Neuromuscular blockade is an essential component of modern anesthesia practice, playing a crucial role in facilitating intubation, optimizing surgical conditions, and managing various medical conditions. These agents act at the neuromuscular junction, interfering with the transmission of nerve impulses to muscles, resulting in muscle relaxation and paralysis. However, some research is investigating whether neuromuscular blockade might have secondary effects on postoperative pain.
There are two main categories of neuromuscular blockade agents (NMBAs): depolarizing and non-depolarizing agents. Depolarizing NMBAs, such as succinylcholine, act as acetylcholine receptor agonists, causing rapid depolarization of the muscle membrane. These agents have a quick onset and short duration of action, making them ideal for rapid sequence intubation. In contrast, non-depolarizing NMBAs compete with acetylcholine for binding sites on nicotinic receptors. They are further classified into two subgroups: aminosteroids (e.g., rocuronium, vecuronium) and benzylisoquinolines (e.g., atracurium, cisatracurium).
The mechanism of action of NMBAs involves their interaction with the neuromuscular junction. When an electrical impulse travels along a motor neuron, it triggers the release of acetylcholine from the presynaptic membrane. This neurotransmitter then binds to nicotinic receptors on the postsynaptic membrane, causing muscle contraction. NMBAs disrupt this process by either competing with acetylcholine for receptor sites (non-depolarizing agents) or by causing prolonged depolarization of the muscle membrane (depolarizing agents).
The effect of neuromuscular blockade on postoperative pain has been a subject of ongoing research. Some studies suggest that deep neuromuscular blockade may indirectly influence postoperative pain management. A study by Stamatakis et al. investigated whether reduced use of NMBAs for abdominal hysterectomy increased postoperative analgesic consumption. Although they found that 24-hour morphine consumption was slightly lower in the group receiving NMBAs, the difference was not statistically significant.
Another study examining the effects of deep neuromuscular block on remifentanil requirements during laparoscopic inguinal herniorrhaphy found that deep NMB significantly reduced intraoperative remifentanil needs compared to moderate NMB. However, postoperative pain scores at the post-anesthesia care unit (PACU) did not differ between the groups.
It is important to note that the relationship between neuromuscular blockade and postoperative pain is complex and may be influenced by factors such as the type of surgery, depth of blockade, and individual patient characteristics. While some studies suggest potential benefits in terms of reduced opioid requirements, the direct impact of NMBAs on postoperative pain remains a topic of debate.
References
1. Naguib M, Brull SJ, Johnson KB. Conceptual and technical insights into the basis of neuromuscular monitoring. Anaesthesia. 2017;72(S1):16-37. doi:10.1111/anae.13738.
2. Murphy GS, Brull SJ. Residual neuromuscular block: lessons unlearned. Part I: definitions, incidence, and adverse physiologic effects of residual neuromuscular block. Anesth Analg. 2010;111(1):120-128. doi:10.1213/ANE.0b013e3181da832d.
3. Tollinche LE, Weiss MS, Benson A, et al. Are NMBAs Worth the Risk in the ICU? A Conversation on the Risks, Benefits, and Importance of Quantitative Monitoring. Clin View. 2022. doi:10.1002/clinv.20220414.
4. Stamatakis E, Hadzilia S, Loukeri A, et al. Does neuromuscular blockade affect postoperative pain? Eur J Anaesthesiol. 2013;30:223-223. doi:10.1097/00003643-201306001-00698.
5. Oh TK, Oh AY, Ryu JH, et al. Effects of deep neuromuscular block on surgical pleth index-guided remifentanil requirements during laparoscopic surgery. Sci Rep. 2022;12(1):19113. doi:10.1038/s41598-022-23876-5.