Recoverability of renal function after relief of acute complete ureteral obstruction: clinical prospective study of the role of renal resistive index

Abstract

Objectives: To study the values of the renal resistive index (RI) before and at different points after relief of obstructive anuria and to correlate these values with the corresponding values of serum creatinine and with the recovery of renal function after release of obstruction.

Methods: A total of 32 consecutive patients with obstructive anuria were prospectively evaluated by measurement of RI before drainage and at 3 days, 1 week, 2 weeks, and 4 weeks after drainage. Serum creatinine was measured at all points of the RI examination. Moreover, RI was measured in an age and sex-matched control group of 24 consecutive healthy donors and volunteers.

Results: The study included 40 obstructed and 48 normal kidneys. In the obstructed kidneys, the mean RI values decreased significantly from 0.78 +/- 0.05 before drainage to 0.70 +/- 0.09 at 3 days after drainage (P <0.001) with an additional significant reduction to 0.68 +/- 0.08 at 7 days after drainage (P <0.01) and stabilized thereafter. Serum creatinine decreased significantly from 8.4 +/- 4.4 mg/dL before drainage to 4.7 +/- 3.8 mg/dL 3 days after drainage (P <0.001) and then to 3.6 +/- 3.7 mg/dL 7 days after drainage (P <0.001) and stabilized thereafter. The correlation between the RI and serum creatinine at the overall points of measurement was good. Obstructed kidneys were classified into two groups according to the recovery of renal function after obstruction relief: those that showed significant improvement of serum creatinine (24 kidneys, group 1) and those with no significant improvement of serum creatinine (16 kidneys, group 2). In group 1, the difference between the mean RI values before and after drainage was statistically significant (0.78 +/- 0.05 versus 0.64 +/- 0.06, P <0.001); in group 2, the difference between the before and after drainage RI values was not significant (0.781 +/- 0.040 versus 0.779 +/- 0.039). The mean RI of the normal kidneys was 0.66 +/- 0.04. A comparison between the mean RI values of the control group and the mean RI values of the obstructed patients after drainage showed no significant difference in group 1; markedly higher values were noted in group 2 at all points after drainage.

Conclusions: In the setting of acute complete renal obstruction, the RI has a good positive correlation with serum creatinine. Recovery of renal function could not be predicted from the changes in RI before obstruction release. However, a reversal of a previously elevated RI could be used as an early indicator that renal function recovery is likely.