Intravenous ketamine or fentanyl prolongs postoperative analgesia after intrathecal neostigmine.

The purpose of this study was to determine whether intravenous (i.v.) ketamine would enhance analgesia from intrathecal (IT) neostigmine compared with combining i.v. fentanyl with IT neostigmine. Sixty patients undergoing vaginoplasty under spinal anesthesia were assigned to one of six groups (n = 10). Patients were premedicated with midazolam plus the i.v. test drug. The IT drugs were 20 mg bupivacaine plus saline or 50 micrograms neostigmine. The control group (CG) received saline i.v. and IT. The neostigmine control group (NCG) received saline i.v. and neostigmine IT. The ketamine group (KG) received ketamine 0.2 mg/kg i.v. and saline IT, and the ketamine neostigmine group (KNG), ketamine i.v. and neostigmine IT. The fentanyl group (FG) received fentanyl 1 microgram/kg i.v. and saline IT, and the fentanyl neostigmine group (FNG), fentanyl i.v. and neostigmine IT. The time to first rescue analgesic was longer for the FNG and KNG compared with the CG, with less rescue analgesic consumption (P < 0.02 and P < 0.01, respectively). Only the FNG had significantly intraoperative nausea/vomiting (P < 0.02). In conclusion, the combination of i.v. ketamine and IT neostigmine results in prolonged postoperative analgesia and less intraoperative nausea and vomiting than the combination of i.v. fentanyl and IT neostigmine.