A 38-year-old woman undergoes interscalene brachial plexus block for shoulder arthroscopy at a tertiary care hospital in Delhi. The anesthesiologist uses 30 mL of 0.5% bupivacaine. Within 3 minutes of injection, the patient develops circumoral numbness, tinnitus, and restlessness. Her blood pressure is 145/92 mmHg and heart rate is 98 bpm. What is the most appropriate immediate next step in management?

Explanation

## Clinical Recognition of Local Anesthetic Systemic Toxicity (LAST) **Key Point:** The patient is exhibiting early signs of LAST with central nervous system (CNS) toxicity: circumoral numbness, tinnitus, and restlessness are classic prodromal symptoms occurring within minutes of local anesthetic injection. ### Pathophysiology Bupivacaine, a long-acting amide local anesthetic, has high cardiotoxicity and CNS penetration. Systemic absorption—especially from highly vascular regions like the interscalene space—can rapidly produce toxicity at doses as low as 2–3 mg/kg. ### Management Algorithm for LAST ```mermaid flowchart TD A[Suspected LAST: CNS or cardiac signs]:::outcome --> B[Stop injection immediately]:::action B --> C[Call for help & lipid emulsion]:::action C --> D[Secure airway, give 100% O₂]:::action D --> E[Initiate IV lipid emulsion 20%]:::action E --> F{Seizure?}:::decision F -->|Yes| G[Small dose benzodiazepine or propofol]:::action F -->|No| H[Continue lipid boluses q 5 min]:::action E --> I{Cardiac arrest?}:::decision I -->|Yes| J[Start ACLS + prolonged CPR]:::urgent I -->|No| K[Monitor continuously]:::action ``` **High-Yield:** The **definitive treatment for LAST is IV lipid emulsion 20%**, not observation, aspiration, or sodium bicarbonate. Lipid emulsion acts as a "lipid sink," sequestering the lipophilic local anesthetic molecule and reducing free plasma concentration. ### Lipid Emulsion Protocol - **Bolus:** 1.5 mL/kg IV over 1 minute (e.g., 100–150 mL for a 70 kg adult) - **Infusion:** 0.25 mL/kg/min after bolus - **Repeat bolus:** Every 5–10 minutes if seizure or cardiac instability persists (max 10–12 mL/kg in first hour) **Clinical Pearl:** Do NOT waste time attempting to aspirate the injection site—the local anesthetic is already in systemic circulation. Early airway management and oxygenation prevent hypoxia-induced worsening of seizure and arrhythmia. **Warning:** Benzodiazepines are NOT first-line for LAST-induced seizures; they are adjuncts *after* lipid emulsion is initiated. Delaying lipid therapy to give benzodiazepines alone is a critical error. [cite:Butterworth 5e Ch 14]