Residual Parenchymal Volume, Not Warm Ischemia Time, Predicts Ultimate Renal Functional Outcomes in Patients Undergoing Partial Nephrectomy

Objective To examine relative contributions of functional parenchymal preservation and renal ischemia following nephron-sparing surgery (NSS). While residual functional parenchymal volume (FPV) is proposed as the key factor in predicting functional outcomes following NSS, efforts to curtail ischemia time continue to add technical complexity to partial nephrectomy. Methods Our kidney cancer database was queried for patients who underwent NSS with warm ischemia time (WIT). Patients with cross-sectional imaging for FPV calculation were included. Cylindrical volume approximation methodology was used to calculate FPV, accounting for the volume of tumor's endophytic component. Percent estimated glomerular filtration rate (eGFR) preservation, perioperatively and at 6 months, was the outcome metric. Spearman correlation and linear regression analyses were used to evaluate associations of WIT and %FPV preservation with renal function preservation. Results Of the 179 patients included, median preoperative eGFR was 88.4 (9.5% chronic kidney disease III or IV), tumor size was 2.7 cm (interquartile range [IQR] 2.0-3.6 cm), and R.E.N.A.L. nephrometry was low in 34%, intermediate in 57%, and high in 9%. Median WIT was 30 minutes (IQR 24-36), resulting in 97.4% FPV preservation. Median postoperative eGFR at 6.4 months was 80.5 (19.1% chronic kidney disease III or IV), a median of 93.1% eGFR preservation (IQR 85.1-101.7). At discharge, WIT (P <.001), not %FPV (P =.112), was associated with %eGFR preservation. However, 6 months following surgery, on multivariable analysis, both preoperative eGFR (linear regression coefficient = -0.208, P =.006) and %FPV preservation (linear regression coefficient = 0.491, P =.001), but not WIT (P =.946), demonstrated statistically significant association with %eGFR preservation. Conclusion Residual FPV, and not WIT, appears to be the main predictor of ultimate renal function following NSS.