to examine changes in arterial blood pressure ( abp ) after birth in extremely preterm infants . prospective observational study of infants 23  26 weeks gestational age ( ga ) . antihypotensive therapy use and abp measurements abp decreased for the first three hours , reached a nadir at 4  5 hours , then increased at an average rate of 0.2 mmhg / hour . the rise in abp from hour 4  24 was similar for untreated infants ( n=164 ) and infants given any antihypotensive therapy ( n=203 ) , a fluid bolus ( n=135 ) , or dopamine ( n=92 ) . abp tended to be lower as ga decreased , but varied widely at each ga . arterial blood pressure increased spontaneously over the first 24 postnatal hours for extremely preterm infants . the immature cardiovascular system is complex and particularly dynamic immediately after birth and this evolving physiology of extremely preterm infants contributes to a wide range in observed arterial blood pressure ( abp ) values during this time . this variability makes it difficult to define normal abp values and to identify expected physiological changes in abp over the first few days for this population . in more mature infants , abp increases with increasing birth weight , higher gestational age ( ga ) at birth , and advancing postnatal age , but these relationships are unclear for extremely preterm infants . data are also limited regarding the effect of commonly prescribed antihypotensive therapies on abp in this population . although abp rises after these therapies are administered , it is not clear whether abp rises at a different rate with these therapies as compared to the spontaneous rise in abp which has been observed previously . . a better understanding of changes in abp occurring in early postnatal life and the effect of antihypotensive therapies on abp during this time may help to decrease clinical variability in abp management for this population and improve infant outcomes . the goals of this investigation were to evaluate changes in abp over the first 24 postnatal hours in infants born at 23  26 weeks ga and to investigate the relationship between antihypotensive therapies and abp values . this is a secondary analysis of a prospective observational study of inborn extremely preterm infants 23  26 weeks ga born at 16 academic centers of the eunice kennedy shriver national institute of child health and human development neonatal research network ( nrn ) . infants were excluded if they died in the delivery room , had a major birth defect , or had intensive care withheld or withdrawn in the first 24 hours . research personnel utilized study specific data forms to record hourly abp measurements and the administration of all antihypotensive therapies in the first 24 hours . antihypotensive therapy included a fluid bolus ( 10 ml / kg of crystalloid ) , dopamine , dobutamine , hydrocortisone , epinephrine , or any blood product . blood pressure values were obtained from a non - invasive abp cuff , umbilical arterial catheter ( uac ) , or peripheral arterial line . this study was approved by the institutional review board of each participating center . at two centers , infants were enrolled after parents signed a study specific informed consent form . at the remaining 14 centers , this study was incorporated into the ongoing generic database ( gdb ) study of the nrn because all infants in this study qualified for gdb enrollment ( on the basis of their ga at birth ) and both studies collected de - identified patient information . the institutional review board of some nrn centers allowed for gdb data collection with a waiver of consent . data analysis was performed at the nrn data coordinating center ( rti international , research triangle park , nc ) . data were entered remotely by electronic submission and were periodically reviewed for quality control . sas 9.3 software was used for statistical analysis . at each postnatal hour , abp percentiles were constructed for different populations ( all infants , infants who did not receive therapy , treated infants , and infants of each specific ga ) using two sets of data : all abp values and only abp values obtained from a uac . after visual inspection of the data , the mixed - effects linear growth models were used to estimate the mean abp rate of rise from hour four to 24 and its standard deviation ( sd ) . infant demographic characteristics and in - hospital outcomes were compared across subgroups defined by the administration of antihypotensive therapy and the rate of rise in abp . the study cohort included 367 infants born at 23  26 weeks ga from july 21 , 2010  january 21 , 2011 . there were 203 ( 55% ) infants who received at least one antihypotensive therapy : 135 were given a fluid bolus , 92 received dopamine , 25 received hydrocortisone , 18 were given dobutamine , and one patient received vasopressin . blood pressure values were obtained from an arterial line for most infants  298 ( 81.2% ) infants had a uac placed and 8 ( 2% ) infants had a peripheral arterial