Renal Ischemia During Partial Nephrectomy: Does Every Minute Still Count?

Abstract

The current state of research on the impact of renal ischemia on renal function (RF) after partial nephrectomy (PN) is presented by Volpe et al [1] in thismonth’s issue of European Urology. The authors, including many of the thought leaders on PN, have presented a thorough overview of this topic including the early research on ischemic injury of the kidney. This backgroundprovides an important historical context for the current concepts of the role of warm ischemic injury during nephron-sparing surgery (NSS). They remind us that normothermic renal ischemia creates a spectrum of injury based on histologic alterations beginning approximately 20 min after clamping andextending>60min. This indicates that the traditional 30-min limit of warm ischemia time (WIT) is a somewhat arbitrary time point and was not based onclinical outcomes. Theypresentmore recentworkonrenal ischemia focusing on solitary kidneys, and one well-known study in particular revealed a 5% increase in risk for acute renal failure for every additional minute of WIT, leading to the conclusion that ‘‘every minute counts’’ when the renal hilum is clamped during PN [2]. This study, more than any other, focusedattentiononthe impactof renal ischemiaonRF and set the stage for much of the debate on what is an acceptable WIT. The most recent research on RF after PN has shifted focus toward the contribution of preserved functional renal parenchyma after NSS. Interestingly, in many of the reports, when the amount of preserved renal parenchyma was evaluated onmultivariate analysis, renal ischemiawas found not to be a significant factor affecting RF. The authors of this review correctly point out that ischemia time and preserved renal parenchymamaybe linkedbasedon the fact that larger, more complex tumors require longer ischemia times and removal of more normal tissue with complex reconstruction [1]. They reach the overall conclusion that RF after PN ismost dependent on preoperative RF and the amount of preserved vascularized renal parenchyma. WIT correlates with the amount of renal tissue preserved, and prolonged warm ischemia periods (>25min) should be avoided. What does this review [1] add to the current understanding of ischemic injury during PN? Simply stated, factors other than renal ischemia must be considered to maintain optimal RF after NSS. These factors can be divided into modifiable and nonmodifiable categories, with the latter being patient age, preoperative RF, and nephrometry score, which takes into account tumor size and location. The modifiable factors are WIT and preserved functional renal parenchyma and are the subject of current debate as to which is most important in maintaining RF after PN. Given the characterization by Lane et al [3] of preserved renal parenchyma as a nonmodifiable factor, it may be reasonable to consider that for a given tumor location and size, there are multiple methods of tumor excision and renorrhaphy, and each technique will result in more or less preserved renal parenchyma. Many surgeons perform tumor enucleation exclusively, whereas others will aim for a 5-mm rim of normal tissue to ensure an adequate surgical margin. Renorrhaphy technique can vary widely as well, from deep sutures running the base of the defect to precise vessel suture ligation to no renorrhaphy at all [4]. Given these variations in surgical approach, the amount of preserved renal parenchyma is dependent on the surgeon, not unlike how long a surgeon may choose to leave a kidney clamped. If the amount of preserved functional parenchyma is potentially more important than renal ischemia in determining RF after PN, then how this measure is determined is vitally important to the stated results and the conclusions EU RO P E AN URO LOGY 6 8 ( 2 0 1 5 ) 7 5 – 7 6