Local Anesthetics Toxicity


 
  • Local anesthetics are typically divided into two classes:
    ■ Esters: Procaine, tetracaine, benzocaine
    ■ Amides: Lidocaine, bupivacaine, mepivacaine
    Effect is usually local only, but may become systemic with:
    ■ Inadvertent injection into a blood vessel
    ■ Use of large volumes
    ■ Premature release of cuff with intravenous regional anesthesia (Bier block)
    Severity is related to dose and route.
    MECHANISM/TOXICITY
    ■ Inhibition of Na++ channels → reversible blockade of the initiation and
    propagation of action potentials along affected nerve.
    ■ Methemoglobinemia is possible with exposure to benzocaine or prilocaine.
    SYMPTOMS/EXAM
    ■ Mild overdose
    ■ Headache, drowsiness, dizziness/lightheadedness
    ■ Anxiety, tinnitus, numbness of mouth
    ■ Hypertension, tachycardia
    ■ Severe overdose
    ■ Confusion, tremors, seizures and coma
    ■ Respiratory depression and apnea
    ■ Hypotension, bradycardia, asystole
    ■ Widening of PR interval and QRS complex, VT or Vfib
    ■ Bupivicaine
    ■ More cardiotoxic than other local anesthetics
    ■ Not indicated for IV regional anesthesia
    DIAGNOSIS
    ■ Usually clear from history and exam
    ■ ECG, as needed
    ■ Co-oximetry if methemoglobinemia is suspected
    TREATMENT
    ■ Supportive care
    ■ Benzodiazepines for seizures
    ■ Standard ACLS for cardiac dysrhythmias
    ■ Discontinue use of agent.
    ■ No role for decontamination or enhanced elimination
    COMPLICATIONS
    ■ Allergic reactions
    ■ Ester anesthetics are responsible for most, likely due to metabolite
    para-aminobenzoic acid (PABA).
    ■ Preservative methylparaben is found in multidose vials of amide anesthetics
    and is chemically related to PABA.
    ■ Inadvertent IV injection of epinephrine (in “with epi” preparations)

 

All amide local anesthetics have two “i”s in their name.

Toxicity is characterized primarily by neurologic symptoms, but may include cardiovascular symptoms in large overdoses

Pregnant women are disproportionately affected by bupivicaine, and it is no longer indicated for obstetric anesthesia.