Succinylcholine is a depolarizing neuromuscular blocker that plays a central role in rapid sequence intubation (RSI), a critical and time-sensitive procedure often performed in emergency departments, operating rooms, and intensive care units. RSI is commonly used when immediate airway control is required in patients at risk of aspiration or when spontaneous breathing is unexpectedly compromised. Succinylcholine is widely preferred in this setting due to its rapid onset and short duration of action, providing the necessary conditions for effective emergency intubation (1).
The mechanism of action of succinylcholine involves its function as an acetylcholine analog. Upon administration, it binds to nicotinic acetylcholine receptors at the neuromuscular junction, causing an initial depolarization that results in transient muscle contractions or fasciculations. This phase is followed by a sustained depolarization that renders the muscles unresponsive to subsequent nerve impulses, resulting in paralysis.
However, the use of succinylcholine is not without risk. One of the most significant concerns is its ability to cause hyperkalemia (elevated potassium levels), especially in patients with pre-existing conditions such as burns, crush injuries, or neuromuscular disorders. These conditions can lead to upregulation of acetylcholine receptors on muscle cells, which increases potassium release when succinylcholine is administered. Hyperkalemia can lead to life-threatening arrhythmias, complicating patient care in emergency situations (2). For this reason, alternative neuromuscular blocking agents such as rocuronium are often considered in at-risk populations. Rocuronium, a non-depolarizing agent, has a slower onset of action compared to succinylcholine, but offers a safer profile in certain patients, particularly those with underlying risk factors for succinylcholine-related complications.
Another notable complication associated with succinylcholine is the risk of malignant hyperthermia, a rare but potentially fatal reaction characterized by rapid hypermetabolism of skeletal muscle, leading to increased body temperature, acidosis, and muscle rigidity. There is a genetic predisposition to this condition, and it can occur after exposure to succinylcholine or certain volatile anesthetic agents. Early recognition and prompt administration of dantrolene, a muscle relaxant that inhibits calcium release in skeletal muscle, is essential to prevent mortality (3). Although malignant hyperthermia is rare, anesthesia providers must be aware of this risk.
In addition to these risks, succinylcholine may cause bradycardia, especially in pediatric patients and after repeated dosing. This bradycardia is mediated by succinylcholine’s effect on muscarinic receptors in the heart, particularly at the sinoatrial node. In cases where bradycardia occurs, the administration of an anticholinergic agent such as atropine can mitigate this side effect (4).
Despite these complications, succinylcholine remains one of the most effective agents for achieving rapid neuromuscular blockade for emergency intubation. Its rapid onset, short duration of action and proven efficacy make it a preferred choice for rapid sequence intubation
in various clinical settings. However, careful patient selection and monitoring are essential to reduce the potential for adverse effects. In certain populations, such as those at risk for hyperkalemia or malignant hyperthermia, alternative agents such as rocuronium, although slower in onset, offer a safer alternative. The choice of paralytic agent should always be tailored to the individual patient’s condition to ensure the safest and most effective outcome in emergency airway management.
References
1. Lee C, Katz RL. Clinical implications of new neuromuscular concepts and agents: so long, neostigmine! So long, sux!. J Crit Care. 2009;24(1):43-49. doi:10.1016/j.jcrc.2008.08.009
2. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s Clinical Anesthesiology. 6th ed. New York: McGraw-Hill; 2018.
3. Larach MG, Brandom BW, Allen GC, Gronert GA, Lehman EB. Malignant hyperthermia deaths related to inadequate temperature monitoring, 2007-2012: a report from the North American malignant hyperthermia registry of the malignant hyperthermia association of the United States. Anesth Analg. 2014;119(6):1359-1366. doi:10.1213/ANE.0000000000000421
4. Apfelbaum JL, Hagberg CA, Caplan RA, et al. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2013;118(2):251-270. doi:10.1097/ALN.0b013e31827773b2
