الفهرس 
Embryology of the respiratory system & the effects of preterm birth on lung functionsOnly 14 pages are availabe for public view
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Abstract
Premature birth interrupts normal in utero lung development and results in an early transition from the hypoxic intrauterine environment to a comparatively hyperoxic atmospheric environment. Respiratory distress is a common emergency responsible for 30-40% of admissions in the neonatal period.
The common causes of respiratory distress in neonates: Respiratory Distress Syndrome (RDS), which results from immaturity of the lungs and surfactant deficiency, meconium aspiration syndrome (MAS), transient tachypnea of the Newborn (TTN), congenital or aquired pneumonia, persistent pulmonary hypertension of the newborn (PPHN), pneumothorax, congenital lung anomalies, cardiac shock or congenital heart disease, hematological causes, neurological causes and metabolic causes.
Newborns are vulnerable to impaired gas exchange because of their high metabolic rate, propensity for decreased functional residual capacity (FRC), decreased lung compliance, increased resistance, and potential for right-to-left shunts through the ductus arteriosus, foramen ovale, or both. Thus, impaired gas exchange is common in newborns. Hypercapnia and hypoxemia may coexist, though some disorders may affect gas exchange differentially.
Noninvasive respiratory support (NRS) is becoming increasingly popular as a method of respiratory support in sick newborn infants. NRS refers to respiratory support provided without use of an endotracheal tube. This support consists of continuous positive airway pressure (CPAP), continuous negative expiratory pressure (CNEP), and noninvasive positive pressure ventilation (NIPPV). nasal cannulae may also provide NRS.
Continuous positive airway pressure (CPAP) treat RDS by maintaining alveolar stability as the major physiologic problem in RDS was the collapse of alveoli during expiration, positive pressure was applied to the airway via an endotracheal tube or nasal prongs during both expiration and inspiration; dramatic improvement was achieved.
CPAP maintains inspiratory and expiratory pressures above ambient pressure, which results in an increase in functional residual capacity (FRC) and improvement in static lung compliance, and decreased airway resistance in the infant with unstable lung mechanics.
CPAP is indicated in the presence of increased work of breathing as indicated by an increase in respiratory rate of > 30% of normal, substernal and suprasternal retractions, grunting, and nasal flaring; the presence of pale or cyanotic skin color and inadequate arterial blood gas values.
Infants with severe respiratory distress, bradycardia <100 b.p.m, capillary refill time >3s are to be intubated and ventilated without a trial of CPAP.
Failure of CPAP is common, as shown in a recent trial that evaluated CPAP as the primary mode of support in extremely pre-term infants (gestational age <28 weeks), that found a failure rate of 46% in the first few days of life. Previous studies on predictors of CPAP failure concluded; gestational age <28 weeks, PPROM, lack of exposure to antenatal steroids (ANS), alveolar-arterial oxygen tension gradient (A-a DO2) >180 mmHg on the first arterial blood gas (ABG) and small for gestational age (SGA).
A prospective study was conducted on 100 preterm in Neonatal Intensive Care Units (NICU) of Benha children hospital and Toukh central hospital between March 2013 and February 2014. Our preterm patients suffered respiratory distress for various causes and were candidate for CPAP. After being on CPAP they were followed up for either success or failure of this treatment modality. We tried to pick up the possible causes of failure and form a clinical score to predict CPAP failure.
CPAP failed in 45% of the cases. The odds for CPAP failure in cases who have sepsis are 11.1 times higher than in cases who do not have sepsis. This is statistically significant, however, Confidence Interval (CI) is so wide (3.2-38.5%) so results should be taken cautiously and future studies should be done with a larger sample.
CPAP is one of the main lines of treatment in all causes of respiratory distress, the success rate of CPAP was as high as the failure rate which is an accomplishment. Even though antenatal steroids were not given, there was a high rate of CPAP success.
We concluded from our study all the following:
A-Risk factors of CPAP failure.
1-Gestational age < 28 weeks.
2-Low birth weight (the failure rate increases with the decrease in birth weight).
3-Higher FiO2 at initiation of CPAP.
4-Higher CPAP pressure at initiation of CPAP.
5-Sepsis which was a statistically significant cause of CPAP failure. And due to small sample size, sepsis was the only significant variable.
6-Moderate to severe RDS.
B-We could not devise a score for CPAP failure due to:
1-We could not find significant predictors of CPAP failure.
2-Small sample size
The presence of sepsis can be considered as a risk factor of CPAP failure.
The strengths of our study include: (i) a prospective follow-up of all enrolled neonates administered CPAP for its failure. It represents the ground reality in developing countries where infants are often managed without surfactant and the number of trained nursing personnel is limited. The major limitation of our study is the small sample size-a larger number of infants with the outcome of interest (CPAP failure) could have identified more variables.
We could not devise a score as we could not find significant predictors of CPAP failure. The presence of sepsis can be considered as a risk factor of CPAP failure.
We administered CPAP using short binasal cannulae, antenatal ’ steroids were not given and so additional research addressing some of these limitations will be needed to validate our findings.
We recommend from our study all of the following:
1.Timing of CPAP initiation will help to decide if the very early use of CPAP reduces morbidity and mortality in neonates with respiratory distress.
2.A larger randomized controlled trials would provide more definitive evidence for causes of CPAP failure, and help devise a better score.
3.Future studies on sepsis scores correlating with CPAP failure could aid in selecting neonates who should start intubation and ventilation without a trial of CPAP.