Effect of IV Nalbuphine on Postoperative Nausea and Vomiting Following Intrathecal Morphine in Patients Undergoing Inguinal Hernia Repair

Bupivacaine hydrochloride is a commonly used local anesthetic in spinal anesthesia, however, the duration of spinal analgesia by bupivacaine is limited to about 75- 150 minutes.2 Therefore, various additives have been used with bupivacaine to prolong its effects and improve the quality of analgesia.(1) Opioids are the most popular used adjuvants added to bupivacaine in spinal blockade to obtain a sufficient intraoperative visceral analgesia and increase the duration and quality of postoperative analgesia, with less sympathetic block and hemodynamic effect .(2) morphine is commonly used for analgesia, but is frequently associated with postoperative nausea and vomiting (PONV) and pruritus, These side effects may lead to patient discomfort and prolonged hospital stay thus limiting the usefulness of IT morphine.

Nalbuphine is a mu receptor antagonist and a ĸappa receptor agonist.10 When added as an adjunct to intrathecal local anesthetics, it provides good analgesia with decreased incidence and severity of mu receptor side effects(3) Morphine binds most readily to the mu-opioid receptor and less well to the kappa-opioid receptor. So, the undesirable adverse events of morphine are thought to result from agonism at the mu-opioid receptor.5 Many drugs have been tried with morphine to potentiate its analgesic effects or to reduce the adverse events.6 Nalbuphine is a mixed opioid agonist-antagonist that acts mainly through kappa-opioid receptors, and it may attenuate mu-opioid receptor related side effects.3 Moreover, recent studies suggested that the analgesic effects of morphine and nalbuphine may be additive.

The addition of nalbuphine to intrathecal bupivacaine plus morphine significantly reduced the incidence and severity of postoperative nausea and vomiting and pruritus without affecting analgesic potency..(4)