A 38-year-old woman undergoes an interscalene brachial plexus block for right shoulder arthroscopy. The anesthesiologist injects 25 mL of 0.5% bupivacaine without epinephrine. Within 3 minutes of injection, the patient develops tinnitus, circumoral numbness, and restlessness. Her blood pressure rises to 160/95 mmHg and heart rate to 115 bpm. Within 2 minutes, she has a generalized tonic-clonic seizure. Which of the following is the most appropriate immediate management?

Explanation

## Clinical Diagnosis: Local Anesthetic Systemic Toxicity (LAST) ### Pathophysiology The patient received 125 mg of bupivacaine (25 mL × 0.5% = 125 mg). The recommended maximum dose of bupivacaine without epinephrine is 2.5 mg/kg; for a 70 kg woman, this is 175 mg, but toxicity can occur at lower doses, especially with rapid intravascular injection or in highly vascular regions (interscalene block has high risk). Bupivacaine is highly lipophilic and cardiotoxic. ### Clinical Presentation of LAST The sequence observed—**CNS toxicity first** (tinnitus, circumoral numbness, restlessness, seizure) followed by cardiovascular instability—is classic for LAST. **Key Point:** Early signs of LAST include: - Tinnitus, metallic taste, circumoral numbness - Restlessness, agitation, confusion - Tremor, muscle twitching - Seizure (threshold ~4–5 μg/mL plasma bupivacaine) ### Management of LAST: The Lipid Rescue Protocol **High-Yield:** Intravenous lipid emulsion (ILE) 20% is the definitive antidote for LAST, especially bupivacaine toxicity. It acts as a "lipid sink," sequestering the lipophilic local anesthetic away from cardiac and neural tissue. **Immediate steps:** 1. **Stop injection** and call for help 2. **Secure airway** and oxygenate with 100% O₂ 3. **Seizure control:** Benzodiazepines (preferred) or small doses of propofol; avoid large-dose barbiturates 4. **Lipid bolus:** 20% ILE 1.5 mL/kg IV over 1 minute (e.g., 100 mL for 70 kg patient) 5. **Repeat boluses** every 5–10 minutes if seizure recurs or hemodynamic instability persists 6. **Infusion:** Start ILE 20% at 0.25 mL/kg/min after initial bolus 7. **Limit epinephrine:** Use doses ≤1 μg/kg in cardiac arrest (standard ACLS doses may worsen outcomes) **Clinical Pearl:** Lipid emulsion should be drawn up and available in the OR before any regional block in high-risk patients. The time to first lipid dose is critical—delays increase morbidity and mortality. ### Why NOT the Other Options | Intervention | Why Inadequate | |---|---| | Diazepam alone | Controls seizure but does NOT address the underlying lipophilic toxin; cardiac collapse may follow | | Sodium bicarbonate | Used for tricyclic antidepressant toxicity, not LAST; no evidence for benefit | | Observation | LAST is a medical emergency; seizure can progress to cardiac dysrhythmia and arrest within minutes | **Warning:** Do NOT rely on standard ACLS alone. Lipid rescue is the game-changer for bupivacaine toxicity; cardiac resuscitation may be prolonged (>1 hour) but successful with lipid support. ### Mnemonic: LAST Management **LASE** — **L**ipid, **A**irway, **S**eizure control, **E**mergency support (ACLS with caution) [cite:Barash Clinical Anesthesia 8e Ch 18]