Local Anesthetics

Abstract

Local anesthetics are used in obstetric practice to achieve analgesia and anesthesia via neuraxial procedures (spinal or epidural). Local anesthetics exhibit their effect by blocking voltage-gated sodium channels on neurons, thereby inhibiting the achievement of an action potential which is required for nerve impulse propagation. There are two major groups of local anesthetics—the aminoamides and the aminoesters. The most commonly used aminoamide local anesthetics in obstetric anesthesia are lidocaine, bupivacaine, and ropivacaine. The most commonly used aminoester local anesthetics in obstetric anesthesia are 2-chloroprocaine and tetracaine. Epinephrine can be added to local anesthetics to prolong their duration of action. The addition of sodium bicarbonate to local anesthetics hastens their onset of action. Local anesthetic systemic toxicity (LAST) can occur when large doses of local anesthetic are administered. Systemic toxicity from local anesthetics can be fatal and must be treated promptly with 20% lipid emulsion. Rarely, anaphylaxis can occur after the administration of local anesthetics. This occurs most commonly with the aminoesters.