A 35-year-old male patient is scheduled for emergency laparotomy following a stab wound to the abdomen. Induction is planned with propofol and a muscle relaxant. The patient has a history of severe burns 6 months ago affecting 40% of his body surface area, now in the healing phase. During intubation, after administration of succinylcholine 1.5 mg/kg IV, the patient develops severe hyperkalemia (K⁺ 7.2 mEq/L), peaked T waves on ECG, and cardiac arrhythmias. What is the most likely explanation for this complication?

Explanation

## Pathophysiology of Succinylcholine-Induced Hyperkalemia in Burn Patients **Key Point:** Succinylcholine causes a transient rise in serum potassium in all patients (0.5–1.0 mEq/L), but life-threatening hyperkalemia occurs in patients with conditions causing upregulation of extrajunctional (non-junctional) acetylcholine receptors. ### Mechanism in Burn Injury 1. **Thermal injury** causes muscle necrosis and denervation-like changes 2. **Extrajunctional AChR proliferation** occurs across the entire muscle membrane (normally present only at the neuromuscular junction) 3. **Succinylcholine depolarization** activates these widespread receptors 4. **Massive K⁺ efflux** from muscle cytoplasm → severe hyperkalemia within seconds ### Timeline of Risk - **Onset:** 24 hours post-injury - **Peak risk:** 7–10 days post-injury - **Duration:** Up to 6–12 months (as in this case) **Clinical Pearl:** Even 6 months after burn injury, extrajunctional receptors may persist, making succinylcholine dangerous. ### Conditions Associated with Exaggerated K⁺ Release | Condition | Mechanism | Risk Window | |-----------|-----------|-------------| | Thermal burns | Muscle necrosis + denervation | Days to months | | Crush injury | Rhabdomyolysis | Days to weeks | | Spinal cord injury | Denervation | Weeks to months | | Prolonged immobilization | Disuse atrophy | Variable | | Muscular dystrophy | Abnormal AChR distribution | Lifelong | | Sepsis | Inflammatory muscle damage | Variable | **High-Yield:** The rise in K⁺ is **independent of dose** once extrajunctional receptors are present — even small doses of succinylcholine can trigger dangerous hyperkalemia. ### Clinical Presentation - Peaked T waves on ECG (earliest sign) - Bradycardia or tachycardia - Ventricular fibrillation (if K⁺ > 8 mEq/L) - Muscle fasciculations followed by paralysis ## Management 1. **Immediate:** Hyperventilation (↓ K⁺), IV calcium gluconate (membrane stabilization), insulin + dextrose, sodium bicarbonate 2. **Prevention:** Avoid succinylcholine in burn patients; use non-depolarising agents (rocuronium, vecuronium) [cite:Stoelting's Pharmacology in Anesthesia Ch 8]