Background: Ketamine decreases postoperative morphine consumption, but its optimal dosing and duration of administration remain unclear. In this study, we compared the effects of ketamine administration on morphine consumption limited to the intraoperative period, or continued for 48 h postoperatively.
Methods: Eighty-one patients scheduled for abdominal surgery were prospectively randomized under double-blind conditions to three groups: (1) PERI group receiving intraoperative and postoperative ketamine for the first 48 h after surgery (2 microg x kg(-1) x min(-1) after a 0.5 mg/kg bolus); (2) INTRA group receiving intraoperative ketamine administration only (2 microg x kg(-1) x min(-1) after a 0.5 mg/kg bolus); and (3) CTRL group receiving placebo. Morphine consumption, visual analog scale scores and side effects (sedation score, nausea-vomiting score, nightmares, psychiatric disorders, or delusions) were recorded for the first 48 h.
Results: Cumulative morphine consumption 24 h after surgery was significantly lower in the PERI group (median = 27 mg, interquartile range = [19]) than in the INTRA group (48 mg [41.5]) and CTRL group (50 mg [21]) (P < 0.005). Postoperative visual analog scale scores were significantly lower in the PERI group and INTRA group than in the CTRL group (P < 0.001). A higher rate of nausea was observed in the CTRL group compared with the PERI group (27% vs 4%, P = 0.005). No difference in sedation scores or psychiatric disorders was observed among groups.
Conclusions: Low-dose ketamine improved postoperative analgesia with a significant decrease of morphine consumption when its administration was continued for 48 h postoperatively, with a lower incidence of nausea and with no side effects of ketamine.