Final answer:
The CO2 A-a gradient generally increases in cases of pulmonary embolism due to ventilation-perfusion mismatch, leading to an impaired exchange of gases and less removal of CO2 through the alveoli.
Step-by-step explanation:
CO2 A-a Gradient in Pulmonary Embolism The CO2 A-a gradient typically increases in the event of a pulmonary embolism (PE). A pulmonary embolism can disrupt the blood flow in the pulmonary circulation, leading to areas of the lung that are ventilated but not perfused. This mismatch results in less carbon dioxide being removed from the venous blood through the alveoli, hence the increase in alveolar-arterial (A-a) gradient.
Normally, the A-a gradient for CO2 is small because CO2 diffuses more readily across the alveolar-capillary membrane compared to oxygen. However, in PE, the obstruction causes ventilation-perfusion (V/Q) mismatch, which impairs the proper exchange of gases, leading to a higher A-a gradient for CO2.