Effect of spontaneous breathing on ventilator-induced lung injury in mechanically ventilated healthy rabbits: a randomized, controlled, experimental study

Sixteen healthy New Zealand white rabbits were randomly placed into a spontaneous breathing group (SB Group) and a control ventilation group (CV Group). Both groups were ventilated for eight hours using biphasic positive airway pressure (BIPAP) with similar ventilator parameters: inspiration pressure (PI) resulting in a tidal volume (VT) of 10 to 15 ml/kg, inspiratory-to-expiratory ratio of 1:1, positive end-expiration pressure (PEEP) of 2 cmH2O, and FiO2 of 0.5. Inflammatory markers in blood serum, lung homogenates and bronchoalveolar lavage fluid (BALF), total protein levels in BALF, mRNA expressions of selected cytokines in lung tissue, and lung injury histopathology scores were determined.Animals remained hemodynamically stable throughout the entire experiment. After eight hours of MV, compared to the CV Group, the SB Group had lower PaCO2 values and ratios of dead space to tidal volume, and higher lung compliance. The levels of cytokines in blood serum and BALF in both groups were similar, but spontaneous breathing led to significantly lower cytokine mRNA expressions in lung tissues and lower lung injury histological scores.Preserving spontaneous breathing can not only improve ventilatory function, but can also attenuate selected markers of VILI in the mechanically-ventilated healthy lung.Ventilator-induced lung injury (VILI) is one of the most serious complications of mechanical ventilation (MV). The main mechanisms involved are over-distension of alveoli at high lung volume (volutrauma) and cyclic opening and closing of peripheral airways at low lung volume (atelectotrauma) [1]. VILI can result in serious lung parenchymal insults, such as increased permeability of the alveolar-capillary barrier, pulmonary edema, atelectasis, and parenchymal damage [2]. It may also result in the development of inflammatory responses in the local pulmonary and systemic circulations (biotrauma) [3,4], which can then affect the functions of other organs [5,6]. It is commonly acce