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Renal function correlates of postnatal diuresis in preterm infants
K S Bidiwala1, J M Lorenz, L I Kleinman
1Department of Pediatrics, University of Cincinnati College of Medicine.
Pediatrics
|July 1, 1988
Summary
In preterm infants, fluid homeostasis involves an initial low urine output, followed by a diuretic phase with increased glomerular filtration rate and sodium excretion. Finally, urine output adjusts to fluid intake.
Area of Science:
- Neonatal Physiology
- Renal Function in Preterm Infants
- Fluid Homeostasis
Background:
- Preterm infants exhibit a distinct fluid homeostasis pattern in the first week of life.
- This pattern includes initial oliguria, followed by diuresis, and then intake-dependent urine output.
Purpose of the Study:
- To investigate the renal mechanisms underlying fluid homeostasis phases in preterm infants.
- To correlate renal clearance measurements with observed changes in fluid balance.
Main Methods:
- Renal clearance measurements were performed on 22 preterm infants between 12 and 120 hours of age.
- Infants were studied across three distinct phases of fluid balance: initial oliguria, diuresis, and intake-dependent output.
- Diuresis was defined by specific urine output and output-to-intake ratios.
Main Results:
- 17 out of 22 infants experienced at least one diuretic phase.
- Glomerular filtration rate (GFR) and fractional sodium excretion (FeNa) were lowest at 12-24 hours.
- Diuresis correlated with a tripling of urine output, increased GFR, and increased FeNa.
- Late in the study (108-120 hours), decreased GFR accompanied reduced urine output despite increased fluid intake.
Conclusions:
- The initial antidiuretic phase is attributed to low GFR and low FeNa.
- Diuresis and natriuresis result from rapid increases in GFR and FeNa.
- Post-diuresis, GFR and FeNa decrease, allowing urine output to align with fluid intake.