line inserted  with 14,593 ( 78% ) invasive abp values recorded . the systolic , diastolic , and mean abp values decreased for the first four hours after birth , reached a nadir at four to five hours , and then increased until 24 hours of age ( figure 1 ) . blood pressure percentiles were similar ( within 2 mmhg ) for each population independent of whether non - invasive abp values were included in the analysis . the estimated mean  sd rate of rise in the systolic , diastolic , and mean abp from hour 4  24 was 0.3  0.6 ( range : -2.15 to 1.66 ) , 0.2  0.4 ( range : -1.10 to 1.32 ) , and 0.2  0.4 ( range : -1.17 to 1.37 ) mmhg / hour , respectively . these rates of rise were similar for the entire cohort ( n=367 ) , untreated infants ( n=164 ) , and infants treated with any antihypotensive therapy ( n=203 ; table 1 ) . demographic data and in - hospital outcomes for treated and untreated infants in whom the mean abp did or did not rise at the expected rate of 0.2 mmhg / hour are presented in table 2 . similarly , the percentages of infants in whom the mean abp decreased , remained the same , increased at a rate 1 mmhg / hour , or increased at a rate > 1 mmhg / hour from hour 4 to 24 were similar across study cohorts ( table 3 , available online with the supplementary material ) . for 21 ( 89% ) of the 24 hours investigated , the 95 , 50 , and 5 percentiles for the systolic , diastolic , and mean abp were higher for treated infants as compared to untreated infants , although these differences were generally 2 mmhg . for untreated infants ( n = 164 ) , systolic , diastolic , and mean abp increased significantly ( p < 0.001 ) at an estimated mean  sd rate of 0.3  0.5 ( range : -2.15 to 1.50 ) , 0.2  0.4 ( range : -1.10 to 1.10 ) , and 0.2  0.4 ( range : -0.90 to 1.25 ) mmhg / hour , respectively . of the 135 infants given a fluid bolus , 72 ( 53% ) also received dopamine , dobutamine , or hydrocortisone . the first bolus was given at a median age of four hours ( range : 1 to 21 ) . of the 92 infants administered dopamine , 14 ( 15% ) also received dobutamine , 20 ( 22% ) received hydrocortisone , and seven ( 8% ) received both dobutamine and hydrocortisone . dopamine infusion was initiated at a median of six hours after birth ( range : 1 to 23 ) . arterial bp values at the initiation of therapy for infants given a fluid bolus or dopamine as well as changes in abp with each therapy are presented in table 1 . at each ga , abp initially decreased , reached a nadir at postnatal hour four to five , and then increased at a similar rate of rise until 24 hours . arterial bp values usually increased as ga increased ( figure 2 ) , but for each ga there was a wide range in each abp parameter at each postnatal hour with significant overlap in abp values across the ga range investigated . the goals of this study were to examine changes in abp during the first 24 hours for extremely preterm infants and to investigate the impact of antihypotensive therapies on abp values during this time . similar to studies of more mature infants , abp increased spontaneously with advancing postnatal age , and a wide range of systolic , diastolic , and mean abp values was observed at each postnatal hour . in this population , abp response to a normal saline bolus or initiation of dopamine was inconsistent  in some infants abp rose quickly with therapy while in others little or no change in abp was observed . our results are consistent with several small retrospective single center studies that also examined abp values in extremely preterm infants . in two of these , the reported rate of rise in the mean abp ( 0.2 mmhg / hour and 0.196 mmhg / hour ) was quite similar to our study ( 0.2 mmhg / hour ) . this may be due to differences in the preterm infant population investigated , methods used to measure abp , or the frequency of antenatal corticosteroid administration  which was substantially higher in our study and has been associated with higher postnatal abp values in preterm infants . similar to more mature infants , a wide range of abp values was observed for infants 23 to 26 weeks ga , with abp values generally increasing with increasing gestational age . there were numerous postnatal hours for which abp percentiles were higher for infants at 23 or 24 weeks ga than for those at 25 or 26 weeks ga ( data not shown ) and there was significant overlap in observed abp values across the entire ga range . it is also worth noting that although abp values were generally higher in this study than previously reported for extremely preterm infants , infants commonly had at least one low abp value . two - thirds of the infants had at least one mean abp less than or equal to their gestational age equivalent ( in weeks ) . the wide range in abp for extremely preterm infants is related to many dynamic changes in physiology during the transition to postnatal life as well as varying disease processes . such abp variability makes it difficult to determine whether a specific abp value at a