Information regarding normal blood pressure (BP) values in preterm infants is critical since both undertreatment and overtreatment of presumed BP abnormalities can be associated with significant complications, including NEC and symptomatic PDA. We studied 116 infants delivered at Parkland Memorial Hospital between 5/1/93 and 4/30/95 with birth weight ≤1500g(mean±SD; 1140±250g, range 630-1490g) and gestational age 28.8±2.0wks (range 24-33 wks) during the first 72h after birth. 55% of the infants were female, 44% Black, 41% Hispanic, and 15% White. BP was measured directly or by oscillometry in 35% and 65% of determinations, respectively. Eleven infants (9.5%) required volume expansion and/or pressor support between one and 36h after birth; only BP values obtained prior to their treatment were used. 35% of the infants developed RDS requiring surfactant replacement therapy, and 92 infants (79%) required mechanical ventilation and/or constant positive airway pressure during the study period. Fluid intake (ml/kg) was 82±17 on day 1, 101±26 on day 2, and 119±32 on day 3; the mean weight loss by day 3 was 8.0±6.2%. Both birth weight and gestational age correlated directly and significantly(p<0.01) with systolic (SBP), diastolic (DBP) and mean (MBP) BP at 1, 6, 12, 24, 48 and 72h respectively. Trends for SBP, DBP, and MBP vs postnatal age are shown in the Table (mmHg;mean±SD). SBP, DBP, and MBP increased 27%, 32% and 32%, respectively, during the initial 72h after birth. Although the mechanism for the increase in BP during the first 72h is unknown, we have shown previously that both urinary PGE2 and plasma 6-keto-PGF1α (stable metabolite of prostacyclin) decrease significantly during the first 3d postnatal in preterm neonates. More recently, we have observed increased vascular smooth muscle function after birth in newborn sheep. Thus, the rise in BP during fetal-neonatal transition may be secondary to decreased activity of vasodilators, which are critical to fetal survival, as well as intrinsic changes in vascular smooth muscle function occurring in the postnatal period, both of which appear to be developmentally regulated.

Table 1 No caption available.
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