Renal Doppler ultrasonography in children with equivocal obstructive uropathy: effect of intravenous normal saline fluid load and frusemide.

Abstract

To study the effect of hyperhydration with normal saline and frusemide on the renal resistive index (RI) in children with equivocal obstructive uropathy. Twelve children (24 kidneys) with unilateral or bilateral hydronephrosis underwent isotopic diuretic renography and Doppler ultrasonography. All children had equivocal obstruction of the hydronephrotic kidneys with half-time drainage (T/2) values of 10-20 min. Doppler studies were carried out both at baseline and after the infusion of normal saline and frusemide. Of the 24 kidneys, five were normal and 19 were hydronephrotic; compared with normal kidneys, the hydronephrotic units had a significantly lower glomerular filtration rate (GFR) and longer T/2. At baseline, the mean RI values of normal and hydronephrotic kidneys were not significantly different (0.70, SD 0.03 and 0.71, SD 0.04, respectively). After the infusion of saline and frusemide, the mean RI of hydronephrotic kidneys (0.67, SD 0.07) was significantly (P = 0.01) higher than that of normal kidneys (0.60, SD 0.02), but the response of RI in hydronephrotic kidneys was variable. Based on the RI at baseline and after infusion, hydronephrotic kidneys could be categorized into three groups. Group 1 (n = 6) had an RI < 0.7 before and after infusion, group 2 (n = 6) had a baseline RI > 0.7 and < 0.7 after infusion, and in group 3 (n = 7) both RIs were > 0.7. Kidneys in group 3 had the lowest GFR and the highest T/2 values. Five of these seven hydronephrotic kidneys eventually had deteriorating GFRs requiring surgical correction; the GFR of the remaining hydronephrotic kidneys remained stable. In children with equivocal obstructive uropathy based on diuretic renography, the determination of RI before and after infusion of normal saline and frusemide could be helpful in distinguishing obstructed from non-obstructed kidneys.