Addition of 5% CO 2 to Inspiratory Gas Prevents Lung Injury in an Experimental Model of Pulmonary Artery Ligation

Unilateral ligation of the pulmonary artery may induce lung injury through multiple mechanisms, which might be dampened by inhaled CO . This study aims to characterize bilateral lung injury owing to unilateral ligation of the pulmonary artery in healthy swine undergoing controlled mechanical ventilation and its prevention by 5% CO inhalation and to investigate relevant pathophysiological mechanisms. Sixteen healthy pigs were allocated to surgical ligation of the left pulmonary artery (ligation group), seven to surgical ligation of the left pulmonary artery and inhalation of 5% CO (ligation + Fi 5%), and six to no intervention (no ligation). Then, all animals received mechanical ventilation with Vt 10 ml/kg, positive end-expiratory pressure 5 cm H O, respiratory rate 25 breaths/min, and Fi 50% (±Fi 5%) for 48 hours or until development of severe lung injury. Histological, physiological, and quantitative computed tomography scan data were compared between groups to characterize lung injury. Electrical impedance tomography and immunohistochemistry analysis were performed in a subset of animals to explore mechanisms of injury. Animals from the ligation group developed bilateral lung injury as assessed by significantly higher histological score, larger increase in lung weight, poorer oxygenation, and worse respiratory mechanics compared with the ligation + Fi 5% group. In the ligation group, the right lung received a larger fraction of Vt and inflammation was more represented, whereas CO dampened both processes. Mechanical ventilation induces bilateral lung injury within 48 hours in healthy pigs undergoing left pulmonary artery ligation. Inhalation of 5% CO prevents injury, likely through decreased stress to the right lung and antiinflammatory effects.