The human body maintains a temperature between 36-37oc. Any excessive variation to this range has a detrimental effect on body functions. As a general observation, it may be said that the human brain does not react well to excessive body heat, and the heart is sensitive to cold.

The body has some natural defence mechanisms against excessive heat and cold. It regulates body heat by sweating, releasing heat through the body surface (heat loss), and through lung moisture evaporation. Cold` is managed by shivering, which generates heat within the body.

Often, environmental influences determine the stability of the human body's temperature. These influences are important in relation to first aid. Heat and cold related conditions may bring on serious functional impairment.

Heat related conditions are those brought on by exposure to high temperatures and humidity. The most spectacular example of a serious heat related problem, is the televised distress suffered by athletes during long distance running events, conducted during hot and humid conditions.

Heat may induce heat cramps, heat exhaustion and/or heat stroke. Less well known are industrial and engine room situations which can mimic tropical conditions while outside temperatures are actually much lower.

Dehydration

Dehydration is a condition caused by the casualty's loss of fluids from perspiration and prolonged exposure to heat and humidity. When the casualty's fluid loss exceeds their input through drinking, dehydration occurs and the blood volume lessens. A prolonged period of dehydration will lead to shock and, in susceptible casualties, such as the frail elderly and very young, this can be fatal.

• pale, cool, clammy skin
  
• rapid breathing
  
• profuse and prolonged sweating
  
• thirst
  
• loss of skin elasticity ('pinch test' on back of hand)
  
• sunken eyes in children

• complete rest in the shade, no further exertion
  
• remove unnecessary clothing
  
• give cool water to drink
  
• ensure casualty has assistance when recovered

Heat cramps

Heat cramps are caused by the loss of complex salts (electrolytes) through an imbalance in the body's fluid requirements - the body is losing more fluids than it is replacing. This debit causes the hard-working muscles to lose their vital electrolyte balance, causing muscular contraction (cramping).

• pale, clammy skin
• sweating if associated with exertion
  
• cramping pains in the limbs or abdomen
  
• nausea
  
• uncontrolled spasms of affected limb(s)

• rest in the shade
  
• gently stretch the affected muscle
  
• apply ice pack
  
• when nausea passes, give sips of cool water to drink (with caution)
  
• avoid massaging affected limb
  
• avoid any further exercise

Heat exhaustion

Heat exhaustion is caused by exertion accompanied by heat and high humidity.

• pale, cool, clammy skin
  
• rapid breathing
  
• profuse and prolonged sweating
  
• cramps in the limbs and/or abdomen
  
• thirst, nausea and/or vomiting
  
• constant headache
  
• exhaustion and lethargy

• complete rest in the shade, no further exertion
  
• lie casualty down
  
• remove unnecessary clothing
  
• cool casualty by sponging with water
  
• when nausea passes, give cool water to drink (cautiously)
  
• ensure casualty seeks medical assistance when recovered

Heat stroke

This condition is not to be confused with ‘sun stroke', the common ailment of headache and nausea suffered by children and careless adults who remain in the sun too long without a hat. Also known as ‘Core Temperature Emergency', with a core temperature above 40.6 oc heat stroke is potentially life threatening.

In this condition, the body's temperature regulation centre in the brain has been rendered inoperable, and the body temperature continually rises, causing eventual brain damage. Immediate, active intervention is necessary to avoid coma and death.

• flushed, hot, dry skin
  
• core temperature 40.6 oc or more
  
• the casualty has ceased sweating
  
• rapid pulse, gradually weakening
  
• irrational or aggressive behaviour
  
• staggering gait, fatigue
  
• visual disturbances, headache
  
• vomiting
  
• collapse and seizures
  
• coma - death

• call '000' for an ambulance
  
• complete rest in shade
  
• remove casualty's clothing
  
• cool casualty by any means possible - ice packs to neck, groin and armpits
  
• cover casualty with wet sheet and keep wet. Fan to increase cooling
  
• be prepared to resuscitate as required
  
• fluids can be given if casualty is fully conscious
  
• if unconscious or semi-conscious, nothing by mouth. Re-hydration is required by intravenous fluids administered by a doctor or ambulance crew

Exposure to cold

Exposure to cold has effects which are no less serious than exposure to heat and humidity. Remember that an elderly person in an unheated house during winter, who is incapacitated and unable to summon assistance, is at risk from exposure to cold and hypothermia.

There are several common situations where persons suffer from exposure to low temperatures. This includes being caught out in inclement weather during walking, being soaked in cold water and unable to change, and being subject to cold winds (wind chill) without proper protection, or not being able to afford adequate heating and clothing.

• pale, cold skin
  
• increasing lethargy, drowsiness, lack of muscular co-ordination
  
• uncommunicative, poor judgement
  
• shivering

• warm slowly by adding additional clothing, heating source, body heat
  
• if wet, change the casualty's clothing if in stable environment
  
• if conscious, give warm, sweet drinks
  
• when able to stand, encourage mild exercise

Hypothermia

Hypothermia occurs when the body's control mechanisms fail to maintain a normal body temperature above 35oc. Hypothermia results from prolonged exposure to cold temperatures.

Factors that commonly increase the risk of hypothermia include advanced or very young age, substance abuse, impaired mental status, or immersion in cold water.

• pale, cold skin - no capillary return when fingernails are pressed
  
• slow pulse, sometimes irregular
  
• slow, shallow respirations
  
• blurred, or double vision
  
• casualty is silent, appears asleep, difficult to rouse; may be unconscious
  
• casualty often feel that they are not ill
  
• absence of shivering
  
• if very cold, may have non-reacting pupils and appear "death-like"

• provide shelter from cold, rain, wet ground, and wind
  
• call "000" for an ambulance
  
• warm casualty, wrap in blanket, "space blanket" or similar. Move to a warm area
  
• remove cold or wet clothing as soon as possible
  
• cover casualties with blankets and keep them out of the wind
  
• once casualty commences shivering, reassess heating
  
• be prepared for sudden collapse and resuscitation
  
• if conscious, give warm, sweet drinks
  
• DO NOT rub affected area
  
• DO NOT expose to excessive heat
  
• DO NOT give alcohol