Characteristics of hypertension in premature infants with and without chronic lung disease: a long-term multi-center study

Blood Pressure Outcomes in NICU-Admitted Infants with Neonatal Hypertension: A Pediatric Nephrology Research Consortium Study

OBJECTIVE

To describe the blood pressure outcomes of infants admitted to the neonatal intensive care unit (NICU) with idiopathic (nonsecondary) hypertension (HTN) who were discharged on antihypertensive therapy.

STUDY DESIGN

Retrospective, multicenter study of 14 centers within the Pediatric Nephrology Research Consortium. We included all infants with a diagnosis of idiopathic HTN discharged from the NICU on antihypertensive treatment. The primary outcome was time to discontinuation of antihypertensive therapy, grouped into (≤6 months, >6 months to 1 year, and >1 year). Comparisons between groups were made with χ2 tests, Fisher's exact tests, and ANOVA.

RESULTS

Data from 118 infants (66% male) were included. Calcium channel blockers were the most prescribed class of antihypertensives (56%) in the cohort. The percentages remaining on antihypertensives after NICU discharge were 60% at 6 months, 26% at 1 year, and 7% at 2 years. Antenatal steroid treatment was associated with decreased likelihood of antihypertensive therapy >1 year after discharge.

CONCLUSIONS

This multicenter study reports that most infants admitted to the NICU diagnosed with idiopathic HTN will discontinue antihypertensive treatment by 2 years after NICU discharge. These data provide important insights into the outcome of neonatal HTN, but should be confirmed prospectively.

Common Clinical Scenarios of Systemic Hypertension in the NICU

Hypertension affects ∼1% to 3% of newborns in the NICU. However, the identification and management of hypertension can be challenging because of the lack of data-driven diagnostic criteria and management guidelines. In this review, we summarize the most recent approaches to diagnosis, evaluation, and treatment of hypertension in neonates and infants. We also identify common clinical conditions in neonates in whom hypertension occurs, such as renal vascular and parenchymal disease, bronchopulmonary dysplasia, and cardiac conditions, and address specific considerations for the evaluation and treatment of hypertension in those conditions. Finally, we discuss the importance of ongoing monitoring and long-term follow-up of infants diagnosed with hypertension.

Neonatal systemic hypertension across the PHIS database: An update

BACKGROUND

The definition of systemic hypertension in the neonatal population remains elusive given the variability of normative blood pressure measurements. Inadequate literature exists about incidence, therapy and long-term management of systemic hypertension in neonates. We aimed to describe the current incidence of neonatal systemic hypertension, differences in demographic and risk factors data.

METHODS

Retrospective cohort of neonates (≤28 days) admitted to a neonatal intensive care unit participating in Pediatric Health Information System (PHIS) between Jan 2010 and December 2020 with an ICD 9/10 code for hypertension. Patients were excluded if they had congenital heart disease lesions that might contribute to systemic hypertension or had incomplete data.

RESULTS

There were a total of 2494 hypertensive patients among the 432,367 NICU patients meeting the study inclusion criteria, with an incidence of 0.6%. Patients with hypertension were significantly more likely to die before discharge compared to patients without HTN (8.4% versus 3.8%, respectively, p < 0.001). Of the 2494, 52.8% received at least one antihypertensive agent, with hydralazine being the most prescribed agent (29.7%).

CONCLUSION

Diagnosis of Systemic hypertension continues to increase in the neonatal population, despite absence of well-defined criteria necessitating targeted medical management. A consensus guideline which addresses this very important condition is beneficial.

Bartter Syndrome: Perspectives of a Pediatric Nephrologist

Bartter syndrome (BS) is one of the most well-known hereditary tubular disorders, characterized by hypokalemic, hypochloremic metabolic alkalosis, and polyuria/polydipsia. This disease usually presents before or during infancy, and adult nephrologists often inherit the patients from pediatric nephrologists since this is a life-long condition. Here, a few case scenarios will be presented to recount how they first got diagnosed and how their clinical courses were during childhood until adulthood, in addition to a brief review of the disease and its treatment.

