Definition: A life-threatening adverse reaction resulting from local anesthetic reaching significant systemic circulating levels. LAST is rare and almost always occurs within minutes of injection of the local anesthetic.

Causes

  • Injection of local anesthetic into the systemic circulation (either errantly as part of a regional block i.e. Bier block)
  • Rapid absorption of local anesthetic injected into a highly vascular area
  • Use of local anesthetic doses in excess of the maximum dose (typically occurs with multiple subcutaneous injections)
  • Common implicated procedures: bronchoscopy, circumcision, tumescent liposuction. Consider diagnosis in any patient coming from outpatient surgical center with cardiac arrest

Commonly Used Anesthetics

Relationship of Signs + symptoms of Lidocaine Toxicity to Serum Concentration

Signs + Symptoms

  • CNS Symptoms
    • Minor Signs/Symptoms
      • Tongue and perioral numbness
      • Parasthesias
      • Restlessness
      • Tinnitus
      • Muscle fasciculations + tremors
    • Major Signs/Symptoms
      • Tonic-clonic seizures
      • Global CNS depression
      • Decreased level of consciousness
      • Apnea
    • Neurologic symptoms typically precede cardiovascular symptoms in lidocaine toxicity
  • Cardiovascular Symptoms
    • Early Signs: Hypertension and tachycardia
    • Late Signs
      • Peripheral vasodilation + profound hypotension
      • Sinus bradycardia, AV blocs
      • Conduction defects (Prolonged PR, Prolonged QRS)
      • Ventricular dysrhythmias
      • Cardiac arrest
    • Cardiovascular symptoms typically present first in bupivacaine toxicity

Differential Diagnosis

  • Anaphylaxis (rare with amide anesthetics)
  • Effect of other sodium channel blockers (i.e. antihistamines, TCAs, cocaine, antimalarials)
  • Anxiety

Management

  • Prevention of toxicity
    • Know + calculate maximum doses of local anesthetic agent prior to use
    • Always aspirate prior to injection to ensure drug is not delivered intra-arterial or intravenous
    • Ask patient about symptoms after injection
    • Consider serial repairs of large or multiple wounds to minimize chance for toxicity
  • Basic Management
    • Institute basic management if ANY sign/symptom is present after local anesthetic use (i.e. new perioral numbness; don’t wait for CV findings!)
    • Stop injection or infusion of agent
    • Establish IV access if not already present
    • Continuous cardiac monitor
  • Aggressive Supportive Care
    • Airway/Breathing
      • Toxicity worsened by hypercapnea, hypoxia and acidosis
      • Use 100% FiO2
      • Hyperventilate
    • Cardiovascular Collapse
      • Consider epinephrine to augment cardiac output and improve peripheral vascular tone
      • Consider bicarbonate infusion for severe acidosis
      • Initiate high-quality CPR in arrest
    • Manage seizures with benzodiazepines over propofol as propofol is a cardiac depressant (Goldfrank’s 2015)
  • Lipid Emulsion Therapy (20% Intralipid)
    • Mechanism of action: unclear. May act as lipid sink, may facilitate redistribution of local anesthetic from target organs
    • Utility in lidocaine vs. bupivacaine
      • Due to lidocaine short 1/2 life, may be unnecessary. CPR alone typically adequate
      • Bupivacaine has longer 1/2 life making intralipid more useful in this form of LAST
    • Dosing (Neal 2012, Cao 2015)
      • Bolus: 1 – 1.5 ml/kg over 1 min
        • Can repeat bolus every 3 minutes up to a total dose of 3 ml/kg
      • Infusion: 0.25 ml/kg/min
        • Continue infusion until hemodynamically stable for at least 10 minutes
        • Can increase infusion to 0.5 ml/kg/min if BP worsens
    • Continue CPR during infusion to circulate drug

Take Home Points

  • The key in managing LAST is prevention. Know your dose, know your maximum dose, always aspirate prior to injection and ask patient about symptoms
  • Lidocaine toxicity CV complications are typically preceded by neurological signs/symptoms. If these develop, stop administration, place patient on monitor and ready your antidote
  • Bupivacaine toxicity can be sudden and catastrophic. If you are using the drug, undershoot your max dose and know where your antidote is
  • Intralipid has been shown to be effective in LAST. Administer the drug anytime there are signs of hemodynamic compromise

Read More:

LITFL: Local Anesthetic Toxicity

Wiki EM: Local Anesthetic Systemic Toxicity

References:

Schwartz DR, Kaufman B. Local Anesthetics. In: Hoffman RS, Howland M, Lewin NA, Nelson LS, Goldfrank LR. eds. Goldfrank’s Toxicologic Emergencies, 10e New York, NY: McGraw-Hill; 2015. Link

Neal JM et al, American Society of Regional Anesthesia and Pain Medicine. American Society of Regional Anesthesia and Pain Medicine checklist for managing local anesthetic systemic toxicity: 2012 version. Reg Anesth Pain Med 2012;37:16–8. PMID: 22189574

Cao D et al. Intravenous lipid emulsion in the emergency department: a systematic review. J Emerg Med 2015; 48(3): 387-97. PMID: 25534900