Atypical chronic lung disease in preterm infants

Bronchopulmonary dysplasia

In the absence of effective interventions to prevent preterm births, improved survival of infants who are born at the biological limits of viability has relied on advances in perinatal care over the past 50 years. Except for extremely preterm infants with suboptimal perinatal care or major antenatal events that cause severe respiratory failure at birth, most extremely preterm infants now survive, but they often develop chronic lung dysfunction termed bronchopulmonary dysplasia (BPD; also known as chronic lung disease). Despite major efforts to minimize injurious but often life-saving postnatal interventions (such as oxygen, mechanical ventilation and corticosteroids), BPD remains the most frequent complication of extreme preterm birth. BPD is now recognized as the result of an aberrant reparative response to both antenatal injury and repetitive postnatal injury to the developing lungs. Consequently, lung development is markedly impaired, which leads to persistent airway and pulmonary vascular disease that can affect adult lung function. Greater insights into the pathobiology of BPD will provide a better understanding of disease mechanisms and lung repair and regeneration, which will enable the discovery of novel therapeutic targets. In parallel, clinical and translational studies that improve the classification of disease phenotypes and enable early identification of at-risk preterm infants should improve trial design and individualized care to enhance outcomes in preterm infants.

Predictors of bronchopulmonary dysplasia

Although significant advances in respiratory care have been made in neonatal medicine, bronchopulmonary dysplasia (BPD) remains the most common serious pulmonary morbidity in premature infants. The development of BPD is the result of the complex interactions between multiple perinatal and postnatal factors. Early identification of infants at the most risk of developing BPD through the use of estimators and models may allow a targeted approach at reducing BPD in the future.

Spectrum of chronic lung disease in a population of newborns with extremely low gestational age

AIMS

To determine how the ability to oxygenate the blood develops after birth in infants of extremely low gestational age (ELGANs) and to find risk factors for chronic lung disease.

METHOD

A prospective, population-based, cohort study was undertaken in one tertiary-care centre. The alveolar-arterial oxygen pressure difference (AaDO(2)) was monitored.

RESULTS

Of 41 survivors, 21 had a period of normal lung function in the first week of life, after which oxygenation deteriorated. Low gestational age and low Apgar score at 5 min were found to be strong and independent predictors of AaDO(2) in the first month of life. Mechanical ventilation did not appear as a risk factor. Lung function at 36 weeks of gestation and duration of oxygen treatment could be better predicted by the severity of lung disease in the first month than by gestational age at birth.

CONCLUSIONS

Difficulty in oxygenation was a general observation in ELGANs and not only a particular subset. Gestational age and Apgar score were independent predictors of the degree of difficulty over the first month of life. As oxygenation failure often developed after a few days, the process may be possible to treat or prevent once the pathogenesis is known.

Correlation of urinary inflammatory and oxidative stress markers in very low birth weight infants with subsequent development of bronchopulmonary dysplasia

Currently, bronchopulmonary dysplasia (BPD) occurs almost exclusively in pre-term infants. In addition to prematurity, other factors like oxygen toxicity and inflammation can contribute to the pathogenesis. This study aimed to compare urinary inflammatory and oxidative stress markers between the no/mild BPD group and moderate/severe BPD group and between BPD cases with significant early lung disease like respiratory distress syndrome (RDS) ('classic' BPD) and with minimal early lung disease ('atypical' BPD). A total of 60 patients who were a gestational age < 30 weeks or a birth weight < 1250 g were included. Urine samples were obtained on the 1(st), 3(rd) and 7(th) day of life and measured the levels of leukotriene E(4) (LTE(4)) and 8-hydroxydeoxyguanosine (8-OHdG). The 8-OHdG values on the 3(rd) day showed significant correlation to duration of mechanical ventilation. The 8-OHdG levels on the 7(th) day were the independent risk factor for developing moderate/severe BPD. In 'classic' BPD, the 8-OHdG values on the 3(rd) day were higher than those of 'atypical' BPD. In 'atypical' BPD, the LTE(4) values on the 7(th) day were higher than the values in 'classic' BPD. These results suggest that oxidative DNA damage could be the crucial mechanism in the pathogenesis of current BPD and the ongoing inflammatory process could be an important mechanism in 'atypical' BPD.

The importance of intra-amniotic inflammation in the subsequent development of atypical chronic lung disease

OBJECTIVE

To examine whether the intra-amniotic inflammation is a risk factor for the development of atypical chronic lung disease (CLD).

STUDY DESIGN

A retrospective cohort study was undertaken in 72 patients who delivered preterm neonates (gestational age: 24-32 weeks) within 5 days of amniocentesis and whose neonates subsequently developed CLD. Atypical CLD was defined as CLD without respiratory distress syndrome (RDS). Intra-amniotic inflammation was defined as an elevated amniotic fluid (AF) concentration of matrix metalloproteinase-8 (MMP-8) (>23 ng/ml).

RESULTS

(1) Atypical CLD was identified in 54.2% (39/72) of cases with CLD; (2) there were no significant differences in the median gestational age at birth and the rate of antenatal corticosteroid use between infants with atypical CLD and CLD with RDS; (3) preterm newborns with atypical CLD had a significantly higher median AF MMP-8 concentration (median 373.1 ng/ml vs. 8.6 ng/ml, p = 0.003) and median AF white blood cell count (median 450.0/mm(3)vs. 5.5/mm(3), p = 0.009), and a higher rate of intra-amniotic inflammation (74.4%vs. 45.5%, p = 0.012) than those with CLD with RDS.