Normative values of renin and aldosterone in clinically stable preterm neonates

BACKGROUND

There is a paucity of literature on the normative levels of plasma renin concentration (PRC) and serum aldosterone (SA) in premature neonates. This study aims to provide normative data on PRC and SA levels in preterm neonates in the first 2 weeks after birth and explore associations with maternal, perinatal, or postnatal factors.

METHODS

Neonates born at 26- to 34-week gestation were recruited from two neonatal intensive care units in Canada and Australia. The direct renin assay PRC and SA were analyzed on day 1 and days 14-21 after birth to compare across categorical variables and to produce normative values.

RESULTS

A total of 262 subjects were enrolled from the Canadian (29%) and Australian (71%) sites. The mean gestational age was 30 weeks, with a mean birth weight of 1457 g. The normative values of PRC and SA for neonates born between 26 + 0 and 29 + 6 weeks and 30 + 0 and 34 + 0 weeks of gestation were produced for day 1 and day 14-21 after birth. Both PRC and SA increased from day 1 to day 14-21. The more premature neonates reached a higher PRC on days 14-21 after birth but exhibited lower SA levels on day 1 after birth. When comparing gender, birth weight, and maternal risk factor categories, no statistical differences in PRC or SA were found. A small but significant decrease in PRC, but not SA, was noted for neonates with placental pathology.

CONCLUSIONS

This study produced normative values of PRA and SA in clinically stable preterm neonates that can be referenced for use in clinical practice. A higher resolution version of the Graphical abstract is available as Supplementary information.

Phthalates cause a low-renin phenotype commonly found in premature infants with idiopathic neonatal hypertension

Since the 1970s, when the initial reports of neonatal hypertension related to renal artery thromboembolism were published, other secondary causes of neonatal hypertension have been reported. Those infants with no identifiable cause of hypertension were labeled with a variety of terms. Herein, we describe such infants as having idiopathic neonatal hypertension (INH). Most, but not all, of these hypertensive infants were noted to have bronchopulmonary dysplasia (BPD). More recently, reports described common clinical characteristics seen in INH patients, whether or not they had BPD. This phenotype includes low plasma renin activity, presentation near 40 weeks postmenstrual age, and a favorable response to treatment with spironolactone. A small prospective study in INH patents showed evidence of mineralocorticoid receptor activation due to inhibition of 11β-HSD2, the enzyme that converts cortisol to the less potent mineralocorticoid-cortisone. Meanwhile, phthalate metabolites have been shown to inhibit 11β-HSD2 in human microsomes. Premature infants can come in contact with exceptionally large phthalate exposures, especially those infants with BPD. This work describes a common low-renin phenotype, commonly seen in patients categorized as having INH. Further, we review the evidence that hypertension in INH patients with the low-renin phenotype may be mediated by phthalate-associated inhibition of 11β-HSD2. Lastly, we review the implications of these findings regarding identification, treatment, and prevention of the low-renin hypertension phenotype seen in premature infants categorized as having INH.

Neonatal hypertension: concerns within and beyond the neonatal intensive care unit

Neonatal hypertension occurs in 1%-2% of neonates in the neonatal intensive care unit (NICU) although may be underdiagnosed. Blood pressure values in premature neonates change rapidly in the first days and weeks of life which may make it more difficult to recognize abnormal blood pressure values. In addition, the proper blood pressure measurement technique must be used to ensure the accuracy of the measured values as most blood pressure devices are not manufactured specifically for this population. In premature neonates, the cause of the hypertension is most commonly related to prematurity-associated complications or management while in term neonates is more likely to be due to an underlying condition. Both oral and intravenous antihypertensive medications can be used in neonates to treat high blood pressure although none are approved for use in this population by regulatory agencies. The natural history of most neonatal hypertension is that it resolves over the first year or two of life. Of concern are the various neonatal risk factors for later cardiovascular and kidney disease that are present in most NICU graduates. Prematurity increases the risk of adulthood hypertension while intrauterine growth restriction may even lead to hypertension during childhood. From neonates through to adulthood NICU graduates, this review will cover each of these topics in more detail and highlight the aspects of blood pressure management that are established while also highlighting where knowledge gaps exist.

