Local anesthetic systemic toxicity (LAST)

Learning objectives

Local anesthetic systemic toxicity (LAST) is a life-threatening adverse event that may occur after the administration of local anesthetics through a variety of routes
A supratherapeutic plasma concentration of local anesthetics has several adverse effects on the central nervous and cardiovascular systems

Central nervous symptoms precede cardiovascular symptoms
Neurological signs/symptoms range between excitation (early) and depression (late)
Early LAST: Excitatory manifestations
Neurological symptoms: Seizures (70%), agitation (10%), loss of consciousness (7%)
Prodromal (early) symptoms: Perioral paresthesia, metallic taste, tinnitus
± 40% of cases present as a sudden, rapid-onset seizure, progressing to cardiac arrest
High dose of LA or inadvertent IV injection: Prodromal (early) central nervous symptoms may be absent and the first manifestation could be cardiovascular toxicity (11%)
Cardiovascular toxicity: Heart conduction anomalies, decreased cardiac contractility, decreased systemic vascular resistance
Early-onset ECG changes: Increased PR and QTc, QRS abnormalities (bundle branch blocks), and increased ST intervals with/without refractory brady-/tachyarrhythmias
Depression of spontaneous pacemaker activity can rapidly lead to high-degree AV blocks or asystole
Cardiogenic shock and refractory hypotension may follow as a result of decreased cardiac contractility and vasomotor control disturbances, caused by peripheral vascular ion-channel alterations

LAST can occur immediately at the time of injection (usually accidental intravascular injection) or up to an hour after it (due to delayed tissue absorption)
Continue monitoring for 30-45 min after injection of large volumes or toxic doses of LAs
Monitor patients with any signs of LAST for 2-6 hrs because cardiovascular depression due to LAs can persist or recur after treatment

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