Ketamine and magnesium association reduces morphine consumption after scoliosis surgery: prospective randomised double-blind study

BACKGROUND: Scoliosis repair is a major orthopaedic surgery associated with severe post-operative pain. Ketamine and magnesium have an established efficacy as morphine-sparing agents. Our purpose was to evaluate the morphine-sparing effect of both magnesium and ketamine given simultaneously compared with ketamine alone during scoliosis surgery. METHODS: Fifty patients scheduled for posterior instrumentation were randomised in a prospective double-blind study. The Gr (K + Mg) received, after induction, an intravenous (IV) bolus of ketamine 0.2 mg/kg and magnesium 50 mg/kg, followed by continuous infusion of ketamine (0.15 mg/kg/h) and magnesium (8 mg/kg/h) until extubation. The Gr (K) received the same dose of ketamine associated with bolus and continuous infusion of normal saline. All patients received multimodal analgesia associated with IV morphine administered via patient-controlled analgesia pump. Morphine consumption, visual analogue scale (VAS) pain scores and occurrence of side effects were followed until 48 h post-operatively. Sleep quality and patient satisfaction were also followed. P < 0.05 was considered statistically significant. RESULTS: The average cumulative morphine consumption was significantly lower in the Gr (K + Mg) compared with the Gr (K) at post-operative hours 4, 8, 12, 18, 30, 36 and 48. The relative difference in the post-operative morphine consumption was 29.5%: Gr (K + Mg) 51.53 mg vs. Gr (K) 73.16 mg. VAS scores were not statistically different between the two groups. However, qualities of sleep and satisfaction scores on the first night were significantly better in the Gr (K + Mg) (P = 0.027 and P = 0.016, respectively). CONCLUSION: Ketamine and magnesium association reduces the post-operative morphine consumption after scoliosis surgery. It seems to provide a better sleep quality and improves patient satisfaction.