Impact of neonatal noninvasive resuscitation strategies on lung mechanics, tracheal pressure, and tidal volume in preterm lambs.

ABSTRACT

This study investigated the relationship between three respiratory support approaches on lung volume recruitment during the first two hours of postnatal life in preterm lambs. We estimated changes in lung aeration, measuring respiratory resistance and reactance by oscillometry at 5 Hz. We also measured intratracheal pressure in subsets of lambs. The first main finding is that sustained inflation (SI) applied noninvasively (Mask SI; n=7) or invasively (endotracheal tube, ETT SI; n=6) led to similar rapid lung volume recruitment (~6 min). In contrast, Mask continuous positive airway pressure (CPAP) without SI (n=6) resuscitation took longer (~30-45 min) to reach similar lung volume recruitment. The second main finding is that, in the first 15 min of postnatal life, the Mask CPAP without SI group closed their larynx during custom ventilator-driven expiration, leading to intratracheal positive end-expiratory pressure of ~17 cmH2O (instead of 8 cmH2O provided by the ventilator). In contrast, the Mask SI group used the larynx to limit inspiratory pressure to ~26 cmH2O (instead of 30 cmH2O provided by the ventilator). These different responses affected tidal volume, being larger in the Mask CPAP without SI group (8.4 ml/Kg, 6.7-9.3 IQR) compared to the Mask SI (5.0 ml/Kg, 4.4-5.2 IQR), and ETT SI groups (3.3 ml/Kg 2.6-3.7 IQR). Distinct physiological responses suggest that spontaneous respiratory activity of the larynx of preterm lambs at birth can uncouple pressure applied by the ventilator to that applied to the lung, leading to unpredictable lung pressure and tidal volumes delivery independently from the ventilator settings.