Renal resistive index in experimental partial and complete ureteral obstruction

Rationale and Objectives.: Recent clinical work suggests that the Doppler resistive index (RI) may be useful in distinguishing obstructive from nonobstructive hydronephrosis. We evaluated the usefulness of the RI in a rabbit model of hydronephrosis. Methods.: Unilateral partial ureteral obstruction was produced in nine rabbits and complete obstruction in another nine. Three sham operations were performed, and these animals served as control subjects. The RI was measured in all kidneys before and 6 hr after surgery and on days 1, 4, and 7 postoperatively. The RI and the difference in RI (ΔRI) between the obstructed and normal kidney were evaluated over time using a two-way analysis of variance. The intravenous urography and Whitaker tests served as gold standards. Results.: Hydronephrosis was observed on sonograms in all obstructed kidneys. Comparing groups, there was no significant difference in mean RI or ΔRI between the three groups at any time point. Looking at individual groups over time, there was no significant change in mean ΔRI, whereas the change in mean RI was significantly elevated above baseline only in the complete obstruction group at 6 hr (p = .002) and on days 4 (p = .008) and 7 (p = .006). In evaluating varying thresholds of RI and ΔRI, we could not consistently discriminate between normal and obstructed kidneys. Conclusion.: Although complete obstruction caused a significant increase in RI, partial obstruction failed to do so. RI and ΔRI values proved to be insensitive predictors of obstruction in this rabbit model.