🚨 Local Anesthetic Systemic Toxicity (LAST): What to Do When It Happens -Based on ASRA guidelines and current clinical reviews (2020–2024)-

2025年10月8日

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Contents

♦️ Introduction

まっすー

Have you ever seen a real case of LAST?

さらりーまん

Just once—back when I was a resident. Rare, but when it happens, it’s serious. That’s why we practice.

なっちゃん

The lipid emulsion—that’s the white bag in the crash cart, right?

さらりーまん

Exactly. You should be able to grab it in seconds. For an average adult, you’ll probably need one full pack.

Local Anesthetic Systemic Toxicity (LAST) is uncommon but potentially life-threatening.
With prompt recognition and early lipid emulsion therapy (Lipid Emulsion Therapy: LET), the prognosis has improved dramatically.

The American Society of Regional Anesthesia and Pain Medicine (ASRA) provides a stepwise checklist that has become the international standard for LAST management.
This article summarizes the clinical workflow and exam-relevant key points.

♦️ Immediate Management ( ASRA-based )

🔷 Stop the infusion and call for help 🔈

Immediately stop administration of the local anesthetic and activate the emergency response.

Continuing the injection while “just watching” is dangerous.
If you are performing a block, stop the syringe or pump first.
If using a catheter infusion, clamp the line immediately—this single action can save a life.

🔷 Airway and breathing 🫁

Provide 100 % oxygen and ensure adequate ventilation.
Prevent hypoxia and acidosis, which worsen cardiotoxicity.リスト

🩺 Clinical note:
Acidosis and hypercapnia increase the unbound fraction of local anesthetic in plasma, amplifying toxicity.
Mild hyperventilation to maintain normal pH is recommended.

📘 Exam tip:
“If asked for the first step in LAST management” → oxygenation and ventilation is the correct answer.

🔷 Seizure control ⚡️

Treat seizures promptly with intravenous benzodiazepines (midazolam or diazepam).
Avoid large doses of propofol or barbiturates, which can cause cardiac depression.

🩺 Clinical note:
Propofol has anticonvulsant properties but also reduces myocardial contractility—creating a “double hit.”
Use benzodiazepines first and maintain ventilation.

📘 Exam tip:
“Which agents should be avoided?” → High-dose propofol and barbiturates.

🔷 Cardiovascular collapse or arrhythmia

Follow ACLS principles, but with key modifications:

Use low-dose epinephrine (< 1 µg/kg)
Avoid vasopressin, β-blockers, and calcium channel blockers
For antiarrhythmics: lidocaine is contraindicated; amiodarone is acceptable

🩺 Clinical note:
High-dose epinephrine increases myocardial oxygen demand and may worsen reperfusion injury.
These drugs differ from standard ACLS because their hemodynamic effects compound the toxicity.

📘 Exam tip:
“Which ACLS modifications are correct for LAST?” → Low-dose epi, no vasopressin, no lidocaine.

🔷 Refractory or Delayed Cases

If there is no response to LET + ACLS, consider ECMO or cardiopulmonary bypass early.
Bupivacaine toxicity, in particular, carries a risk of recurrent collapse—patients should be observed in the ICU for extended monitoring.

♦️ Lipid Emulsion Therapy (LET)

🔹 When to start

Initiate as soon as severe CNS symptoms (e.g., seizures, unconsciousness) or any cardiovascular instability appear.
As NYSORA emphasizes: “Do not wait for cardiac arrest.”

🔹 Standard ASRA regimen

20 % lipid emulsion, 1.5 mL/kg IV bolus over 2–3 min
Continue infusion at 0.25 mL/kg/min
If instability persists → repeat bolus or double infusion rate (0.5 mL/kg/min)
Maximum total dose: ~10–12 mL/kg (follow institutional protocol)

🩺 Clinical note:
The lipid emulsion not only creates a “lipid sink” to sequester lipophilic drugs but also improves myocardial metabolism and contractility.
Early administration correlates strongly with survival.

📘 Exam tip:
“Initial bolus dose of lipid emulsion?” → 1.5 mL/kg (20 %).

♦️ Prognosis

Early LET yields > 90 % survival
Most patients recover fully without neurologic sequelae
Delayed or infusion-related cases carry worse outcomes
Registry data show mortality < 10 % since LET became routine

🩺 Clinical note:
Even after hemodynamic recovery, neurologic symptoms may lag for several hours.
Maintain observation for at least 2 h after seizures and 4–6 h after cardiovascular instability.

♦️ Team Training and Preparedness

Display the ASRA LAST checklist in every block room, OR, and ED.
Keep a “LAST kit” stocked (20 % lipid emulsion, dosing chart, syringes, tubing).
Conduct simulation training once or twice a year.

The educational focus: