Changes in resistive index following extracorporeal shock wave lithotripsy

Background: Extracorporeal shock wave lithotripsy (ESWL) has replaced most surgical and endourologic forms of therapy for upper urinary tract stone disease. Despite its proved safety and efficacy its adverse effects on renal function are still to be identified. A newer diagnostic technique, color Doppler ultrasonography, has brought a new insight into renal function. It enables precise evaluation of the renal vascular supply. Changes in intrarenal vascular resistance after ESWL were studied with Doppler ultrasound techniques. Methods: In 70 consecutive patients the resistive index (RI) was measured at an interlober artery before and 30 min after ESWL in the treated and contralateral kidneys. In 17 patients, a follow-up Doppler study was performed 1 week after ESWL. Results: In the treated kidneys, the RI significantly increased from 0.656 ± 0.053 (mean ± SD) at baseline to 0.682 ± 0.053 (P < 0.0001). There was no significant correlation of increase in RI with patient age (r = 0.010) or with pre-ESWL blood pressure (r = 0.002). Elderly patients (≥ 60 years old n = 31) had higher RI levels on baseline than younger patients (< 60 years old, n = 39). In 18 of the 31 (58.1%) elderly cases the RI were elevated to greater than 0.7, indicating pathologic changes. In younger patients, only 9 (23.1%) experienced increase in RI up to 0.7 or greater. The contralateral untreated kidneys showed significant change in RI before (0.664 ± 0.045) and after (0.679 ± 0.049) lithotripsy in elderly patients (P < 0.005). A follow-up Doppler study showed that the mean RI returned to pretreatment levels after 1 week. Conclusions: Because of higher RI levels on baseline, elderly patients have a higher risk of post-ESWL renal tissue damage than younger patients. Clinical implication of RI change in the contralateral kidneys in this study remains to be answered. The measurement of changes in RI with Doppler ultrasound techniques after ESWL may provide useful information for clinical diagnosis of renal tissue damage.