Am. J. Respir. Crit. Care Med., Volume 160, Number 2, August 1999, 634-639

Positive End-expiratory Pressure Preserves Surfactant Function in Preterm Lambs

JACEK MICHNA, ALAN H. JOBE, and MACHIKO IKEGAMI

Division of Pulmonary Biology, Children's Hospital Medical Center, Cincinnati, Ohio

Ventilation style influences lung injury and the amount of large-aggregate biophysically active surfactant in adult lungs. We asked how positive end-expiratory pressures (PEEP) would influence clinical responses and surfactant pools in surfactant-treated preterm lambs ventilated for 7 h with tidal volumes (VT) of 10 ml/kg. The 126-d gestation preterms were delivered and treated with 100 mg/kg recombinant human surfactant protein C (rSP-C) containing surfactant and ventilated with zero, 4, or 7 cm H₂O of PEEP. A comparison group was treated with natural sheep surfactant and ventilated with zero PEEP. Physiologic measurements were similar for lambs treated with rSP-C surfactant and natural surfactant. PEEP 4 and 7 improved oxygenation and compliance relative to either group of lambs ventilated with PEEP zero. The maximal 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 PEEP 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 PEEP 4 and 4-fold higher for the PEEP 7 groups relative to the PEEP zero group treated with rSP-C surfactant. All large-aggregate surfactants lowered minimal 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.

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