Intrathecal nalbuphine as an adjuvant to subarachnoid block: What is the most effective dose?

Nalbuphine has been used intrathecally as an adjuvant in previous studies, but none clearly state the most effective dose of nalbuphine. The purpose of our study was to establish the effectiveness of intrathecal nalbuphine as an adjuvant, compare three different doses and determine the optimum dose with prolonged analgesic effect and minimal side-effects.

In this prospective, randomized, double-blinded, controlled study, 100 ASA I and II patients undergoing lower limb orthopedic surgery under subarachnoid block (SAB), were randomly allocated to four groups: A, B, C and D, to receive 0.5 ml normal saline (NS) or 0.2, 0.4 and 0.8 mg nalbuphine made up to 0.5 ml with NS added to 0.5% hyperbaric bupivacaine 12.5 mg (total volume 3 ml), respectively. The onset of sensory and motor blockade, two-segment regression time of sensory blockade, duration of motor blockade and analgesia, visual analogue scale (VAS) pain score and side-effects were compared between the groups.

Two-segment regression time of sensory blockade and duration of effective analgesia was prolonged in groups C (0.4 mg nalbuphine) and D (0.8 mg nalbuphine) (P<0.05), and the incidence of side-effects was significantly higher in group D (P<0.05) compared with the other groups.

Nalbuphine used intrathecally is a useful adjuvant in SAB and, in a dose of 0.4 mg, prolongs postoperative analgesia without increased side-effects.