First report of malignant hyperthermia syndrome in an American Guinea hog

A 3-year-old intact female American Guinea hog that was presented for an elective ovariohysterectomy appeared systemically healthy, with no overt medical conditions. Premedication with clonazepam, tiletamine-zolazepam, and xylazine; anesthetic induction with propofol and maintenance with isoflurane with oxygen on spontaneous ventilation; a ketamine infusion; and morphine for analgesia were provided. Approximately 95 min after isoflurane was initiated, the pig acutely became hyperthermic and severely hypercapnic, with hyperkalemia, hyperlactatemia, and severe metabolic and respiratory acidosis. With high suspicion of malignant hyperthermia syndrome (MHS), isoflurane was discontinued, and active cooling, ventilatory support, dantrolene, aggressive fluid therapy, lidocaine, insulin, and dextrose were administered. The pig developed ventricular tachycardia with subsequent cardiopulmonary arrest. Cardiopulmonary resuscitation was attempted without success. Necropsy findings were suggestive of MHS and genetic testing confirmed a dimutant RYR1 gene. Key clinical message: This is the first report of MHS in a subject from a porcine companion breed and of an atypical, delayed onset. As MHS is life-threatening, preanesthetic genetic testing and/or preemptive treatment with oral dantrolene should be considered for pigs undergoing inhalant-based anesthesia.