Effect of quantitative versus qualitative neuromuscular blockade monitoring on rocuronium consumption in patients undergoing abdominal and gynecological surgery: a retrospective cohort study

Anaesthetized patients are often treated with neuromuscular blocking agents (NMBA) [1]. Especially in laparoscopic surgery a deep muscular blockade may even provide better surgical conditions [2‐4].

Disadvantages of any neuromuscular block are in case of incomplete residual neuromuscular blockade complications, such as aspiration, postoperative hypoxemia, pneumonia, and atelectasis [5‐9]. Thus, neuromuscular monitoring can be used for quantification to reduce the likelihood of residual neuromuscular blockade [10].

Neuromuscular monitoring is commonly based on the train-of-four (TOF) stimulation of the ulnar nerve [10]: a series of four supramaximal pulses are applied, the degree of the neuromuscular blockade is measured with the decrement of response of the adductor pollicis muscle to repetitive nerve stimulation. Amplitude or decrement of responses can be quantified either electromyographically or acceleromyographically or estimated with tactile sense [11]. In conventional, tactile neuromuscular monitoring (tactile NMM), muscle contractions are assessed tactilely by the examiner. As a result, this method is prone to sources of error such as changing examiners and different empirical values in the assessment of contraction and thus can be misinterpreted [12].

The differences between intraoperative acceleromyography and tactile NMM analysis by the examiner have already been investigated with regard to postoperative complications resulting from residual blockade [13].

The present study aimed to compare the dosage of the muscle relaxant rocuronium and use of sugammadex between qualitative, tactile neuromuscular monitoring and quantitative neuromuscular monitoring, to proof our hypothesis, that quantitative e monitoring can be used to control the dosage of NMBAs more precisely and therefore contribute a stable level of relaxation than with tactile monitoring.

Approval for the present study was obtained from the local ethics committee of the University Hospital Frankfurt (No. 20-1065) and the study was performed in accordance with the actual Declaration of Helsinki. All data were anonymized. Due to its retrospective design the study was not registered in a trial database.

In total, n = 539 patients were analyzed. Tactile NMM was used to examine 244 patients, and 295 patients were examined with quantitative NMM (Fig. 1).

The present study aimed to compare the dosing of rocuronium and sugammadex usage in regard of two different neuromuscular monitoring methods in 539 patients. We observed significantly higher cumulative doses of rocuronium in patients that were monitored with tactile NMM than patients who were treated by quantitative NMM. Nevertheless, overall sugammadex usage was comparable.

We were able to demonstrate, that in the quantitative NMM-group increments in NMBA-dosage were less frequently administered and the indication to give increments was more frequently guided by quantitative NMM. This could be explained by a better evaluation of the relaxation status of the patient via quantitative NMM, as well as increased user-friendliness and, derived from this, a more accurate dosage of NMBAs.

Recently, most studies in this field compare no monitoring versus tactile NMM, which is shown in the meta-analysis by Naguib et al., who analyzed 53 studies and showed a lower rate of residual curarisation in studies using intraoperative neuromuscular monitoring [13]. Only one of the analyzed studies distinguished between conventional monitoring and acceleromyography [15]; no sub-analysis dividing laparoscopic and open surgery was performed, thus our study is the first to evaluate the influence quantitative NMM in this context. In laparoscopic operations, the patient’s arms are sometimes attached to the patient’s flank, so the acceleromyograph must be attached to the patient’s hand before positioning. If neuromuscular blockade is monitored more frequently and evaluation is objectified via an acceleromyograph, a decrease in relaxation might be detected earlier. This could explain the lower overall dosage of NMBA, with significantly less incremental doses when quantitative NMM is used. The assessment of the count of repeat doses is subject to the bias of the operation time, which did not differ between groups in this study. It seems reasonable to conclude a stable level of neuromuscular blockade is more likely to be maintained in the quantitative NMM, whereas an “up and down” neuromuscular blockade using tactile NMM. Especially in laparoscopic surgery, the neuromuscular block is known to optimize space conditions, shown by a meta-analysis by Bruintjes et al. in 2017 [16]. This might explain our results in the subanalysis: we observed higher dosages of NMBA in laparoscopic surgery than in open surgery and, also higher repeated administrations differences in repetitive administration in the quantitative NMM. In a randomized-controlled clinical trial, Veelo et al. examined 69 patients undergoing thoraco-laparoscopic esophagectomy and compared continuous rocuronium infusion with on-demand neuromuscular blockade, both measured using quantitative NMM. The continuous dosage was 0.6 mg/kgBW/min. There was no improvement of surgical conditions, no difference in postoperative pain scores and no difference in duration of surgery between on-demand rocuronium boluses and continuous application [17]. The dosages measured in our study using the quantitative NMM were almost the same as the continuous rate in this study, even though they were given as boluses. Therefore, it seems reasonable to assume that a nearly continuous neuromuscular blockade can be achieved using the quantitative NMM.

