Determinants of blood pressure in very low birth weight neonates: lack of effect of antenatal steroids

Abstract

Objectives: To define the range of normal blood pressures (BP) for very low birth weight (VLBW;≤1500 g) neonates and to study perinatal variables affecting BP measurements after birth, including the effects of antenatal steroids. Study design: Antenatal steroids were rarely administered at Parkland Memorial Hospital before May 1994, permitting us to establish a cohort of VLBW neonates exposed to antenatal steroids [n=70, 1166±253 (S.D.) g, and 28.7±2.1 weeks] who were matched with neonates delivered during the prior year (n=46, 1100±241 g, 28.9±1.8 weeks). Maternal and neonatal charts were abstracted for pertinent data, and neonatal BP measurements (determined directly when an arterial catheter was available or indirectly by the oscillometric method) were extracted every 3 h for the first 12 h and every 6 h until 72 h postnatal. Results: Antenatal steroids did not affect BP immediately after birth or for the subsequent 72 h postnatal. Therefore, data from all neonates ≤1500 g were combined and the pattern of BP change over 72 h postnatal assessed. Systolic, diastolic and mean BP increased (P<0.001) 33%, 44% and 38%, respectively, during the first 72 h. Although neonates weighing ≤1000 g and 1001–1500 g demonstrated gradual increases (P<0.001) in systolic, diastolic and mean BP by 72 h, values were consistently lower (P<0.01) in neonates ≤1000 g. Of interest, only 11 neonates (9.5%) were treated for clinical hypotension. Conclusions: In VLBW neonates antenatal steroids do not modify BP measurements either immediately after birth or the 30–40% rise occurring in the first 72 h postnatal. Further, BP is developmentally regulated and is gestationally and birth weight dependent. These data provide additional insight into assessing the need for treating hypotension.

Introduction

Very low birth weight (VLBW, ≤1500 g) and very preterm (<32 week gestation) neonates are reported to have low arterial pressures after birth when compared to larger, more mature neonates [1], observations consistent with those reported in developing fetal animals studied across gestation [2]. However, it remains unclear what blood pressures (BP) in VLBW neonates should elicit concern on the part of the clinician and the institution of therapeutic interventions. This is important since ‘abnormalities’ of arterial pressure may be associated with increases in neonatal mortality and morbidity, including increases in the incidence and severity of intracranial hemorrhage (ICH; [3], [4], [5]) and periventricular leukomalacia [6]. On the other hand, inappropriate use of therapies to increase BP, e.g., volume expansion, may in themselves result in a rise in neonatal complications, including increased symptomatic patent ductus arteriosus, ICH, and mortality [7], [8], [9]. Therefore, it is obvious that consideration of normative values for BP in VLBW neonates during the first 72 h after birth is mandatory.

In the past 5 years there has been a dramatic increase in maternal glucocorticoid administration in the presence of expectant preterm delivery in order to facilitate fetal lung maturation. Prenatal glucocorticoid therapy also has been suggested to result in a lower incidence of neonatal hypotension [10], improved cardiovascular stability [11], a decreased need for pressor therapy [12], and higher mean arterial pressures in the first 72 h after birth [3]. These reports, however, have been confounded by an absence of appropriate definitions for stability and hypotension, the frequent use of volume expansion, and importantly, the consideration that improved lung function may also improve cardiovascular stability. Thus, it remains unclear if prenatal steroids improve cardiovascular function and stability.

To examine the effects of maternal glucocorticoid therapy on neonatal BP and to provide normative BP data in VLBW neonates, we examined BP during the first 72 h postnatal in a large population of totally in-born VLBW neonates delivered at Parkland Memorial Hospital. The unique aspect of this study was that before May 1st, 1994, antenatal steroids were rarely if ever used, whereas afterwards it became routine for pregnancies threatened by preterm delivery <34 week gestation in the absence of maternal hypertension and infection. Furthermore, there were minimal changes in neonatal care during this 2-year period, thus avoiding other variables. The purposes of this study, therefore, were to assess in VLBW neonates: (1) the effects of antenatal steroids on BP in the first 72 h after birth, (2) the role of other perinatal factors on BP during this time, especially birth weight and gestational age, and (3) the normal BP ranges in the first 72 h of life, when volume expanders and pressors are most likely to be used.