Nalbuphine as an Adjuvant to Caudal Bupivacaine for Postoperative Analgesia in Children Undergoing Hypospadius Repair

The somatic innervation of the lower urogenital system arises principally from the spinal nerves sacral 2 to sacral 4 by way of the pudendal nerve. After passing under the sacrospinous ligament and over the sacrotuberous ligament through Alcock's canal, the pudendal nerve passes through the transverse perineal muscle to course on the dorsum of the penis as the dorsal nerve of the penis. The dorsal nerve of the penis is thought to be a sensory nerve. The autonomic innervation of the penis arises from the vesical and prostatic plexus, which is composed of sympathetic nerves from lumbar 1 and lumbar 2, and parasympathetic nerves from sacral 2 to sacral 4. The cavernosal nerve leaves the pelvis between the transverse perineal muscles and the membranous urethra before passing beneath the arch of pubis to supply each corporal body.

After the pudendal nerve leaves the pudendal canal, two main terminal branches arise, the inferior rectal and the perineal nerves. The function of the inferior rectal nerve is motor innervation of external anal sphincter and is thought to be devoid of urogenital function. Sensory portions of the inferior rectal nerve are important for perianal skin sensation. The perineal nerve has both a motor and sensory component. The motor efferents are known to innervate the pelvic musculature, mainly the bulbospongiosus muscle. To achieve complete anesthesia (analgesia) for hypospadius repair, afferent blockade must be complete at lumbar 1 through sacral 4.

Nalbuphine is a mixed k-agonist and µ-antagonist opioid of the phenanthrene group; it is related chemically to naloxone and oxymorphone. Nalbuphine leads to activation of spinal and supraspinal opioid receptors which leads to good analgesia with minimal sedation, minimal nausea and vomiting, less respiratory depression and stable cardiovascular functions. Safety and efficacy of nalbuphine have been established in the clinical field and its safety and efficacy also established via the epidural route. Nalbuphine was also added in epidural analgesia for adults and provided an increase in the efficacy and the duration of postoperative analgesia. The effect of nalbuphine addition in caudal anesthesia in pediatrics is not well established.