Abstract
OBJECTIVES:
To determine the association between plasma hemoglobin (HB) at three time-points (birth, postnatal days 0–3 and 0–10) and spontaneous closure of the ductus arteriosus (sDAC).
STUDY DESIGN:
A retrospective case-control study of preterm infants born (2013–2016) between 24 and 29 weeks of gestational age (GA) was conducted in a level three perinatal center in Switzerland. We collected hemoglobin at birth, between days 0–3 and 0–10 in two distinct groups: (i) patients treated for a PDA and (ii) patients with spontaneous closure of the ductus arteriosus (sDAC). Antenatal and postnatal demographic data and neonatal morbidity were collected. Bivariate analysis was performed and a stepwise logistic regression was done to investigate factors associated with sDAC.
RESULTS:
We reviewed the medical chart of 184 premature infants of whom 146 (79.3%) satisfied eligibility criteria. Of these, 74 (51%) were classified as sDAC. Patients with sDAC were older (GA: 28 vs 27, p < 0.001), more stable (clinical risk index for babies score (CRIB score): 2 vs 5, p < 0.001) and had better clinical outcomes than patients who received treatment for a PDA. Infants in the sDAC group had a higher level of hemoglobin during the first ten postnatal days. Multiple logistic regression analysis revealed that lower HB level (day 0–10) were associated with failure of sDAC (p < 0.05).
CONCLUSIONS:
This is one of the first studies to highlight a potential association between hemoglobin during the transitional period and sDAC. The biological nature of this observation requires prospective clarification.
Keywords
Abbreviations
Area under the curve Bronchopulmonary dysplasia Clinical risk index for babies score Ductus arteriosus Extremely low birth weight Fraction of inspired oxygen Gestational age Hemodynamic significant patent ductus arteriosus Inhaled nitric oxide Intra uterine growth retardation Intraventricular hemorrhage Mean airway pressure Necrotizing enterocolitis Partial pressure of arterial oxygen Red blood cell Receiver operating characteristics Retinopathy of prematurity Respiratory severity score spontaneous closure of the ductus arteriosus Spontaneous intestinal perforation Vasoactive-inotropic score Very low birth weight
Introduction
Spontaneous closure of the DA (sDAC) occurs in more than 99% of term newborns within the first 72 hours of life, but fails to occur in around 65% of ex-tremely low birth weight (ELBW) infants during the transitional period [1]. The association of a patent ductus arteriosus (PDA) and neonatal morbidity [2] is well recognized. Research has focused on investigating risk factors [3, 4], predictive factors [4–6], and management [2, 8] of hemodynamically significant PDA (hsPDA), but few studies have characterized predictors of sDAC.
The biological processes involved in PDA closure are complex starting at birth and ending several days to weeks later in a fibrotic ligament [9, 10]. In term infants, vasoconstriction of the DA is an important modulator and leads to vessel hypoxia by decreasing the flow in the vasa-vasorum. To recreate this effect in the ELBW infant, vasoconstrictive drugs are used to close the PDA. Although successful vessel closure occurs in approximately 60% of preterm [1, 11], the hsPDA continues to be problematic.
The mechanism of sDAC is different in preterm in-fants. Specifically, their DA has a smaller muscular media layer, which is free of vasa-vasorum, a thinner intima allowing vessel perfusion, and maintenance of oxygenation by diffusion [9]. Induction of vasoconstr-iction of the DA in preterm infants has likely less impact and the Hagen-Poiseuille equation
We therefore hypothesized that higher levels of hemoglobin in the immediate transitional period would increase rate of sDAC by modulating transductal flow.
