Malignant Hyperthermia Diagnosis and Management

Pathophysiology and Clinical Manifestations

The earliest and most specific sign of malignant hyperthermia is an increase in end-tidal CO2 (ETCO2) despite attempts to control it by increasing minute ventilation, as stated by the American Society of Anesthesiologists 1, 2, 3
Initial clinical features result from homeostatic mechanisms within skeletal muscle cells that compensate for increased cytoplasmic calcium released by triggering drugs, leading to increased intermediary metabolism, and increased oxygen consumption and carbon dioxide production 2, 3
The excessive carbon dioxide production manifests as increased ETCO2 in mechanically ventilated patients or increased respiratory rate in spontaneously breathing patients, which is resistant to control by increasing minute ventilation during an MH reaction 3, 4, 5

Increased ETCO2 is the cardinal clinical feature resulting from excessive carbon dioxide production, and it appears before temperature elevation in the typical progression of MH, according to the American Heart Association 1, 3, 4, 5
Tachycardia accompanies increased carbon dioxide production due to sympathetic nervous system activation, and the upward trend in heart rate is more useful diagnostically than attainment of a specific value, as recommended by the European Society of Anesthesiology 2, 3, 4
Hyperthermia usually starts to increase by the time diagnosis is made, and temperature increase that begins before any evidence of increased carbon dioxide production is not caused by MH, as stated by the American College of Cardiology 5

The presence of increasing carbon dioxide production and heart rate, with exclusion of alternative causes, should be sufficient to diagnose suspected MH and initiate treatment, as recommended by the American Society of Anesthesiologists 4, 5
The timing of MH reactions is highly variable, and may become apparent within 10 minutes of exposure to triggering agents, or may be delayed for several hours, especially with desflurane, according to the European Society of Anesthesiology 1, 2

Delay in commencing treatment is associated with increased mortality and complications, and an unexplained, unexpected progressive increase in carbon dioxide production should lead to a high index of suspicion, as stated by the American Heart Association 6, 7

When MH is suspected based on rising ETCO2, immediate actions should include eliminating the triggering agent, administering dantrolene sodium as a specific antidote, commencing active body cooling, increasing minute ventilation 2-3 times normal, and inserting activated charcoal filters on inspiratory and expiratory limbs of circuit if available, as recommended by the American Society of Anesthesiologists 6, 8, 9