Local anesthetic systemic toxicity.

Local anesthetic systemic toxicity (LAST) is estimated to occur in 1 of 1000 local anesthetic administrations1,2

It results from supratherapeutic levels of local anesthetic in the bloodstream. Most cases occur in hospitals (61%), while fewer occur in outpatient settings (14%), primarily following upper or lower extremity nerve blocks (19%), naso-oropharyngeal infiltration (17%) or spinal and epidural blocks (11%).1 Lidocaine is most commonly implicated in LAST events (44%); however, bupivacaine has a lower safety margin and greater cardiac toxicity.1,2 Ropivacaine has a decreased potential for toxicity.3

Signs and symptoms of LAST typically appear within 1–5 minutes of local anesthetic administration and include oral numbness, metallic taste, dizziness, drowsiness and disorientation2

Severe manifestations may appear up to 6 hours after initial symptom onset, and include seizures, arrhythmias, cardiac arrest and death.1

Extremes of age, pregnancy, renal disease, cardiac disease and hepatic dysfunction may increase risk of LAST1,2

The minimum effective dose of local anesthetic should be used in these populations (generally 10%–20% dose reduction) and patients should be warned to report any signs or symptoms of LAST immediately.1,4 The maximum recommended doses of local anesthetic are as follows: bupivacaine (maximum dose 2 mg/kg, maximum dose with epinephrine 3 mg/kg), lidocaine (maximum dose 5 mg/kg, maximum dose with epinephrine 7 mg/kg), ropivacaine (maximum dose 3 mg/kg, maximum dose with epinephrine 3 mg/kg), prilocaine (maximum dose 6 mg/kg, maximum dose with epinephrine 8 mg/kg) and mepivacaine (maximum dose 5 mg/kg, maximum dose with epinephrine 7 mg/kg).5

Accidental intravascular injection of large doses of local anesthetic is the most important trigger of LAST1

A slow injection technique (< 1 mL/s) with frequent aspirations and ultrasonography guidance for peripheral nerve blocks can decrease the likelihood of this.2 The addition of epinephrine to local anesthetic infiltrations decreases systemic absorption.1

After securing the airway and suppressing seizures, a bolus of 1.5 mL/kg of 20% lipid emulsion followed by infusion at 0.25 mL/kg/min for 30–60 minutes is recommended for patients at first signs of severe LAST3,6

Lipid emulsion absorbs local anesthetic from tissues to attenuate the progression of toxicity.6

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