Local anesthetics (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 Anesthetic Toxicity.
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 anesthetic agent containing a vasoconstrictor congruent with the patient’s functional capacity
Signs and symptoms:
Constriction of pupils (miosis)
Drossiness, lethargy, sedation, unconsciousness, coma
Depressed cardiac conduction, excitability, and contractility
Place patient in a supine position
4 to 6 L/min by nasal cannula
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
Signs of recovery: patient regains consciousness, respiration returns to normal
Signs of deterioration: unconsciousness persists, respiratory depression progressing to respiratory arrest