3.9. Applying Anatomy

Pleural Effusion

This is the accumulation of fluid in the pleural cavity, normally due to infection. The volume of fluid can reach 300ml. A chest drain is the main way to drain the fluid. One possible site for chest drain insertion is the costodiaphragmatic recess – the patient is asked to exhale fully, meaning that when the tube is inserted, the lung is at its smallest possible size, so there is less chance of piercing the lung tissue itself. On an X-ray, the costophrenic angle, i.e. the angle between the ribs and the diaphragm is blurry (technically, this is called effacement or blunting or the costophrenic angle).


Commonly called a ‘collapsed lung’. One of the pleural layers is punctured and air enters the pleural cavity. This means the pressure difference (between intrapleural pressure and alveolar pressure) is disrupted. Air in the cavity combined with the disrupted pressure difference means there is a reduction in the surface tension between the two pleural layers. The lung then collapses and gas exchange cannot occur efficiently. A chest drain is often inserted (sometimes in the fifth intercostal space) to remove the air in the pleural cavity. Search online for X-rays of pneumothoraces – the collapsed lung can be difficult to see!