The pleural cavity is the potential space between the two layers of the pleura, the thin membranes that line the lungs (visceral pleura) and the inside of the chest wall (parietal pleura). Under normal circumstances this space is not a true cavity but contains only a very thin film of lubricating fluid (around 5 to 15 ml), which allows the two pleural surfaces to slide smoothly against each other as the lungs expand and contract with each breath.
The integrity of the pleural cavity is important for normal breathing mechanics. When air enters the pleural space (pneumothorax), the lung on that side can collapse because the negative pressure that keeps it expanded is lost. When excess fluid accumulates in the pleural space (pleural effusion), it compresses the underlying lung and impairs breathing. A tension pneumothorax, in which air progressively accumulates under pressure and shifts the heart and great vessels, is a life-threatening emergency that can cause cardiac arrest.
In the cardiac context, pleural effusions can occur as a complication of heart failure (fluid from the congested venous circulation leaking into the pleural space), following open heart surgery or cardiac catheterisation, or as part of pericarditis or post-cardiac injury syndrome. Small effusions may resolve spontaneously; larger ones causing symptoms may require drainage (thoracocentesis).
Pneumothorax is a recognised procedural risk of central venous catheter insertion in the subclavian or internal jugular veins, performed routinely during critical care admission. It is therefore monitored by chest X-ray after line insertion.
« Back to Glossary Index