Weight minus extracellular fluid as metabolic reference standard in newborn baby.

In 51 babies of differing size and gestational age, rates of oxygen consumption and corrected bromide space (as a measure of extracellular fluid) were measured. The results are used to examine the concept that weight minus extracellular fluid (ECF) is an appropriate metabolic reference standard in the newborn baby. When the whole group, which included large-for-dates and small-for-dates babies, is considered there is a systematic variation wherein the rate of oxygen consumption thus expressed varies with size. However, when appropriately grown babies only are considered, who varied in birthweight from 1210 g to 3820 g, rates of oxygen consumption thus expressed were constant. The implication is that when unusual rates of oxygen consumption per kilogram body weight are found, they should be interpreted bearing in mind the possibility of an unusual proportion of ECF in the baby. An incidental finding was that small-for-dates babies have a relatively large corrected bromide space.