Doppler renal resistivity index in horses: A systematic review

The resistivity index (RI) evaluates haemodynamic based on arterial resistance. Alterations in renal blood flow are important for the early detection of kidney damage, as perfusion might be one of the first affected aspects.

To retrieve published studies on equine renal RI to develop a standardised method of renal ultrasonographic examination and to evaluate the current reference range for the renal RI in horses.

Systematic review.

An electronic search in Science Direct, PubMed, Scopus and Web of Science databases was performed in February 2023 using the terms 'RI' OR 'resistivity index' OR 'IP' OR 'pulsatility index' AND (kidney OR renal) AND (equine OR horse) in titles, keywords and abstracts. The studies were screened for inclusion based on pre-determined criteria and data on the variables of interest were collected from included studies. The SYRCLE risk of bias tool was used to assess the methodological quality.

The electronic searches identified 134 studies, of which 5 were eligible for inclusion in this review. The studies had been conducted in healthy non-sedated horses through the transabdominal technique. The upper limit of normality for the renal RI was 0.58 ± 0.06 for the right kidney of untrained horses, which is considerably lower than the value of 0.70 currently used for humans, cats and dogs. There were heterogenous outcomes among the studies: two of the five demonstrated a difference between the right and left renal RI values, and one of the five showed an increased renal RI in elderly horses compared with foals and adult horses.

Data regarding the RI in horses are still scarce.

Additional studies that establish a reference range for the renal RI in horses are needed and there is a need to ensure consistency of techniques.