Surfactant enhances the distribution of ventilation in partially aerated lungs of preterm rabbits

In very preterm infants, nonuniform lung aeration occurs when regions of the immature lung remain liquid-filled after birth, which restricts gas exchange to aerated lung regions. We have examined the effect of surfactant administration on the uniformity of lung aeration and the distribution of ventilation in mechanically ventilated preterm rabbits. Preterm kittens (28-29 days gestation; term: ∼32 days) were delivered by cesarean section and intubated via tracheostomy. Before the experiment, kittens were initially ventilated (intermittent positive pressure ventilation; iPPV) to achieve whole (both lungs) or partial (one lung) lung aeration. Kittens were then ventilated (volume targeted: 8 mL/kg) with or without an initial sustained inflation (SI), before surfactant. Lung aeration was measured before and after surfactant, using phase contrast X-ray imaging and plethysmography. iPPV alone was unable to aerate unaerated lung regions, resulting in regional overexpansion due to a marked nonuniform distribution of ventilation. Although a SI increased aeration of nonaerated lung regions, the effect of surfactant was markedly greater, resulting in aeration of previously unaerated lung regions and markedly reducing regional overexpansion. Surfactant administration soon after birth greatly increases the uniformity of lung aeration and distribution of ventilation in mechanically ventilated very preterm newborns.<b>NEW & NOTEWORTHY</b> Preterm newborns commonly receive intermittent positive pressure ventilation (iPPV) at birth, but the optimal approach that facilitates uniform lung aeration is unknown, particularly in a partially aerated lung. We have shown that surfactant administration to partially aerated lungs markedly enhances aeration of unaerated lung regions, which redistributes the incoming tidal volume to more evenly ventilate the lung. These experimental findings support the rationale to administer surfactant as soon as possible after birth in preterm infants.