Predictors of the Transition from Off to On Clamp Approach during Ongoing Robotic Partial Nephrectomy: Data from the CLOCK Randomized Clinical Trial

We sought to identify predictive factors of the transition from off clamp to on clamp robotic partial nephrectomy following an intraoperative decision. Materials and methods: In the multicenter, randomized, prospective CLOCK (CLamp vs Off Clamp the Kidney during robotic partial nephrectomy) trial 152 and 149 of the 301 patients with a localized renal mass were assigned to undergo off clamp and on clamp robotic partial nephrectomy, respectively. Surgery was done at a total of 7 referral institutions by 1 surgeon per institution. A localized renal mass was defined as having a R.E.N.A.L. (radius, exophytic/endophytic, nearness to collecting system or sinus, anterior/posterior, location relative to polar lines, hilar) score less than 10. Surgeons had similar experience with at least 100 previous robotic partial nephrectomies. All patients underwent a preoperative and a 6-month renal scan. The current study deals with one of the secondary end points of the trial, comparing cases finalized as clampless (off robotic partial nephrectomy group) with those which were converted (shift robotic partial nephrectomy group). Results: Of the 152 patients randomized to off clamp 61 (40%) were shifted to clamp with a median ischemia time of 15 minutes. In the shift robotic partial nephrectomy group the masses were larger (3.5 vs 2.2 cm) and more complex (R.E.N.A.L. score 7 vs 6). A significant association with transition was found for tumor diameter (OR 1.4) and the R.E.N.A.L. score continuously (OR 1.4) and when recoded in groups, including 4-no risk (referent OR 1), 5-6-low risk (OR 1.8), 7-8-intermediate risk (OR 3.6) and 9 or greater-high risk (OR 6.6). The shift robotic partial nephrectomy group had longer operative time, higher blood loss and increased performance of 2-layer renorrhaphy. No significant differences were noted in postoperative complications or renal function after 6 months. Conclusions: The transition from off to on clamp robotic partial nephrectomy is associated with renal mass diameter and complexity. Under the specific conditions of the current trial no harm was related to this decision.