• Definition: Serum Mg above normal range of 1.3-2.2 mEq/L
  • Toxic: Mg > 4mEq/L
  • Incidence Rare and usually iatrogenic
  • Note ↑Magnesium is closely associated with ↑K and ↓Ca

Causes of hypermagnesaemia

1)    Iatrogenic

  • Hyperalimentation
  • IV and oral magnesium
  • Laxatives, enemas, antacids (especially in elderly and renal failure)

2)    Renal Failure

3)    Other

  • Perforated viscus with continued oral intake
  • Tumour lysis (Increased K, Mg, PO4 and decreased Ca)
  • Rhabdomyolysis

Clinical manifestations

  • Often asymptomatic
  • Serum level >4
    • Muscle weakness, hyporeflexia
    • Nausea and vomiting
    • Hypotension secondary to vasodilation
  • Serum level >10
    • Coma
    • Hypoventilation
    • Neuromuscular Paralysis
    • Cardiac arrhythmias, bradycardia and death


Cardiac arrhythmia and ECG changes

  • ECG (as for hyperkalaemia)
    • Increase PR and QTc
    • Prolonged QRS
    • Peaked T waves and flattened p waves
    • Complete AV block and asystole


  • Discontinue magnesium intake
  • Antagonising Mg with Calcium
  • Removing Magnesium from serum
  1. Dialysis – Treatment of choice
  2. Calcium chloride 10% in 5-10ml repeated
    • Treats life threatening arrhythmia
  3. Forced diuresis
    • IV normal saline and Frusemide
    • Watch for hypocalcemia which can make symptoms worse

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

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