Renal blood flow velocity in non-distressed preterm infants during the first 72 hours of life

Renal blood flow velocity (RBFV) was studied with two-dimensional/pulsed Doppler ultrasound in 28 non-distressed very preterm infants (mean +/- SD gestational age was 27.3 +/- 2.1 weeks and birth weight 907 +/- 214 g) at 6, 12, 24, 36, 48, and 72 h of age. Mean arterial blood pressure (MABP), PaCO2, PaO2, and Hct were determined simultaneously. Mean RBFV increased significantly from 14.5 +/- 1.9 cm/s at 6 h to 20.2 +/- 2.5 cm/s at 72 h (p < 0.005). MABP decreased slightly though significantly between 6 h (36.5 +/- 1.8 mm Hg) and 12 h (34.3 +/- 1.5 mm Hg), but rose thereafter to significantly higher values at 72 h (41.4 +/- 1.3 mm Hg). Renal vascular resistance (RVR = MABP/RBFV) decreased rapidly during the first day of life (2.6 +/- 0.1 mm Hg/cm.s-1 at 6 h vs. 2.0 +/- 0.05 mm Hg/cm.s-1 at 24 h). In conclusion, RBFV increases whereas RVR decreases during the first days of life.