Fentanyl‐induced muscle rigidity in a dog during weaning from mechanical ventilation after emergency abdominal surgery: A case report

A 22.5‐kg, 8.4‐year‐old female mixed breed dog was presented for an emergency ovariohysterectomy for pyometra. No neurological abnormalities were observed on preoperative physical examination. Surgery was completed uneventfully under fentanyl‐ and sevoflurane‐based anaesthesia. Cardiorespiratory indices remained stable under mechanical ventilation throughout the procedure. Approximately 23 min after the discontinuation of fentanyl infusion, the investigator noticed jaw closure and stiffness and thoraco‐abdominal muscle rigidity. To rule out fentanyl‐induced muscle rigidity, naloxone was administered. Following administration of naloxone, there was a return of spontaneous respiratory effort, indicated by capnogram and visible chest wall excursion. Based on the clinical signs and response to naloxone administration, the dog was diagnosed with suspected fentanyl‐induced muscle rigidity. Six minutes after the return of spontaneous respiration, the dog was extubated uneventfully without additional naloxone administration. During 4 days of postoperative hospitalization, no recurrent muscle rigidity was observed, and the patient was discharged safely. The total dose of fentanyl administered was 0.61 mg (27 μg kg(−1)).