WATER, ENERGY AND EARLY POSTNATAL-GROWTH IN PRETERM INFANTS

Non-invasive methods, including stable isotope techniques, indirect ca lorimetry, nutritional balance and skinfold thickness, have given a ne w insight into early postnatal growth in neonates. Neonates and premat ure infants in particular, create an unusual opportunity to study the fluid and metabolic adaptation to extrauterine life because their phys ical environment can be controlled, fluid and energy balance can be me asured and the link between metabolism and the energetics of their pos tnatal growth can be assessed accurately. Thus the postnatal time cour se of total body water, heat production, energy cost of growth and com position of weight gain have been quantified in a series of ''healthy' ' low-birth-weight premature infants. These results show that total bo dy water is remarkably stable between postnatal days 3-21. Energy expe nditure and heat production rates increase postnatally from mean value s of 40 kcal/kg/day during the first week to 60 kcal/kg/day in the thi rd week. An apparent energy balance deficit of 180 kcal/kg can be ascr ibed to premature delivery. The cost of protein metabolism is the high est energy demanding process related to growth. The fact that nitrogen balance becomes positive within 72 h after birth places the newborn i n a transitional situation of dissociated balance between energy and p rotein metabolism during early postnatal growth: skinfold thickness, d ry body mass and fat decrease, while there is a gain in protein and in crease in supine length. This particular situation ends during the sec ond postnatal week and soon thereafter the rate of weight gain matches statural growth. The goals of the following review are to summarize d ata on total body water and energy metabolism in premature infants and to discuss how they correlate with physiological aspects of early pos tnatal growth.