Defasciculation in anesthesia refers to the administration of a non-depolarizing neuromuscular blocking agent prior to the administration of succinylcholine, a depolarizing agent commonly used for rapid sequence induction (RSI). Succinylcholine is valued for its rapid onset and short duration of action, making it ideal for emergency intubation. However, one of its major side effects is the production of muscle fasciculations (visible, involuntary muscle contractions). These fasciculations, although transient, can cause significant postoperative myalgia, especially in young, healthy individuals. As a result, the practice of administering a small dose of non-depolarizing neuromuscular blocking agent has gained traction in an attempt to minimize both fasciculations and their sequelae, such as muscle soreness (1).
The dose used for defasciculation in anesthesia is approximately 10-20% of the full intubation dose of a non-depolarizing neuromuscular blocker, such as rocuronium or vecuronium, and is given prior to the administration of succinylcholine. Some data report that this reduces the intensity of muscle contractions that occur when succinylcholine depolarizes the neuromuscular junction. The proposed mechanism is that the non-depolarizing agent competitively binds to acetylcholine receptors at the neuromuscular junction, preventing full depolarization by succinylcholine. This in turn reduces the number of activated muscle fibers, resulting in fewer fasciculations (2).
Among the non-depolarizing agents, rocuronium has been particularly favored because of its rapid onset of action and ease of reversal. The ability of rocuronium to reduce both fasciculations and postoperative myalgia has been demonstrated in several studies. For example, a randomized controlled trial comparing the efficacy of rocuronium and vecuronium in preventing succinylcholine-induced fasciculations found that rocuronium was more effective in reducing both fasciculations and postoperative myalgia. The effects of rocuronium were not only more pronounced, but also lasted longer, making it the preferred choice in many clinical settings (3).
The administration of defasciculating doses has other clinical implications beyond the reduction of fasciculations and myalgia. The use of succinylcholine is associated with a number of potential complications, including increases in intraocular and intragastric pressure, hyperkalemia, and the risk of inducing malignant hyperthermia in susceptible individuals. Defasciculation may reduce some of these risks by decreasing the intensity of muscle contractions, although it does not eliminate the systemic effects of succinylcholine. Thus, defasciculation is particularly useful in patients in whom fasciculations or their associated side effects would be particularly undesirable, such as those with eye injuries, hernias, or neuromuscular diseases (4).
However, the practice of defasciculation in anesthesia is not without risk. One concern is the potential for residual neuromuscular blockade, particularly if the defasciculating dose is not fully metabolized prior to succinylcholine administration. Residual blockade may result in incomplete recovery of muscle function postoperatively, potentially leading to complications such as respiratory distress or inadequate response to surgical stimuli. Therefore, it is important to
monitor patients closely using neuromuscular monitoring techniques to ensure complete recovery prior to extubation. In addition, newer reversal agents such as sugammadex have improved safety profiles by allowing rapid reversal of rocuronium-induced blockade (4). Another factor to consider is that defasciculation is not always appropriate in all patient populations. The use of non-depolarizing agents in patients with certain conditions, such as myasthenia gravis or severe renal impairment, may complicate anesthetic management due to altered drug metabolism and sensitivity to neuromuscular blockers. Therefore, the use of defasciculating doses must be carefully considered based on individual patient risk factors.
References
1. Bayable SD, Ayenew NT, Misganaw A. The effects of prophylactic intravenous lignocaine vs vecuronium on succinylcholine-induced fasciculation and postoperative myalgia in patients undergoing elective surgery. Int J Gen Med. 2023;16:1187-1194.
2. Joshi GP, Hailey A, Cross S, Thompson-Bell G, Whitten CC. Effects of pretreatment with cisatracurium, rocuronium, and d-tubocurarine on succinylcholine-induced fasciculations and myalgia: a comparison with placebo. J Clin Anesth. 1999;11(8):641-645. doi:10.1016/s0952-8180(99)00109-9
3. Fukano N, Suzuki T, Ishikawa K, Mizutani H, Saeki S, Ogawa S. A randomized trial to identify optimal precurarizing dose of rocuronium to avoid precurarization-induced neuromuscular block. J Anesth. 2011;25(2):200-204. doi:10.1007/s00540-010-1086-z
4. Gupta D. Residual Neuromuscular Blockade (RNMB): Rocuronium’s defasciculating dose, Neostigmine-Induced Weakness, and Awareness During Recovery. Middle East J Anaesthesiol. 2015