Systemic Hypertension in Infants with Bronchopulmonary Dysplasia

PURPOSE OF REVIEW

Neonatal hypertension is increasingly recognized as improvements in neonatal intensive care have led to increased survival of premature infants. Among infants with bronchopulmonary dysplasia (BPD), the rates of hypertension are much higher than the general neonatal population. However, the etiology and pathophysiology of this increased risk of hypertension in neonates with lung disease remain unclear.

RECENT FINDINGS

Among infants with bronchopulmonary dysplasia, the rates of hypertension are much higher than the general neonatal population. New studies suggest outcomes in neonates with BPD with hypertension are usually good, with resolution of hypertension in most infants with lung disease. Several potential mechanisms of hypertension in this patient population have been recently proposed. This review focuses on the recent epidemiologic data on prevalence of hypertension in neonates with bronchopulmonary dysplasia, reviews the typical clinical course, and discusses available strategies for management of infants with bronchopulmonary dysplasia that develop hypertension.

Neonatal Hypertension

Neonatal hypertension is uncommon but is becoming increasingly recognized. Normative blood pressure data are limited, as is research regarding the risks, treatment, and long-term outcomes. Therefore, there are no clinical practice guidelines and management is based on clinical judgment and expert opinion. Recognition of neonatal hypertension requires proper blood pressure measurement technique. When hypertension is present there should be a thorough clinical, laboratory, and imaging evaluation to promptly diagnose causes needing medical or surgical management. This review provides a practical overview for the practicing clinician regarding the identification, evaluation, and management of neonatal hypertension.

Postnatal glucocorticoid use impacts renal function in VLBW neonates

BACKGROUND

Preterm neonates often require glucocorticoids to manage refractory hypotension, prevent, and treat bronchopulmonary dysplasia. We have investigated the effect of cumulative dose and duration of glucocorticoids on blood pressure and renal function in VLBW infants.

METHODS

In this retrospective cohort study, medical records of infants (GA ≤ 35 weeks) born January 2015 to December 2019 were reviewed to extract demographic and clinical characteristics, dose and duration of steroids, blood pressure (BP), and creatinine at the time of discharge from the neonatal intensive care unit.

RESULTS

Two hundred and eighty-three neonates with average GA (28 ± 3 weeks) and birthweight (1060±381 g). Twenty-eight percent (33/116) of infants who received postnatal steroids developed hypertension versus 16% (27/167) of controls (OR = 2.0, p = 0.011). There was a correlation between the cumulative dosage of postnatal steroids and systolic BP (R² = 0.06, p < 0.001). With increasing steroid dose and total steroid days, there was a significant increase in creatinine clearance at the time of discharge (R² = 0.13, p < 0.001; R² = 0.13, p < 0.001, respectively).

CONCLUSIONS

Cumulative dose of postnatal steroids and duration of use is associated with increased systolic BP in premature infants. Postnatal steroids should be used prudently to prevent long-term cardiovascular and renal morbidity.

IMPACT

Preterm neonates are exposed to a high dose of glucocorticoids during their neonatal intensive care stay. The dose and duration of use of postnatal glucocorticoids was associated with significant increase in blood pressure at the time of discharge in preterm neonates. Postnatal glucocorticoid use is associated with improved creatinine clearance likely due to a state of hyperfiltration and may lead to chronic kidney disease later in life. Postnatal glucocorticoids should be used prudently in this highly vulnerable population.

