Changes in Renal Resistive Index Values in Healthy Puppies during the First Months of Life

SIMPLE SUMMARY: The renal resistive index (RRI) is probably the most commonly used parameter to evaluate blood flow in kidney vessels. Alterations in this parameter have been noted in a range of conditions affecting the kidney, such as acute variations in renal vascular resistance and renal damage in multiple-organ dysfunction syndrome. In order to interpret changes of the RRI in pathologic conditions, the normal values of intrarenal arterial RI should be known. In adult healthy dogs, the RRI values have been well established. However, there is little information regarding the RRI values of puppies. The objective of this study is to establish the RRI of normal kidneys in puppies aged from newborn to 20 weeks of age and to determine the age at which RRI reaches adult dog values. The highest value was obtained in the first three weeks of life and then it gradually declined with increasing age reaching adult dog values at 12 weeks of age. ABSTRACT: The purpose of this study is to establish renal resistive index (RRI) of normal kidneys in puppies aged from newborn to 20 weeks of age and to determine the age at which RRI reaches adult dog values. Six healthy adult intact beagles and six puppies from 1 day after birth to 20 weeks of age were used. In the adult dogs, the ultrasonographic scans were performed once, and in the puppies, the ultrasonographic studies were performed on the first day after birth and at 1, 2, 3, 4, 6, 8, 12, 16, and 20 weeks of age. RRI was obtained at the interlobular and arcuate arteries in each kidney. There were no statistical differences between the RRI values obtained between the right and left kidney nor between intrarenal arteries (interlobar and arcuate). The RRI was the highest during the first weeks of life, after which it declined gradually with increasing age reaching adult dog values at 12 weeks of age. In conclusion, the normal mean RRI is age dependent in dogs. Twelve weeks can be regarded as the age at which adult mean RRI criteria can be applied to puppies.