Sustained inflation and incremental mean airway pressure trial during conventional and high-frequency oscillatory ventilation in a large porcine model of acute respiratory distress syndrome

<p>Abstract</p> <p>Background</p> <p>To compare the effect of a sustained inflation followed by an incremental mean airway pressure trial during conventional and high-frequency oscillatory ventilation on oxygenation and hemodynamics in a large porcine model of early acute respiratory distress syndrome.</p> <p>Methods</p> <p>Severe lung injury (Ali) was induced in 18 healthy pigs (55.3 ± 3.9 kg, mean ± SD) by repeated saline lung lavage until PaO₂decreased to less than 60 mmHg. After a stabilisation period of 60 minutes, the animals were randomly assigned to two groups: Group 1 (Pressure controlled ventilation; PCV): FIO₂= 1.0, PEEP = 5 cmH₂O, V_T= 6 ml/kg, respiratory rate = 30/min, I:E = 1:1; group 2 (High-frequency oscillatory ventilation; HFOV): FIO₂= 1.0, Bias flow = 30 l/min, Amplitude = 60 cmH₂O, Frequency = 6 Hz, I:E = 1:1. A sustained inflation (SI; 50 cmH₂O for 60s) followed by an incremental mean airway pressure (mPaw) trial (steps of 3 cmH₂O every 15 minutes) were performed in both groups until PaO₂no longer increased. This was regarded as full lung inflation. The mPaw was decreased by 3 cmH₂O and the animals reached the end of the study protocol. Gas exchange and hemodynamic data were collected at each step.</p> <p>Results</p> <p>The SI led to a significant improvement of the PaO₂/FiO₂-Index (HFOV: 200 ± 100 vs. PCV: 58 ± 15 and T_Ali: 57 ± 12; p < 0.001) and PaCO₂-reduction (HFOV: 42 ± 5 vs. PCV: 62 ± 13 and T_Ali: 55 ± 9; p < 0.001) during HFOV compared to lung injury and PCV. Augmentation of mPaw improved gas exchange and pulmonary shunt fraction in both groups, but at a significant lower mPaw in the HFOV treated animals. Cardiac output was continuously deteriorating during the recruitment manoeuvre in both study groups (HFOV: T_Ali: 6.1 ± 1 vs. T₇₅: 3.4 ± 0.4; PCV: T_Ali: 6.7 ± 2.4 vs. T₇₅: 4 ± 0.5; p < 0.001).</p> <p>Conclusion</p> <p>A sustained inflation followed by an incremental mean airway pressure trial in HFOV improved oxygenation at a lower mPaw than during conventional lung protective ventilation. HFOV but not PCV resulted in normocapnia, suggesting that during HFOV there are alternatives to tidal ventilation to achieve CO₂-elimination in an "open lung" approach.</p>

Abstract licence: CC BY-NC-ND

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