Elimination of Intravenous Di-2-Ethylhexyl Phthalate Exposure Abrogates Most Neonatal Hypertension in Premature Infants with Bronchopulmonary Dysplasia

(1) Background: The incidence of hypertension in very low birthweight (VLBW) infants in a single neonatal intensive care unit (NICU) dropped markedly during a 2-year period when the IV fluid (IVF) in both the antenatal unit and the NICU temporarily changed to a di-2-ethylhexyl phthalate (DEHP)-free formulation. The objective of the current report is to document this observation and demonstrate the changes in incidence of hypertension were not associated with the variation in risk factors for hypertension; (2) Methods: The charts of all VLBW infants born in a single NICU during a 7-year span were reviewed. This time includes 32 months of baseline, 20 months of DEHP-free IVF, 20 months of IVF DEHP re-exposure, and two 4-month washout intervals. The group of interest was limited to VLBW infants with bronchopulmonary dysplasia (BPD). Chi-square analysis was used to compare incidence of hypertension among periods. Vermont Oxford NICU Registry data were examined for variation in maternal and neonatal risk factors for hypertension; Results: Incidence of hypertension in VLBW infants with BPD decreased from 7.7% (baseline) to 1.4% when IVF was DEHP-free, rising back to 10.1% when DEHP-containing IVF returned to use. Risk factors for neonatal hypertension were stable across the 3 study periods in the NICU’s group of VLBW infants; (3) Conclusions: Serendipitous removal of IVF containing DEHP resulted in near elimination of hypertension in one NICU—an effect entirely reversed after the same brand of DEHP-containing IVF returned to clinical use. These results suggest that DEHP exposure from IVF plays a major role in neonatal hypertension.

The hypertensive neonate

Hypertension in neonates is increasingly recognized because of improvements in neonatal intensive care that have led to improved survival of premature infants. Although normative data on neonatal blood pressure remain limited, several factors appear to be important in determining blood pressure levels in neonates, especially gestational age, birth weight and maternal factors. Incidence is around 1% in most studies and identification depends on careful blood pressure measurement. Common causes of neonatal hypertension include umbilical catheter associated thrombosis, renal parenchymal disease, and chronic lung disease, and can usually be identified with careful diagnostic evaluation. Given limited data on long-term outcomes and use of antihypertensive medications in these infants, clinical expertise may need to be relied upon to decide the best approach to treatment. This review will discuss these concepts and identify evidence gaps that should be addressed.

An Unusual Cause of Neonatal Heart Failure

Hypertension is an important and under-recognized cause of acquired cardiomyopathy in newborns. Half the etiologies of neonatal hypertension are undetermined. We present a rare case of severe neonatal hypertension with ventricular dysfunction secondary to substance exposure during pregnancy. This case report emphasizes the importance of a well-focused prenatal history on maternal medications and substance use.

Neonatal hypertension caused by left-to-right shunt flow through a patent ductus arteriosus in a premature infant

Objectives

Though it is rare and challenging to study, neonatal hypertension (HTN) has been explored and studied by many pediatricians. There were some causes reported in preterm infants such as renal diseases and bronchopulmonary dysplasia.

Case presentation

We report a premature female infant who was born at a gestational age of 25 + 6 weeks and developed systemic hypertension on the day of a gestation age of 30 + 3 weeks. This case had a rare cause which involved high-normal serum aldosterone level that could possibly indicate hyperaldosteronism and over-stimulation of renin–angiotensin–aldosterone system (RAAS). We believe elevation of serum aldosterone was caused by a left-to-right shunt flow through a patent ductus arteriosus. Hypertension due to a patent ductus arteriosus sounds like a paradox. However, in our case, the shunt flow was shown to be a possible cause of the systemic hypertension. Surgical closure of the shunt was done and the hypertension resolved. We evaluated serum aldosterone levels and plasma renin activities both, before and after the closure to look for a possible cause.

