The addition of a small-dose ketamine infusion to tramadol for postoperative analgesia: A double-blinded, placebo-controlled, randomized trial after abdominal surgery

BACKGROUND: There are few data on combining ketamine with tramadol for postoperative analgesia in humans. We tested the hypothesis that adding ketamine to tramadol would improve analgesia after major abdominal surgery. METHOD: In this double-blind, randomized, controlled trial, adult patients (n = 120) having elective laparotomy were randomly assigned to a ketamine group (intraoperative ketamine 0.3 mg/kg and postoperative infusion at 0.1 mg·kg·h) or control group (equivalent volume/rate of normal saline). All patients received intraoperative tramadol 3 mg/kg and a tramadol infusion (0.2 mg·kg·h) for 48 h postoperatively and had morphine patient-controlled analgesia available for rescue analgesia. RESULTS: The ketamine group had less pain at rest (P = 0.01) and with movement (P = 0.02) and required less morphine (P = 0.003) throughout the 48-h study period. In the 0-24 h period, ketamine improved subjective analgesic efficacy (P = 0.008), was less sedating (P = 0.03), and required fewer physician interventions to manage severe pain (P = 0.01). Hallucinations were more common in ketamine patients, but other side effects were similar. CONCLUSION: Small-dose ketamine was a useful addition to tramadol and morphine after major abdominal surgery.