Local Anesthetics: Clinical Application as Surface, Infiltration, and Conduction Block Anesthesia

Surface anesthesia applies local anesthetics topically to skin or mucous membranes, producing effects within 5 minutes and lasting about 60 minutes. Infiltration anesthesia injects anesthetics directly into tissues surrounding a surgical site, offering immediate onset and lasting up to 180 minutes. Infiltration requires larger drug concentrations but preserves normal functions, while surface anesthesia risks systemic circulation escape through mucous membranes.

Conduction block anesthesia blocks both sensory and motor impulses at low concentrations and lasts significantly longer than surface or infiltration techniques. It anesthetizes larger distant areas by injecting anesthetics near peripheral nerves or nerve plexuses, effectively blocking nerve impulse transmission. This makes it ideal for regional anesthesia when extensive anesthesia duration and motor paralysis are clinically necessary.

Field block anesthesia involves subcutaneous injection of local anesthetics that anesthetize all nerves within a 2 to 3 cm radius from the injection site. Nerve block anesthesia injects anesthetics into a network of intersecting nerves to anesthetize larger surrounding areas while paralyzing associated muscles. Nerve blocks provide more extensive coverage and motor paralysis compared to the localized field effect of field block anesthesia.

Lidocaine and bupivacaine are the most frequently used drugs for infiltration anesthesia. These agents have immediate onset of action when administered and can last up to 180 minutes. They are preferred for small surgical procedures, wound repairs, and dental procedures because they provide satisfactory anesthesia without disrupting normal functions.

Local anesthetics first block sensory impulses that transmit pain signals, then block motor impulses that control movement. In surface and infiltration anesthesia, motor function is preserved even at high concentrations. Conduction block anesthetics can block both sensory and motor impulses, providing complete regional anesthesia with muscle paralysis for larger surgical areas.

The physical characteristics and amount of injected local anesthetic, the use of vasoconstrictors, and the blood flow rate at the injection site all determine how easily local anesthetics escape into systemic circulation. Surface anesthesia applied to mucous membranes is particularly prone to systemic absorption. Understanding these factors helps clinicians minimize adverse effects and optimize anesthetic efficacy.

Surface anesthesia is effective for only short durations, lasting about 60 minutes, because local anesthetics applied topically escape into the systemic circulation easily, especially through mucous membranes. This rapid absorption limits the anesthetic effect at the application site. For procedures requiring longer anesthesia, infiltration or conduction block anesthesia methods are more appropriate despite requiring injections.