What are the immediate management steps for a patient showing signs of local anesthetic systemic toxicity (circumoral numbness, tinnitus, metallic taste, dizziness, seizures, or cardiovascular collapse) after a regional block?

Immediate Management of Local Anesthetic Systemic Toxicity

Stop the local anesthetic injection immediately, call for help, secure the airway with 100% oxygen, administer intravenous lipid emulsion (1.5 mL/kg of 20% solution over 1 minute followed by 0.25 mL/kg/min infusion), and treat seizures with benzodiazepines. 1, 2

Initial Recognition and Response

When a patient exhibits signs of LAST (circumoral numbness, tinnitus, metallic taste, dizziness, seizures, or cardiovascular collapse):

• Immediately stop administering local anesthetic and call for help 2
• Secure the airway and provide 100% oxygen to prevent hypoxia and acidemia, which worsen cardiotoxicity 2, 3
• Consider early tracheal intubation if the patient shows signs of respiratory compromise 4
• Establish or secure intravenous access if not already present 4

Primary Antidote: Lipid Emulsion Therapy

Administer 20% intravenous lipid emulsion as the cornerstone treatment—do not delay while waiting for definitive diagnosis 3:

• Initial bolus: 1.5 mL/kg over approximately 1 minute (100 mL for adults >70 kg) 1, 5
• Immediately start continuous infusion: 0.25 mL/kg/min 1, 3
• Repeat boluses once or twice for persistent cardiovascular collapse 3
• Continue infusion for 30-60 minutes 3

The American Heart Association gives this a Class 1 (strong) recommendation based on numerous case reports showing life-saving effects 1. Lipid emulsion is particularly critical for bupivacaine toxicity, the most frequently implicated agent in LAST-related cardiovascular collapse 3.

Seizure Management

• Administer benzodiazepines as first-line treatment for seizures (Class 1 recommendation) 1, 4
• Seizure suppression is key to successful resuscitation, as seizures increase oxygen consumption and worsen acidosis 6
• Avoid propofol if cardiovascular instability is present, as it may worsen hemodynamic compromise 3

Cardiovascular Support

For Bradycardia:

• Administer atropine (Class IIa recommendation) 1, 2, 3
• Bradycardia is often the first cardiovascular manifestation of LAST 3

For Wide-Complex Tachycardia:

• Administer sodium bicarbonate to overcome sodium channel blockade (Class IIa recommendation) 1, 2, 3
• This helps reverse QRS prolongation >120 ms, similar to treatment for other sodium channel blocker toxicities 3

For Hypotension:

• Administer 10-20 mL/kg balanced salt solution fluid bolus 3
• Use reduced-dose epinephrine or avoid it initially, as standard 1 mg doses may impair lipid emulsion effectiveness and worsen outcomes 3, 6
• The American Heart Association specifically notes that high-dose epinephrine showed no additional benefit compared to lipid emulsion alone 3
• Avoid vasopressin 6

Cardiac Arrest Management

If cardiac arrest occurs:

• Initiate high-quality CPR immediately 3
• Prioritize lipid emulsion over standard vasopressor therapy 3
• Prepare for prolonged resuscitation, as LAST may require extended CPR efforts 3
• Consider ECMO (extracorporeal membrane oxygenation) for refractory shock (Class IIb recommendation) 1, 3
• Alert the nearest facility with cardiopulmonary bypass capability early in the resuscitation 3, 6

Critical Pitfalls to Avoid

• Do not delay lipid emulsion therapy while attempting to confirm the diagnosis—early administration is crucial 3
• Do not use standard-dose epinephrine (1 mg) as it may worsen outcomes; use small doses only if absolutely necessary 3, 6
• Do not underestimate the duration of toxicity—large-volume depots of dilute local anesthetic can take hours to reach peak plasma levels 5
• Do not assume the patient is stable after initial improvement—continued monitoring and lipid infusion are essential 3

Monitoring During Resuscitation

• Maintain continuous ECG monitoring, as cardiovascular signs represent late manifestations of toxicity 2
• Monitor for unexplained cardiovascular instability during or immediately after local anesthetic administration, which should trigger immediate consideration of LAST 2
• Seizures occur in 77-89% of LAST cases, while cardiovascular toxicity occurs in 32-55% 1

Equipment Preparedness

The American College of Medical Toxicology emphasizes that having 20% lipid emulsion, resuscitation equipment, and benzodiazepines immediately available before starting any regional anesthetic procedure is essential 7. The absence of lipid emulsion at the bedside delays life-saving treatment 7.