Presumptive generalised post-anaesthetic myopathy in a sevoflurane-anaesthetised obese pony

An 18-year-old, obese, female French saddle pony presented with chronic lameness. After being diagnosed with laceration of the manica flexoria of the deep flexor tendon, general anaesthesia for a tenotomy and desmotomy was planned. After induction of general anaesthesia, the horse was positioned in left lateral recumbency. General anaesthesia was maintained for 110 minutes with sevoflurane in 70% inspired oxygen, and controlled mechanical ventilation was provided to maintain normocapnia. Arterial pressure remained within normal limits, with mean arterial pressure above 70 mmHg throughout the procedure. After regaining consciousness, the horse was weak on the left hindlimb, unable to stand and uncomfortable. Creatine kinase was measured at 599 U L-1 (standard range: 110-250 U L-1). A post-anaesthetic myopathy was suspected, and supportive therapies were started, with liberal fluid therapy, acepromazine, phenylbutazone and analgesics administration. Despite these treatments, the condition progressively worsened and became generalised. Attempts at slinging the pony proved ineffective, and the clinical condition deteriorated. Due to the poor prognosis, the owner elected for euthanasia.