Materials and methods
Design
All preterm infants born between 24 and 29 weeks of gestational age (GA), between 2013 and 2016, admitted to the level three perinatal center at the University Hospital of Lausanne, were eligible. We excluded patients with severe heart or lung malfor-mations, suprasystemic pulmonary hypertension, perinatal asphyxia (cord pH or postnatal pH at birth less than 7, APGAR score at five minutes≤3 and≤6 at ten minutes, lactate≥12 mmol/l), hemoglobinopathy, genetic or metabolic diseases, outborn patients transferred after three days of life, or mortality in the first three postnatal days. Our cohort was divided into two groups. Group hsPDA: Patients with a hsPDA during their hospitalization; Group sDAC: patients with either no clinical and/or no echocardiography signs of hsPDA, or who never received treatment, during and/or after the hospitalization. A hsPDA was defined as a transductal diameter of ≥ 1.5 mm on two-dimensional echocardiography with left to right shunt associated with clinical signs of hsPDA (respiratory distress and/or increasing need for oxygen and/or inability to wean oxygen and ventilation support and/or diastolic hypotension and/or acute renal insufficiency, and/or feeding intolerance). Subgroup analysis according to RBC transfusion was made to evaluate the impact of the transfusion on sDAC.
PDA management
The decision to treat a hsPDA was dependent on the staff physician and based on clinical signs, and echocardiography evaluation. The first line treatment was indomethacin (0.1 to 0.2 mg/Kg q12 hrly for 3 to 6 days). Acetaminophen (15 mg/Kg q6 hrly for 3 to 7 days) was given after indomethacin failure or when indomethacin, or surgery were contraindicated. Prophylactic indomethacin was not used. Response to treatment was defined as resolution of the clinical signs and closure or restriction of the DA on echocardiography.
Hematologic data
The practice of delayed cord clamping was not implemented during the study period. Plasma hem-oglobin was measured from capillary, venous, and arterial samples but platelet count was measured only on venous and arterial samples. Blood sampling was performed routinely in all patient on the first postnatal day and subsequently according to the clinical and biological situation.
Data collection
We reviewed the medical records of enrolled patients to collect the maternal demographics (cho-rioamnionitis, preeclampsia, intrauterine growth ret-ardation (IUGR), multiple gestation and course of antenatal steroids), and infant characteristics (gestational age, weight, sex, caffeine treatment). Markers of illness severity during the first three postnatal days (CRIB score, mean airway pressure (MAP), fraction of inspired oxygen (FiO2), respiratory severity score (RSS), blood and platelet transfusion, use of surfactant, inhaled nitric oxide (iNO), inotropes, and vasoactive-inotropic score (VIS), and hematol-ogic parameters (HB and PLT) at birth and during the first three and ten postnatal days were recorded. We also collected information about neonatal morbi-dities (intraventricular hemorrhage (IVH) according to Papile-Burstein’s classification [14], necrotizing enterocolitis (NEC) according to modified Bell’s criteria [15] and/or spontaneous intestinal perforation, retinopathy of prematurity (ROP), pulmonary hemorrhage, changes in renal function defined by an increase creatinine in the blood≥100 mol/l or/and urine output≤0.5 ml/Kg/h, bronchopulmonary dysplasia (BPD) defined as persistent need for respir-atory support at 36 weeks gestational age, mortality, and composite of death or BPD.
Ethics
This study was approved by the Swiss ethics committee and no conflict of interest was declared by any authors.
Objectives
Our primary objective was to look at the association between hemoglobin level at birth, postnatal days 0–3 and 0–10 in both groups. Secondary objective included the comparison of platelet count at birth, and neonatal morbidities in the two groups
Statistics
To detect a difference of 10 g/l of hemoglobin between the two groups, with α = 0.05, β = 0.2 and standard deviation of 15 g/l, would require a total sample size of 70 per group. All data were entered into a Microsoft Excel spreadsheet and statistical analysis was done using STATA13. Descriptive statistics and skewness/Kurtosis test for normality were performed for neonatal demographics, markers of illness severity, and hematologic parameters (mean±standard deviation for normally distributed data; median (int-erquartile range) for non-normally distributed data). Bivariate analysis, using the independent t-test or Wilcoxon rank-sum test for continuous variables and Chi-square test, or Fischer’s exact test for categorical variables, was used to compare the groups.
