Adverse reactions to local anesthetics

Local anesthesia is a relatively common method of anesthesia. It means that while the patient is conscious, anesthetics are injected into a part of the body, which will temporarily block the nerve conduction in a part of the body. Generally, it will not cause damage to any tissue of the patient. Of course, for some patients, some adverse reactions may occur, such as tissue toxicity, which is caused by excessive drug concentration or poor absorption.

Adverse reactions to local anesthetics

1. Tissue toxicity

Factors involved include traumatic injection methods, high drug concentrations, malabsorption, and other mechanical factors that cause macroscopic or microscopic tissue damage. In fact, commonly used anesthetics do not have tissue toxicity. If high-osmotic concentration local anesthetics are injected into the skin or subcutaneously, temporary edema may be caused. Although the addition of epinephrine can improve the degree of edema, it will further increase tissue toxicity. Injection of less than 1% procaine, lidocaine, or mepivacaine solution will not affect wound healing.

2. Neurotoxicity

Direct injection of anesthetics into nerves or nerve bundles can cause functional or structural changes, which are not simply caused by the drug itself, but are related to physical factors (pressure).

3. Hypersensitivity reaction

Tolerance of local anesthetics varies greatly among individual patients. When a small dose of local anesthetic is used, or the dose is lower than the usual dose, and the patient develops early symptoms of toxicity, it should be considered a hypersensitivity reaction. If a reaction occurs, medication should be stopped and treatment should be initiated.

4. Allergic reaction

Allergic reactions are caused by the attachment of cytotropic immunoglobulins to the surface of mast cells and alkaliphilic granulocytes. When the antigen and reagin antibody meet again, histamine and 5-hydroxytryptamine are released from the mast cell granules. These circulating biogenic amines can stimulate a rapid and severe systemic defensive response, resulting in airway edema, bronchospasm, dyspnea, hypotension, and angioedema due to increased capillary permeability, as well as urticaria on the skin accompanied by itching. Severe reactions can endanger the patient's life. The incidence of allergic reactions accounts for 2% of adverse reactions to local anesthetics. Ester local anesthetics are far more likely to cause allergic reactions than amides. It is generally believed that ester local anesthetics form haptens with immunoglobulin E, and the preservatives of local anesthetics can also form haptens, which is another potential factor causing allergic reactions.

5. Central nervous system toxicity

The central nervous system toxicity of local anesthetics manifests as an initial excitatory phase and a terminal inhibitory phase. Initially, the patient experiences restlessness, anxiety, paresthesia, tinnitus, and numbness around the mouth, followed by facial spasms and systemic convulsions, and ultimately develops into severe central nervous system depression, coma, and respiratory and cardiac arrest.

6. Cardiotoxicity

The early manifestations of the cardiovascular system are tachycardia and hypertension indirectly caused by central nervous system excitement, while in the late stage, the direct effects of local anesthetics cause arrhythmia, hypotension and inhibition of myocardial contractile function.