A 32-year-old male patient is scheduled for emergency appendicectomy under general anesthesia. He has a history of severe burns 6 months ago affecting 40% of his body surface area, which has now healed with significant scarring. During induction, succinylcholine 1.5 mg/kg IV is administered for rapid sequence intubation. Five minutes after administration, the patient develops severe hyperkalemia (K+ 7.2 mEq/L), cardiac arrhythmias, and cardiac arrest. What is the most likely mechanism responsible for this life-threatening complication?

Explanation

## Pathophysiology of Hyperkalemia in Burned Patients **Key Point:** Succinylcholine-induced hyperkalemia in burn patients results from proliferation of extrajunctional (immature) acetylcholine receptors that are sensitive to depolarization even at low agonist concentrations. ### Mechanism of Receptor Upregulation Following thermal injury, muscle undergoes denervation-like changes characterized by: 1. Loss of normal neuromuscular junction architecture 2. Proliferation of immature acetylcholine receptors along the entire muscle membrane (not just at the neuromuscular junction) 3. These extrajunctional receptors have lower threshold for activation and allow uncontrolled potassium efflux when depolarized ### Timeline and Risk Factors | Factor | Details | |--------|----------| | **Onset** | Begins 24–48 hours post-burn, peaks at 7–10 days | | **Duration of Risk** | Persists for 6–12 months (sometimes longer) | | **Extent Required** | Typically >15–20% TBSA burn | | **Magnitude of K+ Rise** | Can exceed 10–12 mEq/L, causing cardiac arrest | **Clinical Pearl:** Even healed burns carry residual risk because the structural changes to muscle persist long after wound closure. This patient's 6-month-old burn with 40% TBSA represents significant ongoing risk. ### Why Succinylcholine is Contraindicated Succinylcholine depolarizes muscle membrane by acting as an acetylcholine agonist. In burned patients: - Normal acetylcholine receptors (at NMJ) respond to low doses → small K+ release - Extrajunctional receptors (throughout muscle) respond to the same dose → massive, uncontrolled K+ efflux - Result: severe hyperkalemia, peaked T waves, arrhythmias, cardiac arrest **High-Yield:** The K+ release is **independent of neuromuscular blockade**—it occurs even if the patient is adequately paralyzed. This is why monitoring serum K+ and ECG changes is critical. ### Management Implications **Tip:** In any patient with significant thermal injury (>15–20% TBSA), burns >1–2 weeks old, crush injury, prolonged immobilization, or denervation: - **AVOID succinylcholine** — use rocuronium or vecuronium instead - If succinylcholine is used inadvertently: treat hyperkalemia aggressively (calcium gluconate, insulin + glucose, sodium bicarbonate, hyperventilation) [cite:Miller's Anesthesia 8e Ch 12]