VOLUME 31, ISSUE 1

Residual neuromuscular blockade continues to be an important patient safety issue. Numerous studies have shown that residual paralysis, defined as a train of four ratio (TOFR) < 0.9, results in the blunting of protective airway reflexes and the impairment of upper airway patency and coughing. This can lead to hypoxemia, airway obstruction, subjective feelings of weakness, longer PACU stays, and an increased risk of aspiration and postoperative pneumonia.1 Many studies have shown that 40-60% of patients in the PACU experience some degree of residual paralysis. However, surveys show that the majority of practicing anesthesiologists estimate that the incidence of clinically significant neuromuscular blockade is <1%. Perhaps part of the reason for this disconnect can be supported with the adage “You won’t find a fever if you don’t take a temperature.” If one does not routinely monitor neuromuscular function, how can one be sure that the patients are fully recovered or reversed from neuromuscular blockade at the end of surgery?

Anesthesiologists who do not routinely monitor their patients and who do not believe that residual neuromuscular blockade is a problem may ask, “If residual blockade is so frequent, why isn’t there a higher incidence of patients in the PACU being reintubated or exhibiting signs of respiratory compromise?” They have a point to some extent, because the majority of patients with residual blockade will not have any outward manifestations of that problem, especially if no one is looking specifically for those signs.1 Could it be possible that some patients who previously were ‘slow to wake’ from anesthesia actually had residual neuromuscular blockade? Outward manifestations of residual blockade may also be masked by the use of supplemental oxygen or jaw thrust maneuvers. Also, the diaphragm that contributes 70 to 75% effort to respiration usually recovers first, hence patients are unlikely to show overt signs of residual paralysis. However, patients with morbid obesity, obstructive sleep apnea, pulmonary disease, cardiac disease, sepsis, etc. will be much less tolerant of any degree of residual paralysis. Furthermore, residual paralysis is very difficult to differentiate from the lingering effects of benzodiazepines, opioids, and other anesthetics as well as the effects of poor baseline respiratory function, obesity, or obstructive sleep apnea. The picture can be murky, but it is up to us to eliminate the possibility of residual paralysis with proper neuromuscular monitoring and reversal. Unless a quantitative monitor indicates that the TOF ≥ 0.9, the presence of residual neuromuscular blockade cannot be excluded.

Clinical signs such as a 5-second head lift are poorly sensitive for return of neuromuscular function, as studies have shown that the majority of subjects can maintain a 5-second head lift with a TOF ratio as low as 0.5.2 Clinicians are also very poor monitors of neuromuscular function. The term ‘peripheral nerve monitor,’ which is commonly used, is a misnomer. In fact, the monitor is the anesthesia provider, who uses a visual or tactile assessment to subjectively evaluate the degree of neuromuscular function present. After a TOFR ≥ 0.4, clinicians are no longer able to detect the presence of fade, and thus may incorrectly assume full recovery from neuromuscular blockade.3

In order for neuromuscular monitoring to be incorporated into routine clinical practice, it must be simple, reliable, and accurate. Mechanomyography is the gold standard for monitoring neuromuscular function, but it is cumbersome and not used clinically. The most frequently used method of quantitative monitoring uses acceleromyography, which is based on Newton’s second law (force = mass x acceleration). Currently, there are very few quantitative monitors that are available for routine clinical use. The TOF-Watch (Organon, Dublin, Ireland) is the gold standard that has been used with the most frequency in research studies, but it is no longer being manufactured. It requires calibration prior to the administration of any neuromuscular blocking agent, which can take several minutes. If movement of the piezoelectric crystal that is attached to the thumb is impeded, such as when the arms are tucked, the readings will be erroneous. The TOFscan (Drager Technologies, Canada) is a new device that uses 3D acceleromyography to measure movement of the thumb in multiple planes. When compared to the TOF-Watch SX, there was good agreement between the results, and it has been suggested that the TOFscan is a suitable quantitative monitor for research studies and clinical care.4 Electromyography (EMG) is another method for quantitative neuromuscular monitoring and works even if the arm is tucked and, thus, may be the most user-friendly of the methods. The TwitchView (Blink Device Company, Seattle, WA) is a new FDA-approved device that uses EMG to monitor the depth of neuromuscular blockade and displays the results quantitatively on a stand-alone monitor, which can be integrated into the electronic medical record. As of this writing, no studies have been performed comparing the TwitchView with any pre-existing quantitative monitors.

Some have argued that the introduction of sugammadex, a selective relaxant binding agent, obviates the need for neuromuscular monitoring. That is, however, an erroneous assumption, as the correct dosing of sugammadex requires one to know what depth of neuromuscular blockade is present. Furthermore, slow responders and non-responders to sugammadex have been reported, so it is still necessary to demonstrate a return to a TOFR ≥ 0.9 prior to extubation, regardless of which reversal agent is used. Additionally, re-curarization can occur, especially if a small dose of sugammadex is given to reverse a deep block.

It has been said that it takes about ten years from the time a finding is printed in a journal article for it to be incorporated into standard clinical practice. It has been well over ten years since many authors have proven the relationship between inadequate monitoring and reversal of neuromuscular blockade and increased postoperative morbidity and mortality. With the advent of newer technologies that make quantitative monitoring of neuromuscular function easy and reliable, universal monitoring should hopefully decrease the incidence of residual neuromuscular blockade and increase patient safety in the perioperative period. In 2015, the Association of Anaesthetists of Great Britain and Ireland added to their recommendations for standard monitoring that “a peripheral nerve stimulator must be used whenever neuromuscular blocking drugs are given.” As of this writing, the ASA has not included the need for monitoring of neuromuscular function as part of the Standards for Basic Anesthetic Monitoring, but other organizations such as the Anesthesia Patient Safety Foundation as well as the Enhanced Recovery After Surgery Society have endorsed the use of quantitative monitoring.

What can we do better? Increased awareness and education is the first step. As Naguib et al. express in their recently published consensus statement, the gap between science and practice is not only connected with the acquisition of new knowledge, but the unlearning of old and outdated “knowledge” that must be “deimplemented.”4 The second step is to monitor every single patient that receives a neuromuscular blocking drug. Ideally, the monitor would be quantitative, and monitoring would occur at the adductor pollicis rather than the face, since facial muscles recover earlier than upper airway muscles.5 Third, there must be continuous education and re-assessment of institutional practices. It is up to us to bridge this disconnect between print and practice. Perhaps the future generation of anesthesiologists will think of quantitative neuromuscular monitors like some of the older anesthesiologists think of pulse oximetry and capnography- previously a new technology that then becomes part of standard clinical practice.