A 42-year-old man undergoes an interscalene brachial plexus block for right shoulder arthroscopy. The anesthesiologist administers 30 mL of 0.75% ropivacaine (225 mg total). Within 2 minutes of injection, the patient develops restlessness, tinnitus, and circumoral numbness. His blood pressure rises to 165/95 mmHg, heart rate 118/min, and he begins to have focal seizure activity in the right arm. What is the most appropriate immediate management?

Explanation

## Recognition of Local Anesthetic Systemic Toxicity (LAST) **Key Point:** The clinical presentation of restlessness, tinnitus, circumoral numbness, hypertension, tachycardia, and focal seizure within minutes of local anesthetic injection is pathognomonic for LAST, specifically the CNS phase progressing to seizure. ### Mechanism of LAST Local anesthetics block voltage-gated sodium channels in both peripheral nerves and the central nervous system. Systemic absorption (especially with high-concentration agents like 0.75% ropivacaine) or accidental intravascular injection causes: 1. **Excitatory phase (CNS):** Inhibition of inhibitory GABA neurons → restlessness, tinnitus, perioral numbness, seizure 2. **Depressant phase (CNS/CVS):** Myocardial depression, vasodilation, bradycardia, hypotension, cardiovascular collapse ### Intravenous Lipid Emulsion (IVLE) — First-Line Treatment **High-Yield:** IVLE is now the standard of care for LAST with seizure activity or cardiovascular instability. The lipophilic local anesthetic molecules are sequestered into the lipid phase, reducing free drug concentration in plasma and tissues. **Dosing Protocol:** - **Bolus:** 1.5 mL/kg of 20% lipid emulsion IV over 1 minute (e.g., ~100 mL for a 70 kg adult) - **Infusion:** 0.25 mL/kg/min after bolus - **Repeat bolus:** If seizure or cardiovascular instability persists after 5 minutes, repeat bolus and increase infusion to 0.5 mL/kg/min - **Maximum dose:** 10–12 mL/kg in first hour ### Adjunctive Management | Intervention | Indication | Rationale | |---|---|---| | **Seizure control** | Focal or generalized seizure | Use small doses of succinylcholine or rocuronium; avoid large benzodiazepine doses that delay IVLE administration | | **Airway management** | Seizure, altered consciousness | Intubate and hyperventilate to maintain oxygenation and prevent aspiration; do NOT hyperventilate excessively (CO₂ lowering is not the goal) | | **ACLS modifications** | Cardiac arrest | Use epinephrine ≤1 mcg/kg (avoid doses >1.5 mg in first hour); avoid vasopressin, calcium channel blockers, beta-blockers, and propofol | | **Prolonged resuscitation** | Refractory arrest | Continue CPR for ≥1 hour; ECMO/cardiopulmonary bypass may be required | **Clinical Pearl:** The seizure in this case is a sign of CNS toxicity and should NOT be treated with aggressive sedation alone—IVLE must be started immediately while securing the airway and controlling seizure with minimal sedation. **Warning:** Do not delay IVLE administration to establish IV access for other drugs. Lipid emulsion is the definitive treatment and should be given as soon as LAST is suspected. ### Why Other Options Fail - **Diazepam alone:** Benzodiazepines control seizure but do not reverse the underlying toxicity; they delay definitive IVLE therapy and may worsen CNS depression. - **Hyperventilation alone:** While intubation is necessary for airway protection, hyperventilation does not remove local anesthetic from the body and may worsen acidosis paradoxically (respiratory alkalosis followed by metabolic acidosis from hypoxia). - **Sodium bicarbonate:** Not indicated in LAST; bicarbonate is used for tricyclic antidepressant toxicity (wide QRS), not local anesthetic toxicity.