What happens to the effectiveness of local anesthesia in the presence of an infection?

The effectiveness of local anesthesia is reduced in the presence of an infection primarily due to the altered pH levels in the infected tissues. Infected areas often become more acidic as a result of the metabolic byproducts produced by bacteria and the inflammatory response of the body. Local anesthetics are typically weak bases, and their effectiveness depends on being in their uncharged form, which can easily cross nerve membranes to provide anesthesia.

When the pH is lowered (more acidic) in the presence of infection, a greater proportion of the local anesthetic remains ionized (charged), which does not effectively penetrate the nerve membrane. Consequently, the local anesthetic is less able to reach its site of action within the nerve fibers, leading to a reduced anesthetic effect. This is particularly important to recognize in clinical practice, as it may guide the choice of anesthetic technique or adjunctive measures, such as the use of buffering agents, to improve clinical outcomes in patients with infections.