Question 10 from the second paper of 2003 demands that the ICU trainees discuss malignant hyperthermia, a complication of anaesthesia. This demonstrates just how much of this training program was borrowed from the College of Anaesthetists.

The European Malignant Hyperthermia Group has published some nice guidelines in 2010, which offer an excellent overview of this topic.

Pathophysiology

  • autosomal dominant mutation in the gene coding for the ryanodine receptor
  • incidence 1:5,000 -> 1:65,000 anaesthetics
  • Excess Ca2+ is released from the sarcolemma during muscle contraction, resulting in increased muscle metabolism, which is exothermic and thus leads to hyperthermia.
  • It is triggered by suxamethonium (on the first exposure, frequently) and all volatiles except nitrous oxide (one may experience volatile anaesthesia two or three times before encountering this).

General features

  • Follows the induction of anaesthesia
  • Body temperature rises by 1 degree every 10 minutes

Clinical features

  • Hyperthermia
  • Jaw rigidity persists after sux has worn off
  • Tachycardia and tachypnoea
  • Increased EtCO2
  • Increased O2 consumption
  • Profuse sweating
  • Hyperkalemia
  • Cyanosis
  • Generalised rigidity, increased muscle tone
  • Prolonged bleeding

Complications

  • DIC
  • Rhabdomyolysis
  • Hypotension
  • Lactic and respiratory acidosis

Investigations

  • ABG (lactate, pH and K+)
  • CK
  • Urinary myoglobin

Management

  • Abort the procedure
  • Stop the anaesthetic
  • Give 100% FiO2 and hyperventilate
  • Start active cooling
  • Block the neuromuscular junction with a non-depolarising agent
  • Administer dantrolene: 20mg as a rapid infusion
  • Keep giving dantrolene until features of resolution begin to manifest
  • Give steroids; eg. 2g of methylprednisolone
  • Maintain high urine output to avoid renal damage from rhabodomyolysis
  • Correct coagulopathy

References

Hopkins, P. M. "Malignant hyperthermia: advances in clinical management and diagnosis." British journal of Anaesthesia 85.1 (2000): 118-128.

Glahn, K. P. E., et al. "Recognizing and managing a malignant hyperthermia crisis: guidelines from the European Malignant Hyperthermia Group." British journal of anaesthesia 105.4 (2010): 417-420.