Suspected vagal reflex bradycardia in a calf undergoing surgical resection of an infected urachus

A four-week-old Charolais heifer was referred for surgical treatment of an infected umbilicus. The heifer was sedated with intravenous xylazine, and an indwelling intravenous jugular cannula was placed. General anaesthesia was induced with intravenous ketamine and maintained with isoflurane in 100 per cent oxygen. Surgical exploration of the abdomen revealed an infected urachus originating from the apex of the bladder and bilaterally infected umbilical arteries. Anaesthesia was stable for 35 minutes until surgical traction of the urachus and umbilical arteries resulted in bradycardia and hypoventilation/apnoea, which resolved when the traction was released, but recurred as and when traction was reinitiated. Collaboration between the anaesthetist and the surgeon was necessary to progress the procedure while minimising perturbations in physiology. Towards the end of the procedure, during peritoneal lavage with sterile saline, severe bradycardia developed (heart rate <20 bpm) and was successfully treated with atropine 0.04 mg/kg intravenously. The heifer recovered uneventfully from anaesthesia.