Abstract
Abrupt increase in urine output in preterm infants on 2nd-3rd day of life has been documented. To determine the etiology of this diuresis, sequential changes in renal function during the first five days were studied in 21 preterm AGA infants with gestational age 30.2±.4wks. Infants were entered into the study within 24hrs of life and urine collections were divided into 10 consecutive 12hr periods for 5 days. Diuresis was defined as urine volume (V) ≥ 3ml/kg/hr and output/intake ratio ≥ 1. 16 infants had distinct diuresis, as defined by above criteria. Median diuretic period occurred between 36 and 48 hrs. (Mean 45 hrs)
These results indicate that the low urine output in prediuretic period is not due to high ADH effect (note low Uosm throughout). Diuresis is due to an abrupt rise in GFR which is not simply maturational but more likely hemodynamic, since GFR is actually lower in post diuretic period. Finally, diuresis is due also to decreased tubular reabsorption, most likely in proximal tubule or Henle's loop, since both Na and K excretion were high during diuresis.
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Bidiwala, K., Lorenz, J. & Kleinman, L. 1576 PHYSIOLOGICAL FACTORS IN POSTNATAL DIURESIS IN PRETERM INFANTS. Pediatr Res 19, 373 (1985). https://doi.org/10.1203/00006450-198504000-01600
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DOI: https://doi.org/10.1203/00006450-198504000-01600