Fluid & Electrolyte Balance -- Reference Values

Found at Surgical Tutor, a helpful resource to check when designing enteral feeding regimens with and without concomitant iv therapy:

Fluid and electrolyte balance

Daily requirements

  • For the ‘average’ 70 Kg man
    • Total body water is 42 L (~60% of body weight)
    • 28 L is in the intracellular and 14 L in the extracellular compartments
    • The plasma volume is 3 L
    • The extravascular volume is 11 L
    • Total body Na+ is 4200 mmol  (50% in ECF)
    • Total body K+ is 3500 mmol  (only about 50-60 mmol in ECF)
    • Normal osmolality of ECF is 280 –295 mosmol/kg

Fluid replacement

When calculating fluid replacement for a patients need to consider:

Maintenance requirements

    • Daily maintenance fluid requirements vary between individuals.
      70 Kg male = 2.5 - 3.0L water, 120 – 140 mmol sodium and 70 mmol potassium
      40 Kg woman = 2.0L water,70 – 90 mmol sodium and 40 mmol potassium
  • Daily maintenance fluid requirements for children
    • 0-10 kg is 100 ml/kg
    • 10-20 kg is 1000 ml + 50 ml/kg for each kg > 10
    • >20 kg is 1500 ml + 25 ml/kg for each kg > 20

Replacement of losses

  • Pre-operative or pre-admission
  • Ongoing losses
  • Nasogastric aspirate
  • Vomit, diarrhoea
  • Stoma, drains, fistula etc
  • Most ‘surgical ‘ ongoing losses are rich in sodium and should be replaced with 0.9% saline

Insensible losses

  • Faeces approximately 100 ml/ day
  • Lungs approximately 400 ml/ day
  • Skin approximately 600 ml/ day

Composition of crystalloids


Hartmann’s Solution

 Normal Saline

Dextrose   Saline
Sodium  (mmol/l) 131 150 30
Chloride (mmol/l) 111 150 30
Potassium (mmol/l) 5 Nil Nil
Bicarbonate (mmol/l) 29 Nil Nil
Calcium (mmol/l) 2 Nil Nil

[Note:  Hartman's Solution --  a solution containing sodium chloride, sodium lactate, and phosphates of calcium and potassium; used intravenously as a systemic alkalizer and as a fluid and electrolyte replenisher. ]

Click here to view the full table and notes.