A 42-year-old man undergoes dental extraction under local anaesthesia. The dentist administers 2% lidocaine with 1:100,000 epinephrine for inferior alveolar nerve block. Within 5 minutes of injection, the patient develops tremor, anxiety, tachycardia (HR 110/min), and mild confusion. Blood pressure is 145/92 mmHg. The patient has no prior history of cardiac disease. What is the most likely cause of this acute presentation?

Explanation

## Clinical Presentation Analysis **Key Point:** The constellation of CNS and cardiovascular symptoms (tremor, anxiety, confusion, tachycardia, hypertension) appearing within minutes of local anaesthetic injection is classic for **systemic local anaesthetic toxicity**, most commonly from intravascular injection. ### Mechanism of Lidocaine Toxicity 1. **Intravascular injection** bypasses the depot effect and causes rapid rise in plasma concentration 2. **CNS phase** (lower plasma levels): tremor, anxiety, circumoral numbness, tinnitus, restlessness 3. **Cardiovascular phase** (higher levels): hypertension, tachycardia, then hypotension, arrhythmias, cardiac arrest 4. **Seizures** may occur at intermediate levels ### Why This Case Fits Lidocaine Toxicity | Feature | Lidocaine Toxicity | Allergic Reaction | Vasovagal | ACS | |---------|-------------------|-------------------|-----------|-----| | **Onset** | Minutes (rapid) | Minutes to hours | Sudden drop in BP | Gradual or sudden | | **Tremor/Anxiety** | ✓ (CNS excitation) | ✗ | ✗ | ✗ | | **Hypertension** | ✓ (early phase) | ✗ | ✗ (hypotension) | Variable | | **Tachycardia** | ✓ | ✓ (possible) | ✗ (bradycardia) | ✓ | | **Confusion** | ✓ (CNS) | ✗ | ✗ | ✗ | **High-Yield:** The **early hypertension + tachycardia + CNS excitement** (tremor, confusion, anxiety) is pathognomonic for local anaesthetic toxicity, NOT allergic reaction (which presents with urticaria, bronchospasm, angioedema) or vasovagal syncope (which causes bradycardia and hypotension). ### Management Implications 1. **Stop injection immediately** 2. **Secure airway** and give 100% O₂ 3. **Seizure prophylaxis:** IV benzodiazepine (lorazepam 2–4 mg) 4. **Lipid emulsion therapy** if severe toxicity or cardiac instability (20% lipid emulsion bolus 1.4 mL/kg IV over 1 min, then infusion 15 mL/kg/min) 5. **ACLS** if cardiac arrest develops **Clinical Pearl:** Epinephrine in the local anaesthetic formulation (1:100,000) is added to *reduce* systemic absorption and prolong duration — it does NOT cause the acute CNS symptoms seen here. The symptoms are from lidocaine itself. [cite:KD Tripathi 8e Ch 11]