DEHYDRATION is a medical condition which results when body water loss exceeds fluid intake.

Fluid and salts are lost through sweat, urine, stool, and breathing. The body normally compensates for fluid loss by a number of mechanisms, however, if fluid intake is severely compromised, severe dehydration and death can occur.

Total body water is approximately 60 per cent of the body weight in adults. This changes based on age and sex. Approximately 80 per cent of the body weight of newborns is water and this changes to about 45-50 per cent in the elderly, while females tend to have less body water, approximately 50 per cent, than their adult male counterparts, which is about 60 per cent. This water is also distributed in different compartments of the body. Fluid inside the cells in the body account for approximately 40 per cent of total body weight while fluid outside the cells or extracellular fluid (ECF) is about 20 per cent of total body weight. The fluid inside the blood vessels is approximately one-third of the extracellular fluid or about five per cent of the total body weight with the other two-thirds of the ECF being in the interstitium (between the cells). The primary electrolyte of the fluids outside the cells is sodium while inside the cells, potassium is the main electrolyte. Fluid and salt shifts between these compartments based on the hydration status of the body, through complex processes involved in water and salt regulation.

Causes of dehydration

Common causes of dehydration include:

1. Acute gastroenteritis that can be infectious (viral, bacterial or protozoal) or inflammatory where vomiting and diarrhoea result in fluid loss from the gut;

2. Uncontrolled diabetes due to excess losses through vomiting and urination;

3. Burns due to the loss of skin, so there is no protection from fluid and electrolyte loss;

4. Heat or fever where fluid and electrolytes are lost with excessive sweating;

5. In disabled or bedridden individuals who do not have ready access to water.

Dehydration can be mild, moderate or severe. The features of mild dehydration are very subtle, dry mouth, feelings of thirst, dry mucous membranes, loss of salivary pool and orange-coloured urine. Moderate dehydration results in the above plus fatigue, dizziness, increased heart rate, decreased sweating, and small amounts of concentrated urine are now produced.

Severe dehydration results in altered sensorium, patient may be confused, drowsy, irritable, have seizures, or be in a coma. Blood pressure is low and the heart rate is elevated and fainting may occur. The patient’s skin has loss of turgor, mucous membranes are very dry and parched, eyes are sunken, and urine output is severely diminished.

Treating dehydration

Treatment of dehydration involves resuscitation as well as finding and stopping the cause of any excessive fluid loss.

Mild and moderate dehydration is treated with oral rehydration fluids or pedialyte solutions for children, which replaces both water and electrolyte deficits along with preventing further fluid loss. The patient is usually able to drink enough replacement fluid.

Severe dehydration requires intravenous fluid bolus. Vomiting with an antimetic like dimenhydrinate (gravol) if there is no contraindication, however, this should not be used in children less than 12 years old.

Preventing dehydration

Dehydration is prevented by drinking adequate amounts of water daily. Adults require approximately two to three litres of fluid in total, including solid meals. Solutions such as oral rehydration salts will replace both water and electrolytes at the correct proportion and provides an excellent replacement. People with a condition such as diarrhoea with very high fluid loss will of course require more to prevent dehydration. For those with reduced access to water and decreased sensation of thirst to trigger replacement, such as young children and the elderly, special consideration must be taken by caregivers to ensure adequate daily replacement.

Dr Romayne Edwards is a consultant emergency physician at the University Hospital of the West Indies and an associate lecturer at the University of the West Indies.