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Dehydration in adults

Dehydration happens when more fluid is lost by the body than is replaced by drinking liquids.

The risk of dehydration increases in hot weather and because of severe vomiting or diarrhoea.

Symptoms of dehydration can range from mild to life threatening.

You can help prevent dehydration by drinking enough fluids. There are no official guidelines for how much to drink, but some studies have suggested 1.2 litres or 6-8 glasses of liquid works well for most adults.

Causes of dehydration in adults

Many conditions may cause rapid and continued fluid losses and lead to dehydration:

  • High temperature, heat exposure, and too much exercise
  • Vomiting, diarrhoea and increased urination due to infection
  • Diseases such as diabetes
  • The inability to seek appropriate water and food (an infant or disabled person, for example)
  • An impaired ability to drink (someone in a coma or on a ventilator, or a sick infant who cannot suck on a bottle are common examples)
  • No access to safe drinking water
  • Significant injuries to skin, such as burns or mouth sores, or severe skin diseases or infections (water is lost through the damaged skin)

Symptoms of dehydration in adults

The signs and symptoms of dehydration range from minor to severe.

When to seek medical care

Seek medical advice if the person experiences any of the following:

  • Increased or constant vomiting for more than a day
  • Temperature over 38C (101F) that doesn't settle with temperature-lowering measures and medication
  • Diarrhoea for more than two days
  • Unexplained weight loss
  • Decreased urine production

Seek urgent medical advice if these situations occur:

  • Temperature higher than 39C (103F) that doesn't settle with temperature-lowering measures and medication
  • Confusion
  • Lethargy
  • Headache
  • Seizures
  • Difficulty breathing
  • Chest or abdominal pains
  • Fainting
  • No urine in the last 12 hours

Examinations and tests

The doctor may perform a variety of simple tests at the examination and send blood or urine samples to the laboratory. Through tests and examination, the doctor will try to identify the underlying cause or causes that led to the dehydration:

Vital signs

  • High temperature, increased heart rate, decreased blood pressure, and faster breathing are signs of potential dehydration and other illnesses.
  • Taking the pulse and blood pressure while the person is lying down and then after standing up for one minute can help determine the degree of dehydration. Normally, when you have been lying down and then stand up, there is a small drop in blood pressure for a few seconds. The heart rate speeds up, and blood pressure goes back to normal. However, when there is not enough fluid in the blood because of dehydration and the heart rate speeds up, not enough blood is getting to the brain. The brain senses this condition. The heart beats faster, and if you are dehydrated, you feel dizzy and faint after standing up.
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