Doppler Ultrasonographic Estimation of Renal Resistive Index in Horse: Comparison Between Left and Right Kidneys

The renal resistive index (RI) is the ratio of the difference between maximum and minimum (end diastolic) flow velocity derived from the Doppler spectrum of intrarenal (segmental/ interlobar) arteries. It is a good indicator for acute renal disease, acute tubular necrosis, and renal obstruction. To our knowledge, no reports are available about the values of renal RI in unsedated horses. The aim of this study was to establish a normal reference range (mean ` standard error) and to assess the reliability of the renal RI obtained using transabdominal ultrasonography in unsedated healthy horses. Thirteen conscious Thoroughbred horses judged healthy based on physical examination, complete blood count, biochemical profile, urinalysis, and ultrasonography were included. The peak-systolic and end-diastolic veloc- ities of interlobar and arcuate arteries were measured. Intrarenal arteries were scanned by pulsed Doppler ultrasonography to calculate RI. The comparison of left versus right kidneys was analyzed with analysis of covariance (ANCOVA) procedure. Significant differences (P < .05) for the RI values were observed between left and right kidneys in the geldings (left 0.50 vs. right 0.56) and mares (left 0.50 vs. right 0.57) and were observed between left and right kidneys in trained (left 0.52 vs. right 0.55) and untrained horses (left 0.48 vs. right 0.58). The renal RI has not been modified by sex.