What are the pharmacologic effects, recommended dose, adverse effects, contraindications, and management of complications of succinylcholine?

Succinylcholine: Pharmacologic Effects, Dosing, Adverse Effects, and Management

Mechanism of Action and Primary Clinical Use

Succinylcholine is a depolarizing neuromuscular blocking agent that causes prolonged depolarization at the neuromuscular junction, resulting in rapid-onset muscle paralysis ideal for rapid sequence intubation. 1, 2

• Succinylcholine attaches to nicotinic acetylcholine receptors in the motor end plate and depolarizes the neuromuscular junction, making it refractory to acetylcholine and producing paralysis 2
• It has the fastest onset (approximately 1 minute) and shortest duration of action (4-6 minutes) of all neuromuscular blocking agents, making it the preferred agent for emergency airway management 1, 3
• The short duration results from rapid hydrolysis by the endogenous enzyme butyrylcholinesterase (pseudocholinesterase) 4

Recommended Dosing

Adult Dosing

• Standard intubation dose: 1.0 mg/kg IV 1, 5
• Alternative reduced dose of 0.6 mg/kg produces identical intubation conditions to 1.0 mg/kg but with faster recovery (5.78 minutes to 50% twitch recovery versus 8.55 minutes) 5

Pediatric Dosing (Age-Specific)

Dosing varies significantly by age and must be adjusted accordingly: 6, 1

• Less than 1 month: 1.8 mg/kg
• 1 month to 1 year: 2.0 mg/kg
• 1 to 10 years: 1.2 mg/kg
• Greater than 10 years: 1.0 mg/kg

Special Populations

• In patients with nerve agent poisoning or pyridostigmine pretreatment, the dose should be significantly reduced 1
• Patients with myasthenia gravis require only 50% of the normal dose due to receptor downregulation, though succinylcholine should be avoided entirely in these patients 7

Absolute Contraindications

Succinylcholine is absolutely contraindicated in the following conditions: 8, 1

• Personal or familial history of malignant hyperthermia 8, 6, 1
• Skeletal muscle myopathies (including Duchenne muscular dystrophy, Becker dystrophy) 8, 1, 9
• Known hypersensitivity to succinylcholine 8
• After the acute phase of injury (typically 24-48 hours to 7-10 days post-injury) following:
  • Major burns 8, 9
  • Multiple trauma 8
  • Extensive denervation of skeletal muscle 8
  • Upper motor neuron injury 8
  • Spinal cord injuries 1, 9
• Prolonged immobilization (>3 days) 1, 9
• Neuromuscular diseases 1, 9

Major Adverse Effects

Life-Threatening Complications

Hyperkalemia and Cardiac Arrest

• Succinylcholine can cause severe, potentially fatal hyperkalemia in patients with upregulated acetylcholine receptors 8, 10
• Cardiac arrest can occur within minutes of administration in high-risk patients, particularly those with undiagnosed muscular dystrophy 9
• The risk of hyperkalemia peaks at 7-10 days after injury in burn/trauma patients, though the precise onset and duration of risk are not fully known 8
• Hyperkalemia presents with sudden severe arrhythmias including wide complex tachycardia, bradycardia progressing to asystole, or ventricular fibrillation 9

Malignant Hyperthermia

• Succinylcholine is a known trigger for malignant hyperthermia in susceptible individuals 1, 8, 2
• Presents as masseter spasm, generalized rigidity, tachycardia, and profound hyperpyrexia 9
• Dantrolene must be immediately available wherever succinylcholine is used 1, 9

Cardiovascular Effects

• Bradycardia, especially in children, often requiring pretreatment with atropine 1, 8
• Arrhythmias, tachycardia, hypertension, and hypotension 8

Other Significant Adverse Effects

• Prolonged respiratory depression or apnea (particularly in patients with butyrylcholinesterase deficiency) 8, 4
• Rhabdomyolysis with possible myoglobinuric acute renal failure 8, 10
• Increased intraocular pressure 8
• Muscle fasciculation and postoperative muscle pain 8
• Jaw rigidity and masseter spasm 8, 2
• Excessive salivation 8
• Anaphylactic and anaphylactoid reactions (rare but potentially fatal) 8

