58 - Local Anesthetics

Abstract

Local anesthetics are essential to the practice of dermatology and dermatologic surgery. By blocking the influx of sodium ions into peripheral nerve cells, local anesthetics prevent depolarization and temporarily interrupt nerve conduction. Local anesthesia is most commonly injected intradermally or subcutaneously. Infiltration of the papillary dermis yields more immediate onset with sustained duration of action, whereas subcutaneous infiltration is generally less painful and causes less tissue distortion. Topical anesthesia is particularly useful in children, although its role continues to increase with the evolution of dermatologic procedures. Mucosal surfaces have the highest absorption of local anesthetic, owing to the lack of a keratinized stratum corneum in the epidermis. Regional nerve blocks—the most common of which is the digital nerve block—are performed by injecting local anesthetic around the peripheral nerves located proximally to the cutaneous procedural sites. Regional blocks are beneficial for anesthetizing large areas of skin with minimal tissue distortion and needlesticks. Tumescent anesthesia is commonly employed for liposuction and results in longer-lasting analgesia by direct infiltration of large volumes of solution containing lidocaine, saline, and epinephrine. Adverse effects of local anesthesia are more frequently caused by the associated vasoconstrictors or the act of injecting, rather than as a result of the anesthetic itself. Moreover, allergic reactions to local anesthetics are exceedingly rare. Systemic toxicity is rare in routine dermatologic surgery, although it is important to minimize risk and identify its distinct clinical signs and symptoms.