Methods of evaluating fetal lung maturity

Surfactant status assessment and personalized therapy for surfactant deficiency or dysfunction

Surfactant is a pivotal neonatal drug used both for respiratory distress syndrome due to surfactant deficiency and for more complex surfactant dysfunctions (such as in case of neonatal acute respiratory distress syndrome). Despite its importance, indications for surfactant therapy are often based on oversimplified criteria. Lung biology and modern monitoring provide several diagnostic tools to assess the patient surfactant status and they can be used for a personalized surfactant therapy. This is desirable to improve the efficacy of surfactant treatment and reduce associated costs and side effects. In this review we will discuss these diagnostic tools from a pathophysiological and multi-disciplinary perspective, focusing on the quantitative or qualitative surfactant assays, lung mechanics or aeration measurements, and gas exchange metrics. Their biological and technical characteristics are described with practical information for clinicians. Finally, available evidence-based data are reviewed, and the diagnostic accuracy of the different tools is compared. Lung ultrasound seems the most suitable tool for assessing the surfactant status, while some other promising tests require further research and/or development.

Prediction of Neonatal Respiratory Distress Biomarker Concentration by Application of Machine Learning to Mid-Infrared Spectra

The authors of this study developed the use of attenuated total reflectance Fourier transform infrared spectroscopy (ATR–FTIR) combined with machine learning as a point-of-care (POC) diagnostic platform, considering neonatal respiratory distress syndrome (nRDS), for which no POC currently exists, as an example. nRDS can be diagnosed by a ratio of less than 2.2 of two nRDS biomarkers, lecithin and sphingomyelin (L/S ratio), and in this study, ATR–FTIR spectra were recorded from L/S ratios of between 1.0 and 3.4, which were generated using purified reagents. The calibration of principal component (PCR) and partial least squares (PLSR) regression models was performed using 155 raw baselined and second derivative spectra prior to predicting the concentration of a further 104 spectra. A three-factor PLSR model of second derivative spectra best predicted L/S ratios across the full range (R²: 0.967; MSE: 0.014). The L/S ratios from 1.0 to 3.4 were predicted with a prediction interval of +0.29, −0.37 when using a second derivative spectra PLSR model and had a mean prediction interval of +0.26, −0.34 around the L/S 2.2 region. These results support the validity of combining ATR–FTIR with machine learning to develop a point-of-care device for detecting and quantifying any biomarker with an interpretable mid-infrared spectrum.

Surfactant phospholipid composition of gastric aspirate samples differs between male and female very preterm infants

BackgroundAmong preterm infants, males have a greater incidence of respiratory distress and death than do females born at the same gestational age, likely due to sex-related differences in lung maturation. Our aim was to determine whether surfactant phospholipid composition differs between male and female preterm infants.MethodsGastric aspirate samples from male and female infants born between 25 and 30 weeks of gestation at The Royal Women's Hospital, Melbourne, Australia, were collected within 1 h after birth. Phospholipid composition was analyzed by electrospray ionization tandem mass spectrometry.ResultsPreterm males had higher proportions of total phosphatidylinositol (PI) and phosphatidylserine 36:2, lower proportions of total sphingomyelin (S) and S 33:1 and 35:1, and a greater phosphatidylcholine (PC)/S ratio than did females. The proportions of PC 30:0, PC 34:0, PC 34:2, PC 36:2, PC 36:3, and PC 38:2 differed between the sexes at different gestational weeks of birth; the proportion of PC 32:0 (dipalmitoylphosphatidylcholine) in males was lower than that in females at 25 weeks of gestation but higher at 27 weeks.ConclusionPhospholipid composition in pulmonary surfactant is different between male and female preterm infants of the same gestational age, which may contribute to the increased risk for respiratory morbidities in one sex.

Role of secretoglobin 3A2 in lung development

RATIONALE

Secretoglobin 3A2 (SCGB3A2) was originally identified as a downstream target in lung for the homeodomain transcription factor NKX2-1, whose null mutation resulted in severely hypoplastic lungs. A very low level of SCGB3A2 is expressed in lungs at Embryonic Day (E) 11.5 during mouse development, which markedly increases by E16.5, the time when lung undergoes dramatic morphologic changes, suggesting that SCGB3A2 may be involved in lung development in addition to a known role in lung inflammation.

