Effects of bovine surfactant in premature lambs after intra-tracheal application

Twenty-two premature lambs (gestational age 124-125 days, term 144-160 days) were intubated and supported by infant ventilators immediately after delivery. Respiratory rate was 60/min, inspiratory time 0.4 s, peak inspiratory pressure (PIP) 35 cm H2O, positive endexpiratory pressure (PEEP) 2 cm H2O, FiO2 1.0. 15 min after delivery 10 lambs (group 1) were treated with 35 mg/kg body weight bovine surfactant (SF-RI 1), whereas 1 ml/kg body weight saline was instilled in 12 lambs as controls (group 2). Sequential measurements of blood gases and acid base status (every 30 min) as well as continuous registration of PIP, PEEP, respiratory rate and tidal volume (TV) were performed in all lambs for 300 min. PIP was varied between 20 and 40 cm H2O in order to attain paCO2 values between 35 and 50 mm Hg. Significantly improved oxygenation was observed in group 1 lambs with maximum differences 30 min after delivery for 2 h. Ventilation was likewise affected: paCO2 and PIP values were significantly lower in the surfactant-treated animals (group 1). Total lung-thorax compliances (calculated from TV and delta P, i.e. PIP-PEEP) per kg body weight also significantly reflected the improvement of pulmonary function in group 1 compared to group 2 lambs. Intratracheal instillation of SF-RI 1 improved gas exchange in premature lambs, whereas control animals exhibited severe respiratory failure characteristic of respiratory distress syndrome (RDS).