Local Anaesthetic Toxicity Summary

Risk Factors

  • Inadvertent intravascular injection
  • Too rapid injection
  • Excessive dose
  • Extremes of age
  • Frailty

CNS Symptoms

  • Tinnitus, visual disturbances
  • Dizziness, lightheadedness
  • Perioral/tongue numbness
  • Metallic taste
  • Agitation, confusion, seizures

Cardiovascular Signs

  • Sinus bradycardia
  • Conduction blocks
  • Ventricular arrhythmias
  • Asystole
  • Cardiovascular collapse

Immediate Management

  • Stop injection immediately
  • Call for help
  • Secure airway, 100% oxygen
  • Control seizures (benzodiazepines)
  • IV access

Lipid Emulsion Therapy

  • Bolus: 1.5 ml/kg 20% lipid
  • Infusion: 15 ml/kg/hr
  • Max total: 12 ml/kg
  • Continue CPR during infusion

Prevention

  • Accurate dose calculation
  • Slow injection with aspiration
  • Use of ultrasound guidance
  • Adrenaline as vasoconstrictor
  • Close monitoring first 30 mins

Critical Timing

  • Peak concentration: 10-25 mins
  • Monitor closely first 30 mins
  • Recovery may take >1 hour
  • Report to relevant authorities

Local Anaesthetic Toxicity

Recognition and management of systemic toxicity from local anaesthetic agents

Overview

Local anaesthetic toxicity occurs typically in the setting of regional anaesthesia as a result of excessively high plasma concentrations usually from inadvertent intravascular injection or too rapid injection.

Critical Timing: Following most regional anaesthetic procedures, maximum arterial plasma concentration of anaesthetic develops within about 10 to 25 minutes, so careful surveillance for toxic effects is necessary during the first 30 minutes after injection.

Techniques to Reduce Risk of Toxicity

Dose Management

  • Clear and accurate dose calculations
  • Dose reduction in frail patients or those at extremes of age
  • Use of adrenaline as vasoconstrictor to reduce systemic absorption

Injection Technique

  • Local anaesthetic injected slowly and with regular aspiration (to avoid inadvertent intravascular injection)
  • Use of ultrasound to facilitate nerve blocks
  • Regional nerve blocks to anaesthetise large areas

Monitoring

  • Close observation and monitoring during and after procedure
  • Vigilance during first 30 minutes post-injection
  • Continuous monitoring for catheter infusions

Recognition of Local Anaesthetic Toxicity

Local anaesthetic intoxication can present in many different ways, making it very difficult to recognise. After injection of a bolus of local anaesthetic, toxicity may develop at any time in the following hour. Techniques involving infusion of local anaesthetic through a catheter allow intoxication to develop at any time.

Early Clinical Features

Neurological Symptoms

  • Tinnitus
  • Difficulty with visual focus
  • Dizziness or lightheadedness
  • Perioral and/or tongue numbness
  • Metallic taste

Psychological Symptoms

  • Anxiety, agitation
  • Confusion, disorientation
  • Drowsiness

Signs of Severe Toxicity

Neurological Collapse

  • Sudden alteration in mental state
  • Severe agitation or loss of consciousness
  • Tonic-clonic convulsions (with or without LOC)

Cardiovascular Collapse

  • Sinus bradycardia
  • Conduction blocks
  • Asystole
  • Ventricular tachyarrhythmias

Management of Local Anaesthetic Toxicity

Immediate Management

  1. Stop injecting the local anaesthetic
  2. Call for help - this is a medical emergency
  3. Maintain the airway, and if necessary, secure it with a tracheal tube
  4. Give 100% oxygen and ensure adequate lung ventilation (hyperventilation may help by increasing plasma pH in the presence of metabolic acidosis)
  5. Confirm or establish intravenous access
  6. Control seizures: give a benzodiazepine, thiopental or propofol in small incremental doses
  7. Assess cardiovascular status throughout
  8. Obtain blood for analysis but do not delay definitive treatment to do this

Further Treatment Without Circulatory Arrest

Conventional Therapies

  • Use conventional therapies to treat hypotension, bradycardia and tachyarrhythmia
  • Follow advanced cardiac life support protocols
  • Consider intravenous lipid emulsion early

Further Treatment With Circulatory Arrest

Cardiopulmonary Resuscitation

  • Start cardiopulmonary resuscitation using standard protocols
  • Manage arrhythmias using the same protocols
  • Consider the use of cardiopulmonary bypass if available
  • Give intravenous lipid emulsion as detailed below

Intravenous Lipid Emulsion Protocol

Lipid Emulsion Administration

Initial Bolus

  • Give an initial intravenous bolus of 1.5 ml/kg of 20% lipid emulsion over 1 minute
  • Give a maximum of two further boluses at 5 minute intervals IF cardiovascular stability has not been restored OR if an adequate circulation deteriorates (max. 3 bolus doses in total)

Continuous Infusion

  • Start an intravenous infusion of 20% lipid emulsion at 15 ml/kg/hr
  • Continue the infusion at the same rate, but double the rate to 30 ml/kg/hr at any time after 5 mins IF cardiovascular stability has not been restored OR if an adequate circulation deteriorates
  • Continue the infusion until the patient is stable or has received up to a maximum of 12 ml/kg of lipid emulsion

Critical: Continue CPR throughout treatment with lipid emulsion. Recovery from local anaesthetic-induced cardiac arrest may take > 1 hour.

Follow-up and Reporting

Post-Resuscitation Care

  • Arrange safe transfer to a clinical area with appropriate equipment and suitable staff until sustained recovery is achieved
  • Exclude pancreatitis by regular clinical review, including daily amylase or lipase assays for two days

Mandatory Reporting

  • In the United Kingdom: Report to the National Patient Safety Agency (via www.npsa.nhs.uk)
  • In the Republic of Ireland: Report to the Irish Medicines Board (via www.imb.ie)
  • If Lipid has been given: Also report its use to the international registry at www.lipidregistry.org. Details may also be posted at www.lipidrescue.org

Prevention Strategies

Technical Precautions

  • Always aspirate before injection
  • Inject slowly with frequent aspiration
  • Use test doses with adrenaline
  • Use ultrasound guidance when available
  • Fractionate large doses

Pharmacological Precautions

  • Calculate maximum safe doses carefully
  • Reduce doses in high-risk patients
  • Use adrenaline-containing solutions (unless contraindicated)
  • Consider using less cardiotoxic agents

Monitoring Protocols

  • Continuous monitoring during procedure
  • Close observation for 30 minutes post-injection
  • Regular verbal contact with patient
  • Early recognition of prodromal symptoms