Postnatal weight loss in preterm neonates less than 1,500 g is due to isotonic dehydration of the extracellular volume.
Weight, extracellular volume (ECV; distribution volume of sucrose) and renal function were studied in 13 preterm infants at birth (age 6 h (2-12); median, range) and again when postnatal weight loss exceeded 5% of birth weight (age 84 (64-97) h). Gestational age was 28 (26-32) weeks, and birthweight was 1,170 g (810-1,455). The infants were nursed in incubators and mechanically ventilated. Fluid therapy allowed a weight loss of up to 10% of birthweight. Body weight decreased significantly from 1,101 +/- 202 g at birth to 1,016 +/- 198 g at day 3 and ECV from 499 +/- 155 ml to 413 +/- 118 ml. Mean weight loss of 85 +/- 50 g was the same as mean ECV loss of 86 +/- 48 ml, suggesting that postnatal weight loss is water loss from the ECV. Weight loss was preceded by a marked increase in diuresis, exceeding fluid intake on day 2. Creatinine clearance did not change. The increased urine output led to a significant increase of sodium excretion without inducing hyponatremia but resulted in an isotonic reduction of ECV.
Bauer
K
K
Department of Obstetrics and Gynecology, University of Munich, FRG.
Versmold
H
H
D003404:Creatinine / Q000652:urine; D003681:Dehydration / Q000097:blood / Q000503:physiopathology* / Q000652:urine; D005110:Extracellular Space / Q000032:analysis* / Q000502:physiology; D006801:Humans; D007225:Infant Food; D007230:Infant, Low Birth Weight / Q000502:physiology*; D007231:Infant, Newborn; D007234:Infant, Premature / Q000502:physiology*; D007668:Kidney / Q000503:physiopathology; D012964:Sodium / Q000652:urine; D013395:Sucrose / Q000097:blood / Q000652:urine; D015431:Weight Loss / Q000502:physiology*
D013395:Sucrose; D012964:Sodium; D003404:Creatinine