Predictive role of renal resistance indices in the extracorporeal shock-wave lithotripsy outcome of ureteral stones

Abstract

Doppler ultrasonography (US) can be used to measure renal blood flow and calculate resistance indices. Increased renal resistance indices have been suggested to be associated with upper urinary tract obstruction and may help clinical physicians to differentiate physiological hydronephrosis from urinary tract obstruction. The aims of this study were to investigate the value of renal resistance indices before extracorporeal shock-wave lithotripsy (ESWL) and to determine whether they were predictive of the ESWL outcome. Between May 2005 and May 2006, a total of 84 patients who suffered from ureteral stones with renal colic and were treated with ESWL in the emergency department were enrolled in this study. Blood urea nitrogen and serum creatinine were determined and urinalysis, abdominal plain film X-ray and color Doppler US were performed. The resistive index (RI) and pulsatility index (PI) of the three different measurements of renal upper, middle and lower poles were calculated for both the affected and contralateral kidneys. Sixty of the 84 patients were found to be stone-free after follow-up, and the total stone-free rate was 71%. There was a statistically significant difference between the mean RI of the affected and contralateral kidneys in all patients: 0.672+/-0.046 vs 0.616+/-0.054 (p<0.001). Moreover, there were statistically significant differences between the stone-free group and the residual stone group regarding the RI (0.651+/-0.046 vs 0.723+/-0.029, respectively; p=0.003) and PI (1.143+/-0.162 vs 1.262+/-0.145, respectively; p=0.03) of the affected kidney. Intrarenal resistance indices represent the integration of arterial compliance, pulsatility, and peripheral resistance. Higher pre-ESWL resistance indices correlate with lower ESWL treatment success rates. Doppler US performed before ESWL treatment can therefore aid in making a correct clinical decision.