OBJECTIVES

To determine whether SCGB3A2 plays a role in lung development.

METHODS

To assess a potential role for SCGB3A2 during early lung development, wild-type and Nkx2-1-null fetal lungs of early developmental stages were subjected to ex vivo organ culture in the presence of SCGB3A2. Nkx2-1-null fetuses were exposed to SCGB3A2 during early organogenesis period through intravenous administration of this protein to Nkx2-1-heterozygous pregnant females carrying these null fetuses. Cultured lungs and fetal lungs were subjected to histologic and immunohistochemical analyses. To assess a role for SCGB3A2 in late lung development, SCGB3A2 was administered to pregnant wild-type females during mid- to late organogenesis stages, and the preterm pups and/or their lungs were evaluated for extent of maturity using breathing motion, gross morphology and histology of lungs, expression of gestational stage-specific genes, and phospholipid profiles.

MEASUREMENTS AND MAIN RESULTS

SCGB3A2 significantly promoted both early and late stages of lung development.

CONCLUSIONS

SCGB3A2 is a novel growth factor in lung.

Testing for fetal lung maturation: a biochemical "window" to the developing fetus

Fetal lung maturity testing represents a major milestone in perinatology. This article critically evaluates specific controversies regarding the methodologies used to measure pulmonary surfactant in AF and how well each of these techniques performs both in principle and application. The clinical utility of fetal lung maturity testing as it applies to particularly difficult complications of pregnancy is discussed. These technical and clinical issues are framed by the scientific and empiric evidence that is used as the rationale for such testing and its implementation in the effective management of preterm delivery.

Current perspectives in assessment of fetal pulmonary surfactant status with amniotic fluid

In recent years, improvements in analytical methodology and clinical management of maternal-fetal diseases have altered the understanding of data from amniotic fluid analysis. Delays in phospholipid production or lung function are not currently reported in maternal diabetes. Fetal lung function following glucocorticoid therapy or premature membrane rupture is uncoupled from amniotic fluid phospholipid concentrations, which do not have the usual significance in these circumstances. Phosphatidylglycerol (PG) is present prior to the usual time it is detected by thin layer chromatography (TLC) methods, which vary in sensitivity for PG. Consequently, the significance of its "absence" is highly varied. These observations are discussed in light of the earlier methods and data, along with new perceptions of the functions of the individual phospholipids and apoproteins, the regulatory mechanism of surfactant production, and the relationship of amniotic fluid components to neonatal lung function.

Clinical and economic considerations associated with testing for fetal lung maturity

Performing multiple tests of fetal lung maturity on amniotic fluid samples may not use the individual test results and laboratory personnel most effectively. To determine the best strategy for fetal lung maturity testing, we analyzed our experience with use of a variety of procedures. Clinical usefulness was assessed according to sensitivity, specificity, predictive values, and efficiency. Economic and technical aspects analyzed included time and personnel requirements, availability of tests, and expense of each procedure. Several testing sequence approaches were compared for efficiency and cost. In our laboratory the foam stability index proved to be the most useful initial test of fetal lung maturity, reserving more expensive and time-consuming tests for instances in which the foam stability index is immature. Routine multiple testing did not enhance clinical usefulness and greatly increased costs. Development of a testing strategy using a rapid, inexpensive, and widely available test such as the foam stability index would promote clinical and economic efficiency.

Effect of acetone precipitation on the clinical prediction of respiratory distress syndrome when utilizing amniotic fluid lecithin/sphingomyelin ratios

Amniotic fluid lecithin-to-sphingomyelin ratios are widely used to predict fetal lung maturity. The inclusion of acetone precipitation in the determination of the lecithin/sphingomyelin ratio has been widely accepted as a necessary step for enhancing predictivity. The lecithin/sphingomyelin ratio of 181 amniotic fluid samples was analyzed with and without acetone precipitation. Sensitivity, specificity, and predictive values were compared. Although there was a significant difference in the numeric value (p less than 0.001) between the two methods, the clinical prediction of the respiratory distress syndrome was not significantly enhanced by acetone precipitation. We conclude that acetone precipitation fails to improve the prediction of fetal lung maturity by lecithin/sphingomyelin ratio analysis.

