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

Background 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.Methods Severe lung injury (Ali) was induced in 18 healthy pigs (55.3 +/- 3.9 kg, mean +/- SD) by repeated saline lung lavage until PaO2 decreased 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 PaO2 no 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.Results 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 Conclusion 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.