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Positive end expiratory pressure (PEEP) is important for neonatal ventilation but is not considered in guidelines for resuscitation. Our aim was to investigate the effects of PEEP on cardiorespiratory parameters during resuscitation of very premature lambs delivered by hysterotomy at approximately 125 d gestation (term approximately 147 d). Before delivery, they were intubated and lung fluid was drained. Immediately after delivery, they were ventilated with a Dräger Babylog plus ventilator in volume guarantee mode with a tidal volume of 5 mL/kg. Lambs were randomized to receive 0, 4, 8, or 12 cm H(2)O of PEEP. They were ventilated for a 15-min resuscitation period followed by 2 h of stabilization at the same PEEP. Tidal volume, peak inspiratory pressure, PEEP, arterial pressure, oxygen saturation, and blood gases were measured regularly, and respiratory system compliance and alveolar/arterial oxygen differences were calculated. Lambs that received 12 cm H(2)O of PEEP died from pneumothoraces; all others survived without pneumothoraces. Oxygenation was significantly improved by 8 and 12 cm H(2)O of PEEP compared with 0 and 4 cm H(2)O of PEEP. Lambs with 0 PEEP did not oxygenate adequately. The compliance of the respiratory system was significantly higher at 4 and 8 cm H(2)O of PEEP than at 0 PEEP. There were no significant differences in partial pressure of carbon dioxide in arterial blood between groups. Arterial pressure was highest with 8 cm H(2)O of PEEP, and there was no cardiorespiratory compromise at any level of PEEP. Applying PEEP during resuscitation of very premature infants might be advantageous and merits further investigation.

Obstruction of the fetal trachea is a potent stimulus for fetal lung growth and may have therapeutic potential in human fetuses with lung hypoplasia. However, the effects of increased lung expansion on lung development near midgestation, which is the preferred timing for fetal intervention, have not been well studied. Our aim was to determine the effects of increased lung expansion on lung development at 75-90 d of gestation in fetal sheep. In three groups of fetuses (n = 4 for each), the trachea was occluded for either 10 [10-d tracheal occlusion (TO) group] or 15 d (15-d TO group) or left intact (control fetuses). TO for both 10 and 15 d caused fetal hydrops, resulting in significantly increased fetal body weights. Both periods of TO significantly increased total lung DNA contents from 99.8 +/- 10.1 to 246.0 +/- 5.3 and 246.9 +/- 48.7 mg in 10- and 15-d TO fetuses, respectively. TO for 10 and 15 d also increased airspace diameter, although the percentage of lung occupied by airspace was not increased in 10-d TO fetuses due to large increases in interairway distances; this resulted from a large increase in mesenchymal tissue. The interairway distances at 15 d of TO were reduced compared with the 10-d value but were still approximately 30% larger than control values. We conclude that TO at <90 d of gestation in fetal sheep induces a greater increase in lung tissue growth than later in gestation but also causes fetal hydrops and produces changes in lung structure that are not compatible with efficient gas exchange. Thus, increased lung expansion at a similar stage of development in human fetuses is unlikely to induce changes in lung development that would facilitate gas exchange after birth.