Management of Complications

Hyperkalemia Management

If cardiac arrest occurs immediately after succinylcholine administration, suspect hyperkalemia and treat aggressively: 9

• Calcium gluconate or calcium chloride (immediate membrane stabilization) 9
• Insulin/glucose: 0.1 unit/kg insulin with 400 mg/kg glucose (redistributes potassium within 30-60 minutes) 9
• Sodium bicarbonate (alkalinizes urine and increases urinary potassium excretion) 9
• Hyperventilation 9
• Successful resuscitation often requires 10-12 minutes of CPR 9

Definitive elimination strategies must be initiated early: 9

• Loop diuretics
• Potassium binders
• Hemodialysis (for refractory cases)

Extended monitoring for at least 2-4 hours is mandatory even after initial stabilization due to risk of rebound hyperkalemia 9

Prolonged Paralysis Management

• Continue mechanical ventilation until spontaneous recovery occurs 4
• Obtain butyrylcholinesterase level and dibucaine inhibition test if prolonged paralysis occurs to diagnose hereditary butyrylcholinesterase deficiency 4
• No specific reversal agent exists for succinylcholine 10
• Experimental supramolecular therapeutics (such as water-soluble carboxylatopillar6arene) have shown promise in reversing succinylcholine effects but are not clinically available 10

Malignant Hyperthermia Management

• Immediate administration of dantrolene 1, 9
• Discontinue all triggering agents
• Aggressive cooling measures
• Supportive care including treatment of hyperkalemia and acidosis

Monitoring Requirements

Intraoperative Monitoring

• Continuous heart rate and rhythm monitoring from induction until at least 2 minutes after intubation 9
• Particular attention to bradycardia in children aged 28 days to 8 years 9
• Oxygen saturation monitoring continuously 9

Postoperative Monitoring in Pediatric Patients

• Continuous monitoring until full recovery from anesthesia, including restored airway reflexes, adequate spontaneous ventilation, and ability to maintain airway patency 9
• Vital signs documented at specific intervals until discharge criteria met 9
• Children must remain awake for at least 20 minutes in a quiet environment before discharge 9
• Monitoring in suitably equipped recovery facility with functioning suction and capacity to deliver >90% oxygen 9

High-Risk Patient Monitoring

• Close monitoring of serum creatine kinase and potassium levels to prevent myoglobinuric renal failure and severe dysrhythmias 9
• Neuromuscular monitoring strongly recommended when any muscle relaxant is used in patients with conditions causing receptor upregulation 9

Alternative Agent: Rocuronium

When succinylcholine is contraindicated, rocuronium at doses ≥0.9 mg/kg (preferably 1.0-1.2 mg/kg) is the recommended alternative for rapid sequence intubation. 6, 1

• Rocuronium 1.2 mg/kg provides similar first-pass success rates (79.4%) compared to succinylcholine (82-84%) 1
• Duration of action is 30-60 minutes versus 4-6 minutes for succinylcholine 1, 3
• Sugammadex should be immediately available when rocuronium is used to allow reversal if needed 1, 7
• Protocolized post-intubation analgosedation must be implemented immediately to prevent awareness during prolonged neuromuscular blockade 1

Critical Clinical Pearls and Pitfalls

Common Pitfalls to Avoid:

• Do not give repeat doses of succinylcholine - use non-depolarizing agents instead 9
• Do not assume negative family history rules out malignant hyperthermia susceptibility - patients can develop MH even after previous uneventful anesthetics 1
• Do not underdose rocuronium when using as alternative - doses less than 0.9 mg/kg may not provide adequate intubating conditions 1
• Do not use pretreatment with defasciculating doses of non-depolarizing agents - this does not adequately protect against hyperkalemia in high-risk patients 9
• Do not extubate prematurely in children - ensure patients are fully awake, clear of secretions, and able to maintain upper airway reflexes 9

Key Safety Considerations:

• The choice between succinylcholine and rocuronium should be based on desired duration of muscle relaxation, risk of difficult intubation, presence of contraindications, and whether neuromuscular disease is present or suspected 6
• Atropine should be administered before intubation in children aged 28 days to 8 years, particularly those with septic shock, hypovolemia, or when succinylcholine is used 1
• In rapid sequence induction, cricoid force may need to be reduced if it impedes laryngoscopy or causes airway obstruction 6