Doppler ultrasound for the assessment of renal perfusion in kittens up to three months of age and young adult cats

Abstract

This study aimed to assess the Doppler-based renal resistive index (RI) and pulsatility index (PI) during the first three months of age and compare them with the indices of young adult cats. Forty-eight healthy mixed-breed cats were evaluated in this study, 24 males and 24 females. The client-owned cats and those from breeding catteries were distributed into six groups, each consisting of eight animals, based on their age: G1 - up to 10 days old, G2 - from 11 to 20 days of age, G3 - from 21 to 30 days of age, G4 - between 1 and 2 months of age, G5 - between 2 and 3 months of age, and G6 – between 1 and 3 years of age. After B-mode ultrasound of the right and left kidneys, values of RI and PI were determined with Doppler ultrasound of renal, interlobar, or arcuate arteries. Each artery was evaluated using spectral Doppler to obtain at least three similar, sequential, and complete Doppler waveforms. Only waveforms obtained when the cats were calm were used to obtain the RI and PI. These Doppler-based indices were automatically calculated using the ultrasound device after manual waveform delimitation. No statistical difference was found between the arteries, kidneys, or sexes, regardless of age (P > 0.05). Mean values for RI and PI that included the three arteries were established. Statistical differences among all groups were observed (P < 0.05). RI values in G1, G2, G3, G4, G5, and G6 were 0.75 ± 0.006, 0.73 ± 0.06, 0.70 ± 0.07, 0.66 ± 0.06, 0.67 ± 0.06, and 0.62 ± 0.070, respectively. PI values in G1, G2, G3, G4, G5, and G6 were 1.25 ± 0.196, 1.16 ± 0.182, 1.08 ± 0.193, 1.02 ± 0.177, 1.00 ± 0.160, and 0.97 ± 0.163, respectively. Comparing RI and PI among groups demonstrates the presence of differences between them (P < 0.05), with higher values in G1 (up to 10 days of age) and a gradual drop in values up to G6 (young adults). A positive linear correlation was observed between RI and PI, with a coefficient greater than 0.80, regardless of the age group. In conclusion, the normal renal ultrasonographic indices were age dependent, being the highest values verified during the first month of age. The RI and PI reference values provided can be used for renal evaluation of kittens up to 3 months of age.