Discussion
The importance of nephron-sparing surgery in small renal mass has become more prominent by the demonstration of a direct correlation between RF impairment and cardiovascular disease [11]. While PN has been applied to T1a / b stage tumors until recently, now it is also successfully applied to high-risk kidney tumors in developed centers. The advantages of robotic surgery with its 3D image quality and ergonomic arm structure were provided to the use of PNs in high-risk renal tumors [12]. In addition to this advantage of RPN, the lack of tactile sense and its high cost are the most important disadvantages.
In studies on cost-effectiveness, RPN has been shown to be more expensive than LPN or OPN [6,13]. Although Hyams et al reported that the price difference per case between RPN and LPN decreased from $ 1066 to $ 333 during the period from the start-up to the ideal utilization of the robot, Yu et al. reported the median costs $15,724 for RPN, $12,401 for LPN and $11,817 for OPN in per case according to the surgical approach in the USA. Therefore, the superiority of the two surgical methods to each other is still an important research topic.
Aboumarzok et al. [14] and Zhang X et al.[15] reported that RPN had similar perioperative outcomes with LPN in terms of OT, EBL, conversion rates, LOS, PSMs and complication rates, only WIT was statistically shorter favor to RPN arm in their review and meta-analysis. They didn’t report outcomes of the change in renal functions between the groups. The differences in surgical techniques and comparison criteria between the groups were the important limitations of the studies.
Ji Eun Choi et al. [16] reported that RPN is associated with more favorable results than LPN in terms of conversion rates, lower WIT, shorter LOS, and change of eGFR in their review and meta-analysis of RPN and LPN outcomes. No significant difference was reported in terms of complications, change of serum creatinine, OT, EBL, and PSMs. However, the studies in this review included heterogeneous groups and methodologically different or not specified.
In the current study, we didn’t find any statistical difference between the groups in tumor size (p=0.199), RENAL and PADUA score (p=0.120 and p= 0.073), OT (p= 0.216), WIT (p=0.066), LOS (p=0.580), PSMs (p= 0.636) and complication rates (p=0.969) between the groups. Only EBL was less in RPN group (p=0.027).
The main purpose of PN is to preserve the RFs. Some studies reported that RPN is superior to LPN in the preservation of RF, while some studies reported no difference between groups. Kim et al.[17] reported that eGFR decline rates were similar between RPN and LPN in the early period, but long term recovery in renal function was a favor to RPN. Although they reported that warm ischemia time was significantly shorter in the RPN group, while WIT was an acceptable range in the RPN (23.82 ± 12.03 minutes) compared to literature, in the LPN arm (34.47 ± 11.63 minutes) was higher than the recommended value.
Li et al. [18] evaluated the postoperative split renal function (SRF) between RPN and LPN approaches in Taiwanese patients. They assessed both kidney functions by scintigraphy. They reported advantages of RPN with shorter operation time and WIT, and better SRF at 6 months after the operation. They reported that WIT was associated with a decrease in renal function postoperatively.
In this study, although deterioration renal function was less in the RPN group, there was a significant difference between the groups in terms of WIT, EBL, and OT. Also these values ​​in the LPN arm (43.3 ± 23.5 minutes) were significantly higher than the recommended value in literature.
WIT is the leading factor that affecting the renal functions after PN. Ko et al. reported the predictive factors of prolonged WIT (≥30 minutes) in PN. Surgeon experience, tumor size, and PADUA score were found as predictive factors that prolonged WIT after RPN or LPN. Surgical experience was the most important factor for preventing prolonged WIT, among these factors [19]. Therefore, in studies comparing LPN and RPN in experienced centers, although WIT was shorter in the RPN group than LPN, the change in postoperative renal functions was not statistically significant between the groups if WIT was less than 30 minutes [20,21] in both groups.
Some authors advocated that WIT should be kept less than 30 minutes to the preservation of renal function, while some authors reported that WIT increased deterioration of long-term renal function every minute after 25 minutes [22]. Alimi et al.[23] showed that there was no difference in early eGFR changes between groups in LPN and RPN when performed by highly experienced surgeons. In their study, although WIT less in RPN arm, WIT was under 25 minutes in both groups. Their results supported that a
reasonable WIT will contribute to the preservation of renal functions to the operated kidney. Banapour et al. [24]reported that the postoperative eGFR decline was lower in the RPN group compared to OPN, but they did not report a statistical difference between RPN and LPN in their study comparing the perioperative results of RPN, LPN, and OPN, matched for nephrometry scores. In their study, while WIT was lower than 30 minutes in RLN and LPN groups, it was higher than 30 minutes in the OPN group.
In the current study, WIT time was less than 30 minutes in both groups and comparable to the recommended values in the literature. We did not find any statistical difference between the groups in pre- and postoperative mean eGFRs and eGFR changes at 1 year after the operation (p=0.561, p=0.803, p=503, respectively). We think that such a comparison with similar WIT between the groups will give more accurate results in showing whether the change in RFs will depend on the surgical approach.
Kızılay et al. [25] showed a similar result in terms of OT, EBL, LOS, and PSM in the study of compared the long-term oncological and functional outcomes between the RPN and LPN groups. In this study, however WIT was statistically shorter in the RPN group, WIT was under 25 minutes in both groups. They did not report any difference in eGFR changes 1 year after surgery, similar to our study. In this study, there was no difference in tumor size between groups, whereas RPN consisted of more risky patients in terms of tumor complexity.
The number of studies comparing LPN and RPN with long-term oncological outcomes as well as renal functional outcomes is limited. Kızılay et al.[25] also reported no differences between the groups in long-term (5 years) recurrence-free survival (85.9% vs 90.1%, p=0.710) and overall survival (84.8% vs 82.6, p=0.561) rates between the LPN and RPN, respectively. In the current study, cancer-related death was not observed in either group, while non-cancer specific survival was 93.5% in the PLN group and 94.4% in the RPN group during the follow-up period. However, they reported that the overall survival rates were slightly lower in their study because the patients had more complications and had a higher mean age. Also, we think that the difference in the survival rates between this study and our study could depend on our follow-up period was shorter compared to theirs.
We had some limitations for this study. First, our study was a retrospective and non-randomized. Second, although most of the cases were performed by two experienced surgeons, the experience of the surgeons is an important factor that could affect the outcomes. Third, our case number was relatively low due to cases with less than 1 year of follow-up or missing data were excluded from the study.