A 42-year-old man undergoes arthroscopic knee surgery under interscalene brachial plexus block. The anesthesiologist administers 45 mL of 0.5% bupivacaine with 1:200,000 epinephrine. Fifteen minutes into the procedure, the patient becomes restless and complains of tinnitus and circumoral numbness. His blood pressure rises to 165/95 mmHg, heart rate is 118/min, and he develops generalized muscle twitching. What is the most appropriate immediate management?

Explanation

## Recognition and Management of Local Anesthetic Systemic Toxicity (LAST) ### Clinical Presentation in This Case The patient demonstrates classic early signs of LAST: - **CNS excitatory phase**: restlessness, tinnitus, circumoral numbness, muscle twitching - **Cardiovascular signs**: hypertension and tachycardia (early phase) - **Timing**: symptoms within 15 minutes of injection suggest rapid vascular uptake **Key Point:** The dose of 45 mL of 0.5% bupivacaine = 225 mg, which exceeds the safe limit of 175 mg for interscalene block in a 70 kg patient (2.5 mg/kg without epinephrine consideration). ### Immediate Management Algorithm ```mermaid flowchart TD A[Suspected LAST]:::outcome --> B[STOP injection immediately]:::action B --> C[Call for help & establish IV access]:::action C --> D[Hyperventilate with 100% O₂]:::action D --> E[Seizure control]:::decision E -->|Seizure present| F[Small doses benzodiazepines or succinylcholine]:::action E -->|No seizure| G[Prepare lipid emulsion]:::action F --> H[Lipid Emulsion 20% IV bolus]:::action G --> H H --> I[Repeat bolus every 5-10 min until signs resolve]:::action I --> J[Infusion: 15 mL/kg over 15-20 min]:::action J --> K[Consider ECMO if cardiovascular collapse]:::urgent ``` ### Why This Approach? **High-Yield:** The 2017 ASRA guidelines mandate: 1. **Immediate cessation** of local anesthetic injection 2. **Airway management** with 100% oxygen and hyperventilation (increases seizure threshold, improves oxygenation) 3. **Seizure suppression** with small IV benzodiazepine doses (not full anesthesia) 4. **Lipid emulsion 20%** as the definitive treatment: - Bolus: 1.5 mL/kg IV over 1 minute (≈100 mL for 70 kg patient) - Repeat every 5–10 minutes if cardiovascular instability persists - Infusion: 15 mL/kg over 15–20 minutes **Clinical Pearl:** Lipid emulsion works by creating a "lipid sink" that sequesters lipophilic bupivacaine from the CNS and myocardium, allowing redistribution and metabolism. ### Why NOT Propofol or Diazepam Alone? - **Propofol** is lipophilic and will compete with bupivacaine for the lipid compartment; it may worsen toxicity and is contraindicated - **Diazepam alone** without lipid emulsion is inadequate for LAST and delays definitive therapy **Mnemonic:** **LAST STOP** — Local Anesthetic Systemic Toxicity: Stop injection, Treat seizures, Oxygenate, Prepare lipid emulsion.