Hemorrhagic myelomalacia following general anesthesia in a horse

An 18-month-old male Belgian horse was anesthetized and placed in dorsal recumbency for cryptorchidectomy. Xylazine was used for sedation and guaifenesin with thiamylal for induction of anesthesia. A surgical plane of anesthesia was maintained with halothane. During anesthesia, second-degree atrio-ventricular blocks, hypoventilation and a 1-minute duration rise of mean arterial pressure (80 to 130 mm Hg) occurred. Total anesthesia time was 1 hour. On recovery from anesthesia, the horse exhibited flaccid paralysis of the hind limbs and was only able to elevate himself to a dog sitting position. The horse was humanely euthanized 22 hours postoperatively due to a lack of improvement in clinical signs. Hemorrhagic poliomyelomalacic lesions of the spinal cord were observed on histopathological examination of the spinal cord.