In this single-center retrospective study, although the use of intraoperative neuromuscular monitoring was not an individual factor influencing intraoperative rocuronium consumption, we found that the use of intraoperative neuromuscular monitoring reduced rocuronium consumption by approximately 15% during laparoscopic surgery in elderly patients (age ≥ 65). In other words, without intraoperative neuromuscular monitoring, there is a risk of overusing rocuronium in elderly patients. It is known that elderly patients have a longer duration of action of rocuronium compared to younger patients [5, 12]. One prospective study showed that means ± standard deviation (SD) of duration of action (minutes) after 0.6 mg/kg rocuronium administration in elderly and younger controls were 42.4 ± 14.5 and 27.5 ± 7.1, respectively [5]. Moreover, elderly patients have greater variability in the duration of action of rocuronium compared to younger patients [13]. One prospective study reported that the range of duration of action after 0.6 mg/kg rocuronium administration under sevoflurane anesthesia in elderly patients was 33–119 minutes [13]. The mechanism of this prolongation and increased variability in the duration of action of rocuronium in elderly patients are attributed to decreased plasma clearance of rocuronium due to age-related reduction in liver size [14], decrease in hepatic and renal blood flow [14], and decrease in rocuronium’s distribution volume [5]. The lower rocuronium consumption in elderly patients who underwent quantitative monitoring vs. those who did not undergo such monitoring (and were managed with subjective evaluation) indicates that quantitative monitoring facilitates administration of lower total doses of rocuronium. This may indicate patient safety implications, since the elderly are at higher risk for residual neuromuscular block and attendant complications [4].
According to previous reports, age [5], female sex [6], obesity [7], liver dysfunction [8], renal dysfunction [9], use of inhalational anesthesia [10], and continuous infusion of rocuronium [11] are the factors which decrease intraoperative rocuronium consumption. In our study’s multiple linear regression analysis, BMI and male sex were the independent factors associated with significant decrease in intraoperative rocuronium consumption per body weight. Although statistical difference was not found (p = 0.072), there was a trend that intraoperative rocuronium consumption decreased with age. Therefore, factors other than male sex, which decreased rocuronium consumption in our study, were consistent to previous reports. One prospective study showed that women required approximately 30% less rocuronium than men to maintain the same degree of neuromuscular block [6]. The etiology of the high sensitivity to NMBAs in female sex was reported as more fat, less muscle, and lower distribution volume compared to men [6]. In contrast, male sex had a decrease in rocuronium consumption by 15% in our study. The reason for the apparent contradiction is unknown; however, we speculate that higher age group (median age of approximately 65 years old) in our study compared to previous study (mean age of approximately 30 years old) may have affected the different sensitivity to NMBAs between sex.
Consistent to our previous report [2], we found that the use of intraoperative neuromuscular monitoring significantly reduced the reversal dose of sugammadex in patients undergoing laparoscopic abdominal surgery. In our previous study [2], we compared the reversal dose of sugammadex between NM + and NM- regardless of the type of surgery. We believe that the result of the present analysis of laparoscopic abdominal surgical patients supports our previous conclusion of the use of intraoperative neuromuscular monitoring reducing the reversal dose of sugammadex.
During laparoscopic surgery, it is recommended to maintain a deeper neuromuscular block to improve the quality of surgical field and to reduce the risk of intraoperative adverse events [15]. However, a remaining question is, how deep should the neuromuscular block be during laparoscopic surgery? A recent systematic review concluded that the use of deep neuromuscular block (defined as PTC 1–2) may improve laparoscopic surgical conditions compared with moderate neuromuscular block (TOF count 1–2) [16]. Moreover, a randomized double-blind controlled study reported that deep neuromuscular block improved not only surgical conditions but also postoperative pain in laparoscopic bariatric surgery [17]. In NM + group in our study, 94% of the patients were maintained with moderate neuromuscular block during the surgery. As a first limitation of this study, if all patients were maintained with deep neuromuscular block in NM + group in our study, the difference in intraoperative rocuronium consumption between NM + group and NM- group may have been less.
This study has several other limitations. First, as our study was a single center study, our data may not be applicable to other institutions. However, the present results will be an example of an institution in which routine practice includes unrestricted use of sugammadex and the widespread availability of quantitative neuromuscular monitors in every operating room. Second, in NM- group, additional rocuronium was administered according to the attending anesthesiologist’s subjective evaluation. Subjective evaluation is likely based on each individual’s clinical experience which can be affected by institutional factors and educational background. Given that there was no statistical difference in rocuronium consumption between NM + group and NM- group among young patients (age༜65), we anticipate that excessively high or low doses of rocuronium were not administered even without the use of intraoperative neuromuscular monitoring in our study. Third, due to the relatively high usage (86%) of intraoperative neuromuscular monitoring in this study, the number of patients in NM- group was small. Finally, as with any observational studies, the observed associations may be confounded by unmeasured factors such as patient severity. However, the association of interest remained significant after accounting for previously reported confounding factors.