Conclusions

Neonatologist often treats systemic hypertensive infants considering possible causes in order to prevent hypertensive crisis. Our case shows that possibility of hyperaldosteronism and (RAAS) over-stimulation should be considered as causes in case of severe systemic hypertension in preterm infants with large left-to-right shunt flows.

The changing spectrum of hypertension in premature infants

OBJECTIVE

The objective is to document changes in the etiologic spectrum of hypertension in premature infants.

STUDY DESIGN

We reviewed all cases of systemic hypertension (HTN) in premature infants at two centers over 8 years. Infants were sorted into categorical groups as described in 2012 by Flynn. Analyses included frequency of diagnosis, timecourse of HTN, and diagnostics. Phthalate exposure via intravenous fluid and respiratory equipment was compared among groups and centers.

RESULTS

One hundred and twenty-nine infants having 130 episodes of HTN met the inclusion criteria. Sixty-five percent of cases were classified as pulmonary and 16% as miscellaneous. Plasma renin activity (PRA) was undetectable or <11 ng/mL/h in almost all hypertensive infants. Cases categorized as Pulmonary, medications/intoxications, and miscellaneous presented near 40 weeks postmenstrual age, with low PRA and large phthalate exposures.

CONCLUSIONS

High PRA HTN has been replaced by low PRA in most cases, and may be due to phthalate exposure.

Hemodynamic management in chronically ventilated infants

Positive pressure ventilation can significantly alter hemodynamics. The reduction in systemic venous return and increase in right ventricular afterload in response to an inappropriately high mean airway pressure can decrease pulmonary blood flow and compromise systemic perfusion as a result. In addition to ventilator parameters, the degree of hemodynamic effects depends on the baseline cardiac function and lung compliance. Furthermore, the chronically ventilated infants often have a multitude of comorbidities which may also impact hemodynamics. These include pulmonary and systemic hypertension which can lead to myocardial dysfunction as a result of the increase in the right and left ventricular afterload, respectively. In this section, we aim to outline the hemodynamic changes associated with chronic lung disease and mechanical ventilation and discuss management options.

Pulmonary Function and Systolic Blood Pressure in Very Low Birth Weight Infants at 34 - 36 Weeks of Corrected Age

Purpose

Preterm infants are at increased risk of systemic hypertension compared to term infants. Bronchopulmonary dysplasia (BPD) has been shown to be associated with hypertension in preterm infants albeit with no causation reported. BPD is characterized by abnormal pulmonary function tests (PFTs), specifically elevated passive respiratory resistance (Rrs), decreased passive respiratory compliance (Crs) and decreased functional residual capacity (FRC). There have been no studies comparing PFTs in very low birth weight (VLBW) infants with and without hypertension. We hypothesized that stable VLBW infants with hypertension will have altered PFTs.

Patients and Methods

Retrospective cohort study of infants < 1500 grams at birth (VLBW) who had PFTs performed near 34-36 weeks of corrected gestational age (CGA). We excluded infants with congenital anomalies, known hypertensive disorders or those at risk of medication-induced hypertension. Data obtained included PFT parameters (Rrs, Crs, FRC) and mean systolic blood pressure (SBP).

Results

59 VLBW infants were identified for analysis, 14 with and 45 without hypertension. Hypertensive and normotensive patients were similar in terms of mean gestational age (26.6 vs 27.4 weeks), mean CGA at PFTs (36.1 vs 34.6 weeks) and proportion of BPD (36% vs 36%). The Rrs was significantly higher in hypertensive versus normotensive patients [median Rrs of 0.080 (0.069, 0.090) versus 0.066 (0.054, 0.083) cmH₂O/mL/sec; p = 0.04]. There was no difference in systolic blood pressure in the infants with and without BPD.

Conclusion

In this cohort of contemporary VLBW infants, those with hypertension had increased Rrs. This finding warrants a prospective study with a larger sample size and long-term follow-up.

