Why does fluid build up in the chest?

A pleural effusion is a build-up of fluid in the pleural space, the narrow area between the lungs and the chest wall. Normally, this space contains only a small amount of fluid that allows the lungs to move smoothly during breathing. If this balance is disrupted by disease, fluid can accumulate.

A pleural effusion is not a disease in its own right. It is a sign of an underlying condition. The fluid may build up slowly or rapidly, and identifying the cause is essential for selecting the appropriate treatment.

Lung cancer

Cancer, particularly lung cancer, is an important cause of pleural effusion. Cancer cells may spread to the pleura and interfere with lymphatic drainage. Inflammatory substances released by tumour cells can also make blood vessels more permeable, allowing fluid to enter the pleural space.

This is known as a malignant pleural effusion. The fluid is often rich in protein, may contain blood and can contain tumour cells. Typical features may include:

• shortness of breath that increases as more fluid accumulates;
• a one-sided effusion, often on the side of the tumour;
• rapid recurrence after thoracentesis;
• fatigue, coughing or pressure in the chest.

When the effusion recurs, treatment often focuses on symptom control and quality of life. An indwelling pleural catheter may allow regular drainage at home and reduce repeated hospital visits.

Heart failure

In heart failure, the heart cannot pump blood efficiently enough. Blood backs up in the vessels of the lungs and pressure rises in the pulmonary capillaries. Fluid can then pass through the vessel walls into the pleural space.

This type of effusion is usually transudative: the fluid is clear and contains relatively little protein or cellular material. Typical signs may include effusions on both sides, swelling of the lower legs, weight gain caused by fluid retention and shortness of breath when lying down or during activity.

Treatment primarily addresses the heart failure. If effusions continue to recur despite appropriate treatment, an indwelling catheter may be considered in selected cases.

Breast cancer

Breast cancer can cause a malignant pleural effusion, particularly in advanced or metastatic disease. Cancer cells may reach the chest through the lymphatic system or bloodstream and spread across the pleura. The fluid may return within days after it has been drained.

Possible features include rapid recurrence, pressure or tightness in the chest, loss of appetite, fatigue and weakness, and a one-sided effusion. For some patients, an indwelling catheter provides regular symptom relief at home.

Other cancers

Other cancers can also cause pleural effusion, including ovarian, pancreatic, gastric, liver and bowel cancers. They may spread through the peritoneum or lymphatic system and eventually affect the pleura or obstruct lymphatic drainage. Pleural effusion may occur alongside ascites and significantly reduce physical capacity.

Non-malignant causes

Not every pleural effusion is caused by cancer. Other possible causes include:

• Liver cirrhosis with ascites: fluid may pass through the diaphragm into the chest, often on the right side.
• Heart failure: increased pressure in the pulmonary circulation can cause fluid to accumulate.
• Kidney disease: severe protein loss and fluid imbalance can contribute to an effusion.
• Inflammation or infection: for example pneumonia or tuberculosis.
• Autoimmune disease: including systemic lupus erythematosus or rheumatoid arthritis.
• Pulmonary embolism: a blood clot blocking a vessel in the lung.

Diagnosis commonly involves imaging and analysis of the pleural fluid. Treatment depends on the underlying cause. For recurring effusions, a drainage catheter may also be considered.

Conclusion

A pleural effusion is always a sign that another condition needs to be investigated. Treatment should therefore address both the fluid itself and its cause. Depending on the diagnosis, an indwelling drainage system can support regular symptom relief, greater independence and care at home.

If you have questions, please contact us or speak with your healthcare team.