Response to rapid volume expansion during the postnatal period

Area of Science:

• Neonatal Physiology
• Renal Function in Newborns

Background:

• A transient diuresis is commonly observed in healthy neonates during the second hour of life.
• The underlying physiological mechanisms for this early postnatal diuresis are not fully understood.

Purpose of the Study:

• To investigate the hypothesis that postnatal diuresis results from extracellular volume expansion due to placental blood transfusion.
• To assess the renal response of healthy neonates to a fluid load during the early postnatal period.

Main Methods:

• Seven healthy infants received intravenous infusions of 5% glucose solution.
• Plasma and urine samples were analyzed for osmolality, inulin, and p-aminohippuric acid.
• Calculations included osmolal clearance, free water clearance, glomerular filtration rate, and renal plasma flow.

Main Results:

• Glucose infusion led to a 2- to 4-fold increase in urine output, glomerular filtration rate, and renal plasma flow.
• No consistent changes in urine osmolality were observed.
• The renal response was transient, resolving within 30 minutes post-infusion, with less than 5% of the fluid load excreted in most infants.

Conclusions:

• The kidneys of newborn infants are capable of responding to a water load shortly after birth, similar to neonates a few days old.
• The observed transient postnatal diuresis may be partly attributed to extracellular volume expansion from placental blood transfusion.