Exhaled nitric oxide and tracheal endothelin-1 in preterm infants with and without RDS

Tidal breath eNO measurements in a cohort of unsedated hospitalized neonates-A method validation

AIM

Exhaled Nitric oxide (eNO) is an inflammatory marker. In 2002 Hall et al. [J Appl Physiol. 92:59-66] established an infant eNO measurement method, fulfilling four criteria of feasibility: simple, non-invasive, without impact on the natural breathing pattern, and accounting for flow by NO output (V'NO). Although tidal breathing is accepted as an eNO measurement method in uncooperative patients, it is seldom used outside research labs. The variability and lack of validated methods have restrained from exploring the area in preterm and term neonates the last years. This study aimed to validate clinically feasible longitudinal online tidal eNO and V'NO in a real-life birth cohort of un-sedated, hospitalized preterm, and term neonates.

METHOD

We included 149 newborns, GA 28-42 weeks. Each scheduled for six repeated, non-invasive, on-line eNO measurements with Ecomedics CLD 88sp and NO-free air. We used three 60-second-eNO measurements. The method was adapted to fit preterm and term neonates with unstable respiration, without excluding sighs and surrounding breaths.

RESULT

Protocol measurements with a maximum mutual difference of 1 ppb succeeded in 85-99%, increasing with postnatal age. We performed mixed model analyses in three hierarchical measurement levels. Despite the irregular breathing of newborns, the predictions of individual eNO levels in the average infant was a 0.05 SD. Exhaled NO was flow-dependent (P = 0.028); V'NO but not eNO was associated with preterm birth (P < 0.001) and >24 h CPAP treatment (P = 0.0316).

CONCLUSION

We validated clinically, non-invasive, online eNO measurements in neonates. The method was well tolerated and exhibited low subject-specific-prediction-variance and high success rates.

Exhaled nitric oxide in neonates with or without hypoxemic respiratory failure

BACKGROUND

Exhaled nitric oxide (eNO) is one of the airway condensate derived markers, reflecting mainly airway inflammation in asthma and other lung diseases. The changes of eNO levels as pathophysiology of neonatal hypoxemic respiratory failure (HRF) in early postnatal life have not been thoroughly studied. The present study was to establish a method for measuring eNO concentrations in neonates with or without HRF.

METHODS

Twenty-two newborn infants with HRF and 26 non-NRF controls were included within the first 24 hours of postnatal life. Their eNO levels were detected with a rapid-response chemiluminescence analyzer daily during the first week of their postnatal life, and lung mechanics and gas exchange efficiency were monitored at the same time, such as pulse oxygen saturation (SpO2), inspired fraction of oxygen (FiO2) and other parameters.

RESULTS

During the first two days of postnatal life, eNO values of HRF neonates were significantly higher than those of the control neonates (day 1, 7.9±3.2 vs. 5.8±1.8 parts per billion [ppb], P<0.05; day 2, 8.8±3.2 vs. 6.0±2.4 ppb, P<0.05), but there were no significant differences in the following days. With SpO2/FiO2 increasing, difference of eNO values between the HRF and non-HRF neonates became narrowed, but there was still a two-fold difference of eNO/[SpO2/(FiO2×100)] on days 5-7.

CONCLUSION

We established a method for measuring eNO and found difference in neonates with or without HRF, which diminished with prolonged postnatal days, reflecting pathophysiological characteristics of HRF.

Endothelial NOS gene Glu298Asp polymorphism in preterm neonates with respiratory distress syndrome

RATIONALE

Respiratory Distress Syndrome (RDS) due to prematurity is one of the most important causes of morbidity and mortality in Neonatal Intensive Care Units. According to few studies in recent years, endothelial nitric oxide synthase (eNOS) gene polymorphisms are found to be partially responsible for liability to RDS. The purpose of this study was to determine the association between eNOS gene polymorphism and RDS in preterm neonates.

PATIENTS AND METHODS

The patient group consisted of 152 premature neonates born before 37 weeks of gestation and diagnosed as RDS. The control group consisted of 125 premature neonates born before 37 weeks of gestation, but was not diagnosed as RDS. Genomic DNA from patients and controls was analyzed by polymerase chain reaction.

