Ventilation-Perfusion Mismatch in Patients with Pleural Effusion Effects of Thoracentesis

Pleural effusion (PE) often causes abnormal pulmonary gas exchange. Thoracentesis is commonly used to relieve dyspnea in patients with PE, but its effect upon arterial oxygenation is varied and poorly understood. This investigation sought to: (1) characterize the distribution of ventilation-perfusion (V˙ a/Q˙) ratios in patients with PE and ( 2) assess the effects of PE drainage by thoracentesis upon pulmonary gas exchange. We studied nine patients (two females) with a mean age of 39 ± 20 (SD) yr. All of them had PE of recent clinical onset ( < 2 wk of symptoms), without other apparent medical conditions. Before thoracentesis, PaO2 was 82.3 ± 10.2 mm Hg and AaPo 2 was 28.7 ± 10.0 mm Hg. Patients had broadened unimodal V˙ a/Q˙ distributions with small amounts of blood flow perfusing lung units with low V˙ a/Q˙ ratios ( < 0.1) (1.4 ± 2.2%) and mild intrapulmonary shunt (6.9 ± 6.7%). PaO2 was significantly related to the amount of shunt (rho = − 0.82; p < 0.01) but not to the percentage of blood flow perfusi...