CONCLUSION

Intra-amniotic inflammation confers a greater risk for atypical CLD than for typical CLD with initial RDS. This novel observation strengthens the importance of prenatal inflammation as a mechanism of lung injury.

Fetal growth restriction and chronic lung disease among infants born before the 28th week of gestation

OBJECTIVE

Improvement in survival of extremely premature infants over the past several decades has resulted in an increase in the number of infants with chronic lung disease (CLD). Historical neonatal exposures associated with CLD now less frequently precede the disease. There is now increasing interest in exposures and events before delivery that predict CLD. The objective of this study was to identify current prenatal predictors of CLD.

METHODS

We collected data about prenatal, placental, and neonatal characteristics of 1241 newborns who were delivered before completion of the 28th week of gestation. Associations between prenatal factors, microbiologic and histologic characteristics of the placenta, and selected neonatal characteristics and CLD risk were first evaluated in univariate analyses. Subsequent multivariate analyses investigated the contribution of prenatal factors, particularly fetal growth restriction (FGR), to CLD risk.

RESULTS

Among the prenatal factors, birth weight z scores, used as a marker of FGR, provided the most information about CLD risk. Indicators of placental inflammation and infection were not associated with increased risk of CLD. Within nearly all strata of prenatal, placental, and neonatal variables, growth-restricted infants were at increased CLD risk, compared with infants who were not growth-restricted. FGR was the only maternal or prenatal characteristic that was highly predictive of CLD after adjustment for other risk factors.

CONCLUSIONS

FGR is independently associated with the risk of CLD. Thus, factors that control fetal somatic growth may have a significant impact on vulnerability to lung injury and in this way increase CLD risk.

Patterns of respiratory disease during the first 2 postnatal weeks in extremely premature infants

BACKGROUND

Pulmonary disease among infants of <28 weeks' gestation (extremely low gestational age newborns) often has the following pattern: the infant starts out with little need for supplemental oxygen and ventilatory support in the first postnatal week but then has pulmonary deterioration in the second postnatal week, with an increased need for supplemental oxygen and respiratory support. We evaluated the antecedents and correlates of patterns of early lung disease, with particular emphasis on pulmonary deterioration, in a large cohort study (the Extremely Low Gestational Age Newborn [ELGAN] study).

PATIENTS AND METHODS

We examined data collected prospectively on 1340 infants born between 2002 and 2004 at 23 to 27 completed weeks of gestation and who survived to 14 days. Pulmonary deterioration was defined as receipt of fraction of inspired oxygen < 0.23 on any day between days 3 and 7 and receipt of fraction of inspired oxygen > or = 0.25 on day 14.

RESULTS

One fifth (20%) of the infants had consistently low fraction of inspired oxygen, approximately two fifths (38%) had pulmonary deterioration, and the remaining approximately two fifths (43%) had consistently high fraction of inspired oxygen (early and persistent lung dysfunction). Compared with infants who had consistently low fraction of inspired oxygen, infants who experienced pulmonary deterioration had lower gestational ages and lower birth weights, had higher scores for neonatal acute physiology, and received more intensive modes of respiratory support. Gender, multifetal pregnancy, cesarean delivery, antenatal steroids, chorioamnionitis, and funisitis were not associated with pulmonary deterioration. The incidence of chronic lung disease, defined as oxygen therapy at 36 weeks' postmenstrual age, was 17% in the consistently low fraction of inspired oxygen group, 51% in the pulmonary deterioration group, and 67% in the early and persistent pulmonary dysfunction group. The incidence of death in these 3 groups before 36 weeks' postmenstrual age was 1%, 3%, and 5%, respectively.

CONCLUSIONS

Nearly 40% of extremely low gestational age newborns experience pulmonary deterioration in the first 2 postnatal weeks, and half of these infants develop chronic lung disease. Indicators of developmental immaturity and illness severity were associated with both pulmonary deterioration and chronic lung disease. Studying the antecedents of pulmonary deterioration might provide new insights about chronic lung disease pathogenesis.

Cord blood KL-6, a specific lung injury marker, correlates with the subsequent development and severity of atypical bronchopulmonary dysplasia

BACKGROUND

A considerable number of preterm infants may have been exposed to inflammation in utero and may be born with an inflamed lung.

OBJECTIVES

To determine the impact of antenatal lung injury and inflammatory response on the pathogenesis of bronchopulmonary dysplasia (BPD) according to its clinical pattern, using KL-6 (as a lung injury marker) and C-reactive protein (CRP) (as a marker of inflammatory response).

METHODS

In this case-control study, a total of 74 infants (<32 weeks of gestation) including BPD with minimal early lung disease ('atypical'; 21 infants), BPD with significant early lung disease ('classic'; 29 infants) and the non-BPD (24 infants) groups underwent KL-6 and CRP in cord blood determinations.

RESULTS

The cord plasma KL-6 levels were significantly higher in the atypical and the total BPD groups than in the non-BPD group (median = 60.9 vs. 34.5 U/ml, p = 0.031; 43.5 vs. 34.5 U/ml, p = 0.02). However, the cord plasma CRP levels were not significantly different among the study groups. The cord plasma KL-6 levels in patients with atypical BPD were significantly higher in infants with moderate or severe BPD than in infants with mild BPD (median = 88.3 vs. 41.5 U/ml, p = 0.041) and were found to be significantly correlated with the duration of oxygen therapy (r = 0.502, p = 0.024).

CONCLUSIONS

The present study shows that cord plasma KL-6, a specific lung injury marker, is increased and objectively reflects disease severity in atypical BPD.