UroToday - Time. Among 101 laparoscopic partial nephrectomy patients with preoperative and postoperative data points (1-6 months), the authors noted that exceeding 40 minutes was associated with a definite drop in glomerular filtration rate (determined by the serum creatinine based MDRD formulation), on average 20 ml/min/1.73 m2. This statistically significant difference was more than double the change in the MDRD glomerular filtration when the ischemia time was less than 40 minutes! When looking at < 30 minutes of warm ischemia time vs. > 30 minutes, the difference was not significant but with a p value of 0.132 there is suggestion of a trend. While the authors conclude that up to 40 minutes is safe, I would lean more towards a 30 minute cut off. Shaving additional time off of the 30 minute limit did not appear to favorably impact the outcome in this study.

With the advent of robotic-assisted laparoscopic partial nephrectomy, the surgeon's ability to suture accurately and rapidly appears to be markedly enhanced thereby allowing more surgeons to operate within the safety of the 30 minute window. Indeed, on average, warm ischemia times can be reduced by 10 minutes when changing from straight laparoscopic to a robotic platform. In the editorial comment, the authors note that despite their findings, they are now striving for a 20 minute warm ischemia cutoff, yet provide no data to support this approach other than the concept, that the less the warm ischemia the better.

What we still lack and desperately need is one prospective multicenter study in which all patients are carefully categorized as to risk of postsurgical renal dysfunction (i.e. diabetes, pre-existing renal dysfunction, hypertension) among whom there are several preoperative creatinine levels within 6 months of their surgery and two or more values at least 6 months postoperatively, to obtain a more accurate MDRD given the variability of serum creatinine levels. As part of this study, both preoperative and postoperative CT scans to determine the remaining renal volume would be helpful in order to differentiate a drop in creatinine due to a wide excision vs. impairment solely from warm ischemia.

Godoy G, Ramanathan V, Kanofsky JA, O'Malley RL, Tareen BU, Taneja SS, Stifelman MD
J Urol. 2009 Jun;181(6):2438-43
doi:10.1016/j.juro.2009.02.026

Reported by UroToday Medical Editor Ralph V. Clayman, MD

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