Is succinylcholine (SCh) a suitable neuromuscular blocking agent (NDMR) for general anesthesia?

Succinylcholine as a Neuromuscular Blocking Agent for General Anesthesia

Succinylcholine is a suitable neuromuscular blocking agent (NDMR) for general anesthesia in most cases, particularly for rapid sequence induction, but has important contraindications and safety considerations that limit its use in specific patient populations. 1

Mechanism of Action and Clinical Use

• Succinylcholine is a depolarizing skeletal muscle relaxant that binds to cholinergic receptors at the motor end plate, causing depolarization observed as fasciculations, followed by inhibition of neuromuscular transmission 1
• It has a rapid onset of action (less than one minute after IV administration) and short duration (approximately 4-6 minutes), making it particularly valuable for tracheal intubation 1, 2
• Succinylcholine is indicated as an adjunct to general anesthesia to facilitate tracheal intubation and provide skeletal muscle relaxation during surgery or mechanical ventilation 1

Advantages in Clinical Practice

• The rapid onset and short duration of action make succinylcholine particularly useful for rapid sequence induction in emergency situations, such as patients with full stomachs 2
• Despite the development of newer non-depolarizing agents, none currently available possess both the rapid onset and prompt recovery characteristics of succinylcholine 2
• Succinylcholine is rapidly hydrolyzed by plasma cholinesterase, which accounts for its short duration of action 1, 3

Contraindications and Safety Considerations

• Succinylcholine is contraindicated in patients with primary muscle damage (myopathies) or up-regulation of nicotinic acetylcholine receptors at the motor end plate (chronic motor deficit) 4
• In patients with specific muscle disorders (myopathy, myotonia), succinylcholine can induce generalized contraction with rhabdomyolysis 4
• In patients with up-regulation of nicotinic acetylcholine receptors (chronic damage of motoneurons, extensive burns, prolonged critical illness), succinylcholine can cause life-threatening hyperkalemia 4
• Succinylcholine is specifically contraindicated in patients with Duchenne muscular dystrophy due to risk of acute rhabdomyolysis, hyperkalemia, and cardiac arrest 4

Dosing Considerations

• Standard adult dosing for intubation is typically 1.0 mg/kg (real weight) 4
• Age-appropriate doses for children have been established: < 1 month: 1.8 mg/kg, > 1 month and < 1 year: 2.0 mg/kg, > 1 year and < 10 years: 1.2 mg/kg, > 10 years: 1.0 mg/kg 4
• In the presence of pretreatment with pyridostigmine or under the effects of nerve agent poisoning, the amount of succinylcholine needed for sufficient muscle relaxation should be reduced significantly 4

Monitoring Requirements

• Quantitative neuromuscular monitoring is essential when administering neuromuscular blocking drugs, including succinylcholine 4
• Clinical tests of recovery (sustained head-lift, hand grip, tongue depressor tests) are inadequate for assessing recovery from neuromuscular blockade 4
• Every operating theater where neuromuscular blocking drugs are used should be equipped with a quantitative neuromuscular monitoring device 4

Alternatives to Succinylcholine

• In cases where succinylcholine is contraindicated, rocuronium at doses slightly above the normal intubation dosage (0.6 mg/kg) may be preferred due to its mild vagolytic effect and lack of acetylcholinesterase-dependent metabolism 4, 5
• For rapid sequence induction in children where succinylcholine is contraindicated, rocuronium is recommended as an alternative 4
• Despite the formidable side effect profile of succinylcholine, it has not been completely replaced by non-depolarizing agents for use in emergency conditions 2

Potential Complications and Side Effects

• Succinylcholine may cause changes in cardiac rhythm, including cardiac arrest, due to stimulation of autonomic ganglia and muscarinic receptors 1
• It causes an increase in intraocular pressure immediately after injection and during the fasciculation phase 1
• Overdosage with succinylcholine may result in neuromuscular block beyond the time needed for surgery and anesthesia, manifested by skeletal muscle weakness, decreased respiratory reserve, low tidal volume, or apnea 1
• Prolonged exposure may lead to a transition from the characteristic depolarizing neuromuscular block (Phase I) to a block with characteristics resembling a non-depolarizing block (Phase II) 1

Special Considerations

• In patients with nerve agent intoxication, it is recommended to abstain from using succinylcholine due to potential interactions with acetylcholinesterase inhibitors 4
• Drugs that decrease plasma cholinesterase activity (contraceptive pills, cyclophosphamide, echothiopate, organophosphates) may prolong the effect of succinylcholine 6
• Careful monitoring is essential in patients with potential plasma cholinesterase abnormalities, as this can significantly extend the duration of action 3