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

Local anesthetics or LAs can anesthetize skin, subcutaneous tissue, and peripheral nerves either by surface, infiltration, or conduction block anesthesia.

They first block sensory impulses which transmit pain signals and then motor impulses, which control movement.

In surface anesthesia, LA is applied topically on injured skin or the mucous membranes of the nose or mouth.

In infiltration anesthesia, LAs are injected directly into the tissue under the skin or into intra-abdominal organs to anesthetize small areas. In surface and infiltration anesthesia, there is no motor function loss. Even at high concentrations, these LAs are effective for only short durations.

On the contrary, conduction block anesthetics can block motor impulses and they last longer, even at low concentrations. They are used to anesthetize distant areas, inducing a field or a nerve block.

In field block anesthesia, LAs are injected subcutaneously, anesthetizing all nerves within a field 2 to 3 cm distant from the injection site.

In nerve block anesthesia, LAs are injected into a network of intersecting nerves to anesthetize larger surrounding areas while paralyzing the associated muscles.