Positive end-expiratory pressure preserves surfactant function in preterm lambs

Ventilation style influences lung injury and the amount of large-aggregate biophysically active surfactant in adult lungs. We asked how positive end-e xpiratory pressures (PEEP) would influence clinical responses and surfactan t pools in surfactant-treated preterm lambs ventilated for 7 h with tidal v olumes (VT) Of 10 ml/kg. The 126-d gestation preterms were delivered and tr eated with 100 mg/kg recombinant human surfactant protein C (rSP-C) contain ing surfactant and ventilated with zero, 4, or 7 cm H2O of PEEP. A comparis on group was treated with natural sheep surfactant and ventilated with zero PEEP. Physiologic measurements were similar for lambs treated with rSP-C s urfactant and natural surfactant. PEEP 4 and 7 improved oxygenation and com pliance relative to either group of lambs ventilated with PEEP zero. The ma ximal lung volumes measured at 40 cm H2O pressure after 7 h ventilation for the PEEP 4 and 7 groups were more than double those measured for either PE EP zero group. Alveolar surfactant pools were larger for the PEEP 7 group, and the large-aggregate fraction was increased for the PEEP 4 and 7 groups, resulting in large-aggregate pool sizes that were 3-fold higher for the PE EP 4 and 4-fold higher for the PEEP 7 groups relative to the PEEP zero grou p treated with rSP-C surfactant. All large-aggregate surfactants lowered mi nimal surface tensions of a captive bubble to less than 5 mN/m. In preterm surfactant-treated lambs PEEP improved lung function and maintained more of an rSP-C surfactant in the biophysically active form.