Is off-clamp robot-assisted partial nephrectomy beneficial for renal function? Data from the CLOCK trial

BJU Int. 2022 Feb;129(2):217-224. doi: 10.1111/bju.15503. Epub 2021 Jul 4.


Objectives: To compare the functional outcomes of on- vs off-clamp robot-assisted partial nephrectomy (RAPN) within a randomized controlled trial (RCT).

Materials and methods: The CLOCK study (CLamp vs Off Clamp the Kidney during robotic partial nephrectomy; NCT02287987) is a multicentre RCT including patients with normal baseline function, two kidneys and masses with RENAL scores ≤ 10. Pre- and postoperative renal scintigraphy was prescribed. Renal defatting and hilum isolation were required in both study arms; in the on-clamp arm, ischaemia was imposed until the completion of medullary renorraphy, while in the off-clamp condition it was not allowed throughout the procedure. The primary endpoint was 6-month absolute variation in estimated glomerular filtration rate (AV-GFR); secondary endpoints were: 12, 18 and 24-month AV-GFR; 6-month estimated glomerular filtration rate variation >25% rate (RV-GFR >25); and absolute variation in ipsilateral split renal function (AV-SRF). The planned sample size was 102 + 102 cases, after taking account crossover of cases to the alternate study arm; a 1:1 randomization was performed. AV-GFR and AV-SRF were compared using analysis of covariation, and RV-GFR >25 was assessed using multivariable logistic regression. Intention-to-treat (ITT) and per-protocol analyses (PP) were performed.

Results: A total of 160 and 164 patients were randomly assigned to on- and off-clamp RAPN, respectively; crossover was observed in 14% and 43% of the on- and off-clamp arms, respectively. We were unable to find any statistically significant difference between on- vs off-clamp with regard to the primary endpoint (ITT: 6-month AV-GFR -6.2 vs -5.1 mL/min, mean difference 0.2 mL/min, 95% confidence interval [CI] -3.1 to 3.4 [P = 0.8]; PP: 6-month AV-GFR -6.8 vs -4.2 mL/min, mean difference 1.6 mL/min, 95% CI -2.3 to 5.5 [P = 0.7]) or with regard to the secondary endpoints. The median warm ischaemia time was 14 vs 15 min in the ITT analysis and 14 vs 0 min in the PP analysis.

Conclusion: In patients with regular baseline function and two kidneys, we found no evidence of differences in functional outcomes for on- vs off-clamp RAPN.

Keywords: off-clamp; on-clamp; partial nephrectomy; renal tumour; robotic.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Glomerular Filtration Rate
  • Humans
  • Kidney / physiology
  • Kidney / surgery
  • Kidney Neoplasms* / surgery
  • Nephrectomy / adverse effects
  • Nephrectomy / methods
  • Retrospective Studies
  • Robotic Surgical Procedures* / adverse effects
  • Robotic Surgical Procedures* / methods
  • Robotics*
  • Treatment Outcome