[Effect of low-dose intravenous ketamine in postoperative analgesia for hysterectomy and adnexectomy].

OBJECTIVE: To evaluate the efficacy of low dose ketamine (0.15 mg/Kg i.v.) as a pre-emptive pain relief after general anesthesia.

METHOD: Sixty-nine gynecological surgery patients were enrolled in this prospective, double-blind study. All received total intravenous anesthesia and were randomized to group A (n = 23) to receive preoperative ketamine, to group B (n = 23) to receive postoperative ketamine or to group C (n = 23) to receive placebo. A patient-controlled anesthesia device with morphine and ketorolac was used to provide postoperative pain relief. We evaluated the time taken to resume spontaneous breathing and to administer the first analgesic dose; the pain score on a visual analogue scale at rest at 1, 6, 24, 48 h and on the fifth day, and upon movement on the first and fifth days; and morphine consumption at 6, 24 and 48 h.

RESULTS: Recovery of spontaneous breathing occurred later in group B (10 +/- 5 min) than in group A (6.68 +/- 3.64 min; p < 0.05) or in group C (8 +/- 4 min). The first analgesic dose was infused later in group B (45.24 +/- 16.16 min; p < 0.001) than in group A (26.45 +/- 11.65 min) or in group C (25.47 +/- 9.19 min). The pain scores at rest were similar. On the fifth day, pain upon movement was less intense for patients treated with ketamine (group A 12 [10-21] and group B 13.5 [2-22]) than in patients treated with placebo (group C 23 [15.5-36.75]) (p < 0.05 group C vs. group A; and p < 0.01 group C vs. group B). Morphine consumption at 6 h was less in group B than group C (p < 0.01).

CONCLUSIONS: A low dose of ketamine has no preemptive analgesic effect.