling mechanisms.