What is the protocol for managing local anesthetic systemic toxicity (LAST)?

LAST Protocol: Management of Local Anesthetic Systemic Toxicity

The LAST protocol is a structured emergency response for local anesthetic systemic toxicity that prioritizes immediate cessation of local anesthetic administration, airway management with 100% oxygen, seizure control with benzodiazepines, and early administration of 20% intravenous lipid emulsion (ILE) for cardiovascular toxicity, with modified resuscitation avoiding vasopressin and limiting epinephrine to small doses 1, 2.

Recognition and Diagnosis

LAST presents in a predictable progression based on rising plasma concentrations of local anesthetic:

Early CNS signs:

• Excitation, agitation, metallic taste
• Tinnitus, perioral numbness
• Seizures/convulsions

Cardiovascular manifestations:

• Initial: hypertension, tachycardia, premature ventricular contractions
• Progressive: bradycardia, conduction disturbances
• Severe: circulatory collapse, asystole 2

Critical pitfall: Do not wait for confirmatory testing or full symptom development—treat immediately when LAST is suspected 3.

Immediate Management Algorithm

Step 1: Stop and Call for Help

• Halt local anesthetic administration immediately
• Request assistance and alert team
• Activate emergency response 2

Step 2: Airway and Oxygenation (Primary Intervention)

• Secure airway immediately
• Administer 100% oxygen
• Perform tracheal intubation if necessary
• Initiate artificial respiration as needed
• This is the foundation of all LAST management—oxygenation takes priority over all other interventions 4, 2

Step 3: Seizure Control

• Administer benzodiazepines as first-line therapy for convulsions 2
• Seizure suppression is key to preventing further deterioration 5

Step 4: Lipid Emulsion Therapy (Specific Rescue for Cardiovascular LAST)

20% intravenous lipid emulsion is efficacious for life-threatening local anesthetic toxicity, especially from bupivacaine 1. This represents the highest-level guideline recommendation (2023 AHA).

ILE administration protocol:

• Indicated specifically for severe hypotension and arrhythmias 2
• Consider early in cardiovascular collapse 5
• This is a specific rescue therapy for cardiovascular LAST, not a substitute for airway management 4

Step 5: Modified Advanced Cardiovascular Life Support

Critical modifications for LAST resuscitation:

• Avoid vasopressin entirely 5
• Use epinephrine only in small doses 5
• Standard ACLS algorithms require modification due to local anesthetic's unique cardiovascular effects

Step 6: Escalation to ECMO

Venoarterial extracorporeal membrane oxygenation (VA-ECMO) can be lifesaving for patients with cardiogenic shock or dysrhythmias refractory to other treatment measures 1. Because VA-ECMO implementation takes time, initiate the process early in patients not responding to lipid emulsion and standard measures.

Prevention Strategies

High-risk populations requiring extra vigilance:

• Infants
• Patients with decreased liver function
• Patients with low cardiac output 2

Technical prevention measures:

• Small-dose, divided administration (never bolus large volumes)
• Use agents with lower toxicity profiles (ropivacaine, levobupivacaine preferred over bupivacaine) 2
• Perform aspiration test before injection
• Ultrasound guidance for nerve blocks 6

Required preparedness:

• Guideline-directed monitoring
• Secured venous access
• Immediate availability of seizure medications
• Lipid emulsion kit readily accessible 2, 7

Current Epidemiologic Shift

Important contemporary pattern: The epidemiology of LAST has shifted—an increasing proportion now originates from surgeon- and proceduralist-administered analgesia rather than anesthesiologist-controlled regional techniques 6. Lidocaine (particularly oropharyngeal, topical, and local infiltration) has emerged as the predominant contributor to adverse outcomes including death 6. This means all practitioners administering local anesthetics, not just anesthesiologists, must be prepared to manage LAST.

Differential Diagnosis Considerations

When managing suspected LAST, systematically exclude other common emergencies that may present similarly:

• Vasovagal syncope
• Anaphylaxis
• Myocardial infarction
• Cerebrovascular events 4

The key distinguishing feature is the temporal relationship to local anesthetic administration and the characteristic CNS-then-cardiovascular progression.

Consultation

Timely consultation with a medical toxicologist, clinical toxicologist, or regional poison center facilitates rapid and effective therapy 1. However, do not delay initial management while awaiting consultation.