Local Anesthetic Systemic Toxicity (LAST) is a medical emergency that can occur from an accidental intravascular injection, anesthetic overdose, or rapid systemic absorption from a highly vascular area. Early recognition is vital, as symptoms can progress rapidly from subtle neurological signs to cardiovascular collapse. The cornerstone of treatment involves immediate supportive care, the administration of intravenous lipid emulsion (ILE), and special modifications to standard Advanced Cardiac Life Support (ACLS) protocols.
Immediate Response and Supportive Measures
Call for help and stop the anesthetic
The first priority upon suspecting LAST is to immediately halt the injection or infusion of the local anesthetic. Concurrently, a code or emergency call should be initiated to mobilize additional help and resources, including a "LAST kit" containing lipid emulsion and other necessary medications. Hypoxia and acidosis can worsen LAST, so immediate airway management and administration of 100% oxygen are paramount.
Manage central nervous system (CNS) symptoms
Seizures are a common manifestation of LAST. The primary treatment is the administration of benzodiazepines, such as lorazepam, to control seizure activity. Propofol may be considered as an alternative for refractory seizures, but caution must be exercised, as it can cause further cardiovascular depression.
Administer Intravenous Lipid Emulsion (ILE) Therapy
Intravenous lipid emulsion is the definitive treatment for severe LAST and should be administered promptly upon recognition of persistent CNS symptoms or cardiovascular instability. The proposed mechanism of action is the "lipid sink" theory, where the lipophilic local anesthetic is sequestered into the lipid phase of the bloodstream, reducing its access to vital organs like the heart and brain.
When administering 20% lipid emulsion, healthcare providers should follow established guidelines, such as those from ASRA. These guidelines provide specific recommendations for bolus and continuous infusion based on patient weight and response to therapy. If hemodynamic stability is not achieved after the initial administration, further boluses and adjustments to the infusion rate may be necessary, up to a recommended maximum amount within a specific timeframe.
Modified Advanced Cardiac Life Support (ACLS) for LAST
For patients who progress to cardiac arrest, standard ACLS protocols must be modified to account for the specific cardiotoxic effects of local anesthetics. Certain agents typically used in ACLS can be detrimental in a LAST-induced cardiac arrest.
Managing cardiac arrhythmias
In cases of ventricular tachycardia or fibrillation, amiodarone is the preferred antiarrhythmic. Lidocaine and other Class 1B antiarrhythmics should be avoided, as they can exacerbate toxicity.
Optimizing vasopressor use
When vasopressors are necessary to manage hypotension, epinephrine should be used in reduced, incremental doses. High-dose epinephrine can be counterproductive and may impair the effectiveness of lipid resuscitation. Vasopressin, calcium channel blockers, and beta-blockers should be avoided as they can further depress cardiac function.
A Comparison of LAST vs. Standard ACLS
| Feature | Management of LAST-Induced Cardiac Arrest | Management of Standard Cardiac Arrest |
|---|---|---|
| Antidote | Intravenous Lipid Emulsion (ILE) is the primary antidote. | Not applicable. |
| Antiarrhythmics | Amiodarone is preferred. Avoid lidocaine, as it worsens LAST. | Lidocaine is often a standard option. |
| Vasopressors | Epinephrine is used in small, incremental doses. Avoid vasopressin. | Epinephrine can be used in higher doses. Vasopressin is sometimes used as an alternative. |
| Beta-blockers/CCBs | Avoid beta-blockers and calcium channel blockers, as they can further depress contractility. | May be used in specific standard ACLS scenarios. |
| Early Action | Call for help, stop anesthetic, administer ILE immediately for cardiotoxicity. | Follow standard ACLS pathway. |
Management for Refractory Cases
In cases of severe LAST that do not respond to initial resuscitative efforts, advanced support may be required. Extracorporeal Membrane Oxygenation (ECMO) or cardiopulmonary bypass can be used to maintain circulation and oxygenation while the body clears the toxic local anesthetic. Early consultation with a toxicologist or a team experienced in these procedures is advisable.
Post-Resuscitation Care and Prevention
After achieving hemodynamic stability, patients should be admitted to an intensive care unit (ICU) for observation for at least 12 hours, as symptoms can re-emerge. Prevention is the ultimate goal, and strategies include using the lowest effective dose, incremental injection, aspiration prior to injection, and utilizing ultrasound guidance to avoid inadvertent intravascular administration. The American Society of Regional Anesthesia and Pain Medicine (ASRA) provides a checklist for the management of LAST to aid providers during these critical events. Download the ASRA Checklist here.
Conclusion
Timely and appropriate management is essential for the successful treatment of local anesthetic systemic toxicity. The cornerstone of care involves immediate discontinuation of the local anesthetic, supportive care, and the rapid administration of intravenous lipid emulsion therapy. Healthcare providers must be well-versed in the modified ACLS protocols for LAST, as standard resuscitation measures can be ineffective or even harmful. By prioritizing prompt recognition, following established guidelines, and being prepared for advanced support, clinicians can significantly improve outcomes for patients experiencing LAST.
