Local Anesthetics

Properties of Anesthetic Agents

Local Anesthetic Systemic Toxicity (LAST)

Background

  • Life-threatening adverse reaction to local anesthetic toxicity
  • Occurs in ~0.2% of nerve blocks
  • Generally occurs within minutes of injection

Causes

  • Injection of local anesthetic into systemic circulation
    • Most common source of toxicity
    • Intravascular injection can cause toxicity below the maximum recommended dose
  • Exceeding the maximum dose of local anesthetic (see table above)
  • Absorption of anesthetic into systemic circulation by injection into extremely vascular area

Clinical Features

  • CNS
    • Auditory changes/Tinnitus
    • Metallic taste
    • Seizures or drowsiness
    • Coma
    • Respiratory arrest
  • Cardiovascular
    • Early signs
      • Tachycardia
      • Ventricular dysrhythmia
      • Hypertension
    • Late signs
      • Bradycardia
      • Conduction block
      • Cardiovascular collapse
      • Asystole

Management

  1. Aggressive supportive care: Airway management, ACLS, seizure management
  2. NaHCO3 1 ampule IV q2 minutes for: VT/VF, severe acidosis
  3. Lipid emulsion 20% solution
    1. 1.5 mL/kg bolus over 1 minute
    2. Then, 0.25 mL/kg/min for 20 min or until hemodynamic stability achieved
    3. ↑ to 0.5 mL/kg/min if hemodynamic status declinesc
    4. Maximum total dose 12 mL/kg.

Source

  1. Highland Ultrasound
  2. WikEM