Deviation from the Protocol of a Randomized Clinical Trial Comparing On-Clamp versus Off-Clamp Laparoscopic Partial Nephrectomy (CLOCK II Laparoscopic Study): A Real-Life Analysis

J Urol. 2021 Mar;205(3):678-685. doi: 10.1097/JU.0000000000001417. Epub 2020 Oct 9.


Purpose: We assess factors/additional morbidities related to the conversion of clamping approach during off-clamp vs on-clamp laparoscopic partial nephrectomy in the setting of a randomized study.

Materials and methods: Consecutive candidates for laparoscopic partial nephrectomy from 6 institutions were randomized to on-clamp or off-clamp surgery. The present study analyzed 1) off-clamp arm patients, comparing the procedures finalized per protocol without artery clamping (off-clamp) to those needing renal artery clamping (shift-on-clamp) and 2) on-clamp arm patients, comparing the procedures finalized with artery clamping (on-clamp) to those completed without clamping (shift-off-clamp).

Results: A total of 123 patients were randomized to on-clamp and 126 to off-clamp surgery. Of the off-clamp patients 41 (32.5%) converted to on-clamp. Of the on-clamp patients 70 (56.9%) completed surgery without clamping the renal artery due to subjective intraoperative decision of the surgeon. Tumor size was greater in shift-on-clamp vs off-clamp cases (4 vs 3, p=0.002). Conversely, tumor size (3.7 vs 3 cm, p=0.002) and R.E.N.A.L. nephrometry score (6 vs 5, p=0.038) were lower in shift-off-clamp cases. Shift-on-clamp cases had longer operative times and greater changes in estimated glomerular filtration rate on postoperative day 1. Shift-off-clamp cases had shorter operative times. A higher proportion of patients who completed on-clamp surgery per protocol had a greater than 25% drop in estimated glomerular filtration rate on postoperative day 1 (29.4%) compared to smaller changes (10.3%, p=0.009) in estimated glomerular filtration rate. Increasing tumor size and complete endophytic growth pattern predicted shift-on-clamp while preventing shift-off-clamp. Body mass index above 28 predicted shift-off-clamp.

Conclusions: The likelihood of shift-on/off-clamp relies on tumor size/complexity. The intraoperative need to convert the planned strategy seemed harmless on postoperative course. An advantage in terms of early functional outcomes does exist when avoiding artery clamping.

Keywords: kidney neoplasms; laparoscopy; nephrectomy; surgical instruments.

Publication types

  • Comparative Study
  • Multicenter Study
  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Clinical Protocols
  • Constriction
  • Female
  • Humans
  • Kidney Neoplasms / surgery*
  • Laparoscopy*
  • Male
  • Middle Aged
  • Nephrectomy / methods*
  • Prospective Studies
  • Renal Artery