Hyperthermia

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Hyperthermia, in its advanced state referred to as heat stroke or sunstroke, is an acute condition which occurs when the body produces or absorbs more heat than it can dissipate. It is usually caused by prolonged exposure to high temperatures. The heat-regulating mechanisms of the body eventually become overwhelmed and unable to effectively deal with the heat, causing the body temperature to climb uncontrollably. Hyperthermia is a medical emergency which requires immediate treatment.

Hyperthermia can be created artificially by drugs or medical devices. Hyperthermia therapy may be used to treat cancer and other conditions.^[1] Malignant hyperthermia is a rare complication of some types of general anesthesia.

The opposite of hyperthermia is hypothermia, caused when an organism's temperature drops below that required for normal metabolism. Hypothermia is caused by prolonged exposure to low temperatures and is also a medical emergency requiring immediate treatment.

[edit] Difference between hyperthermia and fever

A summary of the differences between hyperthermia, hypothermia, and fever.
Hyperthermia: Characterized on the left. Normal body temperature (thermoregulatory set-point) is shown in green, while the hyperthermic temperature is shown in red. As can be seen, hyperthermia can be conceptualized as an increase above the thermoregulatory set-point.
Hypothermia: Characterized in the center: Normal body temperature is shown in green, while the hypothermic temperature is shown in blue. As can be seen, hypothermia can be conceptualized as a decrease below the thermoregulatory set-point.
Fever: Characterized on the right: Normal body temperature is shown in green. It reads "New Normal" because the thermoregulatory set-point has risen. This has caused what was the normal body temperature (in blue) to be considered hypothermic.

A fever occurs when the body sets the core temperature to a higher temperature, through the action of the pre-optic region of the anterior hypothalamus. For example, in response to a bacterial or viral infection, the body will raise its temperature to allow the immune system to work better and to deteriorate the condition of the invaders. In contrast, hyperthermia occurs when the body temperature is raised without the consent of the heat control centers.

[edit] Progression

Body temperatures above 40°C (104 °F) are life-threatening. This compares to normal human body temperature of 36-37°C (97-98°F). At 41°C (106 °F), brain death begins, and at 45°C (113°F) death is nearly certain. Internal temperatures above 50°C (122°F) will cause rigidity in the muscles and certain, immediate death.^{[citation needed]}

Heat stroke may come on suddenly, but usually follows a less-threatening condition commonly referred to as heat exhaustion or heat prostration.

After effects may include sensitivity to heat.

[edit] Signs and symptoms

One of the body's most important methods of temperature regulation is perspiration. This process draws heat from inside, allowing it to be carried off by radiation or convection. Evaporation of the sweat furthers cooling, since this endothermic process draws yet more heat from the body. When the body becomes sufficiently dehydrated to prevent the production of sweat this avenue of heat reduction is closed. When the body is no longer capable of sweating, core temperature begins to rise swiftly.

Victims may become confused, may become hostile, often experience headache, and may seem intoxicated. Blood pressure may drop significantly from dehydration, leading to possible fainting or dizziness, especially if the victim stands suddenly. Heart rate and respiration rate will increase (tachycardia and tachypnea) as blood pressure drops and the heart attempts to supply enough oxygen to the body. The skin will become red as blood vessels dilate in an attempt to increase heat dissipation, sometimes leading to swollen lips. The decrease in blood pressure will cause blood vessels to contract as heat stroke progresses, resulting in a pale or bluish skin colour. Complaints of feeling hot may be followed by chills and trembling, as is the case in fever. Some victims, especially young children, may suffer convulsions. Acute dehydration such as that accompanying heat stroke can produce nausea and vomiting; temporary blindness may also be observed. Eventually, as body organs begin to fail, unconsciousness and coma will result.

[edit] First aid

Heat stroke is a medical emergency requiring hospitalization, and the local emergency services should be notified as soon as possible.

The body temperature must be lowered immediately. The patient should be moved to a cool area (indoors, or at least in the shade) and clothing removed to promote heat loss (passive cooling). Active cooling methods may be used: The person is bathed in cool water, a hyperthermia vest can be applied, however, wrapping the patient in wet towels or clothes can actually act as insulation and increase the body temperature. Cold compresses to the torso, head, neck, and groin will help cool the victim. A fan or dehumidifying air conditioning unit may be used to aid in evaporation of the water (evaporative method).

Immersing a patient into a bathtub of cool - but not cold - water (immersion method) is a recognized method of cooling. This method requires the effort of 4-5 persons and the patient should be monitored carefully during the treatment process. This should be avoided for an unconscious patient; if there is no alternative, the patient's head must be held above water. Immersion in very cold water is counterproductive, as it causes vasoconstriction in the skin and thereby prevents heat from escaping the body core.

Hydration is of paramount importance in cooling the patient. This is achieved by drinking water (Oral rehydration). Commercial isotonic drinks may be used as a substitute. Intravenous hydration (via a drip) is necessary if the patient is confused, unconscious, or unable to tolerate oral fluids.

Alcohol rubs will cause further dehydration and impairment of consciousness and should be avoided. The patient's condition should be reassessed and stabilized by trained medical personnel. The patient's heart rate and breathing should be monitored, and CPR may be necessary if the patient goes into cardiac arrest.

The patient should be placed into the recovery position to ensure that the person's airway remains open.

[edit] Prevention

The risk of heatstroke can be reduced by observing precautions to avoid overheating and dehydration. Light, loose-fitting clothing will allow perspiration to evaporate. Wide-brimmed hats in bright colour keep the sun from warming the head and neck; vents on a hat will allow perspiration to cool the head. Strenuous exercise should be avoided during daylight hours in hot weather; so should remaining in enclosed spaces (such as automobiles).

In hot weather people need to drink plenty of liquids to replace fluids lost from sweating. Thirst is not a reliable sign that a person needs fluids.^[2] A better indicator is the color of urine. A dark yellow color may indicate dehydration. It is debated whether water or sports drinks are more effective to regain fluids, however, drinking only water without ingesting any salts will lead to a condition known as hyponatremia, which can cause sudden death from heart attack. Humans lose salts through sweat and urine which also need to be replaced along with fluids.

The Occupational Safety and Health Administration in the United States publishes a heat stress Quick Card ^[3] that contains a checklist designed to help prevent heat stress. This list includes:

• Know signs/symptoms of heat-related illnesses
• Block out direct sun or other heat sources
• Use cooling fans/air-conditioning; rest regularly
• Drink lots of water; about 1 cup every 15 minutes
• Wear lightweight, light colored, loose-fitting clothes
• Avoid alcohol, caffeinated drinks, or heavy meals

[edit] See also

• Dehydration
• Heat cramps
• Heat syndrome
• Heat wave
• Hypernatremia
• Hyperpyrexia
• Hyponatremia
• Perspiration

[edit] References

[edit] External links

• International Red Cross Information on Heat Stroke
• Hiking and Camping Note Book Heat Stroke Advice
• BBC Heat Illness News and Information
• Environment Canada's Heat Index (humidex) Chart
• Working in Hot Environments, from the United States' National Institute for Occupational Safety and Health (NIOSH)
• Excessive Heat Events Guidebook, from the United States' Environmental Protection Agency (EPA)
• Enhanced Home & Family Heatwave Preparedness
• Cold Water Immersion: The Gold Standard for Exertional Heatstroke Treatment
• Physiological Responses to Exercise in the Heat -- Chapter 3 of Nutritional Needs in Hot Environments by the Institute of Medicine of the U.S. National Academies (of Science) (N.B.: entire book is available in HTML format via this link)