The present study revealed that the degree of upper mediastinal narrowness was significantly associated with prolonged thoracic procedure time, suggesting that particular anatomical features may influence the procedural difficulty in RAMIE of the thorax. This effect was similar to that observed for cMIE, as shown previously [6]. These findings suggest that even full articulation of instruments in the robotic surgical system has not yet overcome technical difficulties in cases with a narrow upper mediastinum. To the best of our knowledge, this is the first study to elucidate the factors that influence the difficulty of RAMIE in thoracic procedures.
A flexible scope may have advantages over a rigid endoscope in obtaining a sufficient surgical view in cases with a narrow mediastinum, as the former can look into targets from various directions. Because the da Vinci Xi surgical system only utilizes a rigid endoscope, an insufficient surgical view may be a reason for the prolonged operative time in cases with a narrow mediastinum. Moreover, during upper mediastinal dissection, since the robotic arms face the same vector, the forceps are more likely to interfere with each other, and manipulation becomes more difficult. These factors may increase the thoracic surgery time for RAMIE in patients with narrow mediastinal spaces.
The median UMI and MMI values in the present study were similar to those observed in a previous study [6]. Given that the indices of Japanese patients did not change between studies, a certain number of challenging cases remain. As prolonged operative time is correlated with the duration of the systemic inflammatory response and increased cytokine release after surgery [10, 11], surgeons should focus on shortening the operative time. The preoperative prediction of anatomical difficulties may contribute to surgical planning, including patient positioning and trocar placement.
Due to their short learning curve, young trainee surgeons have opportunities to perform RAMIE without sufficient experience with cMIE. Preoperative prediction of challenging cases enables appropriate case selection for trainee operators and contributes to patient safety. This study indicates that the UMI is a valuable indicator for preoperatively predicting the difficulty of RAMIE.
Meanwhile, the da Vinci SP (Intuitive Surgical, Inc., Sunnyvale, CA, USA), another robotic surgical system, may overcome technical difficulties associated with challenging anatomical factors. This novel system can reduce the forceps interference. In addition, it utilizes a flexible endoscope that may improve visualization of the narrow mediastinum. In addition to improving surgical skills, the choice of surgical instruments and development of devices may solve this problem.
In the present study, we showed that blood loss during the thoracic procedure remained a significant factor associated with prolonged thoracic operative time. This has also been reported in studies on other robotic operations [12, 13]. Increased blood loss in the surgical area may result in poor surgical view and prolongation of each step of the procedure. Technical improvements to control minor bleeding and meticulous hemostasis may lead to a shorter operative time.
This study has several limitations. First, this was a retrospective observational study conducted at a single institution with a limited number of patients. Second, because RAMIE was adopted at our institution in 2020, the results of this study are only the results of the introductory phase. These results should be validated when refining the RAMIE surgical technique. Third, long-term outcomes were not assessed because of the short observation period.
In conclusion, anatomical factors were significantly associated with prolonged thoracic operative time in patients with RAMIE. Understanding that a narrow upper mediastinum is associated with procedural difficulty will allow us to safely perform RAMIE.