Effect of thoracentesis on pulmonary gas exchange.

Abstract

The effect of thoracentesis on pulmonary gas exchange was studied in 33 patients with unilateral pleural effusions of various causes. Arterial blood gases were measured before thoracentesis and at 20 minutes, two hours, and 24 hours after the procedure. In 13 patients alveolar arterial oxygen gradient (PA-ao), physiological dead space:tidal volume ratio (VD/VT), physiological shunt, and "sanatomical" shunt were also determined before and two hours after thoracentesis. The Pao, showed a significant increase at each time, reaching a maximum at 24 hours (mean (SD) increase f 1 (0.74) kPa; 8-17 (5.57) mm Hg). A concurrent significant decrease of PA-ao, was observed (mean (SD) 1-72 (0.77) kPa; 12-92 (5.78) mm Hg). This was accompanied by a small but significant decrease of "anatomical" shunt (2.4% (1-5%)) and a greater decrease of the physiological shunt (6.5% (4-3%)), while VD/VT did not change. The results are probably due to improved ventilation perfusion relationships with, in particular, an increase in the ventilation of parts of the lung previously poorly ventilated but well perfused.The effect of thoracentesis on arterial blood oxygenation is controversial; most studies report a decrease in arterial oxygen tension (Pao)'-' and this has been attributed to alteration of ventilation perfusion (VA/ Q) matching. Two of these studies, however, were limited to measuring the changes in Pao, and only Brown et a1' made measurements of the alveolararterial oxygen tension difference (PA-ao,) and of the "anatomical" shunt fraction. The changed VAIQ relationships have been attributed to interstitial oedema occurring when blood flow increases abruptly through previously compressed lung, and to negative pressure in the capillary bed produced by decompression.' 4In our experience, decrease of Pao, is not a frequent finding and improvement of the-Pao, is the rule. We have studied changes in the arterial-blood gases immediately after thoracentesis and two and 24 hours later. We have investigated the possible causes of observed changes by measuring the PA-ao, physiological shunt, "anatomical" shunt, and the physiological dead space to tidal volume ratio (VD/ VI).

Management of malignant pleural effusions

“…Thoracentesis has short-term effects on pulmonary gas exchange [110]. The effect on arterial oxygen tension (Pa,O 2 ) is variable, and it can increase, remain the same, or decrease [109][110][111][112]. After therapeutic thoracentesis, there appears to be delayed lung volume re-expansion, with or without the coexistence of minimal pulmonary oedema [113].…”

“…Thoracentesis has short-term effects on pulmonary gas exchange [110]. The effect on arterial oxygen tension (Pa,O 2 ) is variable, and it can increase, remain the same, or decrease [109][110][111][112].…”

Respiratory Muscle Strength and Lung Function in Patients Undergoing Medical Thoracoscopy

“…In our study, we used the French calibrated talc for pleurodesis that is not associated with ARDS [3,29]. The secondary improvement of gas exchange in our patients could presumably be due to an increase in ventilation in the parts of the lung previously poorly ventilated, yet perfused following thoracoscopy [30], corroborating that no significant V/Q imbalance nor diffusion limitations were present in our patients [22]. …”

CT Volumetric Analysis of Pleural Effusions

“…Gas exchange is also affected to a lesser degree, with mild improvements in arterial oxygenation and A-a gradients after therapeutic thoracentesis (24,25). In addition, large pleural effusions expand the thoracic cage which in turn shifts the length-tension curve of the inspiratory muscles to an unfavorable position, contributing to the sensation of dyspnea (10).…”