Dehydration occurs when there is an excessive loss of water from the body.
This can happen at any age, but is especially dangerous in infants and the elderly.
Dehydration can be the result of poor intake of fluids, excessive loss through strenuous activity, sweating, vomiting or diarrhoea, or loss of fluid through the kidneys.
The average person needs to consume 2.5 litres of liquid every day to remain hydrated.
Marked lethargy, dizziness, low blood pressure, dry mouth and chapped lips can all be signs of dehydration.
Severe dehydration can lead to organ failure and death.
Increasing oral intake of water or other liquids can generally restore normal hydration but in some cases intravenous rehydration may be necessary.
The replacement of lost electrolytes along with water is also of great importance.
Dehydration occurs when the body is depleted of water. In the adult man sixty-five percent of the body's mass is made up of water. In obese men the percentage is closer to 55% and in women the respective figures are more or less 10% less than those for men.
Two thirds of the total body water is found within the cells and is called intracellular fluid, and a third is outside the cells (the extracellular fluid). A quarter of the latter is in the plasma (i.e. in the arteries, veins and capillaries) and the rest is found in between the cells (in other words outside the cells, but also outside the blood vessels). This is called the intercellular fluid. Essential bodily processes such as circulation of the blood, excretion by the kidneys and sweating, need to be maintained, and this is not possible if there is a drastic loss of fluids. Cells will dry out and malfunction.
Who is at risk?
Young children and the elderly are at greater risk of dehydration, as loss of electrolytes occurs more rapidly in these two groups of people. Children's bodies have a higher percentage of water than those of adults, their metabolic rates are higher and they are at greater risk of infections that cause vomiting and diarrhoea. They are also dependent on others to feed them and give them water.
Older people may have a decreased thirst sensation, their kidneys may not work as efficiently or they may have neurological conditions such as a stroke or Alzheimer's disease, which can make it difficult for them to convey their needs to a caregiver. Incontinence problems may also lead elderly people to limit their intake of water.
Sportspeople who partake in strenuous sporting activities are also at risk of dehydration, particularly in very hot conditions.
Dehydration can occur because of:
Poor intake of fluids or excessive loss through vomiting and diarrhoea or excessive sweating or increased urination.
A varying amount of fluid is lost through normal daily excretion. Approximately 2,5 litres of fluid are therefore needed daily so that the body does not become dehydrated.
Fluids taken in sufficient quantities will prevent dehydration.
The correct treatment of diarrhoea and vomiting will prevent dehydration.
Sportspeople should take liquids frequently when participating in sporting events.
Symptoms and signs
Extreme thirst is always present in the early stages, and young children may show marked irritability. With severe dehydration there is increasing weakness and lethargy and the urge to drink may be lost.
In children, dehydration can set in alarmingly quickly. Signs of dehydration can be dry or chapped lips, oral dryness, restlessness and a sunken appearance of the eyes. Alarming signs of advanced dehydration in infants include a weak pulse, shallow breathing and a blue tinge to the skin, which may feel cold to the touch.
A valuable method of assessing dehydration in children is by gently pinching up the skin on the side of the abdomen. On releasing, it should immediately return to normal. When dehydration is present the skin fold takes much longer to return.
Adults could feel dizzy, be extremely thirsty, may have a heightened body temperature, although their skins may also feel cold to the touch. As a result of the loss of the electrolytes especially sodium and potassium, nausea and muscle cramps can occur. If fluid continues to be lost the blood pressure will drop even further, resulting in shock and damage to internal organs such as the brain and kidneys in particular.
Taking extra fluids by mouth is the obvious treatment for dehydration and the drinking of water or other liquids is recommended.
A solution consisting of half a teaspoon of salt, and eight teaspoons of sugar in a litre of previously boiled water is easily made and suitable for mild cases of dehydration. Rehydration salts in packets are also available at all pharmacies.
If the person is unconsciousness or unable to drink, fluids can be administered intravenously.
If vomiting persists and the situation becomes serious, intravenous rehydration will be necessary. Electrolytes (sodium and potassium) are also lost when someone has become dehydrated and the acid-base balance is disturbed. These imbalances also need to be corrected.
There are certain conditions such as diabetes that could lead to dehydration. Family members should be on the lookout for signs and symptoms of dehydration in these relatives.
In the case of athletes taking part in strenuous sporting activities, rehydration should be a priority. Many balanced solutions containing the correct amounts of carbohydrate and electrolytes suitable for athletes are available commercially.
When to see a doctor
Vomiting and diarrhoea can easily lead to dehydration, especially in the case of infants and older people. If someone's skin feels cold to the touch, they appear dizzy or disorientated, have chapped lips or a dry mouth and they have low blood pressure, they should be given medical attention. Dehydration could lead to serious medical complications.
An adult loses about:
1,2 – 1,5 litres of fluid daily through urination
1 litre through perspiration
A varying amount of fluid is lost through excretion. Approximately 2,5 litres of fluid are therefore needed daily so that the body does not become dehydrated.
Fluids taken in sufficient quantities will prevent dehydration.
The correct treatment of diarrhoea, vomiting and conditions such as diabetes will prevent dehydration. Sportspeople should also take liquids frequently when participating in sporting events.
Previously reviewed by Prof M. Kibel, Emeritus Professor of Child Health
Reviewed by Prof E Weinberg, Emeritus Professor of Paediatrics, May 2011