Epidural Nalbuphine Versus Dexmedetomidine as Adjuvants to Bupivacaine in Lower Limb Surgeries Under Combined Spinal-epidural Anesthesia

Surgical patients need adequate and effective intraoperative anesthesia and postoperative analgesia. Neuroaxial block including lower limb spinal and epidural blocks have a long history of effective anesthesia and lower limb pain relief. Spinal anesthesia is a simple method requiring small dose of local anesthetic agent to give immediate and effective sensory and motor block. But one of its major side effects is hypotension and difficulty in controlling the level of the block [1]. Meanwhile, epidural anesthesia is a safe, well-practiced, not expensive neuroaxial block technique that provides intraoperative anesthesia and postoperative analgesia. So, the combined spinal epidural block (CSE) aims to achieve intense sensory and motor anesthesia and prolong the duration of analgesia intraoperative extending to postoperative period [2].

Neuroaxial anesthesia and analgesia provide perfect analgesic effect by inhibiting nociceptive transmission from peripheral to central neuronal system, but this advantage limited by short half-life of the current local anesthetics. Bupivacaine is a local anesthetic which belongs to amide group of anesthetic agents that has been widely used for local infiltration, peripheral nerve block, spinal and epidural anesthesia and despite relatively long duration of action, still has insufficient time for postoperative analgesia [3].

Several neuroaxial adjuvants such as (opioids, dexamethasone, magnesium sulphate, midazolam and dexmedetomidine) can be added to local anesthetics to prolong its duration of anesthesia and decrease the dose requirement of local anesthetics [4].

Nalbuphine, a derivative of 14-hydroxy morphine is a strong analgesic with mixed kappa agonist and µ antagonist properties. Its potency is equal to morphine, but exhibits a ceiling effect on respiratory depression. It has the potential to maintain and enhance µ-opioid based anesthesia while simultaneously mitigating the µ-opioid side effects [5].

Dexmedetomidine is an imidazole compound. It is a highly selective α-2 adrenergic agonist with an affinity 8 times more specific when compared to clonidine. It has sedative, sympatholytic and analgesic effects that blunt cardiovascular responses both intraoperative and in the perioperative period. Patients remain calm and sedated when undisturbed but arouse readily with stimulation [6]. Dexmedetomidine causes manageable hypotension and bradycardia, but the striking feature of this drug is the lack of opioid-related adverse effects like respiratory depression, pruritis, nausea, and vomiting [7].