The Impact of Body Mass Index on Renal Functional Outcomes Following Minimally Invasive Partial Nephrectomy

Objective: To assess the impact of body mass index (BMI) on perioperative and renal functional outcomes in patients undergoing minimally invasive partial nephrectomy (MIPN). Materials and Methods: In our IRB-approved, prospectively maintained clinical database, we identified 1206 patients who underwent kidney surgery from 2002 to 2013. Estimated glomerular filtration rate (eGFR) was obtained at baseline and each follow-up visit. From this group, patients who underwent MIPN with more than 12 months of follow-up were selected. Patients were separated into 4 cohorts based on BMI: normal weight (<25kg/m²), preobese (25-30kg/m²), obese class 1 (30-35kg/m²), and obese class ≥2 (>35kg/m²). Change in eGFR was compared across demographic and clinical variables through linear and logistic regression models. Results: A total of 235 patients met inclusion criteria with median follow-up of 29 months (interquartile range [IQR] 19, 45). There were no differences in demographic, perioperative, or pathologic features between BMI groups. While controlling for gender, race, Charlson comorbidity score, tumor size, and ischemia time, obese class 1 (odds ratio [OR] 4.68, p=0.019), obese class ≥2 (OR 4.27, p=0.033), and age (OR 1.06, p=0.014) were associated with increased risk of CKD stage ≥3; however, higher baseline eGFR (OR 0.91, p<0.001) was associated with a reduced risk of CKD stage ≥3. While controlling for the same variables, increasing BMI was associated with a significant absolute reduction in eGFR at 1 year (0.38mL/minute/1.73m² reduction in GFR per 1kg/m² increase in BMI, p=0.009). Conclusions: MIPN is technically feasible in obese patients with similar perioperative outcomes to nonobese patients. BMI is an independent risk factor for worsening kidney function following MIPN.