Determinants of blood pressure in very low birth weight neonates: lack of effect of antenatal steroids
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.
Section snippets
Study population
Neonates included in this study were born at Parkland Memorial Hospital, a large public hospital, between May 1st, 1993 and April 30th, 1995. All neonates with birth weight ≤1500 g were identified using a prospectively collected, computerized database that includes all births ≤2200 g, which has been in existence since 1977, and has been verified on several occasions [13], [14], [15]. Antenatal steroids were rarely administered to expectant preterm deliveries prior to May 1st, 1994. After that
Effects of antenatal steroids on neonatal blood pressure
The median number of doses of dexamethasone administered to mothers of Group I neonates was 3 (range 1–25), and the median interval between the final dose and delivery was 8.8 h (range 0.2–199.0 h). Comparing maternal characteristics for Groups I and II revealed that the use of pudendal anesthesia was greater in women with neonates in Group I (14 vs. 0%, P=0.02), while the use of local (10 vs. 27%, P=0.03) and epidural anesthesia (0 vs. 9%, P=0.04) were greater in women with neonates in Group
Discussion
Considerable controversy exists regarding the interpretation of BP measurements obtained in VLBW neonates, resulting in further uncertainty regarding which neonates have hypotension necessitating treatment. Normal BP values for term and preterm neonates were reported by Kitterman et al. 30 years ago [23]; however, only nine neonates with birth weights ≤1500 g were included and survival of VLBW neonates has increased substantially since then. Subsequent reports have expanded on these
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