Multivariate analysis of the factors involved in loss of renal differential function after laparoscopic partial nephrectomy: a role for warm ischemia time

Background: Partial nephrectomy (PN) is now the gold standard for the surgical treatment of small renal masses. We evaluated the effect of WIT and other factors on RDF assessed by preoperative and postoperative renal scintigraphy. Methods: Between 2003 and 2008, 182 consecutive laparoscopic PN (LPN) were performed in an academic centre. Among those, 56 had mercaptoacetyl triglycine (MAG3) lasix renal scintigraphy preoperatively and postoperatively. Results: Medians for age, preoperative estimated glomerular filtration rate and computed tomography scan tumour size were 62 years, 82 mL/min/1.73m(2) and 26 mm, respectively. Median WIT and preoperative RDF were 30 minutes and 50%, respectively. Median loss of RDF after surgery was 14%. Linear regression curves showed that loss in RDF rate was 0.2% per minute when WIT was <30 minutes and 0.7% per minute when WIT was >= 30 minutes. In multivariate analysis, length of WIT and endophytic tumour location were associated with a statistically significant loss of RDF (p < 0.05), but only in the group who experienced >30 minutes of WIT. Interpretation: Our results suggest that the factors associated with loss of RDF are not the same before and after 30 minutes of WIT and that the rate of loss in RDF increases after 30 minutes. Since, the effect of WIT is small up to 30 minutes, we believe that surgery should focus on limiting the resection of normal parenchyma and to ensure negative margins and hemostasis, rather than on premature unclamping.