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Abe et al. Mini-invasive Surg 2023;7:28 https://dx.doi.org/10.20517/2574-1225.2023.15 Page 11 of 14

Several single-center studies have reported that robotic surgery tends to increase thoracic operative time
compared to MIE [16,17] ; however, a recent RAMIE study showed that robotic-assisted surgery significantly
[7]
reduces the operative time . These conflicting results may reflect the fact that most of the previous single-
center studies tended to show longer operative times for robot-assisted surgery because of learning curves in
the early phases after introduction. Therefore, we believe that if RAMIE is standardized at each institution,
the console operative time will improve, as we have reported in our department.

The efficacy of robotic-assisted surgery compared to MIE has not been fully validated. Several systematic
reviews have shown reduced blood loss, an increased number of lymph nodes dissected, and shorter
hospital stays, but most of the reports were single-center studies with a small number of patients; large
[18]
multicenter studies are lacking . The results of ongoing multicenter prospective studies, such as the
[19]
RAMIE and REVATE trials , are warranted.
[15]
Our results showed that the incidence of RLN palsy was reduced in the cases in which standardized RAMIE
was performed. While there have been recent reports that RAMIE reduces the incidence of RLN palsy
compared to MIE [7,16,20] , several studies have demonstrated conflicting results [21-24] .

Therefore, whether RAMIE is superior to MIE in reducing the incidence of RLN palsy is debatable;
however, because the microanatomy detail provided by the multi-joint capabilities and 3D high-definition
images in robotic surgery contributes to improving the accuracy of superior mediastinal lymph node
dissection, we are of the opinion that standardized robotic surgery may contribute to a reduction in the
incidence of RLN palsy. The results of the ongoing REVATE study, in which the primary endpoints are
successful lymph node harvesting around the left RLN and the incidence of left RLN palsy, are very
interesting and eagerly awaited.

Because RLN palsy is a risk factor for postoperative pneumonia [20,25,26] , a reduction in the incidence of RLN
palsy has the potential to decrease the risk of postoperative pneumonia and thereby improve the prognosis.
Therefore, it is important to determine whether robotic-assisted surgery reduces the incidence of RLN
palsy. Our results showed a trend toward a decrease in the incidence of RLN palsy with standardization of
RAMIE but no decrease in the incidence of postoperative pneumonia. These results are similar to previous
studies, and few studies have reported that RAMIE reduces the incidence of pneumonia compared to
MIE [7,16,20] . Because risk factors for postoperative pneumonia vary widely, including intraoperative
[27]
position , postoperative antibiotic management , and the presence of sarcopenia , it may be difficult to
[28]
[29]
demonstrate a reduction in the incidence of pneumonia simply by a reduction in the incidence of RLN palsy
alone.
The incidence of chylothorax tended to be higher in the RAMIE group, at 21%, compared to 13% in the
MIE group (P = 0.081). The reason for the slightly higher incidence of chylothorax compared to other
centers may be attributed to the use of early enteral feeding, which started four hours postoperatively, for
postoperative management at our institution. In addition, the difference in surgical devices used between
MIE and RAMIE may have also affected the incidence of chylothorax: in MIE, the vessel sealing system was
used during periaortic lymph node dissection, whereas in RAMIE, only a monopolar electrocautery scalpel
was initially used. This may have resulted in incomplete closure of lymphatic branches during the periaortic
dissection in the RAMIE group. Therefore, the use of bipolar coagulation method during periaortic lymph
node dissection resulted in a reduced incidence of chylothorax in the RAMIE group (MIE vs. phases II and
III, P = 0.618). Moreover, all patients who developed chylothorax were healed conservatively by
discontinuing enteral nutrition, with no significant impact on the postoperative course.