A 42-year-old woman undergoes an interscalene brachial plexus block for right shoulder arthroscopy under local anesthesia. The anesthesiologist injects 30 mL of 0.75% ropivacaine (225 mg total) after negative aspiration. Within 2 minutes, the patient develops restlessness, tinnitus, and circumoral numbness. Her blood pressure is 145/92 mmHg, heart rate 118/min, and she appears anxious. What is the most appropriate immediate management?

Explanation

## Recognition and Management of Local Anesthetic Systemic Toxicity (LAST) ### Clinical Presentation The patient exhibits **early signs of LAST** — a dose-dependent toxicity from local anesthetic absorption into the systemic circulation. The sequence typically progresses: 1. **CNS toxicity (early):** restlessness, tinnitus, circumoral numbness, anxiety, tremor 2. **CNS toxicity (severe):** seizures, loss of consciousness 3. **Cardiovascular toxicity (late):** arrhythmias, bradycardia, hypotension, cardiac arrest **Key Point:** The patient received 225 mg of ropivacaine — exceeding the recommended maximum dose of 3 mg/kg (126 mg for a 42 kg woman), making LAST highly likely. ### Lipid Emulsion Therapy — Gold Standard **High-Yield:** Intravenous lipid emulsion (ILE) is the **definitive antidote** for LAST and should be initiated immediately upon suspicion, even before seizures develop. **Mechanism:** Lipid emulsion sequesters lipophilic local anesthetics in a lipid compartment, reducing free drug concentration in blood and tissues. **Dosing Protocol:** - **Initial bolus:** 20% lipid emulsion 1.5 mL/kg IV over 1 minute - **Repeat bolus:** every 3–5 minutes if seizures persist or cardiovascular instability continues (max 10–12 mL/kg in first hour) - **Infusion:** 0.25 mL/kg/min after initial bolus **Clinical Pearl:** ILE is effective even in the presence of early CNS signs and is superior to benzodiazepines alone, which only treat seizures symptomatically without addressing the underlying toxicity. ### Supportive Measures | Intervention | Rationale | |---|---| | Stop injection immediately | Prevent further drug absorption | | Call for help & activate LAST protocol | Ensure rapid response | | Secure airway, 100% O₂ | Prevent hypoxemia during seizures | | Seizure control (benzodiazepines) | Symptomatic, NOT curative | | Avoid vasopressors (epinephrine >1 mcg/kg/min) | May precipitate arrhythmias; use lipid first | | ACLS modifications for cardiac arrest | Prolonged CPR (>1 hour); avoid propofol | **Mnemonic: LAST Management = "LACE"** - **L**ipid emulsion (1.5 mL/kg bolus) - **A**irway & oxygen - **C**all for help & CPR if needed - **E**arly recognition & treatment ### Why Lipid Emulsion is Superior to Other Options **Lipid emulsion addresses the root cause** (sequestration of local anesthetic) and is effective for both CNS and cardiovascular manifestations. Benzodiazepines only treat seizures symptomatically and do not reduce systemic drug levels. [cite:Miller's Anesthesia 8e Ch 16]