Anesthesia often seeks to control muscle movement to facilitate surgery, whether through temporarily paralyzing muscles or returning normal function. Monitoring muscle activity is useful in the perioperative setting, primarily during recovery from a neuromuscular blockade after anesthesia. On the flip side, some patients may pose challenges due to having muscle twitching under anesthesia.

To assess and monitor recovery from neuromuscular blockade, patterns of twitch stimulation were established in the 1970s that are still used today. The most widely used pattern is train-of-four (TOF), in which four stimuli of equal strength are delivered in succession. Measuring the resultant muscle twitching provides information on muscle function under or after anesthesia. When a non-depolarizing neuromuscular blockade is administered, there is a decrease in muscle strength and contraction is lost, beginning with T4, followed by T3, then T2, and finally T1. During recovery, the reverse is true: the first twitch appears, followed by the second, the third, and finally the fourth twitch. The TOF ratio is defined as the ratio between T4 (fourth twitch of the TOF series) and T1 (first twitch). This helps clinicians monitor recovery from the neuromuscular blockade. Before tracheal extubation, a ratio of 0.9 should be achieved. In the case of depolarizing neuromuscular block, the standard TOF pattern is less useful.¹

Because no fade occurs during the administration of a depolarizing neuromuscular blockade, such as seen during succinylcholine–induced paralysis, a modified TOF ratio – T4/Tref – has been recommended because it does not require a fade like its standard counterpart. Instead, it uses Tref, a reading which is taken before the administration of the neuromuscular blockade. In a study by Schmartz et al., they compared monitoring the neuromuscular blockade with single twitch stimulation to monitoring with this modified TOF ratio. Although both techniques delivered accurate results, clinicians demonstrate poor adherence to single-twitch stimulation monitoring, which checks for a single twitch at 1 Hz. Schwartz et al. conclude that clinicians are unfamiliar with the technique and so recommend the modified TOF approach.²

When considering patient safety during anesthesia and surgery, unexpected muscle twitching is a significant concern. A case study by Khan et al. reported that unexpected diaphragmatic twitching was caused by overstimulation of the right phrenic nerve because the nerve runs near the lateral wall of the right atrium. This occurred because the patient used a pacemaker and following the initiation of atrial pacing, there was a marked decrease in intrinsic atrial rate. Patients with atypical positions of pacemakers should be evaluated carefully for the possibility of muscle twitching under anesthesia, before surgery begins.³

Another high-risk patient for unexpected muscle twitching under anesthesia is someone diagnosed with Isaacs’ syndrome. This is a rare disorder of peripheral nerve hyperexcitability which has symptoms such as muscle twitching, cramps, and increased sweating. The syndrome is sometimes seen in association with autoimmune diseases. The case study by Kim et al. discussed techniques for managing muscle twitching in a 74-year-old female diagnosed with Isaacs’ syndrome, who underwent surgery for rotator cuff repair. Vigilant neuromuscular monitoring is recommended during the administration of prolonged anesthesia for these patients.

References

1. Verghese, Roshan Simon, et al. “Monitoring Techniques: Neuromuscular Blockade and Depth of Anaesthesia.” Anaesthesia & Intensive Care Medicine, vol. 24, no. 5, May 2023, pp. 307–12, doi:10.1016/j.mpaic.2023.01.00
2. Schmartz, Denis, et al. “A Modified Train-of-four Ratio to Assess Recovery From Depolarizing Neuromuscular Blockade After Succinylcholine, a Prospective Observational Study.” Journal of Clinical Monitoring and Computing, vol. 35, no. 5, July 2020, pp. 1133–38, doi:10.1007/s10877-020-00560-5.
3. Tanabe, Kanae, et al. “Sudden Onset Pacemaker-induced Diaphragmatic Twitching During General Anesthesia.” JA Clinical Reports, vol. 5, no. 1, June 2019, doi:10.1186/s40981-019-0257-7.
4. Kim, Young Mi, et al. “Anesthetic Experience Using Total Intravenous Anesthesia in a Patient With Isaacs’ Syndrome -A Case Report-.” Korean Journal of Anesthesiology, vol. 64, no. 2, Jan. 2013, p. 164, doi:10.4097/kjae.2013.64.2.164.

Related posts:

Groupons for Healthcare Treatment Updates on Value Based Care 2021 Nobel Prize in Medicine Pain Relief from Melatonin