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Ovid: Oxford Handbook of Acute Medicine

Editors: Ramrakha, Punit S.; Moore, Kevin P. Title: Oxford Handbook of Acute Medicine, 2nd Edition Copyright ©1997,2004 Oxford University Press (Copyright 1997, 2004 by Punit S Ramrakha and Kevin P Moore) > Table of Contents > Chapter 9 – Endocrine emergencies > Malignant hyperthermia Malignant hyperthermia Malignant hyperthermia is a drug- or stress-induced catabolic syndrome characterized by excessive muscular contractions, a sudden rise in body temperature, and cardiovascular collapse. The incidence is ~1:15 000, with a 30% mortality. The cause is unknown, but may involve abnormal calcium homeostasis in skeletal muscle cells. The condition seems to be inherited in an autosomal dominant manner with variable penetrance. Drugs precipitating malignant hyperthermia

  • Halothane
  • Succinylcholine
  • Methoxyflurane and enflurane
  • Ketamine
  • Phencyclidine
  • Cyclopropane

Halothane and succinylcholine account for 80% of cases Drugs considered safe in malignant hyperthermia

  • Barbiturates
  • Nitrous oxide
  • Diazepam
  • Tubocurare
  • Pancuronium
  • Opiates

Diagnosis

  • Malignant hyperthermia most commonly presents in the early 20s. The early signs are muscular rigidity, sinus tachcardia and SVTs, increased carbon dioxide production, and hypertension.
  • Hyperthermia occurs late, and may be rapidly followed by hypotension, acidosis, and hyperkalaemia, which gives rise to ventricular tachycardia.
  • The condition almost always occurs peri-operatively.
  • The differential diagnosis includes phaeochromocytoma, thyrotoxic crisis, narcotic-induced hyperthermia in patients taking MAOIs, and drug-induced hyperthermia (caused by cocaine, phencyclidine, amphetamine, LSD, tricyclics, and aspirin), and certain injections such as malaria.
  • Plasma CPK is high.

Treatment The aim of therapy is to decrease thermogenesis, and promote heat loss.

  • Dantrolene: 1–2.5mg/kg intravenously every 5–10 minutes to a maximum dose of 10mg/kg. The dantrolene should then be continued at a dose of 1–2 mg/kg (iv or orally every 6 hours for 2 days).
  • Stop any anaesthetic agent.
  • External cooling by submersion is helpful. All adminsitered fluids should be chilled.
  • Procainamide should be given to all patients to prevent ventricular dysrhthmias (↑ uptake of calcium and may reduce hyperthermia).
  • Hypotension should be treated with saline/colloids ± isoprotenerol. Dopaminergic and α-adrenergic agonists reduce heat dissipation and should be avoided.
  • Some authorities advocate prophyalctic anti-convulsants as seizures are common.

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