Prediction of idiopathic respiratory distress syndrome by the stable microbubble test on gastric aspirate

Use of surfactant beyond respiratory distress syndrome, what is the evidence?

Surfactant replacement therapy is currently approved by the United States Food and Drug Administration (FDA) for premature infants with respiratory distress syndrome (RDS) caused by surfactant deficiency due to immaturity. There is strong evidence that surfactant decreases mortality and air leak syndromes in premature infants with RDS. However, surfactant is also used "off-label" for respiratory failure beyond classic RDS. This review discusses current evidence for the use of off-label surfactant therapy for (1) term infants with lung disease such as meconium aspiration syndrome (MAS), pneumonia/sepsis, and congenital diaphragmatic hernia (2) premature infants after 72 h for acute respiratory failure, and (3) the use of surfactant lavage. At last, we briefly describe the use of surfactants for drug delivery and the current evidence on evaluating infants for surfactant deficiency.

Gastric Aspirate Phosphatidylcholine Species in Preterm Neonates Receiving Aerosolized Surfactant

OBJECTIVE

To characterize phosphatidylcholine (PC) molecular species in serial gastric aspirates as biomarkers for lung maturity, delivery of aerosolized surfactant (AS), and need for intubation.

METHODS

In a phase II clinical trial of aerosolized surfactant in preterm neonates with respiratory distress syndrome receiving noninvasive ventilation, infants received a maximum of 2 doses of nebulized beractant. Gastric aspirates were collected before and after each dose and were analyzed for PCs using liquid chromatography mass spectrometry.

RESULTS

Of 149 infants enrolled, gastric aspirates were obtained before (n = 91) and after (n = 94) dose 1, and before (n = 56) and after (n = 57) dose 2 of nebulized beractant. The mean ± SD values of birthweight, gestational age, and age at collection of baseline gastric aspirate were 1.7 ± 0.6 kg, 31.7 ± 2.8 weeks, and 5.5 ± 1.7 hours, respectively. The most abundant PC in beractant and gastric aspirates was PC(16:0/16:0). Advancing gestational age and number of antenatal corticosteroid doses predicted increased gastric aspirate PC(16:0/16:0), whereas maternal diabetes predicted a decrease. Several PCs increased significantly (P < .05) after nebulized beractant, consistent with effective aerosol delivery. Infants who received intubation within 72 hours of birth were more likely to have lower PC(16:0/16:0) levels in baseline gastric aspirates compared with those who did not (P = .024).

CONCLUSIONS

PC molecular species in gastric aspirates of preterm neonates are potentially novel and precise biomarkers to assess lung maturity, aerosol delivery, and need for endotracheal intubation.

Predictors and Outcomes of Early Intubation in Infants Born at 28-36 Weeks of Gestation Receiving Noninvasive Respiratory Support

OBJECTIVE

To identify predictors and outcomes of early intubation in preterm infants with respiratory distress, and predictors of need for brief respiratory support (≤1 day).

STUDY DESIGN

Secondary analysis of data from a randomized trial comparing nasal high-flow with continuous positive airway pressure as primary respiratory support in preterm infants born at 28-36 weeks of gestation. Intubation was assessed within 72 hours of randomization.

RESULTS

There were 564 included infants with a mean (SD) gestational age of 32.0 (2.2) weeks and birth weight 1744 (589) g; 76 infants (13.5%) received early intubation. On multivariable analysis, lower gestational age and higher pre-randomization fraction of inspired oxygen (FiO₂) predicted intubation. A test based on gestational age of <30 weeks and an FiO₂ of ≥0.30 produced a likelihood ratio of 9.1. Intubation was associated with prolonged duration of respiratory support and supplemental oxygen, with pneumothorax and nasal trauma, and in infants born at <32 weeks of gestational, with bronchopulmonary dysplasia and patent ductus arteriosus requiring treatment. Greater gestational age and lower FiO₂ predicted the need for ≤1 day of respiratory support. A test based on a gestational age of ≥34 weeks and an FiO₂ of 0.21 produced a likelihood ratio of 4.7.

