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SUMMARY1. Serial measurements of minimal oxygen consumption (ro,) have been obtained from nineteen healthy new-born infants in order to find out how body weight, gestational age and age after birth affected V0o. The first measurement of Vo. 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 ro, was closely correlated with birth weight in all babies and appeared to be directly proportional to it. The value for Jo,/kg was similar in all groups. Po, was not related to gestational age per se. However, in the two normally grown groups ro, was roughly related to gestational age because birth weight was related to gestational age.4. In all babies minimal Io, rose progressively with increasing age after birth; a marked increase in V0, occurred in the first week of life, despite a small decline in body weight. JUNE R. HILL AND D. C. ROBINSON groups were mostly less than 10 %, and in general the differences were not statistically significant.Values for minimal o02 in all four groups were roughly: 5 m. 02/kg. min at < 12 hr of age. 7 ml. 02/kg.min at 7-14 days of age. 9 ml. 03/kg. min at about 2 months of age. 6. It is concluded that:(a) At birth minimal 'o, is largely determined by birth weight.Jo,/kg is little affected by either rate of growth in utero or gestational age.(b) Minimal ro, is a function of age after birth as well as of body weight, and the value for Io2/kg increases as the baby gets older.

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From the departments of medicine, surgery, obstetrics and gynecology, and anesthesia,