Pleural effusion: Nursing

Pleural effusion is a condition in which excess fluid accumulates in the space between the visceral layer and parietal layer of the pleura, called the pleural space.

Normally, this space contains 20 to 25 milliliters of fluid that provides lubrication, allowing the two pleural layers to slide over each other during breathing. This pleural fluid forms as a filtrate from pleural blood vessels. At the same time, it is drained into the lymphatic vessels, and this allows for regular renewal of the fluid.

Now, pleural effusion is typically caused by increased production or impaired drainage of the pleural fluid. Depending on the cause, the excess fluid in pleural effusion can be protein-poor, called transudate, or protein-rich, called exudate.

Transudate, also called hydrothorax when it involves the pleural space, forms when too much fluid starts to move from the pulmonary capillaries into the pleural space, either because of increased hydrostatic pressure or decreased oncotic pressure within the pulmonary capillaries. So increased hydrostatic pressure occurs usually in the context of heart failure, where the heart can’t pump blood effectively, so it backs up into the pulmonary vessels, leading to pulmonary hypertension; ultimately, the high pressure forces fluid out of the pulmonary capillaries and into the pleural space. On the other hand, decreased oncotic pressure can be caused by cirrhosis, which leads to decreased hepatic production of plasma proteins like albumin; or nephrotic syndrome, where renal filtration of blood is impaired, so the proteins are lost in urine.

On the other hand, exudate forms when there’s increased permeability of the pulmonary capillaries, which allows fluid, immune cells, and large proteins, along with lactate dehydrogenase or LDH, to leak out of the capillaries and into the pleural space. This can be caused by trauma, malignancy, such as lung cancer, inflammatory conditions like pancreatitis, and systemic lupus erythematosus, or an infection like pneumonia.