Discussion
tubular obstruction, ischemia, reperfusion injury, AKI, renal damage
ISCHEMIA
The present study analyzes a relatively consistent number of consecutive patients enrolled under the umbrella of a RCT. The study protocol imposed in all the enrolled patients to obtain a renal scintigraphy before and 6 months after surgery.All surgical procedures respected some mandatory steps and were performed by a limited number of surgeons, featured by a homogeneous profile of experience. The main finding was that warm ischemia interval up to 10 min had no consequences on functional outcomes, while above this limit, there was a proportional and statistically significant functional impairment. However, these differences remained far from being clinically relevant, with negligible differences in global and split renal functions above and below 10 min of WIT (4 ml/min and 3%, respectively). Clearly, such considerations should be accepted only for patients with features similar those of patients enrolled by the CLOCK trial (two kidneys, regular baseline function, RENAL score ≤ 10).In standard conditions, partial nephrectomy preserves 80% and 90% of ipsilateral and global eGFR, respectively, achieving a stable plateau in a few months after surgery [Theoretically, ischemia could injury nephrons with different mechanisms (vasoconstriction and abnormal endothelial response; tubular obstruction and urine backflow; reperfusion injury [Conversely, in patients with normal baseline renal function there is limited evidence on which is the optimal threshold of WIT. The majority of the authors accept a conventional limit of 25–35 min [Altogether our results are in line with the above mentioned, but there are also some differences to be remarked. The median reduction in global eGFR in our cohort was − 5.5% (IQR − 15.9% to − 1%), and remained stable at further controls (data not presented: 12 months − 6.2%, 18 months − 5.3%, 24 months − 5.6%), confirming that RAPN leads to a mild global eGFR reduction stable along time. Such concept is in line with the findings by Porpiglia et al. who described renal damage status/postlaparoscopic PN stable over time within a cohort of 54 patients studied for a minimum follow-up of 4 years with radionuclide renal scan [The median reduction in SRF was lower than previously reported (− 4.7%; IQR − 12.8% to 0%) and similar to the degree of the global reduction. This could be due to several factors: the timing of scintigraphic control, set at 6 months, i.e., out of the recovery phase for the ipsilateral kidney based on previous renal scan studies; differences in the methodology used to measure global function among studies; the inclusion of patients with regular baseline function, two normal kidneys and relatively small masses; the involvement of surgeons out of their learning curve probably reflecting in a minimal parenchymal sacrifice during resection and reconstruction. Similarly to other studies, we found that baseline eGFR and AKI impaired postoperative global renal function, and that baseline SRF and nephrometry were related to postoperative SRF. Finally, we demonstrated that WIT has a role on all functional outcomes according to a so-called “hinge threshold effect”: up to 10 min no significant differences were noted, while above there was a proportional functional impairment. Noteworthy, although statistically evident, the degree of impairment was almost clinically negligible, in agreement with our previous study referring to the primary endpoint of the trial [This study, although coming from a prospective and controlled data collection regulated by the protocol of a RCT, is not devoid of limitations: first, the aim of this analysis was not the primary endpoint of the study; second, the amount of healthy tissue removed or damaged by surgery has not been objectively measured, but just approximate by nephrometry as surrogate; the inclusion criteria of the RCT restrict the validity of our conclusions to patients with similar features; we were not in the condition to test longer duration of WIT, given that the vast majority of cases remained under 16 mins.