Why is succinylcholine contraindicated in a patient with a burn injury after the first 24 hours?

Succinylcholine Contraindication in Burn Patients After 24 Hours

Succinylcholine is absolutely contraindicated in burn patients after 24 hours post-injury due to the risk of life-threatening hyperkalemia from upregulation of acetylcholine receptors at the muscle membrane, which can cause cardiac arrest. 1

Pathophysiology of Hyperkalemia Risk

Burn injuries trigger a systemic upregulation of nicotinic acetylcholine receptors (nAChRs) throughout skeletal muscle, not just at the burn site. This process involves:

• Proliferation of "immature" acetylcholine receptors characterized by substitution of the epsilon subunit with gamma protein, which spread beyond the neuromuscular junction to cover the entire muscle membrane surface 2
• These upregulated receptors become more ionically active, leading to massive potassium efflux when depolarized by succinylcholine 3
• Gene expression studies demonstrate significant upregulation of alpha7 and gamma nAChR subunits in burn patients, with this effect occurring systemically in non-muscle tissues distant from the injury site 4

Critical Time Window

The FDA explicitly states that succinylcholine is contraindicated "after the acute phase of injury following major burns," with the risk period beginning as early as 24 hours post-injury 1. The temporal characteristics include:

• Risk begins within 24-48 hours after thermal injury 5, 3
• Peak risk occurs at 7-10 days post-burn, though the precise onset and duration remain somewhat unpredictable 1
• The contraindication extends for at least 2 years after burn injury, as receptor alterations persist throughout this period 2
• Risk correlates with burn severity: burns exceeding 15% total body surface area produce the most significant receptor changes 2

Clinical Consequences

The hyperkalemic response to succinylcholine in burn patients is dose-dependent, unpredictable, and can result in immediate cardiac arrest 2. Key features include:

• Cardiac complications occur rapidly, often within minutes of administration, presenting as severe arrhythmias including wide complex tachycardia, bradycardia progressing to asystole, or ventricular fibrillation 3
• The magnitude of potassium release is directly related to the dose administered, the post-burn delay, and the extent of burned body surface area 2
• Even small doses (0.1-0.2 mg/kg) demonstrate hypersensitivity in burn patients, though these lower doses may not cause metabolic disturbances or cardiac arrest 2

Safe Alternative: Rocuronium

Rocuronium at doses ≥0.9 mg/kg (preferably 1.0-1.2 mg/kg) is the recommended alternative for rapid sequence intubation in burn patients 5, 3, 6. Important considerations include:

• Rocuronium provides excellent intubating conditions within 60 seconds with first-pass success rates comparable to succinylcholine (74.6-79.4%) 6
• Duration of action is 30-60 minutes versus 4-6 minutes for succinylcholine, but this safety benefit outweighs the disadvantage of prolonged paralysis 3, 6
• Burn patients paradoxically demonstrate resistance to non-depolarizing agents like rocuronium due to the same receptor upregulation, starting around day 7 and peaking between days 15-40 post-injury 2, 7
• Higher doses of rocuronium may be required in burn patients during the resistance phase, though initial dosing should not be modified 6

Critical Management Points

When managing airway emergencies in burn patients beyond 24 hours post-injury:

• Use an uncut endotracheal tube to allow for subsequent facial swelling 5
• Implement protocolized post-intubation analgosedation immediately when using rocuronium to prevent awareness during the prolonged neuromuscular blockade 6
• Have sugammadex rapidly available for reversal of rocuronium if needed 6
• Monitor for signs of difficult airway including hoarseness, dysphagia, drooling, stridor, carbonaceous sputum, or singed facial/nasal hairs 5
• Insert a gastric tube after securing the airway, as this may become difficult later due to progressive swelling 5

Common Pitfalls to Avoid

Do not assume the first 24 hours post-burn is completely safe - the FDA contraindication begins "after the acute phase," which can be as early as 24 hours, and some sources suggest avoiding succinylcholine from as early as 5 days post-injury 1, 2

Do not rely on serum potassium levels to predict safety - the hyperkalemic response is unpredictable and can occur even with normal baseline potassium 2

Do not underdose rocuronium - doses less than 0.9 mg/kg may not provide adequate intubating conditions; use 1.0-1.2 mg/kg for optimal results 6

Do not forget that burn patients may require higher doses of non-depolarizing agents during the resistance phase (7 days to 2 years post-injury), though initial dosing should follow standard protocols 2, 7