Why is residual neuromuscular blockade a universal issue?

Keywords: :

• Complications of general anesthesia
• Neuromuscular blocking drugs
• Residual neuromuscular blockade
• Train of four

Residual neuromuscular blockade (rNMB) has been a problem plaguing anesthesiologists with over 200 articles published on the subject. In this issue of CMRO, Yu et al.1 examined the incidence of rNMB in 1571 patients across 32 hospitals in China. Neuromuscular blockade for patients undergoing abdominal surgery (67% laparoscopic) was assessed intraoperatively and in the post anesthesia care unit (PACU) with acceleromyography (AMG) after a normalized baseline was established. The criteria for rNMB was a train of four (TOF) ratio <0.9. At the time of tracheal extubation in the operating room 57.8% had TOF <0.9 while 45.2% also had rNMB on admission to the post anesthesia care unit (PACU). In both areas, about 30% of the patients had TOF <0.7. Reversal was not used for 22%. The results clearly show the widespread presence of rNMB in China. The authors demonstrated that age greater than 45, neostigmine administration less than 10 minutes prior to extubation, and time from last NMB administration less than 60 minutes were associated with rNMB. However, there were no differences in the proportion of hypoxia, shortness of breath, difficulty in swallowing or speaking between those with and without rNMB.

So, why is rNMB a persistent issue? There are several factors that may contribute to this. Ali et al.2 demonstrated that at TOF 0.75, patients had a 5 second head lift, vital capacity of 15–20 ml/kg and an inspiratory force of −25 cm H₂O. The criterion of TOF <0.9 is based on studies of healthy volunteers. Extrapolations of the untoward consequences of rNMB in the postoperative period to patients may be confounded by multiple factors that are obvious to the anesthesiologist including co-existing diseases, narcotic administration, anesthetic regimens, and the surgical procedures themselves. Postoperative pulmonary complications have been associated with presence of a nasogastric tube, preoperative sputum production, and the duration of the anesthetic3. Hypoxemic episodes may be more related to arousals from sleep after abdominal surgery rather than to respiratory disturbances4. Investigators, who have used elegant statistical methods to demonstrate a variety of complications associated with rNMB in the postoperative period, including the possibility of untoward events with the administration of too much neostigmine5, invariably present caveats associated with their observational data. As anesthesiologists, we treat what we see as blatantly evident, e.g. pain or over-sedation with narcotics. In the eyes of the clinician, unless there is overt weakness, the potential effects of rNMB are not clinically observed when all of the other postoperative factors are taken in consideration.

A crucial prerequisite to the assessment of rNMB is how we monitor or don’t monitor our patients. One has to be fastidious with placement of electrodes, when using TOF monitors. Often the ulnar nerve is not available for stimulation and the electrodes are placed ‘somewhere’. To be accurate, the AMG should have an established baseline that most clinicians will not spend the time to achieve and even then a ‘quantitative’ TOF count that can be charted in the anesthesia record may be clinically meaningless. Therefore, we should also explore other methods to prevent rNMB. In the absence of accurate TOF monitoring, clinical assessment of the patient’s response to mechanical ventilation may prove a reliable surrogate. With advanced anesthesia mechanical ventilators, the anesthesiologist can readily see when a patient demonstrates excellent tidal volumes on low levels of pressure support, which is in essence similar to a spontaneous breathing trial that is used in intensive care units prior to extubation. Why not consider this sign a confirmation of full recovery from neuromuscular blockade?

The key to diminishing rNMB is vigilance and common sense. Clearly, a form of monitoring for the determination of the depth of neuromuscular blockade is mandatory. Studies have demonstrated that even with the administration of sugammadex, that some consider a panacea for reversal, rNMB is significant when intraoperative monitoring is not done6. With an adequate TOF between 0.75 and 0.9 and clinical evidence of the return of muscle strength as advocated by Ali et al.2 our patients can be safe.

Transparency

Declaration of funding

This editorial was not funded.

Declaration of financial/other relationships

R.M.P. has disclosed that he has no significant relationships with or financial interests in any commercial companies related to this study or article.