Objective: To identify preoperative characteristics in patients with renal masses that influence operative time during robot-assisted partial nephrectomy (RAPN) and evaluate the relationship between operative time and length of stay (LOS), complication rates, and overall outcome. Materials and Methods: We queried our institutional database to identify a cohort of patients who underwent RAPN by two experienced robotic surgeons between 2012 and 2019. A multivariable regression model was developed to analyze operative time, LOS, and any grade complication within 30 days postoperatively using the bootstrap resampling technique. Results: A total of 392 patients were included. On multivariable analyses, prior abdominal surgery (p = 0.001) was associated with 22 minutes of increase in operating room time, as well as adhesive perirenal fat (22 minutes, p = 0.001). For each one unit increase in nephrometry score, there was a 4-minute increase in operating room time (p = 0.028), and for each one-cm increase in tumor size, there was an associated 12-minute increase in operating room time (p < 0.001). For each 1 year increase in age, there was an associated 0.024-day increase in LOS [odds ratio (OR) (0.013-0.035)]; in addition, for every one-cm increase in tumor size there was a 0.18-day associated increase in LOS [OR (0.070-0.28)]. Each 1-hour increase in operating room time was associated with a 0.25-day increased LOS [OR (0.092-0.41)]. Only tumor size was found to be associated with any grade complication. Conclusions: Patients with a history of abdominal surgery, larger complex tumors, and significant Gerota's fat undergoing robotic partial nephrectomy should anticipate longer operative times. Older patients with larger tumors and longer operative times can anticipate a longer LOS. Tumor size appears to be the common determinant of all three outcomes: operative time, LOS, and any grade Clavien complication.

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