RESEARCH DESIGN Multicenter, randomized, controlled trial. RECRUITMENT Entry criteria Preterm infants 28-35 6/7 weeks' gestation and less than 48 hours of age who have a clinical diagnosis of respiratory distress syndrome. Infants who are on NCPAP and FiO2 ≥0.30 will randomized to curosurf or infasurf via MIST.

Exclusion criteria Infants will be excluded if there is a congenital anomaly or an alternative cause for respiratory distress.

Babies who require emergent intubation will not be enrolled in the interventions.

Parental Consent will be obtained prior to randomization.

INTERVENTION Infants who on CPAP who reach the threshold of 30% oxygen will be randomized to calfactant (Infasurf), 3ml/kg or poractant alfa (Curosurf), 2.5ml/kg, administered under direct laryngoscopy using a surfactant instillation catheter (MIST) 16G Angiocath (Becton Dickinson, Sandy, UT, USA).

A second dose of calfactant (Infasurf) 3ml/kg or poractant alfa (Curosurf), 1.25ml/kg, will be administered via MIST their fiO2 reaches the threshold of 30% between 6 and 48 hours after the first dose.

No further surfactant should be given in the first 7 days unless the infant reaches the intubation criteria.

POST-INTERVENTION MANAGEMENT Other than the requirement to adhere to intubation criteria in the first week, and in some cases perform a room air trial at 36 weeks corrected gestation, management will be at the discretion of the clinical team.

Titration of CPAP pressure is encouraged, with a permitted maximum of 8 cm H2O. Use of nasal IPPV is allowable for apnea, but discouraged for RDS and should only be after at least one dose of surfactant has been given. Early caffeine therapy is expected.

Criteria for intubation:

Enrolled infants on CPAP will be intubated if:

• FiO2 ≥0.45 for 15 minutes, or if there is unremitting apnea (> 6 episodes/hour requiring intervention or in the opinion of the treating physician) or persistent respiratory acidosis (pH<7.25 and pCO2 >60) on blood gasses at least 30 minutes apart or metabolic acidosis refractory to treatment.
• Need for an anesthetic or an intervention requiring intubation

These criteria apply during the first week of life, and to the first episode of intubation only. If the infant is intubated it is expected that another dose of surfactant will be administered.

Inclusion Criteria:

• Preterm infants 28-35 6/7 weeks' gestation and less than 48 hours of age who have a clinical diagnosis of respiratory distress syndrome confirmed by a chest x-ray on nasal continuous positive airway pressure (NCPAP) and FiO2 ≥0.30

Exclusion Criteria:

• Infants will be excluded if there is a congenital anomaly or an alternative cause for respiratory distress.
• Infants who require emergent intubation will not be enrolled in the interventions.

Surfactant will be sent from Investigational Pharmacy