specific time for a specific patient is appropriate , too high , too low , rising too quickly , or remaining unchanged for too long . the average rate of rise in each abp parameter was similar for untreated infants , treated infants , infants who only received a fluid bolus , and infants given dopamine . each of these groups also had a similar percentage of infants for whom the abp value at hour 24 was below the abp value at hour four . however , for both treated and untreated infants there was substantial variability in the range of observed abp values at each postnatal hour . the rate of change in abp after the initiation of antihypotensive therapies also varied considerably for treated infants . table 2 suggests variability in the rate of change in abp between treated and untreated infants may be partly related to variability in circumstances at the time of delivery and the presence of different morbidities for infants who receive therapy . additional explanations for the observed variability in abp values include the possibility infants who receive an antihypotensive therapy were sicker , varying rates of antihypotensive therapy use across neonatal intensive care units , different etiologies for low abp , varying impact of antihypotensive therapies on abp values , and patient to patient differences in the pharmacokinetics and pharmacodynamics of some antihypotensive therapies . the substantial variability in observed abp values and unpredictable response to antihypotensive therapies increases the difficulty of developing effective therapeutic algorithms for administering antihypotensive therapies and evaluating their impact on preterm infant outcomes . study strengths include the large number of abp measurements obtained , the narrow ga range of the study population , and uniform data collection by experienced research personnel . a potential limitation is the lack of a uniform approach to abp management across study sites . administration of antihypotensive therapy was at the discretion of the clinical care team , and only one participating center had a written protocol for abp management . additional factors that were not recorded , such as clinical assessment of perfusion or the presence of a metabolic acidosis , may have been incorporated into the decision to initiate antihypotensive therapy . the hourly abp measurement recorded may not have been representative of most abp values observed during a specific postnatal hour . in addition , although most infants had a uac placed shortly after birth , it typically takes several hours to establish invasive abp monitoring . there were a significantly higher percentage of non - invasive abp measurements in first few hours as compared to each later postnatal hour ( data not shown ) . hence , the observed drop in abp over the first four postnatal hours may reflect a true decrease in abp or may be due to a transition from oscillographic abp measurements to invasive monitoring methods since abp values obtained from a uac are lower in this population . this study demonstrates that abp increases spontaneously during the first postnatal day for extremely preterm infants born  26 weeks ga , with a wide range in abp values at each postnatal hour . although abp values tend to increase with increasing ga , we observed significant overlap in abp values across the entire ga range for this population of infants . future studies of extremely preterm infant hemodynamics should consider these findings when evaluating the effectiveness of cardiovascular therapies . we found that abp variably decreased , increased at a rate similar to untreated infants , or increased more rapidly . this variability in response to therapies makes it difficult to assess their risks and benefits . a single criterion for institution of therapy  such as a numeric abp cutoff is not likely to reliably predict which infants will respond to or benefit from treatment . until more information on these medications is available , a cautious approach to abp management is warranted .
objectiveto examine changes in arterial blood pressure ( abp ) after birth in extremely preterm infants.study designprospective observational study of infants 230/7  266/7 weeks gestational age ( ga ) . 
 antihypotensive therapy use and abp measurements were recorded for the first 24 hours.resultsa cohort of 367 infants had 18,709 abp measurements recorded . 
 abp decreased for the first three hours , reached a nadir at 4  5 hours , then increased at an average rate of 0.2 mmhg / hour . the rise in abp from hour 4 
 24 was similar for untreated infants ( n=164 ) and infants given any antihypotensive therapy ( n=203 ) , a fluid bolus ( n=135 ) , or dopamine ( n=92 ) . 
 ga specific trends were similar . 
 abp tended to be lower as ga decreased , but varied widely at each ga.conclusionarterial blood pressure increased spontaneously over the first 24 postnatal hours for extremely preterm infants . 
 the rate of rise in abp did not change with antihypotensive therapy .