From the Guidelines
Lidocaine toxicity is a serious condition that can progress rapidly, and immediate action is necessary if a patient reports a metallic taste or exhibits other symptoms of toxicity, such as perioral numbness, lightheadedness, or tinnitus, during local anesthesia administration. The symptoms of lidocaine toxicity can be divided into mild and severe manifestations. Mild symptoms include:
- Perioral numbness
- Metallic taste
- Lightheadedness
- Tinnitus These symptoms can progress to more severe manifestations, such as:
- Confusion
- Seizures
- Respiratory depression
- Cardiovascular collapse According to a recent study 1, minor adverse events, including metallic taste, were reported in 6.8% of patients who received intravenous lidocaine. The study also highlighted the importance of careful dosing and monitoring to prevent catastrophic events.
The administration of intravenous lipid emulsion is recommended for local anesthetic poisoning, and benzodiazepines should be used to treat seizures associated with local anesthetic systemic toxicity 1. To prevent toxicity, it is essential to:
- Aspirate before injecting to avoid intravascular administration
- Inject slowly
- Use the minimum effective dose
- Consider using formulations with epinephrine (unless contraindicated) to slow systemic absorption In cases of life-threatening toxicity, additional treatments, such as sodium bicarbonate for wide-complex tachycardia and atropine for bradycardia, may be necessary 1.
From the FDA Drug Label
Central nervous system manifestations are excitatory and/or depressant and may be characterized by light-headedness, nervousness, apprehension, euphoria, confusion, dizziness, drowsiness, tinnitus, blurred or double vision, vomiting, sensations of heat, cold or numbness, twitching, tremors, convulsions, unconsciousness, respiratory depression and arrest. Restlessness, anxiety, tinnitus, dizziness, blurred vision, tremors, depression or drowsiness may be early warning signs of central nervous system toxicity.
The symptoms of lidocaine toxicity include:
- Central nervous system manifestations:
- Excitatory: light-headedness, nervousness, apprehension, euphoria, tinnitus, twitching, tremors
- Depressant: confusion, dizziness, drowsiness, blurred or double vision, vomiting, sensations of heat, cold or numbness, convulsions, unconsciousness, respiratory depression and arrest
- Early warning signs: restlessness, anxiety, tinnitus, dizziness, blurred vision, tremors, depression or drowsiness However, metallic taste is not mentioned as a symptom of lidocaine toxicity in the provided drug labels 2, 2, 2.
From the Research
Symptoms of Lidocaine Toxicity
The symptoms of lidocaine toxicity, also known as local anesthetic systemic toxicity (LAST), include:
- Numbness of the tongue 3
- Dizziness 3
- Tinnitus 3
- Visual disturbances 3
- Muscle spasms 3
- Convulsions 3, 4
- Coma 3
- Respiratory and cardiac arrest 5, 3, 6
- Paresthesias of the mouth and face 4
- Spasticity 4
- Irritability 4
- Diffuse tremors 4
- Metallic taste is not explicitly mentioned in the provided studies, but it is a known symptom of local anesthetic toxicity
Treatment of Lidocaine Toxicity
Lidocaine toxicity can be effectively treated with lipid emulsion therapy 5, 3, 6, 7. The mechanism of action of lipid emulsion therapy is not well defined, but it has been postulated to work by both a "lipid sink," decreasing circulating amounts of drugs to the periphery, or through a direct "energy source" to the myocardium 6. Intravenous lipid emulsion (ILE) has become the first-line treatment for LAST and has achieved notable success in the treatment of LAST 7.