Definition: A life-threatening adverse reaction resulting from local anesthetic reaching significant systemic circulating levels. Local Anesthetic Systemic Toxicity (LAST) is rare and almost always occurs within minutes of injection of the local anesthetic.

Causes:

Common implicated procedures: bronchoscopy, circumcision, tumescent liposuction. Consider diagnosis in any patient coming from outpatient surgical center with cardiac arrest

Use of local anesthetic doses in excess of the maximum dose (typically occurs with multiple subcutaneous injections)

Injection of local anesthetic into the systemic circulation (either errantly as part of a regional block i.e. Bier block)

Gains rapid entry to the brain thus producing CNS symptoms early on

All of the local anesthetic agents are sodium channel blockers

Continue infusion until hemodynamically stable for at least 10 minutes

Can repeat bolus every 3 minutes up to a total dose of 3 ml/kg

Bupivacaine has longer 1/2 life making intralipid more useful in this form of LAST

Due to lidocaine short 1/2 life, may be unnecessary. CPR alone typically adequate

Mechanism of action: unclear. May act as lipid sink, may facilitate redistribution of local anesthetic from target organs

Manage seizures with benzodiazepines over propofol as propofol is a cardiac depressant (Goldfrank’s 2015)

Institute basic management if ANY sign/symptom is present after local anesthetic use (i.e. new perioral numbness; don’t wait for CV findings!)

Consider serial repairs of large or multiple wounds to minimize chance for toxicity

Always aspirate prior to injection to ensure drug is not delivered intra-arterial or intravenous

Know + calculate maximum doses of local anesthetic agent prior to use

Take Home Points

The key in managing LAST is prevention. Know your dose, know your maximum dose, always aspirate prior to injection and ask patient about symptoms

Lidocaine toxicity CV complications are typically preceded by neurological signs/symptoms. If these develop, stop administration, place patient on monitor and ready your antidote

Bupivacaine toxicity can be sudden and catastrophic. If you are using the drug, undershoot your max dose and know where your antidote is