Anaesthesia of pigs sensitive to malignant hyperthermia
Lucke, J.N.; Hall, G.M.; Lister, D.
Veterinary Record 100(3): 45-48
1977
ISSN/ISBN: 0042-4900 PMID: 319590 Document Number: 121525
The factors which appear to be linked in this syndrome are breed, low fat:muscle ratio, high incidence of PSE meat, susceptibility to stress and anaesthetic-induced malignant hyperthermia (MH). In this study, stress induced by mating or by handling a nearby animal caused the death of two Pietrain pigs. Halothane anaesthesia elicited symptoms of tachycardia, tachypnoea, rigidity of limb muscles, acidosis, hypercapnia, skin cyanosis and raised body temperature (45 deg C), which were fatal in all cases. Biochemical changes (including raised serum potassium and phosphate levels) preceded the rise in muscle temperature, after which nasal and rectal temperatures rose; while abdominal skin temperature decreased throughout. Despite the acidosis and hyperkalaemia, the heart responded to the increased metabolic rate by tachycardia and increased cardiac output. Belgian Landrace and Poland China pigs were slower to show these effects with halothane, while crossbred Landrace pigs were even less susceptible. When halothane was given during barbiturate/nitrous oxide/oxygen anaesthesia, one third of the animals died, but more slowly. The remainder developed MH if doses of 50 mg suxamethonium were given i/v. With suxamethonium, there was an apparently correlated rise in plasma lactate and catecholamines (particularly noradrenaline), which constituted a viscious circle, perpetuating the MH syndrome. When this was blocked by reserpine, phentolamine or propronolol, the increase in muscle metabolic rate occurred, but without some or all of the MH syndrome. Recommendations for MH susceptible pigs include avoidance of Immobilon, use of pre-anaesthetic sedation, induction of anaesthesia by i/v barbiturate, and maintenance of anaesthesia by oxygen-rich nitrous oxide. A non-depolarizing neuromuscular blocking agent may be used for additional muscle relaxation. If MH symptoms arise, oxygen and sodium bicarbonate should be given to combat acidosis, and procaine, magnesium sulphate or dantrolene may correct changes in muscle metabolism, if these have not progressed too far. The effect of magnesium on the heart may have to be corrected by giving calcium salts.