Postnatal change of renal artery blood flow velocity and its relationship with urine volume in very low birth weight infants during the first month of life

Although the renal artery blood flow velocity has been investigated recently using the ultrasound Doppler method, little is known about the longitudinal change of renal artery blood flow velocity and its relationship with urine volume in very low birth weight infants. Thus, we measured renal artery blood flow velocities by means of the pulse Doppler method in 28 very low birth weight infants. Maximum, minimum, and mean blood flow velocities were determined at postnatal days 0, 1, 2, 3, 4, 5, 6, 13, 20, and 27. The resistance index was also calculated. The maximum and mean blood flow velocities increased gradually after birth, and were significantly higher at 13, 20, and 27 days after birth. The minimum blood flow velocity and the resistance index were relatively constant during the study period. The mean blood flow velocities were also analyzed for any correlation with urine volume. There was a poor correlation between urine volume (ml/kg/day) and mean blood flow velocity (cm/s) (Y = 2.38X + 57.4, Y: urine volume, X: mean blood flow velocity, n=161, r=0.338, P<0.01). However, if the mean renal artery blood flow velocity was less than 10 cm/s, oliguria was observed in most cases. The measurement of the renal artery blood flow velocities appears to be useful in understanding the background condition of renal function in very low birth weight infants.