A stepwise logistic regression model was developed to determine clinical and biological variables associated with sDAC. We decided a priori to include variables with a p value less than 0.1 in the model. A covariance matrix of coefficients of logistic model analyze was done. A receiver operating curve (ROC) model was created to investigate the relationship between hemoglobin and sDAC. A p-value<0.05 was considered statistically significant with a confident interval of 95%.
Results
Between January 2013 and December 2016, 184 VLBW infants were admitted to the NICU. In total, 38 patients were excluded (died before three days of life (n = 14), not hospitalized at our institution during the first three days of life (n = 12), birth as-phyxia (n = 7), other causes (n = 5) suprasystemic pulmonary hypertension during the first days of life, hemoglobinopathy, wrong GA, and hsPDA after hospitalization). Of 146 VLBW infants who satisfied eligibility criteria, 74 (51%) patients were considered to have sDAC and 72 (49%) received PDA treatment.
Neonatal demographics
There were differences in baseline demographics between groups. Patients in the sDAC group were marginally more mature and heavier at birth, more frequently received a full course of antenatal steroid, and were less frequently exposed to maternal chorioamnionitis (Table 1). Several markers of illness severity were also lower in infants in the sDAC group (Table 2). The median and IQR of the VIS score was not different between the two groups due to a low number of patients under inotrope. However, the univariate analysis shows a significant difference between the groups (Table 2). We therefore replace the IQR by the range to have a better understanding of these restults. Infants who received surfactant were more likely to need later treatment for a hsPDA.
Baseline demographics in both groups (sDAC and hsPDA), in the overall population and the subgroup who never received and received a blood transfusion between days 0–10
Baseline demographics in both groups (sDAC and hsPDA), in the overall population and the subgroup who never received and received a blood transfusion between days 0–10
BW: Birth weight; GA: Gestational Age; HB: Hemoglobin; hsPDA: hemodynamic significant patent ductus arteriosus; IUGR: Intra uterine growth restriction; n: number of patients; sDAC: spontaneous ductus arteriosus closure.
Comparison of illness severity between the two groups (sDAC and hsPDA), in the overall population and subpopulations who received and never received a blood transfusion between days 0–10
CRIB score: score clinical risk index for babies score; FiO2: fraction of inspired oxygen; HB: Hemoglobin; iNO: inhaled nitric oxide; hsPDAT: hemodynamic significant patent ductus arteriosus; n: number of patients; RSS: respiratory severity score; sDAC: spontaneous ductus arteriosus closure; VIS: vasoactive-inotropic score.
Mean hemoglobin was higher between days 0–3 and 0–10 in the sDAC group, but only a non-significant trend was noted at birth (Table 3). Platelet levels was only different between postnatal days 0–10.
Comparison of hematologic parameters between the two groups (sDAC and hsPDA), in the overall population and the subgroup who received and never received a blood transfusion between days 0–10
Comparison of hematologic parameters between the two groups (sDAC and hsPDA), in the overall population and the subgroup who received and never received a blood transfusion between days 0–10
HB: Hemoglobin; hsPDA: hemodynamic significant patent ductus arteriosus; sDAC: spontaneous ductus arteriosus closure; SD: Standard deviation.
Most neonatal short-term outcomes were better in the sDAC group (Table 4). Specifically, infants with sDAC had lower rates of grade III-IV IVH, pulmonary hemorrhage, ROP, BPD, death, composite outcome of death or BPD, abnormal renal function or home’s discharge. The number of patients with NEC/SIP were not significantly different between the groups.
Differences in outcome between the two groups (sDAC and hsPDA), in the overall population and subpopulations who received and never received a blood transfusion between days 0–10
Differences in outcome between the two groups (sDAC and hsPDA), in the overall population and subpopulations who received and never received a blood transfusion between days 0–10
BPD: Bronchopulmonary dysplasia; HB: Hemoglobin; hsPDA: hemodynamic significant patent ductus arteriosus; IVH: Intraventricular hemorrhage; n: number of cases; NEC/SIP: Necrotizing enterocolitis/Spontaneous intestinal perforation; sDAC: spontaneous ductus arteriosus closure; ROP: Retinopathy of prematurity: SD: Standard deviation.
