Warm Ischemia Time and 
Preservation of Renal Function


WIT measures the time the organ remains at body temperature after its blood supply has been cut off. The “safe” duration of warm ischemia during partial nephrectomy remains controversial. Examining WIT in five minute intervals, an estimated cut point of 25 minutes provided the best threshold for preventing negative renal function outcomes, and led to authors to conclude that “every minute counts when the hilum is clamped during PN.”52

However, in a subsequent analysis, the same authors compared 660 patients undergoing PN with warm or cold ischemia and found that when controlling for age, tumor size, pre-operative estimated glomerular filtration rate (eGFR), ischemia time, and percentage of renal parenchyma spared, long-term renal function after PN was determined primarily by the quantity and quality of renal parenchyma preserved, not duration of ischemia.53


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While these data send mixed messages, a working hypothesis may be that every effort should be made to reduce WIT during PN. A previous surgical benchmark to minimize renal injury during LPN was a WIT less than 30 minutes,54 and reported WITs in contemporary RPN series range from 18.2-35.3 minutes39, 41 with minimal change in serum creatinine 
or eGFR.27, 30, 35, 51

When directly comparing RPN and LPN, a consistent finding across large series was a reduced WIT in patients undergoing RPN,8, 29, 36 which may be due to ease of reconstruction and intracorporeal suturing with the robotic platform when compared to the more technically demanding laparoscopic approach. Improving ischemia times through the RPN collective experience have been attributed to increasing surgeon experience as well as emerging techniques to reduce the time devoted to renal reconstruction, such as cutting and removing needles following hilar unclamping, pre-placement of needles,55 and the “sliding clip” renorrhaphy technique.24 Increasing surgeon experience and comfort with the robotic platform has expanded the indications for RPN to include more anatomically complex renal masses. 


Oncologic Outcomes 


LPN has consistently demonstrated equivalent oncologic outcomes (margin status, local recurrence rates) with intermediate to long-term follow up when compared to OPN.56 Initial experience with RPN has demonstrated positive margin rates ranging from 1.5%-5.7% in large single institution series18, 34-36 and 3.8% in multi-institutional series,51 which is consistent with historical rates for OPN (1.3%) and LPN (2.9%) in experienced hands.3 While reported margin rates may be approximately equal between RPN and OPN, the longest duration of median follow up in the reported RPN literature is less than 24 months,17 until long-term data is available for RPN, extrapolation of long term oncologic efficacy from the durable experience with LPN will be necessary.56

Future Considerations


Evolving techniques with RPN are primarily directed at reducing WIT, particularly in patients with complex tumors and poor baseline renal function. Novel regional ischemia techniques include use of the laparoscopic Simon clamp (Aesculap AG, Tuttlingen, Germany) which provides local ischemia for polar tumors without hilar clamping, and “zero ischemia” selective branch microdissection of the renal artery and vein coupled with carefully timed intraoperative reduction in blood pressure.57

In addition, “off clamp” RPN without hilar occlusion has been described in select patients, with increased EBL and decreased OR time when compared to traditional cases utilizing traditional local ischemia.58 Novel methods in the early phases of investigation to reduce time for hilar dissection, improve identification of accessory vessels poorly evident on preoperative imaging, and improve tumor identification include the use of laparoscopic doppler ultrasound59 and near infrared fluorescence imaging following injection with indocyanine green (Firefly daVinci technology).60

One of the most rapidly evolving areas in the field of minimally invasive surgery is laparoendoscopic single site (LESS) surgery, which consists of single port surgery as well as natural orifice transluminal endoscopic surgery (NOTES). Although performance of PN has been described using LESS techniques,61 challenges to its use include clashing of the laparoscope and working instruments as well as limited maneuverability with loss of instrument triangulation.

Taking advantage of improved instrument articulation with the daVinci system through either a multi-channel single port (Triport, Advanced Surgical Concepts, Dublin, Ireland) with an adjacent robotic port through the same incision, or a GelPort (Applied Medical, Ranch Santa Margarita, Calif.) as the surgical platform (R-LESS), Stein et al recently presented their initial experience with 11 R-LESS procedures which included one successful partial nephrectomy.62 Although we expect the role of R-LESS to continue to evolve and take on broader applications, until significant improvements are made in existing instrumentation and surgical platforms, these procedures will be considered experimental.


Conclusions


RPN is an emerging option for patients desiring minimally-invasive treatment for localized renal tumors. Short-term outcomes from early institutional experiences have confirmed the safety and feasibility of RPN, even for anatomically complex tumors. Although current data are limited, comparative series with LPN suggest a reduced WIT and decreased learning curve using the robotic platform, which may extend the benefits of minimally invasive nephron-sparing surgery to an increasing number of urologists without significant laparoscopic experience.

Although early data are encouraging, it is unclear whether RPN is equally efficacious to OPN or LPN with regard to cancer control. Efforts to further improve surgical techniques and reduce WIT are underway with intriguing results. Until more definitive prospective evidence is available, decisions regarding the optimal surgical approach for the small renal mass will be determined by individual patient and surgeon preference.

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