15. Malignant Hyperthermia

Triad of hyperthermia, muscle rigidity, and metabolic acidosis

– Occurs in genetically susceptible individuals (both autosomal dominant and recessive inheritance patterns)

– Triggered by general anaesthetics (volatile gases, succinylcholine)

– Hypermetabolic state induced in skeletal muscle

– Mortality decreased from 90% to 7 % with appropriate treatment

– Muscle biopsies can be used to test for susceptibility

– Disordered calcium regulation in skeletal muscle fibres may play a role in the pathophysiology of MH. There is decreased ability to retain and regulate calcium in the sarcoplasmic reticulum.

Increased intacellular calcium may lead to excessive and prolonged muscle contraction with resulting excessive heat production

Increased calcium also uncouples oxidative phosphorylation

MH is resistant to neuromuscular blockers

Dantrolene is a direct skeletal muscle relaxant which blocks calcium release from the sarcoplasmic reticulum

Dose is 2 mg/kg iv q5min until resolution

Procainamide has similar action to dantrolene and is the drug of choice for MH associated dysrhythmias

 Associated with depolarizing neuromuscular blocking agents or volatile general anesthetics in genetically susceptible individuals

Treatment: withdrawal of inciting agent, supportive care, and dantrolene administration.

 

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