CONCLUSIONS

In preterm infants 28-36 week of gestation receiving primary noninvasive respiratory support, lower gestational age, and higher FiO₂ predicted need for intubation within 72 hours. Intubation was associated with adverse respiratory outcomes. Greater gestational age and lower FiO₂ predicted need for ≤1 day of respiratory support. It may be reasonable to defer the use of respiratory support in more mature infants with low FiO₂ requirements. TRIAL REGISTRATION AUSTRALIAN NEW ZEALAND CLINICAL TRIALS REGISTRY: ACTRN12613000303741.

Rapid diagnosis of respiratory distress syndrome by oral aspirate in premature newborns

OBJECTIVE

The stable microbubble test on gastric aspirate and on amniotic fluid has been used for the diagnosis of respiratory distress syndrome in the newborn. However, no study has performed this test on oral aspirates from premature infants. The objective of this study was to evaluate the performance of the stable microbubble test on oral aspirates from preterm newborns to predict respiratory distress syndrome.

METHOD

This study included infants with gestational age <34 weeks. Oral fluids were obtained immediately after birth and gastric fluids were collected within the first 30 minutes of life. The samples were frozen and tested within 72 hours.

RESULTS

The sample was composed of paired aspirates from 64 newborns, who were divided into two groups: respiratory distress syndrome group (n=21) and control group (n=43). The median (interquartile range) of the stable microbubble count in the oral samples of infants with respiratory distress syndrome was significantly lower than that of infants who did not develop respiratory symptoms: respiratory distress syndrome group=12 (8-22) stable microbubbles/mm²; control group=100 (48-230)microbubbles/mm² (p<0.001). The correlation between microbubble count in gastric and oral aspirates was 0.90 (95% confidence interval=0.85-0.95; p<0.001). Considering a cut-off point of 25microbubbles/mm², the sensitivity and the specificity of the stable microbubble test were 81.4% and 85.7%, respectively.

CONCLUSION

The study suggests that the stable microbubble test performed on oral aspirate is a reliable alternative to that performed on gastric fluid for the prediction of respiratory distress syndrome in the newborn.

Diagnostic accuracy of lamellar body count as a predictor of fetal lung maturity: A systematic review and meta-analysis

Objective

This study aimed to synthesize evidence from published studies about the diagnostic accuracy of lamellar body count (LBC) as a predictor of fetal lung maturity.

Study design

We searched Medline (via PubMed), EBSCO, Web of Science, Scopus and the Cochrane Library for relevant published studies assessing the accuracy of LBC as a predictor of fetal lung maturity. Studies were classified according to the counting essays, centrifugation protocols, and the reported optimum cut off values. Data of the true positive, true negative, false positive, and false negative were extracted and analyzed to calculate the overall sensitivity and specificity of the LBC.

Results

Thirty-one studies were included in the final analysis. Fourteen studies reported data for centrifuged amniotic fluid (AF) samples, 13 studies reported data for uncentrifuged samples, and four studies did not have enough information about whether centrifugation was done. LBC showed an area under the curve >80% in diagnosing lung immaturity with variable cut off values. Pooled analysis showed that LBC a 100% specificity to exclude respiratory distress syndrome (RDS) at a cut off value of 15,000 and 100% sensitivity to diagnose RDS at a cut off value of 55,000.

Conclusion

Cases with LBC < 15,000 are considered to have lung immaturity while cases with LBC > 45,000 in centrifuged AF samples or >55,000 in uncentrifuged AF samples are likely to have mature lungs. Cases with LBC ranging between these maturity and immaturity limits should be considered for further evaluation by other lung maturity tests.

Surfactant deficiency in full-term newborns with transient tachypnea delivered by elective C-section

INTRODUCTION

Previous studies have suggested that full-term newborns delivered by elective cesarean section who develop transient tachypnea have low gastric microbubble counts. In the present study, microbubble concentrations in oral fluid samples were used to evaluate pulmonary maturity.

