Ventilation-Perfusion Mismatch in Patients with Pleural Effusion

Abstract

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 (VA/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 AaPO2 was 28.7+/-10.0 mm Hg. Patients had broadened unimodal VA/Q distributions with small amounts of blood flow perfusing lung units with low VA/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 perfusing low VA/Q units. While thoracentesis drained 693+/-424 ml of fluid and caused a significant fall in mean pleural pressure (by -10.7 +/- 7.1 mm Hg; p < 0.01), PaO2, AaPO2, and shunt remained unchanged; only the amount of blood flow perfusing low VA/Q ratios increased slightly (2.4+/-2.6%; p < 0.05). This study shows that: (1) intrapulmonary shunt is the main mechanism underlying arterial hypoxemia in patients with PE and (2) effective thoracentesis has minor short-term effects upon pulmonary gas exchange. These findings are in accord with delayed (> 30 min) pulmonary volume re-expansion after thoracentesis with or without the coexistence of mild ex vacuo pulmonary edema.

Effect of Ultrasound-Guided Thoracocentesis on Clinical and Physiological Outcomes in Mechanically Ventilated Patients

“…When the pleural effusion is large or chest wall compliance is reduced, effusions cause hypoxia by collapsing lung with consequent physiologic shunt [9]. Drainage of pleural effusions allowing re-expansion of collapsed lung and improvement of hypoxia, which yield variably over the subsequent 24 h and may continue for several weeks [10].…”

“…A recent meta-analysis of a total 118 patients demonstrated an overall 18% improvement in the PaO 2 /FiO 2 ratio after effusion drainage [13]. Improvement in oxygenation may occur after drainage as areas of collapsed, poorly ventilated lung reexpand, improving ventilation-perfusion matching in these areas and reducing arteriovenous shunting [9].…”

The Correlation of Lung Function Indexes and Survival Time of Patients with Advanced Lung Cancer

“…In our study, we found that lung diffusion function indicators in lung cancer group were significantly lower than those in normal control group with statistically significant difference, which mean that lung cancer may cause the decline of diffusion function. The mechanism for this may as follows: Firstly, the obstructive pneumonia, atelectasis and pleural diseases related with lung cancer can cause the reduction of lung volume, limitation of ventilation function and reduction of diffusion area, at the same time, the compensatory of surrounding lung tissue can increase the ventilation, thus cause the ventilation/perfusion imbalance [10,11]; Secondly, the blood vessels around the tumor may be blocked due to the mechanic compression, and the reduction of blood flow may increase the ventilation/perfusion ratio; Thirdly, the lung cancer cells may be transferred via the blood stream, blocking small vessels and leading to ventilation/perfusion ratio further disorder [12].…”

The management of benign non-infective pleural effusions

“…In a small number of patients, despite best efforts, it may not be possible to reach a clear diagnosis and in others it may be that treatment targeted at addressing symptoms may be a pragmatic approach preferred over and above ongoing and potentially more invasive investigations, particularly in patients with a poor prognosis. Interestingly, the removal of pleural fluid appears to result in an improvement in breathlessness not mirrored directly by the degree of improvement in gas exchange [55].…”