Hypernatraemia can be caused by a number of critical illnesses


  • water depletion (decreased intake, hypotonic fluid loss – renal/non-renal)
  • solute excess (Na+ or other)

Decreased intake

  • common
  • elderly with altered cognitive function -> inappropriate response to thirst

H2O loss

  • GI loss
  • intrinsic renal disease
  • hypercalcaemia
  • hypokalaemia
  • solute diuresis
  • glucosuria
  • diabetes insipidus (central or nephrogenic)



(1) correct H2O deficit
(2) reduce ongoing excessive urinary H2O losses

Calculate water deficit

Water deficit = 0.6 x premorbid weight x [1 – 140/serum Na+]

  • formula assumes TBW = 60% and does not account for ongoing water losses


  • treat cause
  • decreased intake: rehydration
  • central DI: DDAVP (1-2mcg) + 5% dextrose to correct H20 deficit
  • nephrogenic DI: Na+ restriction, thiazide diuretics, large doses of DDAVP

References and Links

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.