When can succinylcholine (SCh) cause adverse reactions?

Succinylcholine Adverse Reactions: Clinical Scenarios and Contraindications

Succinylcholine causes life-threatening hyperkalemia in patients with upregulated nicotinic acetylcholine receptors, including those with burns (>24-48 hours post-injury), prolonged immobilization (>3 days), muscular dystrophies, denervation injuries, spinal cord injuries, and critical illness lasting >16 days. 1, 2, 3

Absolute Contraindications

Muscular Dystrophies and Myopathies

• Duchenne muscular dystrophy and other skeletal muscle myopathies are absolute contraindications due to risk of acute rhabdomyolysis, massive potassium release, and immediate cardiac arrest 1, 2, 4
• Cardiac arrest can occur within minutes of injection in these patients, often without warning signs 2
• The American Academy of Pediatrics specifically warns that cardiac arrest immediately after succinylcholine in young patients should raise suspicion for undiagnosed muscular dystrophy 2

Malignant Hyperthermia

• Personal or family history of malignant hyperthermia is an absolute contraindication 1
• Succinylcholine triggers malignant hyperthermia in susceptible individuals, presenting as masseter spasm, generalized rigidity, tachycardia, and profound hyperpyrexia 3
• Dantrolene must be immediately available wherever succinylcholine is used routinely (except pre-hospital settings where impractical) 5

Time-Dependent Contraindications (Receptor Upregulation)

Burn Injuries

• Contraindicated from 24-48 hours post-burn until complete wound healing 2
• Risk peaks at 7-10 days after injury and persists throughout the healing phase 3
• Extensive or deep burns cause widespread receptor upregulation leading to massive potassium efflux 2

Immobilization and Critical Illness

• Contraindicated after >3 days of immobilization 1
• In ICU patients, hyperkalemia risk increases dramatically with length of stay, with 37% developing potassium ≥6.5 mmol/L after 16 days versus only 1% in the first 16 days 6
• Prolonged pharmacologic neuromuscular blockade itself can predispose to severe hyperkalemia 7

Denervation and Neurologic Injuries

• Contraindicated in spinal cord injury, stroke, or chronic motor neuron damage from the acute phase through months of recovery 2, 3
• Upper motor neuron injuries cause receptor upregulation throughout affected muscle groups 3
• Patients with chronic abdominal infection, subarachnoid hemorrhage, or degenerative nervous system conditions require extreme caution 3

Other Significant Adverse Reactions

Cardiovascular Effects

• Bradycardia occurs commonly in children and may occur in adults, especially with repeat dosing 8
• Tachycardia and arrhythmias can result from hyperkalemia or autonomic effects 3
• Cardiac arrest may be the presenting sign of hyperkalemia, requiring immediate aggressive treatment with calcium, insulin/glucose, and hyperventilation 2

Anaphylaxis

• Succinylcholine is the most immunogenic neuromuscular blocker, involved in 80% of anaphylactic reactions during anesthesia 9
• Life-threatening anaphylactic reactions occur in 1 in 1,000 to 1 in 25,000 anesthetic procedures, with 3.4-6% mortality 9
• Cross-reactivity with other neuromuscular blockers has been reported 3

Other Complications

• Increased intraocular pressure, intragastric pressure, and intracranial pressure from fasciculations 8
• Postoperative myalgia from muscle fasciculations 3
• Masseter spasm may be an early sign of malignant hyperthermia 3
• Prolonged paralysis in patients with atypical pseudocholinesterase 3

Safe Alternative: Rocuronium

When succinylcholine is contraindicated, rocuronium 0.9-1.2 mg/kg provides comparable intubating conditions within 60 seconds with dramatically superior safety profile 1, 4

• Duration of action is 30-60 minutes versus 4-6 minutes for succinylcholine, but this disadvantage is outweighed by safety benefits in high-risk patients 1
• Sugammadex should be rapidly available for reversal if needed 1
• No risk of hyperkalemia or malignant hyperthermia 2

Critical Clinical Pitfalls

• Never assume a patient without known myopathy is safe: undiagnosed muscular dystrophy, particularly in young boys, can present as sudden cardiac arrest after succinylcholine 2
• The 16-day threshold in ICU patients is critical: after this point, the risk of severe hyperkalemia increases 37-fold 6
• Pretreatment with defasciculating doses of non-depolarizing agents does NOT protect against hyperkalemia in high-risk patients 2
• Clinical signs of hyperkalemia may be absent: cardiac arrest can be the first and only manifestation 2