Bubble CPAP support after discontinuation of mechanical ventilation protects rat lungs with ventilator-induced lung injury

Abstract

Background: Bubble continuous positive airway pressure (BCPAP) has been used in neonates with respiratory distress for decades, but its lung-protective effect and underlying mechanism has not been investigated. Objectives: To test the hypothesis that BCPAP use after extubation decreases lung injury and that alterations to lung nitric oxide synthase (NOS) 3 expression may be one of the underlying mechanisms. Methods: We compared gas exchange, lung injury severity, and lung NOS expression among rats with ventilatorinduced lung injury (VILI) treated with either BCPAP or spontaneous breathing. After high tidal volume ventilation for 30 min, the rats were randomly divided to three groups: a control group underwent spontaneous breathing (n = 7), and two BCPAP groups were treated with the bubble technique with either a 2.5-mm-diameter (n = 7) or a 5.5-mm-diameter (n = 7) expiratory limb for 2 h. Results: The bubble technique 2.5 and 5.5 mm diameter combined) resulted in a significantly higher Pa O 2 , decreased alveolar protein levels (1.01 vs. 1.43 mg/kg, p < 0.05), a lower lung injury score (3.87 vs. 4.86, p < 0.05), and decreased NOS3 expression (1.99 vs. 3.32, p < 0.05) compared to spontaneous breathing in the control group. BCPAP with a 2.5-mm-diameter and with a 5.5-mmdiameter expiratory limb was not different with regard to gas exchange, alveolar protein levels, and lung injury scores, but there was a trend for lower NOS3 expression in the 5.5-mm group (1.41 vs. 2.56, p = 0.052). Conclusions: BCPAP decreases lung injury in rats with VILI after stopping mechanical ventilation. Attenuation of lung NOS3 expression may be one of the underlying mechanisms.