Factors that affect proportional glomerular filtration rate after minimally invasive partial nephrectomy

Background and Purpose: Several factors have been shown to impact the overall glomerular filtration (GFR) rate after partial nephrectomy. Change in overall GFR, however, does not necessarily reflect the impact of these factors on the operated kidney. Using preoperative and postoperative renal scintigraphy, we sought to assess the impact of patient, tumor, and operative factors on GFR of the affected kidney (proportional GFR). Patients and Methods: We identified 73 patients who underwent minimally invasive partial nephrectomy with preoperative and postoperative renal scans from two institutions. Patient, tumor, and operative characteristics were recorded. We used multiple linear regression to determine the patient and clinical factors predictive of postoperative proportional GFR in the operated kidney. We tested for an interaction between preoperative proportional GFR and nephrometry score and ischemia. We further fitted two separate linear models to compare the proportion of variance (R²) explained by ischemia time in change in renal function in the operated kidney with the change in renal function in both kidneys. Results: Surgical parameters (procedure approach, ischemia time, and estimated blood loss) and preoperative proportional GFR were significantly associated with postoperative proportional GFR. Preoperative proportional GFR (β=5.93, 95% confidence interval [CI]: 3.88, 7.97, P<0.0005) and procedure approach (β=8.67, 95% CI: 4.50, 12.80, P<0.0005) were strongly associated with outcome while ischemia time (β=-1.80, 95% CI: -3.48, -0.11, P=0.04) and estimated blood loss (β=-1.15, 95% CI: -0.29, -0.01, P=0.04) just reached statistical significance. The interaction term between preoperative proportional GFR and nephrometry score or ischemia time was not statistically significant (nephrometry, P=0.2 continuous or P=0.6 categorical, and ischemia, P=0.7, respectively). Conclusion: Lower preoperative proportional GFR, longer ischemia times, and higher blood loss all negatively impact postoperative proportional GFR while tumor complexity as gauged by morphometry scoring does not. Larger studies are needed to determine whether renal scintigraphy is a more accurate method of measuring the impact of the ischemia time on postoperative proportional GFR.