Heat Illness
Exercise and Environmental factors are the most common causes of heat related illness. However several other factors can play a part including medical illness (eg. infection), drugs/medication, dehydration, being overweight, lack of acclimitization and the extremities of age.
Preparation
Heat acclimatization and avoidance of precipitating factors (such as dehydration) are important in avoiding heat stress. Proper acclimatization takes 2 weeks and aims to increase the amount of sweating (at a lower temperature) and reduce salt loss from the kidneys/urine. Dehydration causes reduced skin blood flow and sweating leading to a rise in core body temperature. Experience has shown that we are poor at assessing our own hydration levels. Adequate clothing and sun protection is vital as well as avoiding exercise in the hot part of the day.
Heat-related Illness
Minor Heat Syndromes
Conditions such as heat oedema, heat rash, heat syncope and cramps are common. Heat syncope (fainting) is due to dilation (enlargement) of the veins and small blood vessels causing volume depletion. This is obviously worsened by dehydration. A similar mechanism explains why athletes can ‘faint’ in the post-race shower. The best avoidance of cramps is adequate training – working muscles way past exhaustion will cause cramps despite adequate hydration and electrolyte levels. Hhydration (water) and electrolytes (Sodium, Potassium, Magnesium) obviously still do play a role.
Heat Exhaustion
Patients can have a variety of symptoms including dizziness, feeling ‘unwell’, nausea/vomiting, headache, muscular aches/pains and/or syncope. Whilst their temperature can be elevated it is under 40 degrees C and they have no Central Nervous System (Brain) symptoms (eg. Confusion). They are usually dehydrated and can have varying Sodium levels when tested. Depending on the level of dehydration and presence/absence of nausea patients may require intravenous fluid.
Heat Stroke
Describes someone with a core temperature over 40 deg C who has Central Nervous System (CNS) effects and may/may not still be sweating. The CNS effects include irritability, confusion, hallucinations, unsteadiness and even seizures and coma. This is a serious, life-threatening condition that requires management in hospital with intravenous fluid and electrolyte replacement and cooling. Simple ways of cooling pre-hospital include evaporation (removing clothes, fanning, water spray) and ice-packing (eg. Groin and arm pits). Another method is immersion (eg. in a cool pond) however this can be cumbersome, lead to shivering and risk drowning.
