Comparative evaluation of morphine versus nalbuphine as intrathecal adjuvants to 0.5% hyperbaric bupivacaine for subarachnoid block in lower abdominal surgeries: a prospective randomized double blind study.

Spinal anesthesia is the most frequently used procedure for lower abdominal surgeries as this technique is both easy to administer and very economical. It has the benefit of being cost-effective, easy technique of administration, rapid onset of action, and relatively fewer adverse effects, and most importantly patient remaining aroused throughout the procedure. A  postoperative period free from pain and stress definitely helps in early mobilization and recovery, thereby reducing morbidity and mortality. However, due to the short duration of action and early arising post-operative pain the role of various adjuvants has been proposed and evaluated. Post-operative pain and tissue injury associated with surgery initiate a systemic stress response that has neuroendocrine, immunological, and hematological responses. Intrathecal (IT) administration of adjuvants to local anesthetics improves quality and duration of the spinal blockade, prolongs post-operative analgesia and also reduce the dose and amount of local anesthetic drugs during the subarachnoid block (SAB). The most commonly utilized adjuvants which are used to improve the quality and duration of neuraxial anesthesia include intrathecal opioids (morphine, nalbuphine , fentanyl and sufentanil), alpha 2 adrenergic agonists (clonidine and dexmedetomidine). The technique of intrathecal administration of opioids along with local anesthetics has been extensively studied and found to provide superior quality of analgesia in a number of surgical procedures. The rationale for the combination of opioids and local anesthetics is that these drugs eliminate pain by acting at two different sites. Local anesthetics act at the nerve axon and the opioid at the receptor site in the spinal cord. Morphine is the basic reference opioid to which all analgesics of its kind are compared. It is a phenanthrene derivative, the prototypical agonist opiate at mu and kappa opioid receptors. Its poor lipid solubility favours its behaviour when injected into the intrathecal space-producing slow analgesic onset with long duration and rostral migration that facilitates some of its side effects such as pruritus, emesis, hypothermia, and respiratory depression. Nalbuphine is highly lipid soluble synthetic opioid analgesic with agonist-antagonist activity. It acts as antagonist at µ-receptors and agonist at κ-receptors. Its affinity to k-opioid receptors results in analgesia, sedation, and cardiovascular stability with minimal respiratory depression. Nalbuphine is widely studied as an adjuvant to local anesthetics in central neuraxial techniques to improve the quality of perioperative analgesia as it provides reasonably potent analgesia for visceral nociception.The present study is aimed to comparatively evaluate the clinical efficacy of morphine with nalbuphine when co-administered intrathecally with 0.5% hyperbaric bupivacaine for lower abdominal procedures.