We included six different variables (hemoglobin, chorioamnionitis, antenatal course of steroid, gestational age, CRIB score, and use of surfactant) in the regression model and all of them had a p-value < 0.1 on bivariate analysis.
In accordance with the different studies showing the influence of platelets on the PDA, we have repeated the logistic regression using platelet count but no relationship was noted.
Subgroups analysis according to RBC transfusion
Subgroup analysis of patients who received with those who didn’t receive blood transfusion was performed. Baseline demographics and markers of illness severity of the patients in both subgroups were comparable to the total population (Table 1 and 2). For patients who received a transfusion, the hemoglobin was not different between sDAC and hsPDA. The magnitude of difference, however, was greater between 0–10 days between these groups compared to the total population (Table 3).
For patients who never received a transfusion, the difference in hemoglobin between the sDAC and hsPDA groups was similar to the total population. Patients in the sDAC group however, had a higher hemoglobin at birth, between days 0–3 and 0–10 (Table 3 and Fig. 1). No significant difference in platelet levels at 0–10 days was noted for the patients who never received a transfusion (Table 3).
Evolution of the hemoglobin between days 0–10, in the overall population and subgroup who receive and did not receive a blood transfusion between days 0–10 hsPDA: hemodynamic significant patent ductus arteriosus; sDAC: spontaneous closure of the ductus arteriosus.
Most neonatal short-term outcomes were better in the sDAC group, regardless of group allocation.
Logistic regression analysis, for the subgroup without transfusion demonstrated that hemoglobin level at birth predicted sDAC with an odds ratio of 1.1 (1.0, 1.1 (95% CI)). With regards to the subgroup with transfusion, only the hemoglobin level between day 0–10 predicted sDAC with an odds ratio of 1.07 (1.01, 1.12 (95% CI)) (Table 5).
Logistic regression analysis of hemoglobin at birth, between postnatal days 0 and 3 and days 3 to 10. Results displayed as Odds ratio and 95% CI
D: Days; CRIB score: score clinical risk index for babies score; HB: Hemoglobin.
This study highlights an association between higher level of hemoglobin during the transitional period of life and sDAC in VLBW infants. It confirms the results of small studies [16–18] demonstrating lower mean hemoglobin in patients with a PDA. It suggests that lower hemoglobin may be a contributor to ongoing patency and higher shunt volume rather than a consequence. In fact, even after having adjusted our results according to the gestational age, a surfactant administration, and a chorioamnionitis, the HB remained a significant contributor to a sDAC (Table 5).
Our research showed that patients with a higher hemoglobin during the ten first days of life have the highest rate of sDAC (Table 3). This result is amplified in the subpopulation of patients who never received a blood transfusion and who had the highest plasma hemoglobin from birth to ten days (Table 3). Interestingly, as highlighted in Fig. 1, the level of hemoglobin of sDAC groups was never below 135 g/l, in contrast to the hsPDA group. We hypothesize therefore that a higher and more stable level of hemoglobin during the ten first days of life may promote normal closure of the DA. It is therefore possible that sDAC may be promoted by a higher hemoglobin level and/or the maintenance of a certain hemoglobin level during the transition period. This hypothesis generated by our results is in accordance with Poiseuille’s law and could explain the results of the subgroup with transfusion. This hypothesis should be the subject of further research.
The lack of major changes in hemoglobin in the group without transfusion may relate to illness acuity with less severe IVH and pulmonary hemorrhage, and/or lower rates/volumes of blood sampling. However, the different scores used to observe illness severity (CRIB, RSS, and VIS) are on the lowest side and places the two groups (sDAC and hsPDA) in a low risk group (Table 2). In addition, on logistic regression analysis, the effect of illness severity as adjudicated by CRIB score was not significant (Table 5).
