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Postnatal control of water and electrolyte homeostasis in pre-term and full-term infants
Insights
Newborn infants, both preterm and full-term, have limited ability to manage salt and water balance. Renal function, including sodium excretion and urine concentration, matures over the first two years of life.
Area of Science:
- Neonatology
- Pediatric Nephrology
- Renal Physiology
Background:
- The renal control of water and sodium homeostasis is critical for newborn infants.
- Infants, particularly preterm neonates, exhibit immature renal function compared to adults.
Purpose of the Study:
- To review advancements in understanding renal water and sodium regulation in newborns of varying gestational ages.
- To elucidate the developmental trajectory of renal excretory capacity in early life.
Main Methods:
- Literature review of studies published over the last decade.
- Analysis of data on salt load excretion, sodium balance, and urine concentrating/diluting capacities in neonates.
Main Results:
- Both preterm and full-term infants show a low capacity for rapid salt excretion, with gradual improvement up to 15 months.
- Preterm infants (<35 weeks gestation) exhibit higher basal sodium excretion and impaired sodium retention.
- Urine concentrating capacity is initially low but matures rapidly in the first postnatal weeks; diluting capacity is supranormal in some preterm infants.
Conclusions:
- Renal water and sodium handling capabilities in newborns are significantly different from adults and mature progressively over the first two years.
- Understanding these maturational changes is crucial for managing fluid and electrolyte balance in neonates.
Abstract:
A review is given of the progress which has been made during the last decade within the field of renal control of water and sodium homeostasis in newborn infants of varying gestational age. Both preterm and full-term infants have a low capacity for rapid excretion of a salt load. The natriuretic response improves gradually up to the age of 15 months. The capacity to excrete a load of sodium bicarbonate is higher than to excrete a load of sodium chloride. Under basal conditions preterm infants of a gestational age below 35 weeks have a higher renal sodium excretion than full-term infants. They also appear to be unable to retain sodium when in negative balance. The capacity to concentrate the urine is low in newborn infants, the maximal osmolality being only slightly above that of plasma. The concentrating capacity increases relatively fast during the first 4-6 postnatal weeks in full-term as well as in pre-term infants but does not reach the adult level until the second year. Water loaded newborn infants are able to excrete a urine with a osmolality as low as 30-50 mOsm per kg. In full-term infants free water clearance per unit filtered water is higher than in adults. Water-loaded pre-term infants with a gestational age of more than 30 weeks also have a supernormal diluting capacity.