High-amplitude bubble CPAP versus a high-flow tracheal comparator in a rat model of acute lung injury

Bubble continuous positive airway pressure (BCPAP) superimposes pressure oscillations on baseline distending pressure, but the incremental benefit of greater oscillation amplitude remains uncertain. We compared high-amplitude BCPAP with conventional BCPAP and a non-bubbling high-flow tracheal comparator in a rat model of acute lung injury induced by saline lavage followed by a 30-min ventilation-associated second mechanical insult. Rats were assigned to high-amplitude BCPAP (135° expiratory limb, n=8), conventional BCPAP (0°, planned n=4), or the high-flow tracheal comparator (n=8). Sequential waveform recordings in one additional rat showed oscillation amplitudes of 0.96 and 0.70cm H₂O and mean airway pressures of 5.35 and 5.08cm H₂O for 135° and 0°, respectively; these descriptive measurements were not subjected to inferential testing. Compared with the high-flow tracheal comparator, high-amplitude BCPAP was associated with higher PaO₂ and pH, lower PaCO₂, and lower lung wet-to-dry ratio, bronchoalveolar lavage fluid protein, TNF-α, and IL-6. Compared with conventional BCPAP, no sustained blood-gas advantage was detected; IL-6 was lower and respiratory rate was lower only at 140min. Histological injury scores did not differ among groups. These findings support a benefit of the high-amplitude BCPAP configuration over the high-flow tracheal comparator for selected outcomes, but do not establish a consistent incremental benefit over conventional BCPAP or an effect attributable specifically to oscillation amplitude.