This is one of the first studies investigating the relationship between hemoglobin and the biological contributors of sDAC in VLBW infants. Prior studies have investigated the role of platelet count in facilitating normal ductal closure due to their role in clot formation after vasoconstriction and limitation of transductal flow [9]. It is important to recognize, however, that both hemoglobin and platelets contribute to blood viscosity which also influences transductal flow and vessel wall perfusion. In contrast to previous studies of delayed cord clamping [19] and liberal transfusion [20] policies we demonstrated an association between hemoglobin and sDAC. This difference may be partially explained by the fact that we focused on the transitional period of life and the relationship between HB and sDAC as a primary objective. Moreover, previous trials of delayed cord clamping and blood transfusion are limited by the lack of a standardized definition of hsPDA. Our data is clinically relevant as we looked specifically at VLBW infants who are known to have the lowest rate of sDAC and the highest risk of developing a hsPDA. We specifically looked at the transitional period where the complications of a hsPDA, such as IVH and pulmonary hemorrhage, are greater [5, 22], and adjusted our results according to different con-tributing factors of hsPDA. Lower rates of neonatal morbidities in our subpopulation of patients with sDAC may reflect decreased illness severity but it may also support the hypothesis that targeting higher hemoglobin values in the first week of life in these VLBW infants may aid sDAC and potentially impact transitional hemodynamic morbidities. Our finding of higher rates of hsPDA in patients who received surfactant is important and may be explained by a decrease in pulmonary vascular resistance with secondary increase in shunt volume, impairing normal ductal closure. We took this important factor into consideration and included it into our logistic model and the HB was still significant.
Our results provide a novel perspective on the relationship between hemoglobin and the pathophysiology of the sDAC. The role of hemoglobin is likely to be diverse and may include the following; first, a higher level of hemoglobin could improve oxygen delivery to the medial muscular layer of the ductal wall through diffusion or via the vasa-vasorum leading to vasoconstriction of the DA. Therefore, as the diameter of the vessel decreases, according to Poiseuille’s law, blood flow across the DA falls. Second, a higher hemoglobin may impact the amount of shunt through the DA by modifying two components of Poiseuille’s law: increased blood viscosity and decreased pressure gradient between the systemic and pulmonary vascular beds [19]. Finally, it is also plausible that the composite effect of higher hemoglobin and normal platelet count on blood viscosity, may improve clot formation [23] thus increasing sDAC.
This study has several limitations. First, it is a ret-rospective study which limits the quality of data abst-raction and creates inherent biases related to group allocation. The population of patients at increased risk of PDA physiology are more likely to be immature, sicker, and have a higher rate of co-morbidities which influence PDA closure. Nevertheless, after adj-ustment for these factors on regression analysis a signal remains, which warrant prospective study. Until 2017 the NICU at our institution did not have a standardized approach to managing the hsPDA. Routine echocardiography measurements of shunt volume were not performed which may impact group allocation. We also hypothesized that the hemoglobin improves the sDAC by his impact on blood viscosity, but we were not able to measure other blood components and we did not have the opportunity to know the amount of blood received by the patients. Nevertheless, as hemoglobin is the principle component of blood viscosity in preterm infant, it is unlikely that the other blood components would have significantly altered the results [24, 25]. Finally, blood sampling for hemoglobin was not standardized and the effect of sampling route of sampling might relevant.
Conclusion
Our data suggests an association between higher level of hemoglobin in VLBW infants during the tra-nsitional period of life and sDAC, which may relate to blood viscosity and/or other components of Poise-uille’s law. Future prospective studies should confirm our results and investigate the effect of hemoglobin thresholds or blood transfusions on sDAC, modulation of shunt volume and PDA treatment success.
Author’s contribution
Conceptualization: S.J. and N.S.; Formal analysis: S.J. and R.E.G.; Methodology: S.J., N.S. and P.J.M; Writing the original draft: S.J., N.S., P.J.M, J-F.T.
Ethics
This study was approved by the Swiss ethics committee on August 14, 2017. ID: 2017-01033
Funding statement
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Competing interest
None to declare
Patient consent for publication
Not required by Swiss ethics committee
Patient and public involvement
None
ORCID iD
Sébastien Joye: http://orcid.org/0000-0001-8115-9977.