MALIGNANT HYPERTHERMIA
MALIGNANT HYPERTHERMIA
- Genetically determined life-threatening medical emergency.
- Occurs during or immediately after anesthesia.
MOA:
- Suddenly raised intracellular calcium due to stored calcium release in sarcoplasmic reticulum → stimulating contraction, rhabdomyolysis & hypermetabolic state → increased heat production.
- Receptor involved – Ryanodine.
Drugs causing malignant hyperthermia
- Succinylcholine (most common).
Inhalational anesthetics:
- Halothane (most common).
- Desflurane.
- Isoflurane.
- Enflurane.
- Sevoflurane.
- Methoxyflurane.
- Tricyclic antidepressants.
- Cyclopropane.
- Phenothiazines.
- Ether.
- Lignocaine.
- MAO inhibitors.
- Combination of Sch and Halothane has a much higher incidence.
Clinical features & diagnosis:
- Rise in end-tidal CO2 (>100 mm Hg) – Earliest & most sensitive indicator.
- (Normal value – 32-42 mm Hg).
- Tachycardia, arrhythmias & hypertension.
- Hyperthermia.
- Hyperkalemia.
- Metabolic acidosis.
- Elevated creatinine phosphokinase.
- Differentiates thyrotoxicosis & malignant hyperthermia.
- Muscle rigidity.
- Masseter spasm – If patient develops severe masseter spasm after suxamethonium –> Significant possibility of malignant hyperthermia.
- Increased myoglobin.
- Renal failure.
Diagnosis:
Definitive diagnostic procedure:
- Muscle biopsy contracture test.
- Most sensitive & specific test.
“Gold standard” test:
- Caffeine Halothane Contracture test (CHCT).
- Performed on freshly biopsied muscle.
Management
- IV dantrolene sodium – DOC.
- Stop all anesthetics immediately.
- Hyperventilation with 100% oxygen.
- Cooling of body by ice cooling.
- Correct acidosis and hyperkalemia.
- Maintain urine output.
Exam Important
- Receptor responsible for malignant hyperthermia is Ryanodine receptor
- Agent causing malignant hyperthermia is Succinylcholine
- Hyperkalemia, Metabolic acidosis & Hypertension are seen in malignant hyperthermia
- Halothane, Lidocaine, Isoflurane & Suxamethonium trigger malignant hyperthermia
- Sevoflurane is contraindicated for induction of anaesthesia in patient with H/O malignant hyperthermia
- Increased muscle metabolism by excess of calcium ions causes increased heat production in malignant hyperthermia
- Malignant hyperthermia is best treated with Dantrolene sodium
- End-tidal CO2 is increased to maximum level in Malignant hyperthermia
- Difference between thyrotoxicosis and malignant hyperthermia is Elevated serum CPK level in MH
- Malignant hyperthermia is caused due to Increased intracellular Ca.
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