The influence of timing of systemic ketamine administration on postoperative morphine consumption

Abstract

Study Objective: To determine the influence of timing of systemic ketamine administration on postoperative morphine consumption. Design: Prospective randomized study. Setting: Operating rooms, postanesthesia care unit, and gynecology service of a university hospital. Patients: Forty-five patients undergoing laparotomy for benign gynecologic pathologies were randomized into 3 groups. Interventions: In Group 1, before surgical incision. patients received 0.5 mg/kg ketamine IV, followed by normal saline infusion and normal saline IV at wound closure in group 1 (n = 15). In group 2 (n = 15), patients received 0.5 mg/kg ketamine IV before surgery, followed by ketamine infusion 600 mu g kg(-1) (.) h(-1), until wound closure and normal saline IV at that time, In the other group (group 3, n = 15), patients received normal saline IV before surgery, followed by saline infusion and then 0.5 mg/kg ketamine IV at wound closure. In the postoperative period, patient-controlled analgesia TV morphine was used for postoperative pain relief. First requested analgesic medication time was recorded. Postoperative pain was assessed by measuring morphine consumption at 0 to 2, 0 to 4, and 0 to 24 hours and visual analog scale (VAS) pain scores in response to cough at 2nd, 4th. and 24th hours and during rest at 0 to 2, 0 to 4, and 0 to 24 hours after surgery. Measurement and Main Results: First requested analgesia was shorter in group 1 than the others (P <.01). Mean VAS pain scores in response to cough at 24th hour in groups 2 and 3 were significantly lower than in group 1 (P <.001 and P <.01, respectively), Mean VAS pain scores during rest at 0 to 24 hours in groups 2 and 3 were significantly lower than in group 1 (P <.0 1 and P <.05, respectively). Morphine consumption was lower in groups 2 and 3 at 0 to 2 hours (P <.001 and P <.01). Moreover, morphine consumption at 0 to 4 hours in group 2 was significantly lower (P <.01). Conclusions: Lower pain scores and morphine consumption in groups 2 and 3 may be related to higher plasma ketamine concentrations caused by the higher doses and later administration. Our findings suggest that a single preoperative dose of ketamine provided less analgesia compared with other dosing regimens that included intraoperative infusions or postoperative administration.