Respiratory metabolism in preterm infants: the measurement of oxygen consumption during prolonged periods.

We have developed a method for measuring oxygen consumption (Vo2) in preterm infants in their normal incubator environment over prolonged periods. The results of measurements made over 24 h in 18 infants are presented. In normally grown infants, the mean Vo2 was 9.66 +/- 1.25 liters/kg X 24 h (SD) (6.71 +/- 0.87 ml/kg X min), and in small for gestation infants it was 10.09 +/- 1.21 liters/kg X 24 h (7.00 +/- 0.84 ml/kg X min). During the 24-h measurements, the highest mean Vo2 during 3 consecutive h was 7.75 +/- 0.89 ml/kg X min and the lowest was 5.95 +/- 0.92 ml/kg X min. The difference between the highest and the lowest values was significant (p less than 0.001). There is room for considerable error if short term measurements are assumed to represent values over a whole day. "Short" measurements should be made over at least 6 h.