Local anesthetic systemic toxicity

Background

  • Acronym: LAST
  • Life-threatening adverse reaction to local anesthetic toxicity.
  • Incidence = ~0.2% of nerve blocks
  • Generally occurs within minutes of injection

Causes[1]

  • Injection of local anesthetic into systemic circulation
  • Exceeding the maximum dose of local anesthetic (see table below)
  • Absorption of anesthetic into systemic circulation by injection into extremely vascular area.

Maximum Doses of Anesthetic Agents

Agent Without Epinephrine With Epinephrine Duration Notes
Lidocaine 5 mg/kg (max 300mg) 7 mg/kg (max 500mg) 30-90 min
  • 1% soln contains 10 mg/ml
  • 2% soln contains 20 mg/ml
Mepivicaine 7 mg/kg 8 mg/kg
Bupivicaine 2.5 mg/kg (max 175mg) 3 mg/kg (max 225mg) 6-8 hr
  • 0.5% soln contains 5 mg/ml
  • May cause cardiac arrest if injected intravascularly
  • Do not buffer with bicarbonate
Ropivacaine 3 mg/kg
Prilocaine 6 mg/kg
Tetracaine 1 mg/kg 1.5 mg/kg 3hrs (10hrs with epi)
Procaine 7 mg/kg 10 mg/kg 30min (90min with epi)

Diphenhydramine as Local Anesthetic

  • Injectable 1% diphenhydramine (10 mg/mL) can be used as a local anesthestic alternative to ester/amide anesthetics[2]
    • Sodium channel blocker mechanism
    • 1-2 mL of 1% diphenhydramine at a time, to not exceed excessive sedation dose
    • Typical vial is 50 mg/mL, so to make 10 mg/mL:
      • 10 mL NS removed from 50 mL vial
      • Add 10 mL of 50 mg/mL diphenhydramine to 40 mL of NS
      • Sedation is dose related and is similar to what would be expected for IM doses
      • Relative contraindications are the same for IM diphenhydramine administration

Clinical Features

Clinical course tends to be a dose-dependant progression from CNS symptoms to CVS symptoms and death[3]

  • CNS symptoms
    • Agitation
    • Auditory changes
    • Metallic taste
    • Seizures or drowsiness
    • Coma
    • Respiratory arrest
  • Cardiovascular[1]
    • Early signs
      • Tachycardia
      • Ventricular dysrhythmia
      • Hypertension
    • Late signs
      • Bradycardia
      • Conduction block
      • Cardiovascular collapse
      • Asystole

Differential Diagnosis

  • Anaphylaxis
  • Anxiety
  • Methemoglobinemia - local anesthestics oxidize Fe2+ to Fe3+ in Hb

Sodium Channel Blockade Toxidrome

Evaluation

  • Clinical diagnosis

Workup

  • Directed by clinical picture
  • Blood levels of anesthetic are available, but not clinically useful.

Management

  • Aggressive supportive care (including airway management) and application of ACLS
    • Ventilate with 100% FiO2 - bolus dose of 50-100mg IV succinylcholine paralyzes without depressing CNS or CV[4]
    • Hypercapnia, hypoxia, acidosis all worsen toxic effects[5]
    • Manage seizures with benzodiazepines; propofol is an option but may worsen cardiovascular toxicity
  • 1 amp of sodium bicarbonate IV q2 min for:
    • VT or VF
    • Severe acidosis
  • Lipid emulsion, (Intralipid) 20% solution[5]
    • Lipid sink, binds to local anesthetic
    • 1.5 mL/kg bolus over 1 minute
    • Then, 0.25 mL/kg/min for 20 min or until hemodynamic stability achieved
      • ↑ to 0.5 mL/kg/min if hemodynamic status declines
  • ACLS modifications per ASRA (Am Soc of Regional Anesthesia):
    • Avoid vasopressin
    • Avoid calcium-channel blockers and beta-blockers
    • Amiodarone preferred in ventricular dysrhythmias

Disposition

  • Admit

See Also

External Links

References

  1. 1.0 1.1 Fencl JL. Local anesthetic systemic toxicity: perioperative implications. AORN J. 2015 Jun;101(6):697-700.
  2. Pavlidakey PG et al. Diphenhydramine as an Alternative Local Anesthetic Agent. J Clin Aesthet Dermatol. 2009 Oct; 2(10): 37–40.
  3. Kamel I, Trehan G, Barnette R. Intralipid Therapy for Inadvertent Peripheral Nervous System Blockade Resulting from Local Anesthetic Overdose. Case Reports in Anesthesiology. 2015;2015:486543. doi:10.1155/2015/486543.
  4. GlobalRPH. Management of Local Anesthetic Emergencies. http://www.globalrph.com/local-anesthetics.htm
  5. 5.0 5.1 Dillane D, Finucane BT. Local anesthetic systemic toxicity. Can J Anaesth. 2010 Apr;57(4):368-80.

Authors:

Ross Donaldson