Background: Applying mechanical ventilation (MV) to premature lungs carries many risks, up to lung injury and bronchopulmonary dysplasia. Stabilization with continuous positive airway pressure (CPAP) avoids intubation and invasiveness.    
Aim of work: To evaluate the predictors of outcome of nasal CPAP on preterms with respiratory distress syndrome (RDS).
Material and Methods: This prospective observational study included all preterms with RDS that necessitated CPAP introduction (according to the European Consensus Guidelines on the Management of RDS), who were admitted to the Neonatal Intensive Care Unit (NICU) of Department of Pediatrics, Cairo University Hospitals, from February to July 2019. CPAP was initiated in the first 2 hours of life. Respiratory compromise was assessed using Silverman score. Hematological scoring system (HSS) was studied as a predictor of outcome. Those who did not need subsequent intubation were labeled CPAP success group and were compared to the group where CPAP failed.
Results: Over 6-months, 508 preterm with gestational age (GA) 27-33 weeks with RDS were admitted to our NICU, of them 61 (mean GA± SD of 32.08 ± 1.98 weeks) were included in the study. Of them 35 (57.4%) were males and 26 (42.6 %) females. CPAP was successful in 37 (60.7%) and Silverman score improved 2 hours after CPAP. Their initial median (IQR) of Silverman score was 5 (range 3-6) and improved to 1 (range 1-2) 2 hours after CPAP, while in the failure group, it was 6 (range 5-7) initially and worsened to 8 (range 7.5-9) (p=0.026). Antenatal steroids administration was highly protective (p= 0.000) but not GA p=0.086) or gender (p=0.521). Initial severe RDS in chest X-ray at birth was present in 1 (2.7 %) preterm in the CPAP success group and 10 (41.7 %) in the failure group (p=0.000).  The systolic blood pressure ≤ 66, HSS, chest X-ray before CPAP, non-improvement of chest X-ray after CPAP and apnea were the important predictors for CPAP failure (p= 0.023), (p= 0.090), (p= 0.025), (p= 0.011) and (p= 0.049) respectively.
Conclusion: Trials of CPAP for preterms with severe RDS with hemodynamic stability are effective in obviating the need for more invasive MV. Factors including hypercarbia, apnea, poor respiratory efforts, systemic hypotension, higher Silverman score and HSS ≥5 were the most significant associations of failed CPAP.