Oxygen consumption in normally grown, small-for-dates and large-for-dates new-born infants.

1. Serial measurements of minimal oxygen consumption (V(O2)) have been obtained from nineteen healthy new-born infants in order to find out how body weight, gestational age and age after birth affected V(O2). The first measurement of V(O2) was done within 12 hr of birth, and further measurements were made at intervals until the baby left hospital.2. The majority of the infants (seventeen) weighed less than 2.5 kg at birth, and were ;premature' according to international definition. Gestational age, calculated from the mother's last menstrual period, was corroborated by clinical data and obstetrical history. The babies were divided into four groups according to birth weight and gestational age combined (see Table 1). Babies in the first two groups were the appropriate weight for dates (i.e. normally grown), babies in the other two groups were either small-for-dates or large-for-dates.3. At birth minimal V(O2) was closely correlated with birth weight in all babies and appeared to be directly proportional to it. The value for V(O2)/kg was similar in all groups. V(O2) was not related to gestational age per se. However, in the two normally grown groups V(O2) was roughly related to gestational age because birth weight was related to gestational age.4. In all babies minimal V(O2) rose progressively with increasing age after birth; a marked increase in V(O2) occured in the first week of life, despite a small decline in body weight.5. At a given age after birth differences in V(O2)/kg between the four groups were mostly less than 10%, and in general the differences were not statistically significant. Values for minimal V(O2) in all four groups were roughly:5 ml. O(2)/kg.min at < 12 hr of age.7 ml. O(2)/kg.min at 7-14 days of age.9 ml. O(3)/kg.min at about 2 months of age.6. It is concluded that:(a) At birth minimal V(O2) is largely determined by birth weight. V(O2)/kg is little affected by either rate of growth in utero or gestational age.(b) Minimal V(O2) is a function of age after birth as well as of body weight, and the value for V(O2)/kg increases as the baby gets older.