RESULTS

It was found that Glu/Glu, Glu/Asp, and Asp/Asp genotype frequencies of the eNOS gene polymorphism were 35.2%, 59.2%, and 5.6% of the control group, and 32.9%, 65.1%, and 2.0% of the patient group, respectively (P > 0.05). However, significant increases in Glu/Glu genotype and Glu allele frequencies were noted in the RDS groups when the preterm neonates were divided into two groups (24-30 weeks and 31-36 weeks) by gestational age. Additionally, Glu/Asp genotype and Asp allele were markedly less frequent among the RDS groups (P < 0.05). Asp allele frequency in boys and Glu allele frequency in girls were significantly high in RDS group (P < 0.05).

CONCLUSIONS

These data suggest that there were significant gestational age-related differences between RDS and control groups in terms of Glu298Asp polymorphism. Therefore, RDS seems to develop with alterations in eNOS Glu298Asp genotype frequencies in the Turkish population.

Impact of chorioamnionitis on exhaled nitric oxide and endotracheal aspirate levels of nitrites-nitrates and interleukin-8 in mechanically ventilated preterm neonates

OBJECTIVES

To assess the influence of maternal chorioamnionitis on early exhaled nitric oxide (NO) and levels of nitrites-nitrates and interleukin (IL)-8 in endotracheal aspirate fluid in mechanically ventilated preterm neonates.

STUDY DESIGN

Cross-sectional study. PATIENT-SUBJECT SELECTION: Between September 2007 and August 2009, 54 mechanically ventilated preterm neonates were included. Patients were divided into two groups according to the presence or absence of maternal chorioamnionitis, and those without chorioamnionitis (controls) were further stratified into two subgroups by birth weight < or ≥ 2,000 g.

METHODOLOGY

The ventilator used was a Babylog 8000. The NO level assessed was the plateau value given by the software of the Sievers NOA apparatus. Collection of endotracheal aspirate fluid samples was performed coinciding with routine aspirations and using the dry technique.

RESULTS

The two groups of control neonates showed statistically significant differences in exhaled NO expressed as nl/min and normalized exhaled NO expressed as either nl/min or nl/min/kg, so they are not homogeneous and cannot be used in clinical practice. Serum C-reactive protein and endotracheal aspirate levels of nitrites-nitrates were significantly higher in the chorioamnionitis group than in controls (3.6 vs. 1.07 µmol/L; P = 0.035). Nitrites-nitrates levels were positively correlated with exhaled NO in ppb (ρ = 0.367; P = 0.006). Minute exhaled endogenous NO was significantly higher in the chorioamnionitis group (0.48 vs. 0.27 nl/min/kg; P = 0.021).

CONCLUSIONS

In mechanically ventilated preterm infants weighing <2,000 g, maternal chorioamnionitis was associated with an increase of early exhaled NO (nl/min/kg) and serum levels of C-reactive protein and levels of nitrites-nitrates in endotracheal aspirate fluid.

Attempt to normalize simulated exhaled nitric oxide according to ventilatory settings

BACKGROUND

Simulated exhaled nitric oxide (eNO) depends on ventilatory settings used in different experimental conditions.

OBJECTIVES

To normalize the simulated minute exhaled nitric oxide according to different ventilatory settings.

WORKING HYPOTHESIS

Different ventilatory settings influence the concentrations of exhaled nitric oxide and these results can be normalized. METHODOLOGY AND STUDY DESIGN: We used a rubber lung model (50 ml) with an orifice through which a 3 mm endotracheal tube was introduced. The NO, which simulated that of endogenous production, was delivered through the base of the lung using a unidirectional rotameter and obtaining a concentration of around 25 ppb. The sample of gas was recorded through a 6 F arterial catheter introduced into the endotracheal tube to its tip. The ventilator used was a Babylog 8000. Air delivered was compressed and filtered and had an NO content of under 0.3 ppb. The NO level assessed was the plateau value given by the software of the Sievers NOA apparatus. Each experiment involved sampling during 1 min, three times. Normalization was done using a multiple cubic regression formula.

RESULTS

An increase in respiratory frequency or in peak of inspiratory pressure were accompanied by a decrease in eNO (ppb). Minute volume was adjusted for the percentage of leakage given by the ventilator. Normalization was obtained analyzing 518 respirations with different ventilatory settings. The coefficient of variation fell from 15.5% to 0.27%. Validation of the normalization formula was performed in other three groups (320, 372, and 372 respirations) with different simulated NO concentrations (25, 16, and 50 ppb), resulting in reduction of the coefficient of variation from 42.7% to 9.3%, from 42.3% to 10.6% and from 45.2% to 9.6%, respectively.

CONCLUSIONS

Normalization of simulated minute eNO according to ventilatory settings is possible using the equipment and experimental set-up reported. Extrapolation to patients is not possible without constraints.

