Nalbuphine group (Group N)
Epidural bolus dose of 12 ml (10 ml 0.25% bupivacaine plus 10 mg nalbuphine (Nalbuphine-Sunny Pharmaceutical, Nalbuphine HCL 20 mg/ml) in 2 ml volume, top-up dose of 8 ml (6 ml 0.25% bupivacaine plus 2 mg nalbuphine in 2 ml volume) [