Defined as a reduction in EC fluid volume that occurs when salt and fluid losses exceed intake on a sustained basis

• Obligatory urine production/day to excrete waste solutes = 500mL per day (600mOsm/day)
• Need to be urinating at least once every 6 hours

Causes

• Bleeding
• Diarrhoea - excess fluid loss in faeces
• Vomitting - Fluid losses
• Diabetes - excess polyuria (glycosuria)
  • DI = lack of ADH secretion
• Iatrogenic - medications (diuretics)

Clinical features

• dry mucous membranes
• loss of skin turgor
• sunken eyes
• Low JVP
• weak pulse
• Reduced urine output
• severe dehydration - tachycardia, hypotension, delirium