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Sweat production diminishes and the body temperature rises to temperatures of around 39-41°C. The skin becomes dry and red; severe headaches occur. Dark urine means the body has concentrated the urine because it is low on fluids. You also lose salts when sweating.
Heat illnesses include:- Heat Cramps - caused by insufficient salt. Replace salt and fluid and stretch the affected muscle(s).
- Heat Syncope (fainting) - In an effort to increase heat loss, skin blood vessels dilate to such an extent that blood flow to the brain is reduced resulting in faintness, dizziness, headache, increased pulse rate, nausea and vomiting. Dehydration contributes significantly to this.
- Heat Exhaustion - where fluid losses from sweating and respiration are greater than fluid reserves. The lack of fluid causes the body to constrict blood vessels especially in the arms and legs (making the skin pale and clammy), have decreased urine output and make the affected person feel weak, dizzy and thirsty with possible nausea and vomiting.
- Heat Stroke - A life-threatening condition where the core body temperature rises to above 41°C. There are two types of heat stroke:
- Fluid Depleted Heat Stroke - despite fluid loss due to sweating and inadequate fluid replacement, the person continues to function.
- Fluid Intact (fast onset) Heat Stroke - heat challenge overwhelms body's active heat loss even though fluid level is sufficient. The cause is generally overexertion despite already being overheated. Signs include hot, pale skin (may be dry or wet); severe change in mental status and motor/sensory function; possible dilation and unresponsiveness of pupils to light.
Sweat not only contains substantial amounts of sodium (1gm per liter), but also modest amounts of potassium and small amounts of minerals such as iron and calcium. The muscles selfishly want more blood because of the oxygen it contains, while the skin demands blood for cooling. Hiking in hot weather often causes fingers and hands to become swollen and puffy, so much so that it may become hard to make a fist. If one is not taking in adequate electrolytes, the imbalance in salt levels between the blood stream, the cells, and the extracellular spaces essentially results in a trapping of the water in the tissues as the sodium is lost in sweat.
The same thing can happen if too much salt is being taken.
Treatment & Prevention
The only method of treatment is by cooling the afflicted person. Putting half a teaspoon of salt and half a teaspoon of baking soda in each liter of water helps to replace lost electrolytes, as do 'oral rehydration salts'. Cool (but not cold), wet cloths should be used to reduce body temperature; using a fan will increase cooling by evaporation. Before exercising in hot weather (best avoided though, if possible), drink half a liter of water on waking up and add some salt to your breakfast to make sure you do not start the day dehydrated or low on sodium.
Drink and rest regularly. After exercise, continue drinking regularly for the rest of the day to replace lost fluids.
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