Preoperative epidural administration of lidocaine-methadone or lidocaine-fentanyl in female dogs undergoing elective ovariohysterectomy

We compared the analgesia and cardiopulmonary changes induced by epidural methadone or fentanyl in combination with lidocaine in female dogs undergoing elective ovariohysterectomy and anesthetized with propofol. Eighteen female dogs were randomly assigned to two groups and given either methadone (0.3 mg kg?¹) + 2% lidocaine without vasoconstrictor (LM) or fentanyl (5 µg kg?¹) + 2% lidocaine without vasoconstrictor (LF). The drugs were administered epidurally in a volume of 0.25 ml kg?¹. Heart rate (HR), respiratory rate (RR), rectal temperature (RT), systolic blood pressure (SBP), and blood glucose levels were recorded before and 15 minutes after premedication (T0 and T1); 15 minutes after epidural administration (T2); five minutes after dermotomy (T3); five minutes after clamping of the ovarian pedicle (T4); five minutes and 1, 3, 6, 12, 18, and 24 hours (T5, T6, T7, T8, T9, T10, and T11, respectively) after surgery. The number of additional propofol injections and total propofol dose (mg kg?¹) were recorded. Analgesia was assessed using a numerical descriptive scale. SBP and HR were similar in both groups, but hypotension was detected in animals from both groups at different times. Respiratory rate decreased significantly at T6 in the LF group and was lower than in the LM group. Hypothermia was observed in animals from both groups, but RT was significantly lower than baseline values only at T4 in the LM group. Blood glucose levels increased significantly only in the LF group at T4, T7, and T8. All animals in the LF group and eight animals in the LM group required additional propofol injections at T4, but no significant differences were detected in the number of propofol injections and total propofol dose between the LF (3 ± 1 injections, 7.5 ± 4.5 mg kg?¹) and LM (2 ± 2 injections, 4.5 ± 3.4 mg kg?¹) groups. The latency period, anesthetic period, and the duration of surgery were similar in both groups. No animals required rescue analgesia. The lidocaine-methadone and lidocaine-fentanyl combinations caused minimal cardiorespiratory changes, but did not abolish pain at the time of handling of the ovarian pedicle.