Apprehension and anxiety can be significant problems and good patient rapport and a thorough explanation of the procedure and expectations is required. Also, placement of regional blocks and administration of adequate anesthesia is a learned technique requiring experience and skill. One must also consider the various toxicities of the agents, their delay to onset, the risk of nerve damage and the reduced effectiveness in the presence of infection. Physiology and Pharmacology Nerve impulses depend on the flow of ion currents through channels in the cell's membrane. When a cell is stimulated it becomes depolarized and an action potential occurs.
Local anesthetics work by stabilizing the cell membrane and preventing depolarization.
Factors which affect a nerve's exposure to the anesthetic agent or the ability of the agent to optimally function thus directly affect the efficacy of anesthetic blockade. This includes the acidity and pH of the local environment and the competition between diffusion of agent to a nerve and its clearance by systemic absorption or metabolism by plasma pseudocholinesterase. Toxicity The most common and serious toxicities of local anesthetic are CNS and cardiac, starting with excitement and confusion and ultimately causing seizures, myocardial depression and cardiac arrest with prolonged toxic doses. Other less common toxicities include allergy, fetal toxicity, methemaglobonemia, local complications such as nerve injury, syncope, and aspiration. The maximum recommended doses of all drugs used for a given procedure should be known and not exceeded.