A 35-year-old male with severe burns is brought to the operating theatre for escharotomy. The anaesthetist avoids succinylcholine despite its rapid onset. Which clinical feature of depolarising agents explains this contraindication in burn patients?

Explanation

## Succinylcholine in Burn Patients: The Hyperkalaemia Risk ### Why Succinylcholine is Contraindicated in Burns **Key Point:** Succinylcholine (a depolarising agent) causes sustained depolarisation of muscle membranes. In burn patients with extensive muscle injury and necrosis, this depolarisation triggers **massive potassium efflux from damaged myocytes**, leading to severe and potentially **fatal hyperkalaemia**. ### Mechanism of Hyperkalaemia 1. **Normal muscle:** Succinylcholine depolarises the muscle membrane → brief K^+^ efflux → serum K^+^ rises by 0.5–1 mEq/L (usually tolerated) 2. **Burned/denervated muscle:** Extensive muscle necrosis exposes intracellular K^+^ stores → depolarisation triggers uncontrolled K^+^ release → serum K^+^ can rise by **10–15 mEq/L** → cardiac dysrhythmias, cardiac arrest ### High-Risk Scenarios for Succinylcholine-Induced Hyperkalaemia | Condition | Mechanism | Risk Onset | | --- | --- | --- | | **Severe burns** | Massive muscle necrosis and denervation | Immediate (within minutes) | | **Crush injuries** | Rhabdomyolysis and muscle breakdown | Immediate | | **Spinal cord injury** | Denervation atrophy of paralysed muscles | 24 hours onwards (peaks at weeks) | | **Prolonged immobilisation** | Muscle atrophy and denervation | Days to weeks | | **Severe sepsis / critical illness** | Catabolic muscle breakdown | Variable | | **Malignant hyperthermia** | Abnormal calcium handling in muscle | Immediate (also triggers MH crisis) | **Clinical Pearl:** In burn patients, the risk of hyperkalaemia is **highest within the first 24–48 hours** after injury, when muscle necrosis is most active. It remains elevated for weeks. ### Clinical Consequences of Succinylcholine-Induced Hyperkalaemia ```mermaid flowchart TD A[Succinylcholine in burn patient]:::action --> B[Depolarisation of damaged muscle]:::outcome B --> C[Massive K+ efflux from myocytes]:::outcome C --> D[Serum K+ rises to 10-15 mEq/L]:::urgent D --> E{Cardiac effects}:::decision E -->|Peaked T waves| F[Peaked T waves on ECG]:::outcome E -->|Bradycardia| G[Severe bradycardia]:::outcome E -->|Dysrhythmia| H[Ventricular fibrillation]:::urgent H --> I[Cardiac arrest]:::urgent ``` **Warning:** Even a serum K^+^ of 7–8 mEq/L can trigger life-threatening dysrhythmias in the perioperative setting. ### Management Strategy **High-Yield:** In burn patients requiring rapid intubation: - **Avoid succinylcholine** entirely (even though onset is fast) - **Use rocuronium** (non-depolarising, rapid onset ~60 sec with high dose) or **vecuronium** - If succinylcholine is unavoidable, **pre-treat with a non-depolarising agent** (defasciculation) to reduce K^+^ efflux - **Monitor serum K^+^** and ECG closely - Have **calcium gluconate, insulin + glucose, and sodium bicarbonate** ready for emergency hyperkalaemia management **Mnemonic:** **BURNT** patients avoid **S**uccinylcholine = **B**urns, **U**ncontrolled muscle injury, **R**habdo, **N**euromuscular disease, **T**rauma → all contraindications to depolarising agents