What are the signs and symptoms of lidocaine toxicity?

Signs and Symptoms of Lidocaine Toxicity

Lidocaine toxicity primarily manifests as central nervous system symptoms, which occur at lower concentrations than cardiovascular effects, and include light-headedness, perioral numbness, tinnitus, and confusion, potentially progressing to seizures and respiratory arrest. 1, 2

Central Nervous System Manifestations

The earliest and most common signs of lidocaine toxicity affect the central nervous system:

• Early symptoms (often first indicators of high blood levels):

  • Perioral numbness and tingling
  • Light-headedness
  • Tinnitus (ringing in ears)
  • Metallic taste
  • Dizziness
  • Drowsiness
  • Blurred or double vision 1, 2

• Progressive symptoms (as toxicity worsens):

  • Confusion
  • Slurred speech
  • Agitation
  • Muscle twitching
  • Tremors
  • Seizures/seizure-like activity
  • Unconsciousness
  • Respiratory depression and arrest 1, 2, 3

It's important to note that excitatory manifestations may be brief or absent, with drowsiness progressing directly to unconsciousness and respiratory arrest 2.

Cardiovascular Manifestations

Cardiovascular symptoms typically occur at higher plasma concentrations and are generally depressant:

• Bradycardia
• Hypotension
• Cardiovascular collapse
• Cardiac arrest 1, 2

These cardiovascular effects are late manifestations of lidocaine toxicity, appearing after neurological symptoms 1.

Risk Factors for Lidocaine Toxicity

Several factors increase the risk of toxicity:

• Patient factors:

  • Age >70 years
  • Low body weight
  • Congestive heart failure
  • Cardiogenic shock
  • Hepatic dysfunction (lidocaine is almost exclusively eliminated by the liver)
  • Severe renal dysfunction
  • Preexisting neurologic dysfunction 1
  • Acidemia (increases free lidocaine in plasma) 1
  • Hypoalbuminemia (increases free drug in plasma) 1

• Administration factors:

  • Rapid absorption
  • Inadvertent intravascular injection
  • Excessive dosage
  • Prolonged infusion (>24 hours) 1, 2
  • Medication interactions (e.g., beta-blockers, amiodarone) 1

Monitoring and Prevention

To prevent toxicity:

1. Calculate dosage based on ideal body weight rather than actual body weight
2. Implement upper infusion rate limits (e.g., 120 mg/h) regardless of weight-based calculations
3. Reduce infusion rates by approximately 50% after 24 hours
4. Monitor for early neurological symptoms, which precede cardiovascular toxicity
5. Use ECG monitoring, though cardiovascular signs are late manifestations 1

Management of Toxicity

When lidocaine toxicity is suspected:

1. Stop the lidocaine infusion immediately
2. Provide supportive care (airway management, oxygen)
3. Consider intravenous lipid emulsion (ILE) therapy for severe toxicity 3
4. Treat seizures with benzodiazepines
5. Provide cardiovascular support as needed 1, 4

Important Considerations

• Toxicity can occur even with therapeutic dosages and undetectable serum concentrations 3
• Symptoms may persist even after lidocaine levels decrease below therapeutic thresholds 4
• Human error in dosing, infusion programming, or drug administration is often responsible for catastrophic events 1
• There is no specific antidote for lidocaine toxicity; treatment is primarily supportive 4

Maintaining vigilance for early signs of toxicity is crucial, as prompt recognition and intervention can prevent progression to more severe manifestations.