OBJECTIVE

To evaluate lung maturity in full-term newborns delivered by elective caesarean section using the stable microbubble test in oral aspirates collected at birth.

METHOD

The study involved newborns with gestational age >37 weeks delivered by elective cesarean section. Oral fluid samples were obtained in the delivery room immediately after birth, and gastric fluid was collected within the first hour of life. Samples were frozen and analyzed by two blinded researchers.

RESULTS

The sample comprised 544 newborns. Twenty-two were diagnosed with transient tachypnea of the newborn by the assisting physician, and required admission to the Neonatal Intensive or Intermediate Care Unit. The median (interquartile range) of the number of microbubbles in the oral samples of these patients was 67.5 (45-150) microbubbles/mm(2) . The remaining 498 newborns without respiratory difficulties had a count of 350 (150-750) microbubbles/mm(2) -P < 0.001. Gastric fluid tests revealed a count of 150 (82.5-700) microbubbles/mm(2) for neonates with respiratory difficulties, and of 600 (216-1125) microbubbles/mm(2) -P < 0.05 for those without respiratory symptoms.

CONCLUSION

The present results suggest that transient tachypnea of the newborn is associated with surfactant dysfunction. Pediatr Pulmonol. 2016;51:596-600. © 2015 Wiley Periodicals, Inc.

The stable microbubble test for determining continuous positive airway pressure (CPAP) success in very preterm infants receiving nasal CPAP from birth

BACKGROUND

Very preterm infants can be treated with nasal continuous positive airway pressure (CPAP) from birth, but some fail. A rapid test, such as the stable microbubble test (SMT) on gastric aspirate, may identify those who can be managed successfully using CPAP.

OBJECTIVE

To determine if SMT can identify soon after birth, very preterm infants who may be successfully managed on CPAP alone.

METHODS

Stable microbubbles (diameter <15 µm) were counted in gastric aspirates taken <1 h of age from infants <30 weeks' gestation, who received CPAP from birth. Infants failed CPAP if intubated at <72 h of age. Clinicians were masked to SMT results. A receiver operating characteristic curve was generated to determine the relationship between number of microbubbles/mm(2) and subsequent intubation.

RESULTS

68 infants of mean (SD) 28.1 (1.4) weeks' gestation received CPAP in the delivery room at a median (interquartile range) pressure 7 (6-8) cmH2O and FiO2 0.25 (0.21-0.3). Gastric aspirates were taken at a median (interquartile range) age of 0.5 (0.3-0.6) hours. The best cut-off point for predicting CPAP success or failure was a SMT count of 8 microbubbles/mm(2). The area under the receiver operating characteristic curve was 0.8 (95% CI 0.7-0.9). A SMT count ≥8 microbubbles/mm(2) had a sensitivity of 53%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 60% for predicting CPAP success.

CONCLUSION

Infants treated with CPAP from birth, who had SMT counts ≥8 microbubbles/mm(2) on their gastric aspirate, did not fail CPAP.

Lamellar body count and stable microbubble test on tracheal aspirates from infants for the diagnosis of respiratory distress syndrome

OBJECTIVES

To evaluate the performance of lamellar body count in tracheal aspirates from intubated preterm babies to predict respiratory distress syndrome.

DESIGN

Case-control study.

SETTING

Three neonatal intensive care units.

PATIENTS

Seventy-two patients not older than 3 days were included in the study, 38 preterm infants with respiratory distress syndrome, 16 preterms without respiratory distress syndrome, and 18 term infants. All required mechanical ventilation.

INTERVENTIONS

Lamellar body count was performed in an automated cell counter. Tracheal samples were diluted in dithiothreitol without centrifugation and kept frozen at -20°C until use. Samples were placed in a dithiothreitol-containing test tube at a ratio of one part tracheal aspirate to six parts dithiothreitol solution, vortexed for 10 secs, and aspirated by the cell counter. Lamellar body count was performed using the platelet channel. All results were multiplied by seven. The stable microbubble test was done for comparison.