Inhaled nitric oxide for the prevention of bronchopulmonary dysplasia

This review provides the readers with background information on the state of the art and science of inhaled nitric oxide (iNO) as therapy for prevention or amelioration of bronchopulmonary dysplasia (BPD) in preterm infants. The goal is to review and critique relevant published information. A total of six clinical trials, all placebo-controlled, four out of six blinded, four out of six multi-centered with a predetermined outcome of reduction in death or BPD, have been reported in full text. These definitive studies have included a total of > 2100 preterm, mostly very preterm, infants. Their designs were informed by results of earlier non-definitive studies which cumulatively enrolled > 350 preterm patients. This very substantial experience provides a firm framework for asserting that iNO will be useful in this population of patients. The use of iNO can reduce the occurrence of BPD and possibly the severity of the disorder. Optimal time of initiation, dosing (both initial dose, duration of treatment and possibly the route of administration) and most importantly, optimal patient subset selection, are not determined. Any clear adverse neurological finding in iNO-treated infants will of course limit or halt the use of this promising therapy.

Lung function and exhaled nitric oxide levels in infants developing chronic lung disease

Chronic lung disease (CLD) is a common outcome of neonatal intensive care. To determine whether the results of serial exhaled nitric oxide (eNO) measurements during the perinatal period differed between infants who did and did not develop CLD. In addition, we wished to assess whether eNO results were more predictive of CLD development than lung function test results or readily available clinical data (gestational age and birthweight). The patients were 24 infants with a median gestational age of 27 (range 25-31) weeks. Measurements of eNO levels, functional residual capacity (FRC), and compliance of the respiratory system (CRS) were attempted on postnatal days 1, 3, 5, 7, 14, and 28 days. The 12 infants who developed CLD were of significantly lower birthweight and gestational age than the rest of the cohort; in addition, they had lower median FRC (P < 0.02) and CRS (P < 0.02) results, but not higher eNO levels, in the first week after birth. Construction of receiver operator characteristic (ROC) curves demonstrated that the CRS and FRC results on Day 3 were the best predictors of CLD development; the areas under the ROC curves were 0.94 and 0.91, respectively. Early lung function test results, but not eNO levels, are useful in predicting CLD development, but are not significantly better than birthweight.

Pulmonary nitric oxide synthases and nitrotyrosine: findings during lung development and in chronic lung disease of prematurity

BACKGROUND

Nitric oxide mediates and modulates pulmonary transition from fetal to postnatal life. NO is synthesized by 3 nitric oxide synthase isoforms. One key pathway of nitric oxide metabolism results in nitrotyrosine, a stable, measurable marker of nitric oxide production.

OBJECTIVE

The purpose of this study was to assess, by semiquantitative immunohistochemistry, nitric oxide synthase isoforms and nitrotyrosine at different airway and vascular tree levels in the lungs of neonates at different gestational ages and to compare results in control groups to those in infants with chronic lung disease.

DESIGN/METHODS

Formalin-fixed, paraffin-embedded, postmortem lung blocks were prepared for immunohistochemistry using antibodies to each nitric oxide synthase isoform and to nitrotyrosine. Blinded observers evaluated the airway and vascular trees for staining intensity (0-3 scale) at 5 levels and 3 levels, respectively. The control population consisted of infants from 22 to 42 weeks' gestation who died in < 48 hours. Results were compared with gestation-matched infants with varying severity of chronic lung disease.

RESULTS

In control and chronic lung disease groups, 22 to 42 weeks' gestation, staining for all 3 of the nitric oxide synthase isoforms was found in the airway epithelium from the bronchus to the alveolus or distal-most airspace. The abundance or distribution of nitric oxide synthase-3 staining in the airways did not show significant correlation with gestational age or severity of chronic lung disease. In the vascular tree, intense nitric oxide synthase-3 and moderate nitric oxide synthase-2 staining was found; nitric oxide synthase-1 was not consistently stained. Nitrotyrosine did stain in the pulmonary tree. Compared with controls where nitrotyrosine staining was minimal, regardless of gestation, in infants with chronic lung disease there was more than fourfold increase between severe chronic lung disease (n = 12) and either mild chronic lung disease or control infants (n = 16).

CONCLUSIONS

All 3 of the nitric oxide synthase isoforms and nitrotyrosine are detectable by immunohistochemistry early in lung development. Nitric oxide synthase ontogeny shows no significant changes in abundance or distribution with advancing gestational age nor with chronic lung disease. Nitrotyrosine is significantly increased in severe chronic lung disease.