Local Anesthetic Systemic Toxicity - Lipid Emulsion and Resuscitation

Key Points

• LAST can present with neurologic symptoms, cardiovascular toxicity, or both; the textbook sequence is not required.
• Stop local anesthetic administration immediately and call for the LAST rescue kit.
• Hypoxemia, hypercapnia, and acidosis amplify cardiotoxicity and should be corrected aggressively.
• Benzodiazepines are preferred for seizures.
• Use 20% lipid emulsion early for severe LAST according to the current ASRA checklist.
• Resuscitation differs from routine ACLS: use smaller epinephrine doses and avoid vasopressin, beta blockers, calcium-channel blockers, and additional local anesthetic.
• Amiodarone is preferred for ventricular arrhythmias when an antiarrhythmic is needed.
• Consider VA-ECMO or cardiopulmonary bypass early for refractory cardiovascular collapse.
• Observation after recovery should reflect the severity and duration of neurologic and cardiovascular toxicity.

Algorithm

1. Recognize possible LAST during or after local anesthetic administration and stop the drug immediately.
2. Call for help, bring the LAST kit and 20% lipid emulsion, and begin continuous ECG and hemodynamic monitoring.
3. Give oxygen, support ventilation, and avoid hypoxemia, hypercapnia, and severe acidosis.
4. Treat seizure with benzodiazepine and protect the airway when necessary.
5. For severe neurologic or cardiovascular toxicity, start 20% lipid emulsion using the current ASRA checklist.
6. If arrest or unstable dysrhythmia occurs, perform high-quality CPR using LAST-modified medication principles.
7. Repeat lipid bolus or increase infusion according to the checklist if instability persists.
8. Activate extracorporeal circulatory support early when shock or arrest is refractory.
9. Continue monitored observation after recovery and document dose, timing, treatment, and suspected mechanism.

Clinical Synopsis & Reasoning

LAST should be considered whenever new neurologic or cardiovascular instability occurs during or after local anesthetic administration. Classic early neurologic symptoms include circumoral numbness, metallic taste, tinnitus, dizziness, agitation, dysarthria, or visual disturbance, followed by seizure or central nervous system depression. Cardiovascular toxicity can include hypertension or tachycardia early, then conduction delay, ventricular arrhythmia, bradycardia, hypotension, or cardiac arrest. The classic sequence is not mandatory. Deep sedation or general anesthesia can obscure neurologic warning signs, and some events present primarily with cardiovascular collapse.

Risk depends on total dose, injection site vascularity, rate of absorption, accidental intravascular injection, drug potency and lipid solubility, and patient factors that increase the biologically active fraction of local anesthetic. Extremes of age, pregnancy, low cardiac output, significant liver disease, severe renal disease, and reduced protein binding can increase vulnerability. Bupivacaine is particularly concerning because of strong myocardial sodium-channel binding, but serious toxicity can occur with any local anesthetic. Ultrasound guidance and incremental aspiration reduce accidental intravascular injection risk but do not eliminate LAST.

Recognition is clinical. Do not wait for serum local anesthetic concentrations. Immediately stop injection or infusion and call for help. Bring the LAST rescue kit and 20% lipid emulsion to the bedside. Priorities are airway control, oxygenation, ventilation, seizure suppression, and circulatory support. Hypoxemia, hypercapnia, and acidosis worsen local anesthetic cardiotoxicity and should be corrected promptly. Consider alternative causes such as high neuraxial block, anaphylaxis, vasovagal event, hemorrhage, pulmonary embolism, myocardial ischemia, or drug error, but when LAST is plausible treatment should proceed while those alternatives are assessed.

Treatment Strategy & Disposition

Provide 100% oxygen initially and support ventilation to avoid hypoxemia, hypercapnia, and severe acidosis. Intubate when airway protection or ventilation is inadequate, but use drugs and doses appropriate for the hemodynamic state. Benzodiazepines are preferred for seizures. Small doses of propofol may suppress seizure activity in a hemodynamically stable patient, but large propofol doses are undesirable during cardiovascular instability because propofol itself can depress circulation.

For severe LAST with seizure, significant dysrhythmia, hypotension, or cardiovascular collapse, start 20% lipid emulsion according to the current ASRA checklist. A commonly used weight-based regimen for patients under 70 kg is a bolus of approximately 1.5 mL/kg followed by an infusion of approximately 0.25 mL/kg/min. For larger adults, the ASRA checklist provides simplified volumetric dosing. If cardiovascular stability is not restored, the bolus can be repeated and the infusion increased according to the checklist. Avoid excessive cumulative lipid dosing and use the current institutional LAST card or ASRA checklist during the event rather than relying on memory.

Cardiac arrest from LAST requires high-quality CPR but differs from routine ACLS in several important ways. ASRA recommends smaller epinephrine doses, generally no more than 1 mcg/kg per bolus, and avoidance of vasopressin, calcium-channel blockers, beta blockers, and additional local anesthetics. Amiodarone is preferred for ventricular arrhythmias. Prolonged resuscitation may succeed because lipid therapy and drug redistribution take time. In refractory shock or arrest, activate VA-ECMO or cardiopulmonary bypass capability early when available.

After stabilization, continue monitoring because recurrence can occur after an initially successful response, especially after a large or long-acting dose. The duration depends on whether the event was limited to transient neurologic symptoms or involved seizure, arrhythmia, or cardiovascular instability. Document the local anesthetic, concentration, estimated total dose, injection site, timing, lipid dose, and response. Report serious events through local medication-safety systems and consider toxicology or poison-center consultation.

Epidemiology / Risk Factors

• LAST is uncommon relative to the large number of regional and local anesthetic procedures performed.
• Risk rises with highly vascular injection sites, large doses, potent long-acting agents, and accidental intravascular injection.
• Cardiovascular disease, pregnancy, extremes of age, and conditions altering protein binding can increase susceptibility.
• Most institutions treat LAST preparedness as a system-level safety requirement rather than an event that can be managed ad hoc.

Investigations

Do and Do Not

Pharmacology

Prognosis / Complications

• Prompt recognition, oxygenation, seizure control, lipid rescue, and effective circulation can result in complete recovery.
• Delayed recognition after prolonged hypoxemia or cardiac arrest increases neurologic and cardiac morbidity.
• Refractory toxicity may still be reversible with prolonged resuscitation and extracorporeal support.
• Recurrence is possible after initial stabilization, so observation is required after clinically important events.

Patient Education / Counseling

• Explain that the reaction reflects systemic toxicity from a local anesthetic rather than an IgE allergy in most cases.
• Document the exact agent and circumstances so future anesthetic planning can distinguish dose-related toxicity from allergy.
• Tell the patient that future local or regional anesthesia may still be possible with specialist planning and dose modification.
• Provide clear follow-up if neurologic symptoms, cardiac injury, or a prolonged resuscitation occurred.
• Encourage the patient to share the event with future anesthesia clinicians.

Notes

LAST management is a crisis in which cognitive aids improve reliability. The ASRA checklist should be immediately available in any location performing regional blocks, high-volume local infiltration, tumescent anesthesia, or other procedures using potentially toxic local anesthetic doses.

The safest prevention strategy combines dose calculation, patient-specific dose reduction when appropriate, incremental injection, aspiration, vigilance for early symptoms, and immediate access to resuscitation equipment and lipid emulsion. No single preventive measure eliminates risk.

References

1. ASRA Pain Medicine Checklist for Treatment of Local Anesthetic Systemic Toxicity — Link
2. ASRA Pain Medicine Guidelines and LAST Resources — Link