Heat illness

Heat stroke is defined as a temperature of greater than 40.6 C due to environmental heat exposure with lack of thermoregulation. This is distinct from a fever, where there is a physiological increase in the temperature set point of the body.

Treatment involves rapid mechanical cooling.

Classification
A number of heat illnesses exist including&lt;ref&gt;&lt;/ref&gt;:


 * Heat stroke as defined by a temperature of greater than &gt;40.6 C due to environmental heat exposure with lack of thermoregulation.
 * Heat exhaustion
 * Heat syncope
 * Heat edema
 * Heat cramps
 * Heat tetany

Sign and symptoms
Heat stroke presents with a hyperthermia of greater than &gt;40.6 C in combination with confusion and a lack of sweating.&lt;ref&gt;&lt;/ref&gt;

Causes
Substances that inhibit cooling such as alcohol, stimulants, and age related physiological changes predispose to heat stroke.

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)&lt;ref&gt;Avoiding Classic Heat Stroke, Institute for Good Medicine at the Pennsylvania Medical Society, http://www.myfamilywellness.org/MainMenuCategories/FamilyHealthCenter/Heat-Stroke/Classic-heat-stroke.aspx&lt;/ref&gt;.

In environments that are not only hot but also humid, it is important to recognise that humidity reduces the degree to which the body can lose heat by evaporation. In such environments, it helps to wear light clothing such as cotton, that is pervious to sweat but impervious to radiant heat from the sun. This minimises the gaining of radiant heat, while allowing as much evaporation to occur as the environment will allow. Clothing such as plastic fabrics that are impermeable to sweat and thus do not facilitate heat loss through evaporation, can actually contribute to heat stress.&lt;ref name=" textbookofmedicalphysiology5thed"&gt;Arthur Guyton (1976) Textbook of Medical Physiology. (5th ed). Philadelphia: W.B. Saunders&lt;/ref&gt;.

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.&lt;ref&gt;Working in Hot Environments. NIOSH Publication No. 86-112. National Institute for Occupational Safety and Health. 1992. Accessed May 21, 2009.&lt;/ref&gt; 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 &lt;ref&gt; http://www.osha.gov/Publications/osha3154.html &lt;/ref&gt; 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

Treatment
Treatment involves rapid mechanical cooling along with standard resuscitation measures.&lt;ref&gt;&lt;/ref&gt;

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 or a hypothermia 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 people 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.