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Local Anesthetic Systemic Toxicity: The Signal Jammer You Have to Recognize Early | Anesthesia Clinical Concepts

LAST is rare — roughly 0.27 episodes per 1,000 peripheral nerve blocks — but when it happens, it is one of the few true emergencies in anesthesia where the clock, not the diagnosis, decides who lives.

The reason it kills is not that it is hard to treat. It is that it is hard to see. AUnder sedation or general anesthesia, the classic neurologic prodrome — circumoral numbness, metallic taste, tinnitus, agitation — is gone. All you have is a patient who suddenly does not look right.

This episode covers the mechanism, the history, and the response. It talks about the ASRA response and the ASRA-modified resuscitation protocal.

One last point that saves lives: up to a quarter of patients can relapse. Highly lipophilic agents redistribute and produce delayed recurrence. Observe long enough after apparent recovery to catch it.

Key Takeaways

• Under sedation or general anesthesia, the neurologic prodrome may be absent. Isolated cardiovascular collapse can be the first sign.

• Intravascular injection produces symptoms in one to three minutes. Overdose may peak at twenty to thirty minutes.

• Mechanism: sodium channel blockade. At toxic concentrations, that block reaches the myocardium — reduced action potential duration, bradycardia, hypotension, collapse.

• Treatment order: stop injecting, call for help, 100% oxygen, benzodiazepines for seizures, 20% lipid emulsion early for serious LAST.

• Lipid emulsion dosing: 1.5 mL/kg bolus over one minute, then 0.25 mL/kg/min. Double to 0.5 mL/kg/min if blood pressure remains low. Cumulative ceiling roughly 12 mL/kg.

• ASRA-modified resuscitation: avoid large epinephrine doses, vasopressin, calcium channel blockers, and beta-blockers — they may worsen toxicity.

• Relapse is real. Up to 25% of patients develop recurrent toxicity. Observe long enough after apparent recovery to catch it.

Timestamps

00:00 — The signal Jammer

01:52 — One trick pony

02:35 — First, the brain, then the heart

03:26 — Bupivicaine: the one to fear

04:22 — The safer cousins

04:36 — Antidote is not a channel drug but fat

05:01 — History: a single alarmed editorial

06:58 — From Theory to Practice

08:46 — The ASRA Sequence

09:26 — The price tag on every local anesthetic

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