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 μg/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 μg/kg/h in MG and CG, respectively) was administered after a loading dose (5 and 10 μg/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.