A computer-generated randomization table was used to allocate patients equally into two groups, saline-fentanyl (SF) group (n=36) and Nefopam-fentanyl (NF) group (n=36). SF group, the control group received i.v. PCA with 100 ml solution containing 1250 µg of fentanyl in normal saline (12.5 µg/ml), while NF group, received i.v. PCA with the same volume of solution containing 1250 µg fentanyl plus 120 mg of nefopam in normal saline (fentanyl 12.5 µg/ml and nefopam 1.2 mg/ml). For both groups, a bolus of 1 ml with an 8-min lockout time was set, without any background continuous infusion during the study period.