Rapid enzyme analysis of amniotic fluid phospholipids containing choline: a comparison with the lecithin to sphingomyelin ratio in prenatal assessment of fetal lung maturity

The relation between the choline containing surfactant phospholipids lecithin and sphingomyelin in amniotic fluid and fetal lung maturity is well established. An enzymatic method that had been automated and optimised for use on a centrifugal analyser was used to measure the total choline containing phospholipids in amniotic fluid. The total time taken for this assay was 10 minutes. The results obtained from 100 patient samples, using this procedure, compared favourably with the results obtained by the thin layer chromatography procedure used to determine the lecithin to sphingomyelin ratio (r = 0.93). A clinical study of 60 patients showed that this assay predicted prenatal respiratory distress syndrome as well as the lecithin to sphingomyelin ratios. The advantage of this assay over existing procedures is that it requires minimum preparation of the specimen and no extraction, is quick, and shows a high degree of precision.

Effect of blood contamination on lecithin to sphingomyelin ratio in amniotic fluid by different detection methods

Amniotic phospholipid detection methods such as cupric acetate measure unsaturated lecithin whereas others such as phosphomolybdate detect both unsaturated and saturated lecithin. Because of the extreme unsaturation in serum and red blood cell lecithin, we compared lecithin (L) and sphingomyelin (S) content of maternal blood as well as the effect of blood contamination on amniotic fluid L/S ratios. L/S ratios were obtained by thin-layer chromatography utilizing both cupric acetate and phosphomolybdate for phospholipid detection. The L/S value (mean +/- SD) of maternal serum obtained by cupric acetate was 1.90 +/- 0.19 and that for phosphomolybdate 1.78 +/- 0.17. The results of increasing serum concentrations in amniotic fluid prior to analysis suggest that as little as 0.5% contamination alter results and by 2% contamination values approach the L/S ratio of actual serum whether the amniotic fluid was initially mature or immature by either method. The serum L/S ratio by cupric acetate equaled its maturity threshold of 2.0 while the serum L/S ratio by phosphomolybdate was below its threshold of 3.0. Whereas both methods would have falsely immature values in the presence of blood only phosphomolybdate would assure against false maturity.

Fluorescence polarization in gastric aspirate and in amniotic fluid and its relationship to the respiratory distress syndrome

Fluorescence polarization of diphenylhexatriene (DPH), added to amniotic fluid can be used to estimate fetal lung maturity. In this study we estimated the fluorescence polarization (FP) value of gastric aspirates of newborns and of amniotic fluids and studied the relationship between the FP value and neonatal lung function. Gastric aspirates of 51 newborns and amniotic fluids of 13 cases were mixed with a DPH-phosphate buffered saline solution and incubated for 30 minutes at 37 degrees C. Fluorescence polarization was measured at 22 degrees C. The FP values of amniotic fluid are in accordance with results previously found. A highly significant negative correlation was present between the FP value in amniotic fluid and gestational age. The highest FP values were found in amniotic fluids of infants in whom respiratory distress developed. The FP values of gastric aspirates decreased also with gestational age. A rather poor negative correlation, however, was found between these FP values and gestational age. We also noticed that, before the 36th week of gestation, the FP values in gastric aspirates tend to be lower than those in amniotic fluids. Both high and low FP values were estimated in gastric aspirates of infants with RDS and of infants without respiratory problems. These results show that the measurement of the FP value in gastric aspirates of newborns is not an useful method to determine whether the infant will develop RDS or not.

HPLC of phospholipids in biological fluids -- application to amniotic fluid for the prediction of fetal lung maturity

Because of both the advantage of speed compared with thin layer chromatography (TLC) and the dearth of high pressure liquid chromatography (HPLC) methods for phospholipid separation, it was decided to investigate the use of HPLC with a differential refractometer as detector for the separation and quantitation of amniotic fluid phospholipids required for the prediction of fetal lung maturity. A method was devised which gave results which compared well with those from TLC both in terms of quantitation and predictive value. Despite this, the method was found to lack sufficient reliability for application to the routine clinical assessment of fetal lung maturity. The method does, however, offer a good alternative to two dimensional TLC with phosphate analysis in research work involving quantitation of phosphatidyl inositol, phosphatidyl glycerol and particularly lecithin.