Abstract
Thank you for your interest and comments in our research. Despite a significant body of research demonstrating an increased risk of complications in obese patients across open surgeries, our large retrospective cohort did not demonstrate effects of obesity in increasing complication rate. 1 We suspect that the increased observation provided by the robotic apparatus may obviate some of the technical challenges of open surgery in obese individuals.
As our colleagues referenced, Bravi et al. examined patients who developed acute kidney injury (AKI) after surgery and went on to develop CKD. Several important contextual points should be made. First is the differentiation between surgical and medical chronic kidney disease (CKD), as expounded by Lane et al. 2 Although obesity reflects a propensity toward medical renal impairment, in our cohort these patients also trended toward having slightly larger tumors with higher rates of malignancy, putting them at a higher risk for surgical impairment as well. We have previously shown that the predominant predictor of renal function declines after robotic partial nephrectomy (RPN) is the size and complexity of the tumor, which leads to an increase in the amount of Non-Neoplastic Parenchymal Volume removed. 3 Nonetheless despite variations of warm ischemia time, AKI, although clearly a requisite for eventual development of CKD, does not invariably lead to it de novo as these patients can often have both a second healthy kidney as well as a compensatory response, combined with recovery of the acutely injured nephrons. 4 These prior findings, and the findings in our analysis are on the surface somewhat at odds with the findings of Bravi et al, but an important distinction should be made. First, our studies looked at the role of obesity and warm ischemia time in impacting long-term renal function. Both of these factors can play specific roles in AKI that they may not play in CKD. By its nature AKI is often caused by an acute insult (i.e., warm ischemia, or underresuscitation in an obese patient) and can lead to recovery. It is not surprising, therefore, that this effect was obviated at 1 year after surgery. Meanwhile, Bravi's research focused on an all-encompassing role of partial nephrectomy on AKI, which includes the most important factor, the size and complexity of the tumor and surgical removal of tissue. In fact in Bravi's research only 61% of patients who did not develop an AKI regained 90% of their baseline function, reinforcing that the surgical removal of tissue plays the significant role in determining long-term renal function.
Thankfully, our data had minimal conversions to radical and open nephrectomy. Without significant numbers to power these analyses, these few patients were excluded from the analysis rather than potentially leading to misleading conclusions. To answer our colleagues final inquiry, when using the WHO breakdown the patients most vulnerable to AKI postoperative were in obesity class II (body mass index [BMI] 35–39.99): OR 1.76; 95% CI 1.03–2.96; p = 0.035.
Our data demonstrate that the robotic platform can obviate many of the risks in obese patients that had previously been seen in open surgery. Importantly, they demonstrate that robotic partial nephrectomy is a surgical option regardless of patient BMI, and should encourage the role of nephron-sparing surgery in these patients.