ABSTRACT
Local anesthetics prevent conduction of nerve impulses by inhibiting passage of sodium ions through ion-selective channels in nerve membranes. Decreased permeability to sodium slows the rate of depolarization so that threshold potential is not achieved and therefore an action potential is not propagated. Stabilization of sodium channels likely occurs in the inactivated-closed state preventing changes in sodium permeability. Excessive doses or accidental intravascular injection of local anesthetics may lead to toxic symptoms. Lidocaine may be safely administered intravenously but, at high doses, can cause central nervous system and cardiovascular toxicity. Central nervous system toxic effects include sedation, nausea, ataxia, nystagmus, and tremors. Local anesthetics may cause complete loss of sensation to the body region being treated. A small number of animals may experience anxiety following regional anesthesia. Tranquilization may help in these animals. Local anesthetics can markedly reduce requirements for general anesthetics. Addition of epinephrine delays absorption and prolongs local anesthetic action.
