The benefits of intraoperative small-dose ketamine on postoperative pain after anterior cruciate ligament repair

In a randomized, double-blinded study with three parallel groups, we assessed the analgesic effect of intraoperative ketamine administration in 45 ASA physical status I or II patients undergoing elective arthroscopic anterior ligament repair under general anesthesia. The patients received either IV ketamine 0.15 mg/kg after the induction of anesthesia and before surgical incision and normal saline at the end of surgery (PRE group); normal saline after the induction of anesthesia and before surgical incision and IV ketamine at the end of surgery (POST group); or normal saline at the beginning and the end of surgery (CONT group). Anesthesia was performed with propofol (2 mg/kg for induction, 60-200 mu g.kg(-1).min(-1) for maintenance), sufentanil (0.2 mu g/kg 10 min after surgical incision, followed by an infusion of 0.25 mu g.kg(-1).h(-1) stopped 30 min before skin closure), vecuronium (0.1 mg/kg), and 60% N2O in O-2 via a laryngeal mask airway. Postoperative analgesia was initially provided with IV morphine in the postanesthesia care unit, then with IV patient-controlled analgesia started before discharge from the postanesthesia care unit. Pain scores, morphine consumption, side effects, and degree of knee flexion were recorded over 48 h and during the first and second physiotherapy periods, performed on Days 1 and 2. Patients in the ketamine groups required significantly less morphine than those in the CONT group over 48 h postoperatively (CONT group 67.7 +/- 38.3 mg versus PRE group 34.3 +/- 23.2 mg and POST group 29.5 +/- 21.5 mg; P < 0.01). Better first knee flexion (CONT group 35 +/- 10 degrees versus PRE group 46 +/- 12 degrees and POST group 47 +/- 13 degrees; P < 0.05) and lower morphine consumption (CONT group 3.8 +/- 1.7 mg versus PRE group 1.2 +/- 0.4 mg and POST group 1.4 +/- 0.4 mg; P < 0.05) were noted at first knee mobilization. No differences were seen between the PRE and POST groups, except for an increase in morphine demand in the PRE versus the POST group (P < 0.05) in the second hour postoperatively. Implications: We found that intraoperative small-dose ketamine reduced postoperative morphine requirements and improved mobilization 24 h after arthroscopic anterior ligament repair. No differences were observed in the timing of administration. Intraoperative small-dose ketamine may therefore be a useful adjuvant to perioperative analgesic management.