[Effect of thoracentesis on arterial blood gas tension]

The effect of thoracentesis on arterial blood gas tension was studied in 30 patients with unilateral free pleural effusions of various causes. Arterial blood gases were measured before thoracentesis and at 20 minutes, two hours after the procedure. P(A-a)O2 was determined at the same time. The PaO2, PaCO2 and HCO3 showed significant decrease but the concurrent significant increase of the P(A-a)O2 before thoracentesis. The PaO2 showed increase and P(A-a)O2 decrease but the PaCO2 not changes after thoracentesis 20 minutes and two hours. The results suggested that pleural effusion might result in hypoxaemia and chronic compensated alkalosis.