597 - Low gas flow rates reduce early preterm lung injury in preterm lambs

Poster Number: 597
Publication Number: 597.1596

Background: Gas flow is fundamental for tidal ventilation, but currently recommended gas flow rates to support the preterm lung after birth are without an evidence base.

Objective: To determine the role of gas flow rates to generate positive pressure ventilation in initiating early lung injury pathways in the preterm lamb lung.

Design/Methods: Initially 124-127d steroid exposed preterm lambs (n=44) were randomly allocated (8-10/group) to 15 min of standardised respiratory support using 4, 6 and 8-10 L/min gas flow during placental circulation to determine the role of flow rates in initiating lung injury. Lung mechanics and aeration were measured throughout and lung tissue and bronchoalveolar fluid analysed for regional lung injury, including proteomics. Based on the lack of injury differences between 4 and 6 L/min, the study was repeated using 2 groups (4-6 and 8-10 L/min flow rates) during 90 min of respiratory support in 126-129d steroid exposed and surfactant-treated preterm lambs (n=45, 15/group) to further elucidate the role of gas flow on potentiation of lung injury.

Results: Tidal volume, applied pressure, dynamic compliance, mechanical power and gas exchange were the same at all flow rates, but the speed of pressure and volume (and acceleration) change during inflation was faster with increasing flow rates. Lower flow rates resulted in less bronchoalveolar fluid protein (p=0.003 and 0.047; 15 and 90 min one-way ANOVA), better lung morphology and less detached epithelial cells (Figure 1). Proteomics analysis found gravity-dependent differences across all groups. Overall, there was greater protein change from unventilated fetal controls using 8-10 L/min, and greater abundance of acute inflammatory and innate responses compared to 4-6 L/min. Interestingly,4-6 L/min increased platelet-derived growth factor signalling (decreased signalling associated with BPD).

Conclusion(s): Supporting the preterm lung from birth with slower gas flow rates than currently used clinically resulted in less lung injury without compromising tidal ventilation or gas exchange.