A 52-year-old man undergoing interscalene brachial plexus block for shoulder surgery develops sudden onset of circumoral numbness, tinnitus, and tremor 3 minutes after local anesthetic injection. All of the following are appropriate management steps EXCEPT:

Explanation

## Clinical Case: Intraoperative Local Anesthetic Toxicity ### Scenario Analysis **Key Point:** The patient's symptoms (circumoral numbness, tinnitus, tremor) are classic early signs of CNS toxicity from local anesthetic overdose or intravascular injection during regional block. ### Phases of Local Anesthetic Toxicity | Phase | CNS Signs | Cardiovascular Signs | Mechanism | |-------|-----------|----------------------|----------| | **Early (Excitatory)** | Tinnitus, circumoral numbness, tremor, restlessness, talkativeness | Hypertension, tachycardia | Inhibition of inhibitory pathways | | **Late (Depressant)** | Seizures, loss of consciousness, apnea | Hypotension, bradycardia, arrhythmias, cardiac arrest | Global CNS depression | | **Cardiovascular** | (May occur without CNS signs with bupivacaine) | Profound hypotension, VF, asystole | Direct myocardial depression | ### Correct Management Algorithm ```mermaid flowchart TD A[Circumoral numbness, tinnitus, tremor]:::outcome --> B[STOP injection immediately]:::action B --> C[Call for help, position supine]:::action C --> D[Establish IV access]:::action D --> E[100% O₂, prepare airway]:::action E --> F{Seizures develop?}:::decision F -->|Yes| G[Benzodiazepine or propofol]:::action F -->|No| H[Observe closely, prepare lipid]:::action G --> I[Prepare 20% lipid emulsion]:::action H --> I I --> J[Lipid bolus 1.4 mL/kg IV over 1 min]:::action J --> K[Lipid infusion 15 mL/kg/min]:::action K --> L[Monitor, repeat bolus if needed]:::action ``` ### Why Dantrolene Is Incorrect **Warning:** Dantrolene sodium is **NOT** indicated in LAST. Dantrolene is used for: - Malignant hyperthermia (MH) — a pharmacogenetic disorder triggered by volatile anesthetics and/or succinylcholine - Neuroleptic malignant syndrome - Muscle rigidity in MH, not in local anesthetic toxicity **High-Yield:** LAST and MH are **distinct entities**: - LAST: drug overdose/intravascular injection → CNS/cardiac toxicity - MH: genetic susceptibility + triggering agent → hypermetabolism, muscle rigidity, hyperthermia - Treatment differs: LAST → lipid emulsion; MH → dantrolene **Clinical Pearl:** Confusing LAST with MH is a common exam trap. The presence of circumoral numbness and tinnitus (classic LAST signs) should NOT trigger dantrolene; these are CNS toxicity signs, not MH signs. ### Correct Management Steps for This Patient 1. **Stop injection** — prevent further drug absorption 2. **Airway management** — 100% O₂, secure airway if seizures occur 3. **Seizure control** — benzodiazepines or propofol (NOT succinylcholine, NOT dantrolene) 4. **Lipid emulsion** — 20% emulsion 1.4 mL/kg IV bolus, then infusion 5. **CPR if needed** — prolonged resuscitation may be required [cite:Barash Clinical Anesthesia 8e Ch 14; ASRA LAST Guidelines 2020]