Neonatal hypertension: an educational review

Hypertension is encountered in up to 3% of neonates and occurs more frequently in neonates requiring hospitalization in the neonatal intensive care unit (NICU) than in neonates in newborn nurseries or outpatient clinics. Former NICU neonates are at higher risk of hypertension secondary to invasive procedures and disease-related comorbidities. Accurate measurement of blood pressure (BP) remains challenging, but new standardized methods result in less measurement error. Multiple factors contribute to the rapidly changing BP of a neonate: gestational age, postmenstrual age (PMA), birth weight, and maternal factors are the most significant contributors. Given the natural evolution of BP as neonates mature, a percentile cutoff of 95% for PMA has been the most common definition used; however, this is not based on outcome data. Common causes of neonatal hypertension are congenital and acquired renal disease, history of umbilical arterial catheter placement, and bronchopulmonary dysplasia. The treatment of neonatal hypertension has mostly been off-label, but as evidence accumulates, the safety of medical management has increased. The prognosis of neonatal hypertension remains largely unknown and thankfully most often resolves unless secondary to renovascular disease, but further research is needed. This review discusses important factors related to neonatal hypertension including BP measurement, determinants of BP, and management of neonatal hypertension.

Neonatal hypertension: cases, causes, and clinical approach

Neonatal hypertension is increasingly recognized as dramatic improvements in neonatal intensive care, advancements in our understanding of neonatal physiology, and implementation of new therapies have led to improved survival of premature infants. A variety of factors appear to be important in determining blood pressure in neonates, including gestational age, birth weight, and postmenstrual age. Normative data on neonatal blood pressure values remain limited. The cause of hypertension in an affected neonate is often identified with careful diagnostic evaluation, with the most common causes being umbilical catheter-associated thrombosis, renal parenchymal disease, and chronic lung disease. Clinical expertise may need to be relied upon to decide the best approach to treatment in such patients, as data on the use of antihypertensive medications in this age group are extremely limited. Available data suggest that long-term outcomes are usually good, with resolution of hypertension in most infants. In this review, we will take a case-based approach to illustrate these concepts and to point out important evidence gaps that need to be addressed so that management of neonatal hypertension may be improved.

Phthalate-associated hypertension in premature infants: a prospective mechanistic cohort study

BACKGROUND

Phthalates are associated with increased blood pressure in children. Large exposures to di-(2-ethylhexyl) phthalate (DEHP) among premature infants have been a cause for concern.

METHODS

We conducted a prospective observational cohort study to determine if DEHP exposures are related to systolic blood pressure (SBP) in premature infants, and if this exposure is associated with activation of the mineralocorticoid receptor (MR). Infants were monitored longitudinally for 8 months from birth. Those who developed idiopathic hypertension were compared with normotensive infants for DEHP exposures. Appearance of urinary metabolites after exposure was documented. Linear regression evaluated the relationship between DEHP exposures and SBP index and whether urinary cortisol/cortisone ratio (a surrogate marker for 11β-HSD2 activity) mediated those relationships. Urinary exosomes were quantified for sodium transporter/channel expression and interrogated against SBP index.

RESULTS

Eighteen patients met the study criteria, nine developed transient idiopathic hypertension at a postmenstrual age of 40.6 ± 3.4 weeks. The presence of urinary DEHP metabolites was associated with prior IV and respiratory tubing DEHP exposures (p < 0.05). Both IV and respiratory DEHP exposures were greater in hypertensive infants (p < 0.05). SBP index was related to DEHP exposure from IV fluid (p = 0.018), but not respiratory DEHP. Urinary cortisol/cortisone ratio was related to IV DEHP and SBP index (p < 0.05). Sodium transporter/channel expression was also related to SBP index (p < 0.05).

CONCLUSIONS

Increased blood pressure and hypertension in premature infants are associated with postnatal DEHP exposure. The mechanism of action appears to be activation of the MR through inhibition of 11β-HSD2.