Malignant hyperthermia

MH is caused by a defect in the gene coding for the ryanodine receptor, which releases calcium ions from the sarcoplasmic reticulum. In MH, the receptors open and stay open, uncoupling contraction from excitation. MH is common in some breeds of pig, but probably occurs in all species. It is usually triggered by the anaesthetic halothane.

In the full-blown syndrome there is a rapid and sustained rise in body temperature, without shivering, either in the operating theatre or in the recovery room, in the absence of any obvious cause such as infection or a hot and humid environment. Tachycardia, cyanosis, generalised muscle rigidity, and cardiac arrhythmias are common clinical signs. There may be heating and rapid exhaustion of the soda-lime canisters. Acidosis is an early finding and there may also be hyperkalaemia, hyperphosphataemia, and hypocalcaemia from muscle-cell breakdown. Rhabdomyolysis is an important feature of the syndrome and is best demonstrated by measuring serum CK, which usually peaks on the second or third day after the reaction. Tenderness and swelling of muscles may develop, especially in the thighs. Myoglobinaemia and myoglobinuria are common and renal failure may result from the rhabdomyolysis. Another complication is disseminated intravascular coagulation.

If your pig goes rigid, stop administration of halothane, ventilate with oxygen and cool down with cold water. The definitive treatment is the ryanodine receptor antagonist dantrolene. Unfortunately, dantrolene is expensive and never available when needed.

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