The zero ischemia index (ZII): a novel criterion for predicting complexity and outcomes of off-clamp partial nephrectomy.

PURPOSES: Although several anatomical classification systems that aimed to standardize the description of renal tumors were previously reported, a special classification system is required to help predict the complexity and perioperative outcomes of off-clamp nephron-sparing surgery (NSS). We developed a novel criterion-zero ischemia index (ZII), aiming to help predict the perioperative outcomes after off-clamp NSS and guide patient selection.

METHODS: We retrospectively evaluated 149 patients between June 2009 and July 2014 in our institution who underwent off-clamp NSS with available computed tomography images. ZII was defined as the product of the tumor diameter and depth within renal parenchyma. ZII was then analyzed to investigate its association with perioperative outcomes. A specific ZII score was further selected to best guide patient selection in off-clamp NSS.

RESULTS: ZII was significantly associated with estimated blood loss >500 mL (OR 1.270, 95% CI 1.036-1.557, p = 0.021), operative time >2 h (OR 1.286, 95% CI 1.051-1.573, p = 0.014), surgical complications (OR 1.251, 95% CI 1.035-1.511, p = 0.020), overall complications (OR 1.208, 95% CI 1.016-1.436, p = 0.032), and >10% decrease in estimated glomerular filtration rate (OR 1.362, 95% CI 1.045-1.776, p = 0.022). Patients with ZII > 6 may bear a higher risk of hemorrhage, perioperative complications, and a longer operative time, if they underwent an off-clamp NSS, compared to those with ZII ≤ 6.

CONCLUSIONS: The ZII is a novel and readily measurable criterion which can help predict renal complexity of tumor and risk of perioperative outcomes after off-clamp NSS. ZII = 6 is established as a preliminary threshold for patient selection of off-clamp NSS. A more robust criterion is to be validated with more samples in a prospective study.