Neuraxial Block: Epidural Adjuvants

Abstract

Epidural analgesia is a versatile and widely utilized anesthetic and analgesic modality in four primary areas surgery, obstetrics, chronic and acute pain management. Epidural solutions containing local anesthetics are often combined with adjuvant agents such as α-2 adrenergic agonists or opioids and administered as a bolus or infusion. Studies have demonstrated that spinal and peripheral blockade may be reliably augmented by the administration of any supplemental analgesic regardless of route. Clonidine, an α-2 adrenergic agonist, exerts analgesic effects through several mechanisms including direct activation of α-2 adrenergic receptors within the dorsal horn, direct cholinergic effect and direct inhibition of C and Aδ fibers. Co-administration of epidural clonidine and local anesthetic demonstrate several advantages including effective analgesia with reduced incidence of motor block, modulation of stress response and reduced post-operative opioid requirements. Opioids exert spinal and supraspinal analgesia through their action on μ receptors. The lipophilicity of the selected opioid will determine the onset of action, duration of action and spread. Combined therapy has been demonstrated to be superior to IV opioid patient controlled analgesia (PCA).