Blood pressure ranges in premature infants. I. The first hours of life.

We studied blood pressure in the first hours of life in a cohort of 1105 preterm infants weighing 501 to 2000 gm; these infants represented 83% of all births at these weights that resulted in admission to three intensive care nurseries during a 34-month period between 1984 and 1987. To assess the effects of specific risk factors, we identified 244 healthy infants, 164 infants who received mechanical ventilation but had no other conditions, 47 infants whose only risk factor was the presence of hypertension or preeclampsia in the mother, and 86 infants with depressed Apgar scores regardless of the presence of the other conditions. We documented each infant's minimum and maximum systolic (Smin, Smax) and diastolic (Dmin, Dmax) pressures during the first 3 to 6 hours of life. In the healthy group, Smin was 47 mmHg; Smax, 59 mmHg; Dmin, 24 mmHg; and Dmax, 35 mmHg. In the ventilation group, Smin was 41 mmHg; Smax, 57 mmHg; Dmin, 22 mmHg; and Dmax, 35 mmHg. The Smin and Dmin values were both significantly lower in infants who received mechanical ventilation than in healthy infants (p < 0.01). In the maternal hypertension group, Smin was 49 mmHg; Smax, 59 mmHg; Dmin, 25 mmHg; and Dmax, 34 mmHg. Only the Smin value was significantly higher than in healthy infants. In the group with low Apgar scores, Smin was 33 mmHg; Smax, 51 mmHg; Dmin, 19 Hg; and Dmax, 34 mmHg. Thus all these values were significantly lower than in all the other groups (p < 0.05). Of infants with low Apgar scores, 20% to 50% had values below the 5th percentile for healthy infants. Birth weight and gestational age correlated with blood pressure limits only in the infants with low Apgar scores. We conclude that in healthy premature infants the limits of systolic and diastolic blood pressure are independent of birth weight and gestational age. Infants with low Apgar scores tend to have lower pressures, and infants whose mothers have hypertension have higher pressures than infants in the healthy cohort.