Improvement of Pain Treatment after Major Abdominal Surgery by Intravenous S(+)-Ketamine

The use of intraoperative racemic ketamine for pain prevention after abdominal surgery is controversial. We compared one preincisional IV injection of S(+)-ketamine with its preincisional and repeated intraoperative use in 45 patients undergoing surgery with epidural and general anesthesia. S(+)-ketamine is a new drug formulation that contains the more potent S(+)-stereoisomer of ketamine. Patients were randomized to receive placebo, 0.5 mg/kg preincisional S(+)ketamine, or 0.5 mg/kg preincisional and 0.2 mg/kg intraoperative S(+)-ketamine repeated at 20-min intervals. In the postoperative period, epidural ropivacaine (2 mg/mL; 0.12 mL · kg^-1 · h ^-1) was infused for pain therapy. Patients who received repeated S(+)-ketamine reported smaller pain scores than those who received placebo after awakening and 3 and 6 h later (P ≤ 0.05). Fewer patients with repeated S(+)-ketamine required additional analgesics than those with placebo (P ≤ 0.05). Cumulative consumption of additional diclofenac and dextropropoxyphene at 24 h was less after single (P < 0.05) and repeated (P < 0.05) S(+)-ketamine versus placebo. After awakening, patients who received repeated S(+)-ketamine reported being in a better mood than those in the other groups (P < 0.05). No psychotomimetic side effects were noted. In conclusion, preincisional and repeated intraoperative small-dose S(+)-ketamine added to general and epidural anesthesia causes better postoperative pain relief than general and epidural anesthesia alone.