MEASUREMENTS

Lamellar body count and stable microbubble test.

MAIN RESULTS

Lamellar body count was significantly lower in the respiratory distress syndrome group compared with the non respiratory distress syndrome preterm group and also with the term group. The median and interquartile range obtained for lamellar body count were 38,500/μL (14,000-112,000) for the respiratory distress syndrome group, 822,500/μL (442,000-962,500) for the non respiratory distress syndrome preterm group, and 633,000/μL (322,000-1,608,000) for the term group (p < .001). The sensitivity and specificity of lamellar body count and stable microbubble test for the diagnosis of respiratory distress syndrome were calculated, taking into consideration the respiratory distress syndrome and the non respiratory distress syndrome preterm groups. Considering a cutoff point of 200,000 lamellar bodies/μL, lamellar body count sensitivity was 92.1% (95% confidence interval 78.6-98.3) and lamellar body count specificity was 93.8% (95% confidence interval 69.8-99.8). The area under the curve was 0.94 (95% confidence interval 0.84-1.00).

CONCLUSIONS

Lamellar body count and stable microbubble test can be rapidly and easily performed on tracheal aspirates and they seem to have very good performance for diagnosing respiratory distress syndrome in intubated patients.

Surfactant deficiency in transient tachypnea of the newborn

OBJECTIVE

To evaluate surfactant production and function in term neonates with transient tachypnea of the newborn (TTN).

STUDY DESIGN

Samples of gastric aspirates collected within 30 minutes of birth from 42 term newborns with gestational age ≥ 37 weeks (21 patients with TTN and 21 control subjects), delivered via elective cesarean delivery, were analyzed with lamellar body count and stable microbubble test.

RESULTS

Results of lamellar body counts and stable microbubble tests were significantly lower in the TTN group than in control subjects (P = .004 and .013, respectively). Lamellar body counts were significantly lower in infants with TTN requiring oxygen for ≥ 24 hours after birth than in infants requiring oxygen for < 24 hours (P = .029). When the cutoff point was 48 hours, the stable microbubble count was significantly lower in the group requiring oxygen for ≥ 48 hours than in the group requiring oxygen for < 48 hours (P = .047).

CONCLUSIONS

Term infants with TTN had low lamellar body counts associated with decreased surfactant function, suggesting that prolonged disease is associated with surfactant abnormalities.

Stable Microbubble Test on Tracheal Aspirate for the Diagnosis of Respiratory Distress Syndrome

BACKGROUND

Exogenous surfactant should be used as early as possible in the presence of respiratory distress syndrome (RDS), but diagnosis may only become clear late in the course of the disease. The stable microbubble test (SMT) in the tracheal aspirates could help in the decision to give early surfactant to preterm babies with respiratory distress.

OBJECTIVES

The objective of this study was to evaluate the accuracy of the SMT on tracheal aspirate for the diagnosis of RDS in newborns requiring mechanical ventilation.

METHODS

The test was performed on specimens obtained from 74 infants requiring mechanical ventilation, through routine suctioning.

RESULTS

Patients with RDS and meconium aspiration syndrome (MAS) had a significantly lower stable microbubble count than non-RDS and non-MAS patients. Preterm infants without RDS had a significantly higher microbubble count than preterm babies with RDS and a similar count to that of term babies. Considering a cutoff point of 120 microbubbles/mm(2) for the diagnosis of RDS, the sensitivity of the microbubble test was 96.3% (95% CI: 79.1-99.8) and the specificity 97.6% (95% CI: 85.9-99.9).

CONCLUSIONS

The SMT on tracheal aspirates is accurate for RDS diagnosis and may be useful to support the decision to give surfactant to newborns on mechanical ventilation.