What is dehydration?

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• WHAT IS DEHYDRATION?

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Dehydration is the loss of water from the body
in excess of the amount consumed.
Dehydration

• WHAT IS IT?
• Dehydration occurs when the body loses more water
  than is taken in. It is often accompanied by
  disturbances in the body's mineral salt or
  electrolyte balance - especially disturbances in
  the concentrations of sodium and potassium. 
  read more

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HOW IS IT CAUSED?

• Mild dehydration is common and usually caused by
  not drinking enough fluids throughout the day. In
  children, diarrhoea is a common cause.  read
  more
• CONSEQUENCES
• A loss of body water equivalent to about 1 of
  body weight is normally compensated within 24
  hours. Thirst stimulates drinking, so intake is
  increased and there is also a reduction in water
  loss by the kidneys. If losses are greater than
  this, reductions in physical and cognitive
  performance may occur and there may be some
  impairment of thermoregulation and cardiovascular
  function.  read more

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WHAT IS DEHYDRATION? (1)

• Dehydration occurs when the body loses more water
  than is taken in. It is often accompanied by
  disturbances in the body's mineral salt or
  electrolyte balance - especially disturbances in
  the concentrations of sodium and potassium.
• Under typical circumstances the body loses and
  needs to replace approximately 2 to 3 litres of
  water daily. Breathing, urinating, defecating,
  and perspiring all cause water losses that need
  to be replaced on a daily basis. If water is lost
  from the bloodstream, the body can compensate
  somewhat by shifting water from cells into the
  blood vessels, but this is a very short-term
  solution. If the lost water is not replenished,
  the body may suffer serious consequences.

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WHAT IS DEHYDRATION? (2)

• The body is able to monitor the amount of water
  it needs to function. The thirst mechanism
  signals the body to drink when the body water
  content is reduced. Hormones, including
  anti-diuretic hormone (ADH), work with the kidney
  to limit the amount of water lost in the urine
  when the body needs to conserve water. Water
  intake and output are highly variable but closely
  matched to less than 0.1 over an extended period
  through homeostatic control. Electrolyte intake
  and output are also closely linked, both to each
  other and to the hydration status.
• Failure to match intake and loss of water and
  minerals, especially sodium and potassium, may
  lead to dehydration. Depending on the ratio of
  water to electrolyte loss, dehydration can be
  classified as isotonic, hypertonic or hypotonic

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Isotonic dehydration

• Is characterised by isotonic loss of both water
  and solutes from the extracellular fluid, that is
  when both water and sodium are lost in equivalent
  amounts, e.g. through vomiting, diarrhoea or
  through inadequate intake. There is no osmotic
  shift of water from the intracellular space to
  the extracellular space. This type of dehydration
  accounts for cases of dehydration in young
  children.

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Hypertonic dehydration

• In hypertonic dehydration water loss exceeds salt
  loss, that is when more water than sodium is lost
  (e.g. through inadequate water intake, excessive
  sweating, osmotic diuresis and diuretic drugs).
  This is characterised by an osmotic shift of
  water from the intracellular fluid to the
  extracellular fluid. This type of dehydration is
  more common in people who have diabetes, and it
  accounts for approximately 10 to 20 percent of
  all paediatric cases of dehydration with
  diarrhoea.

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Hypotonic dehydration

• In hypotonic dehydration more sodium than water
  is lost, e.g. in some instances of high sweat or
  gastro-intestinal water losses or when water and
  electrolyte deficits are treated with water
  replacement only, it is characterised by an
  osmotic shift of fluid from the extracellular
  area to the intracellular. It also occurs with
  excessive intakes of plain water or other liquids
  with little or no sodium content. This type of
  dehydration accounts for approximately 10 to 15
  percent of all paediatric cases of dehydration
  with diarrhoea. This complication can be
  life-threatening if swelling causes pressure on
  the brain (cerebral oedema). This is called
  hyponatraemia.

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Reminder

• WHAT IS DEHYDRATION?
• HOW IS DEHYDRATION CAUSED?
• CONSEQUENCES OF DEHYDRATION