What is the management of ECG (Electrocardiogram) changes in Local Anesthetic Systemic Toxicity (LAST)?

Management of ECG Changes in Local Anesthetic Systemic Toxicity (LAST)

When ECG changes occur in LAST, immediately administer 20% intravenous lipid emulsion (1.5 mL/kg bolus over 1 minute, followed by 0.25 mL/kg/min infusion) while providing aggressive cardiovascular support and avoiding standard-dose epinephrine. 1, 2

Immediate Recognition and Response

ECG changes in LAST indicate severe cardiotoxicity requiring urgent intervention. The characteristic ECG findings include:

• Bradycardia - often the first cardiovascular manifestation 1, 3
• Wide-complex tachycardia - from sodium channel blockade 4, 1
• Conduction delays and QRS prolongation - similar to sodium channel blocker toxicity 4
• Arrhythmias progressing to cardiac arrest - the most severe presentation 4, 3

The American Heart Association emphasizes that LAST causes profound inhibition of voltage-gated sodium channels in cardiac cell membranes, with bupivacaine being particularly cardiotoxic. 4, 2

Primary Treatment: Lipid Emulsion Therapy

Lipid emulsion is the cornerstone antidote and should not be delayed while waiting for definitive diagnosis. 1

Dosing Protocol

• Initial bolus: 1.5 mL/kg of 20% lipid emulsion over approximately 1 minute 1
• Continuous infusion: 0.25 mL/kg per minute immediately after bolus 1
• Repeat boluses: May repeat once or twice for persistent cardiovascular collapse 1
• Duration: Continue infusion for 30-60 minutes 2

The mechanism involves creating a "lipid sink" that sequesters lipophilic local anesthetics from plasma while also increasing cardiac inotropy. 2, 5

Specific Management of ECG Abnormalities

For Bradycardia

• Administer atropine (Class IIa recommendation from the American Heart Association) 1, 3
• This is first-line pharmacologic therapy for bradycardia in LAST 1

For Wide-Complex Tachycardia

• Give sodium bicarbonate to overcome sodium channel blockade (Class IIa recommendation) 1, 3
• This is the same approach used for sodium channel blocker toxicity 4
• Sodium bicarbonate helps reverse QRS prolongation greater than 120 ms 4

For Cardiac Arrest

• Use reduced-dose or avoid epinephrine initially - standard 1 mg doses may impair lipid emulsion effectiveness and worsen outcomes 2
• The American Heart Association specifically notes that high-dose epinephrine showed no additional benefit compared to lipid emulsion alone 2
• Prioritize lipid emulsion as the primary antidote over standard vasopressor therapy 2
• Prepare for prolonged resuscitation - LAST may require extended CPR efforts 1

Critical Pitfall: Epinephrine Dosing

This is the most important deviation from standard ACLS protocols. The American Heart Association recommends that standard-dose epinephrine (1 mg) should be reduced or avoided in LAST cardiac arrest because it may impair lipid emulsion therapy effectiveness. 2 Animal studies showed lipid emulsion was superior to standard vasopressor therapy for return of spontaneous circulation. 2

Supportive Cardiovascular Measures

• Administer 10-20 mL/kg balanced salt solution fluid bolus for hypotension 1
• Secure airway early - hypoxia and acidemia worsen cardiotoxicity 1
• Provide 100% oxygen ventilation 1, 3
• Continue high-quality CPR if cardiac arrest occurs 2

Refractory Cases

For cardiac arrest or refractory shock unresponsive to lipid emulsion and standard measures:

• Consider ECMO (extracorporeal membrane oxygenation) - Class IIb recommendation 4
• The American Heart Association notes that ECMO may be beneficial for refractory shock from reversible causes such as drug toxicity 4
• Alert the nearest facility with cardiopulmonary bypass capability early in the resuscitation 1

Bupivacaine-Specific Considerations

Bupivacaine is the most frequently implicated agent in LAST-related cardiovascular collapse and requires particularly aggressive lipid emulsion therapy. 2 The American Heart Association specifically recommends lipid emulsion for patients with cardiac arrest due to bupivacaine toxicity. 4, 2

Post-Stabilization Monitoring

Extended observation is essential even after initial stabilization. 5 Patients require:

• 24-hour monitoring minimum for potential biphasic toxicity 5
• Continuous cardiac monitoring for recurrent arrhythmias 5
• This is particularly important in older or high-risk populations 5

Medications to Avoid

• Avoid propofol if cardiovascular instability is present 1
• Avoid vasopressin in cardiac arrest from LAST 6
• Limit epinephrine to small doses only if absolutely necessary 6, 2