Lidocaine Toxicity(Archived)

Excerpt

Lidocaine is a local anesthetic drug that produces a transient loss of sensory, motor, and autonomic function when the drug is injected or applied in proximity to neural tissue. It is the most commonly used local anesthetic in nearly all medical specialties. It is also commonly used as an antiarrhythmic agent to suppress ventricular arrhythmias. Infusions of lidocaine (and procaine) have been used to supplement general anesthetic techniques, as they are capable of reducing the minimum alveolar concentration of volatile anesthetics by up to 40%, while also providing pain relief in the perioperative phase. It is in the class of the local amide anesthetics, which, compared to the ester-type local anesthetics, is usually well tolerated with only rare occasions of allergic reactions. Amide local anesthetics are metabolized (N-dealkylation and hydroxylation) by microsomal P-450 enzymes in the liver.

Applied either by injection, inhalation, or as a topical agent to provide anesthesia, lidocaine has a good safety margin before reaching toxic blood levels. Since it can be administered in various forms to the same patients, care must be taken to track the total dose administered to minimize systemic toxicity. In addition, clinicians should consider the dose of any other local anesthetics that may have been administered to the same patient, as toxic doses appear to be additive. Lidocaine toxicity is not only determined by the total dose (usually 4.5 mg/kg) but also by the rate of absorption, which is dependent on the blood flow of that tissue. To reduce blood flow to the injection site and the absorption rate, vasoconstrictors such as epinephrine 1:200000 are frequently used and may increase the toxic dose to 7 mg/kg.

Lidocaine toxicity to muscles and peripheral or neuraxial nerves can occur locally at the site of injection. Transient neurologic symptoms (TNS) after high-concentration lidocaine spinal anesthetics have been described multiple times and have led to either reducing the concentration of the dose or switching to a different agent.

In addition to direct nerve toxicity, systemic toxicity affecting the brain or cardiac muscle can lead to sudden and dramatic changes in the patient’s vital signs. Finally, there are the side effects of a relative overdose at the site of injection, which can be quite dramatic. Examples include total spinal anesthesia or subdural injection of the drug that can cause severe hemodynamic compromise, such as hypotension or bradycardia, up to cardiac and respiratory arrest.