Sparing Effect of a Low Dose of Intrathecal Morphine on Fentanyl Requirements During Spinal Surgery: A Preliminary Clinical Investigation in Dogs

OBJECTIVE: To evaluate the effect of preoperative intrathecal administration of a low dose of morphine on intraoperative fentanyl requirements in dogs undergoing cervical and thoracolumbar spinal surgery. STUDY DESIGN: Prospective randomized clinical study. ANIMALS: Dogs (n=18) matched by surgical procedure administered intrathecal morphine (MG) or no-treatment (control group, CG). METHODS: After premedication with romifidine (4 microg/kg, intravenously) and induction with propofol, anesthesia was maintained with sevoflurane in oxygen. Intrathecal morphine 0.03 (0.023-0.034) mg/kg was administered at lumbar level 41 (25-65) minutes before surgery in MG. Ketamine (0.5 mg/kg) was administered hourly, starting before incision. Fentanyl infusion (1.2 and 4.2 microg/kg/h in MG and CG, respectively) was administered after a loading dose (5 and 10 microg/kg in MG and CG, respectively), and boluses were given if an increase >20% in heart rate and arterial blood pressure was observed. Total amount of fentanyl administered was recorded, to calculate hourly requirements and predict plasma concentration using a computer simulation. RESULTS: Hourly fentanyl consumption and predicted plasma concentrations at the time of response to surgery were significantly lower in MG compared with CG. CONCLUSIONS: Preoperative administration of a low dose of intrathecal morphine has a sparing effect on intraoperative fentanyl requirements. CLINICAL RELEVANCE: Preoperative intrathecal administration of a low dose of morphine at the lumbar level represented a safe and effective mean of providing intraoperative analgesia in dogs undergoing cervical and thoracolumbar spinal surgery.