The Analgesic Efficacy of Perineural Nalbuphine as an Adjuvant to Bupivacaine in Ultrasound Guided Superficial Cervical Plexus Nerve Block for Thyroid Surgeries. A Double Blinded Randomized Controlled Trial.

Thyroidectomy is a common and painful procedure demanding analgesia. Patients may experience discomfort in swallowing, burning sensation in the throat, nausea, and vomiting, which are all caused by the surgical procedures or general anaesthesia. Thyroid surgeries induce brief postoperative pain caused by several mechanisms. One of the mechinsims of this Post-operative pain, believed to be due to the interruption of the rich nerve supply present in the neck.

A lot of drugs have been used to decrease this postoperative pain such as non-steroidal anti inflammatory drugs , opioids or regional blocks. Traditionally, opioids have been the mainstay of postoperative analgesia, specifically at thyroid and parathyroid surgical centers, where narcotic analgesics make up the major component of their postoperative pain control regimens. However, the use of opioids has been linked to an increased risk of postoperative complications that include ventilatory depression, sedation, postoperative nausea and vomiting (PONV), pruritis, difficulty of voiding, ileus and surgical site infections which can in turn contribute to delayed hospital discharge. Further acute and chronic opioids can have significant effects on the endocrine system. Longer-term use of opioids may lead to dependence and substance abuse disorder.

The skin overlying the neck, ear, angle of the mandible, shoulder, and clavicle is supplied by the superficial cervical plexus (SCP), which is a sensory neural plexus formed from the ventral rami of the first four cervical nerves (C1-C4). It emerges behind the posterior border of sternomastoid muscle.

Bilateral superficial cervical plexus block (SCPB) has shown good intraoperative and postoperative analgesia in upper neck surgeries especially in thyroidectomies, this regional block can be facilitated by using ultrasound guided technique as it provides good visualisation of the anatomical structures and decreases the complications.

There has always been a search for ideal adjuvants in peripheral nerve blocks which prolong the duration of analgesia with lesser adverse effects, Recently, nalbuphine was studied frequently as an adjuvant to local anesthetics in spinal and epidural and the results of all studies concluded that nalbuphine is effective when used as an adjuvant to local anaesthetics in spinal and epidural as it significantly prolongs the block duration.

The mechanism of perineural nalbuphine has not been clearly identified till now, previous studies demonstrated underlying mechanism could be interpreted that inflammatory response increases the synthesis of opioid receptors in the dorsal root ganglion neurons and enhances axonal transport and accumulation of opioid receptors in the sensory nerve endings in the inflamed tissue. Moreover, nalbuphine is an opioid receptors antagonist that allows for the peripheral analgesic effects of opioids in addition to the analgesic effect of its systemic absorption.

However, nalbuphine has not been studied extensively as an additive for peripheral nerve blocks as there was a minor research about it as an adjuvant to bupivacaine in brachial plexus block for upper limb surgeries and it showed that it prolongs the duration of sensory and motor blockades and reduces the requirement of analgesics in postoperative period. The superficial cervical block is a sensory block carrying sensory nerve fibers only with different axonal chemistry .

To our knowledge, no study till date compared the analgesic effect of perineural nalbuphine as an adjuvant to the superficial cervical block.