Anesthesiologists must consider many additional factors when administering anesthesia to patients with neuromuscular disorders (NMD). For example, these patients are more likely to have cardiomyopathies or respiratory weaknesses; they also have a greater risk of increased sensitivity to sedatives; thus, vital signs and hemodynamic stability should be consistently monitored throughout the operative process [1].  

Temperature management is an important consideration, since NMD patients are more prone to both hypothermia and hyperthermia [2]. Through vasodilation, anesthetics lower body temperature; this effect is increased for people with reduced muscle mass. In addition, hypothermia can further increase these patients’ sensitivity to certain sedatives and non-depolarizing muscle relaxants [3]. Under anesthesia, the skeletal muscle cells of hyperthermia-prone individuals are affected, which can lead to generalized muscle cramping, rhabdomyolysis, and life-threatening conditions [4]. Most NMD patients have autosomal dominant mutations in the skeletal muscle ryanodine receptor (RYR1) gene, which encodes the major muscular calcium channel [5]. An abnormally sensitive RyR1 channel allows for a massive influx of calcium ions from the sarcoplasmic reticulum to the cytoplasm, a risk factor for cardiac arrhythmias, renal failure, and possibly death [4].  

Muscle relaxants are a crucial element of many surgeries. Generally, NMD patients have less muscle force and mass, which decreases the necessary amount of muscle relaxants required for efficient surgery [6]. Depolarizing muscle relaxants activate the acetylcholine receptor, causing excitation of the end plate and enabling muscle contraction. Since the drug’s binding time is longer than the original ligand’s, the receptor is desensitized, causing muscle relaxation. On the other hand, non-depolarizing muscle relaxants are antagonists, or competitive inhibitors, of the acetylcholine receptor. They bind to the receptor without activating it, decreasing the number of available receptors, causing muscle relaxation [4]. Succinylcholine is the only depolarizing muscle relaxant still in use; it can result in uncontrolled muscle contractions, which may then predispose the individual to severe arrhythmias and death. The neuromuscular effect of succinylcholine cannot be counteracted with cholinesterase inhibitors; use of these inhibitors will actually exacerbate the consequences [3,7]. The FDA no longer recommends succinylcholine for NMD patients; instead, non-depolarizing muscle relaxants should be used in adjunct with consistent monitoring, which can be done through train-of-four stimulation (measuring the twitches associated with stimulation to certain muscle groups).  

Patients with Becker’s or Duchenne’s muscular dystrophies have a higher risk of anesthesia-induced rhabdomyolysis and subsequent cardiac arrest. Volatile anesthetics are thought to contribute to this relatively uncommon phenomenon. However, alternatives such as ketamine, propofol, and benzodiazepines each have their own specific disadvantages and risks in NMD patients [8,9]. In all muscular dystrophies, acetylcholinesterase inhibitors should be avoided because of their antagonistic effect on muscle relaxation [10]. In patients with periodic paralysis and metabolic myopathies, prolonged fasting should be avoided because of possible liver disorders. Patients with congenital myasthenic syndrome may be particularly sensitive to non-depolarizing muscle relaxants, so additional caution with these individuals must be applied [4].  

Neuromuscular disorders patient safety depends on the diligence of anesthesiologists during the perioperative course. Systematic sharing of data is an important resource for patient safety as well as future interventions. Additionally, extensive communication by the patient’s entire medical team is necessary to ensure the best outcomes.  

References 

1. Katz, J. A., & Murphy, G. S. (2017). Anesthetic Consideration for Neuromuscular Diseases. Current Opinion in Anesthesiology, 30(3), 435–440. https://doi.org/10.1097/ACO.0000000000000466  

2. Rowland, L. A., Bal, N. C., & Periasamy, M. (2015). The Role of Skeletal-Muscle-Based Thermogenic Mechanisms in Vertebrate Endothermy: Non-shivering Thermogenic Mechanisms in Evolution. Biological Reviews, 90(4), 1279–1297. https://doi.org/10.1111/brv.12157 

3. Rosenberg, H., Pollock, N., Schiemann, A., Bulger, T., & Stowell, K. (2015). Malignant Hyperthermia: A Review. Orphanet Journal of Rare Diseases, 10(1), 93. https://doi.org/10.1186/s13023-015-0310-1  

4. Bersselaar, L. R. van den, Snoeck, M. M. J., Gubbels, M., Riazi, S., Kamsteeg, E.-J., Jungbluth, H., & Voermans, N. C. (2021). Anesthesia and Neuromuscular Disorders: What a Neurologist Needs to Know. Practical Neurology, 21(1), 12–24. https://doi.org/10.1136/practneurol-2020-002633  

5. Carpenter, D., Robinson, R. L., Quinnell, R. J., Ringrose, C., Hogg, M., Casson, F., Booms, P., Iles, D. E., Halsall, P. J., Steele, D. S., Shaw, M.-A., & Hopkins, P. M. (2009). Genetic Variation in RYR1 and Malignant Hyperthermia Phenotypes. British Journal of Anesthesia, 103(4), 538–548. https://doi.org/10.1093/bja/aep204  

6. Putzu, A., Tramèr, M. R., Giffa, M., & Czarnetzki, C. (2020). The Optimal Dose of Succinylcholine for Rapid Sequence Induction: A Systematic Review and Meta-analysis of Randomized Trials. BMC Anesthesiology, 20(1), 54. https://doi.org/10.1186/s12871-020-00968-1  

7. Veyckemans, F., & Scholtes, J.-L. (2013). Myotonic Dystrophies Type 1 and 2: Anesthetic Care. Pediatric Anesthesia, 23(9), 794–803. https://doi.org/10.1111/pan.12120  

8. Hopkins, P. M. (2010). Anesthesia and the Sex-linked Dystrophies: Between a Rock and a Hard Place. British Journal of Anesthesia, 104(4), 397–400. https://doi.org/10.1093/bja/aeq036  

9. Schmitt, H. J., Schmidt, J., & Muenster, T. (2007). Dystrophin Deficiency, Inhalational Anesthetics, and Rhabdomyolysis. Pediatric Anesthesia, 17(1), 94–95. https://doi.org/10.1111/j.1460-9592.2006.02046.x  

10. Hayes, J., Veyckemans, F., & Bissonnette, B. (2007). Duchenne Muscular Dystrophy: An Old Anesthesia Problem Revisited. Pediatric Anesthesia, 0(0), 070719021123002-??? https://doi.org/10.1111/j.1460-9592.2007.02302.x  

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