Local Anaesthetics Toxicity

Local anaesthetics (LAs) are nonselective voltage-gated sodium channel blockers. This nonselective blockade is not only the source of LAs’ efficacy in blocking action potentials in Aδ and C fibers, but it is also responsible for LAs toxic properties related to the blockade of other sensory, motor, and autonomic fibers. Toxic reactions (Table 14) may result from (1) excessive dosage, (2) repeated doses, (3) rapid absorption, (4) unintentional intravascular injection, (5) low plasma protein binding, and (5) slow metabolism or elimination of the LA or its metabolites.

Table 14. Local Anaesthetic Toxicity.

  • Determine dosage
    • Based on weight
      • mg of drug per pound of body weight
    • If patient weighs ≥150 lbs.
      • No more than maximum recommended dose (MRD)
    • The dose of local anaesthetic agent containing a vasoconstrictor congruent with the patient’s functional capacity
Signs and symptoms:
  • Nausea, vomiting
  • Constriction of pupils (miosis)
  • Drowsiness, lethargy, sedation, unconsciousness, coma
  • Respiratory depression
    • Respiratory arrest
  • Depressed cardiac conduction, excitability, and contractility
    • Ventricular arrhythmias
    • Atrioventricular block
    • Cardiac arrest
Emergency response:
  • Place patient in a supine position
    • Administer oxygen
      • 4 to 6 L/min by nasal cannula
    • Activate EMS
      • Monitor vital signs
        • If at any time the patient becomes unresponsive, no normal breathing, and no palpable pulse consider the diagnosis of cardiac arrest
          • Immediate CPR and defibrillation congruent with current recommendations
Nota bene:
  • Signs of recovery: mental state improves, vital signs return to baseline values
  • Signs of deterioration: altered consciousness progressing to coma, vital signs labile
  • Accurate statistics on local anaesthetic-related deaths are not readily available
    • Estimates range from 1 in 1.4 million to 1 in 45 million
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