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Isotonic dehydration

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Water comprises about 60% of the body weight in adult males, 50 to 55% in females and up to 75% in a newborn infant (1).

  • in infants, extracellular compartment contains more water than intracellular space while in adults about two-thirds of total water is in the intracellular space, whereas one-third is extracellular water.

Dehydration can be defined broadly as the process of loosing body water which leads eventually to hypohydration (1).

classification of dehydration

Dehydration can be classified according to the ratio of fluid to electrolyte loss:

  • isotonic
    • characterised by isotonic loss of both water and solutes from the extracellular fluid (ECF) e.g., - vomiting, diarrhoea or through inadequate intake
    • no osmotic water shift from the intracellular fluid (ICF) to the ECF.
  • hypertonic
    • water loss exceeds salt loss e.g. - through inadequate water intake, excessive sweating, osmotic diuresis and diuretic drugs
    • characterised by an osmotic shift of water from the ICF to the ECF
  • hypotonic
    • sodium loss is higher than water loss e.g. in some instances of high sweat or gastro-intestinal fluid losses or when fluid and electrolyte deficits are treated with water replacement only
    • characterised by an osmotic shift of water from the ECF to the ICF (1)

Dehydration is common in several types of patients:

  • neonates
  • elderly
  • unconscious

The features of dehydration are:

  • hypotension
  • circulatory failure
  • usually, hypernatraemia


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