Gas exchange during weaning in patients with chronic obstructive pulmonary disease

In patients with chronic obstructive pulmonary disease (COPD), weaning from mechanical ventilation further aggravates ventilation-perfusion (VA/Q) inequalities. This is related to the development of an abnormal ventilatory pattern, characterized by rapid and shallow breathing, but also to the increase of cardiac output secondary to an abrupt increase in venous return to the lungs. These changes are not associated with further hypoxemia because of the complex interplay between intrapulmonary (i.e., VA/Q mismatch) and extrapulmonary factors (overall ventilation and cardiac output). Cardiac dysfunction together with oxygen consumption can influence arterial PO2 and alter the balance between intrapulmonary and extrapulmonary determinants of arterial blood gases resulting in further hypoxemia and causing unsuccessful weaning.