An assessment of the utility and repeatability of the renal resistive index in horses

Abstract

The aim of this study was to establish the value of the renal resistive index (RI) of intrarenal arteries in healthy warmblood non-racing horses of different ages to assess the influence of physiologic factors and repeatability of measurement. The kidney ultrasonography examination was performed in three age groups: 15 foals, 15 adults and 15 elderly horses. The procedure was performed in unsedated standing animals. RI values were measured using pulsed-wave Doppler at the medial part of each kidney in the intrarenal arteries. To evaluate repeatability, all measurements were repeated two hours after the first examination. Statistical analysis of the relationship between groups was carried out using Fisher’s test. The relationship between the RI value and the physiological parameters was evaluated using linear regression. Repeatability of measurements was determined based on the Bland-Altman plot. The mean RI value in the studied horses was 0.48 ± 0.05 in the left kidney and 0.49 ± 0.05 in the right kidney. There were no statistically significant differences between the RI values in foals and adult horses. The elderly horses had a significantly higher RI value. Pulse pressure was the only physiological parameter affecting the RI value. The repeatability coefficient was 0.089 for the right kidney and 0.09 for the left kidney. The presented result suggest that elderly healthy horses have higher RI values than younger animals, which should be taken into account in clinical practice. The arterial pulse pressure should also be considered when interpreting RI values. The measurements have high repeatability, but in the authors’ opinion, this procedure is time consuming and requires experience.

Transabdominal Renal Doppler Ultrasound in Healthy Adult Holstein-Friesian Cows: A Pilot Study

“…As far we are aware, this is the first report describing normal RI values for cattle, and therefore, there is no information available in the scientific literature with which to compare our results. Our findings are consistent with those of other studies, in humans [ 34 , 35 ], in healthy dogs and cats [ 12 , 36 ], donkeys [ 24 ], and horses [ 33 ] that did not find any differences between the right and left kidney in physiological conditions, although other studies have reported differences in horses [ 24 , 25 ] and cats [ 9 ]. Although it is difficult to explain this difference, more data must be collected to determine whether the difference is due to technical or anatomical variants.…”

“…The limit may be more similar to that in other large animals, but there is no relevant information available in the scientific literature. Recent studies in horses and donkeys [ 24 , 33 ] did not establish a cut-off value, but the RI values were below 0.7 for both kidneys, as in our study. In relation to PI, the value we propose in cattle is much lower than those reported for dogs (1.52) and cats (1.29) [ 12 ].…”

“…Nevertheless, the values are different from those in new-born and childhood [ 9 , 17 , 20 ]. Siwinska et al [ 33 ] also found that RI values were higher in elderly horses (>18 years) than in foals and adults, but were always below the upper value of 0.70. These differences should be investigated in future studies in cattle.…”

“…A notable difference between the RI in the left and right kidney is considered an important diagnostic factor in detecting upper urinary tract obstructions in human patients [ 37 ]. Renal RI values are not specific markers of any particular type of kidney disease but help the clinician to detect renal impairment [ 10 , 33 ], even when subtle or no change in B-mode US is visible.…”

“…Regarding the weight of the animal, most veterinary research has not found any correlation between renal RI and body weight, similarly to our study in cattle. Park et al [ 38 ] described a weak correlation in cats, whereas Ostrowska et al [ 17 ], Freccero et al [ 24 ] and Siwinska et al [ 33 ] did not detect any statistically significant differences in respectively cats/dogs or horses/donkeys.…”