Time-dependent changes of resistive index in acute renal obstruction during nonsteroidal drug administration

Objective To evaluate Doppler ultrasonography (DUS) and assess time-dependent changes of the renal resistive index (RI) in acute unilateral renal obstruction during treatment with nonsteroidal analgesic for the relief of renal colic.

Patients and methods In 31 patients with symptoms of renal colic, treated with ketoprofen, unilateral obstruction was confirmed by intravenous urography. The patients were divided into four groups according to the duration of their symptoms, i.e. < 23 h, 24-47 h, 48-72 h and > 72 h. In each patient, the RI was measured over the arcuate, segmental and renal arteries of both kidneys using DUS. The values obtained in the obstructed kidney were compared with those for the contralateral kidney.

Results The mean (sd) RIs for all 31 patients were 0.71 (0.05) for the obstructed and 0.60 (0.05) for the contralateral kidney (P < 0.001), the mean difference (dRI) being 0.12 (0.07). In those with obstruction for < 23 h the mean RI of the obstructed kidney was 0.70 (0.05) and of the contralateral healthy one 0.62 (0.07). Values of RI were similar in the group with obstruction for 24-47 h and 48-71 h. In those with obstruction for > 72 h the mean RI of the obstructed kidney was 0.69 (0.07) and of the contralateral one 0.60 (0.04), with a dRI of 0.09 (P < 0.005). The RI was 87% sensitive and 90% specific for detecting renal obstruction.

Conclusion Although the patients were given ketoprofen, their mean RI for the obstructed kidney remained above the discriminatory threshold (> 0.70) during the first 71 h of obstruction. Only in those obstructed for > 72 h was the mean RI on the obstructed side slightly below the threshold, but the difference between the kidneys was significant. The measurement of RI is a reliable diagnostic method for detecting acute renal obstruction. With a longer duration of symptoms, the difference in RI between the kidneys becomes clinically more relevant.