Toxicology – Local Anesthetic Systemic Toxicity

Source

Local anesthetics associated with systemic toxicity include procaine, chloroprocaine, tetracaine, lidocaine, mepivacaine, and bupivacaine. Toxicity most often occurs after unintended entry of the drug into the bloodstream during a regional or local anesthetic procedure.

Typical Presentation

A patient receiving a nerve block or other local anesthetic injection develops early neurological symptoms such as ringing in the ears and numbness around the mouth, followed by altered consciousness, seizures, or cardiovascular instability.

Clinical Features

Symptoms often progress from neurological to cardiovascular toxicity:

• Perioral or tongue numbness
• Tinnitus
• Light-headedness
• Confusion
• Loss of consciousness
• Seizures
• Hypotension, arrhythmias, or cardiac collapse in severe cases

Mechanism of Action

Local anesthetics block voltage-gated sodium channels. At excessive systemic concentrations, this interferes with electrical conduction in the brain and heart, producing both neurotoxicity and cardiotoxicity.

Management

Treatment is primarily supportive and includes:

• Immediate airway and respiratory support
• Continuous cardiac monitoring
• Benzodiazepines for seizures
• IV lipid emulsion therapy for significant systemic toxicity, particularly severe cardiovascular toxicity
• Advanced resuscitation measures for cardiovascular collapse

Key Points

• Neurological symptoms commonly appear before cardiovascular toxicity.
• Bupivacaine is particularly associated with severe cardiotoxicity and may cause neurological and cardiac effects at the same time.
• Accidental intravascular administration is a classic cause of local anesthetic systemic toxicity.