BACKGROUND: Ketamine is a noncompetitive antagonist that blocKs the ion channel coupled to the N-methyl-D-aspartate receptor. This class of drugs may be useful for treatment of acute postoperative pain due to prevention of central sensitization of nocieceptors. We examined the effect of adding Ketamine to a patient-controlled epidural analgesia (PCEA) regimen. METHODS: Sixty parturients undergoing a Cesarean section received lumbar epidural anesthesia using 0.75% ropivacaine with 50ng of fentanyl and a PCEA using 0.15% ropivacaine and 50ng/mL of butorphanol with the addition of Ketamine 50 mg (K50, n = 20), 100 mg (K100, n = 20), or without (control, n = 20). The PCEA device was programmed to deliver 4 mL of a regimen (total 300 mL of solution with 0.15% ropivacaine plus 50ng/mL of butorphanol) with a 10 minute locKout interval. Visual analogue pain score, side effects and PCEA drug consumption were checKed during 48 hours postoperatively. RESULTS: PCEA drug consumption and incidence of nausea and vomiting were decreased by 25% and 25% (K50) and 35% and 29% (K100) compared with the control group. The severity of sedation was increased in the K50, and K100 groups more than the control group (P < 0.05). There were no differences in visual analogue pain score and other side effects among the groups. CONCLUSIONS: We conclude that adding low-dose Ketamine in a PCEA regimen using ropivacaine and butorphanol decreases the consumption of the PCEA drug and the incidence of nausea and vomiting and increases the severity of sedation.