Aortic Blood Pressure During the First 12 Hours of Life in Infants with Birth Weight 610 to 4,220 Grams

Abstract

Systolic, diastolic and mean aortic blood pressure measurements were taken during the first 12 h of life in 16 clinically stable, untransfused infants who weighed 610-980 g at birth. These infants were selected from 207 infants weighing < 1000 g admitted to the hospital between 1965-1978. Selection criteria were pH .gtoreq. 7.25, PaCO2 [arterial CO2 partial pressure] < 50 torr, PaO2 > 50 torr, hematocrit > 40%, inspired O2 .ltoreq. 40% at 6 h of age. Blood pressures of appropriate for gestational age and small for gestational age infants of comparable weight were similar. From linear regressions of blood pressures on birth weight, average values and 95% confidence limits for 2 different birth weights were derived. For infants weighing 750 g the mean aortic blood pressure, measured in torr, was 33 (range 24-42); systolic, 44 (range 34-54); diastolic, 24 (range 14-34). Mean blood pressures of infants weighing 1000 g were 34.5 (range 25-44); systolic, 49 (range 39-59); diastolic, 26 (range 16-36). These values are lower than those extrapolated from larger infants using a parabolic regression. Data from these 16 infants were combined with data from 45 larger infants to compute new nomograms for aortic blood pressures during the first 12 h of life in infants weighing 610-4220 g. The relations between blood pressures and birth weights were best described by linear regressions. The lower limits of normal mean aortic blood pressure are 25 torr at 750 g, 29 torr at 1500 g and 37 torr at 3000 g; the lower limits of normal systolic blood pressure are 34 torr at 750 g, 40 torr at 1500 g and 51 torr at 3000 g. These extended nomograms should replace the parabolic regression of mean aortic blood pressure vs. weight, which may have inaccurately indicated hypotension in infants of very low birth weights.