We did not control the neuromuscular function in the PACU. However, the more frequent need for oxygen in the recovery room in patients with tactile NMM monitoring might be explained by a higher rate of unrecognized residual neuromuscular block. This is in accordance to Murphyet al., who compared 185 patients and showed a significantly reduced incidence, severity and duration of hypoxemic events in patients monitored by acceleromyographic monitoring [18]. This leads to the conclusion that a residual blockade is more likely to be misdiagnosed using the tactile NMM. Kotake et al. demonstrated that even with NMBA reversal via sugammadex, a risk of residual blockade exists and needs to be identified using neuromuscular monitoring [19]. In contrast, the POPULAR-study by Kirmeier et al. demonstrated in a multicenter, prospective observational cohort study that the use of NMBAs is associated with an increased risk of postoperative pulmonary complications, but the use of neuromuscular monitoring (both tactile and quantitative) was not associated with a reduction of this risk [20], while a secondary analysis showed that a raise of the TOF-ratio > 0.95 (instead of > 0.9) reduced the adjusted risk of postoperative pulmonary complications by 3.5% (0.7–6.0%) [8].

The difference in analyzed patients between the operating room and PACU can be explained by the fact that, in some rare cases, patients were not admitted to the PACU postoperatively.

Besides the well-known limitations of conducting a retrospective analysis, the examiner is a factor that should not be neglected; the assessment of neuromuscular blockade in the tactile NMM group varies depending on the examiner. Due to the study’s retrospective design and changes of in-house standards, the data acquisition for the compared groups did not take place at the same time, as until August 2019 (in abdominal surgery) and December 2019 (in gynecological surgery), respectively tactile monitoring was the only available device and was replaced with quantitative NMM afterwards. We only included cases in which NMM was used, so no confounders for choosing one of the techniques can be analyzed.

When both arms are attached to the patients flank the acceleromyograph must be attached to the patient’s hand before positioning. With tactile monitoring the examiner had to touch the patients’ thumb which might make the examination more complicated and unhandy. It is not documented weather both arms were attached. It is also not documented whether all users of the quantitative NMM have performed a baseline evaluation before neuromuscular blockade, which is a potential bias. The factor of whether patients with a higher BMI were dosed according to their ideal body weight or their actual bodyweight was also not considered. The surgeons did not evaluate the surgical conditions. Preoperatively established peridural anesthesia may reduce the need for muscle relaxants. This was not investigated in the present study; further investigations should investigate this aspect in detail. Furthermore, no neuromuscular monitoring was performed in the PACU, therefore differences in oxygen demand between groups cannot be attributed to residual neuromuscular blockade.

Rocuronium dosage given by the provider differs significantly depending on the monitoring system used. The significantly lower dosage, less repetitive applications, no significant difference in the need for antagonization and fewer respiratory complications suggest that using quantitative monitoring allows a more continuous neuromuscular blockade. Especially in laparoscopic surgery, patients might benefit from continuous neuromuscular blockade.