Inhaled CO vs. Hypercapnia Obtained by Low Tidal Volume or Instrumental Dead Space in Unilateral Pulmonary Artery Ligation: Any Difference for Lung Protection?

Background: Unilateral ligation of the pulmonary artery (UPAL) induces bilateral lung injury in pigs undergoing controlled mechanical ventilation. Possible mechanisms include redistribution of ventilation toward the non-ligated lung and hypoperfusion of the ligated lung. The addition of 5% CO to the inspiratory gas (FiCO) prevents the injury, but it is not clear whether lung protection is a direct effect of CO inhalation or it is mediated by plasmatic hypercapnia.