Pleural Effusion: Causes, Thoracentesis, and How to Prevent Recurrence

When your lungs feel like they’re trapped under a heavy blanket, even breathing becomes a struggle. That’s what pleural effusion does-fluid builds up between the lung and chest wall, squeezing the lung and making every breath harder. It’s not a disease on its own, but a sign something deeper is wrong. About 1.5 million people in the U.S. deal with this each year, and for many, it’s linked to heart failure, pneumonia, or cancer. The good news? We know how to find the cause, remove the fluid safely, and stop it from coming back.

What Causes Pleural Effusion?

Transudative effusions make up about half of all cases. They’re usually from heart failure. When the heart can’t pump well, pressure builds in the blood vessels around the lungs, and fluid gets pushed out. Liver disease and kidney problems like nephrotic syndrome can also cause this type. In these cases, the fluid is clear and low in protein.

Exudative effusions are more serious. They’re caused by infections, cancer, or blood clots. Pneumonia is the biggest culprit-40 to 50% of exudative cases come from lung infections. Cancer is next, responsible for 30 to 40%. That’s why doctors don’t ignore even small amounts of fluid. About 25% of effusions that seem unexplained turn out to be cancer when tested.

Other causes include pulmonary embolism (a blood clot in the lung), tuberculosis, and even after heart surgery. The fluid here is thicker, with higher protein and enzyme levels. A simple test called Light’s criteria helps tell them apart. If the fluid’s protein is more than half the blood’s protein, or if the LDH enzyme is too high, it’s exudative. This test is 99.5% accurate.

How Thoracentesis Works-and Why Ultrasound Is Essential

But here’s the thing: doing it without ultrasound is risky. Ten to 30% of unguided procedures cause complications. Pneumothorax-a collapsed lung-is the most common. You might not feel it right away, but you’ll start coughing or struggling to breathe. Hemorrhage and re-expansion pulmonary edema (fluid flooding the lung after it reopens) are rarer but dangerous.

Ultrasound changes everything. It shows exactly where the fluid is, avoids hitting the lung or blood vessels, and cuts complication rates by nearly 80%. Studies show the risk of pneumothorax drops from 18.9% to just 4.1% when ultrasound is used. That’s why it’s no longer optional-it’s the standard.

Doctors usually insert the needle between the 5th and 7th ribs on your side, near the armpit. For diagnosis, they take 50 to 100 milliliters. For relief, they can safely remove up to 1,500 milliliters in one go. More than that increases the risk of re-expansion edema. That’s why they monitor pressure during the procedure now. If pressure stays below 15 cm H2O, you’re unlikely to have complications.

The fluid gets tested for protein, LDH, pH, glucose, and cancer cells. A low pH (below 7.2) or low glucose (under 60 mg/dL) means infection or inflammation is advanced. High LDH (over 1,000 IU/L) often points to cancer. Cytology finds cancer cells in about 60% of malignant cases. If it’s negative, they may need a biopsy later.

Stopping Recurrence: It All Depends on the Cause

For heart failure patients, recurrence drops from 40% to under 15% when doctors optimize treatment. That means diuretics like furosemide, ACE inhibitors, and beta-blockers. Monitoring NT-pro-BNP levels helps fine-tune doses. When done right, the effusion doesn’t return.

With pneumonia, the goal is to clear the infection and drain the fluid before it turns into empyema-a pus-filled infection. If the fluid’s pH is below 7.2, glucose under 40 mg/dL, or Gram stain is positive, you need a chest tube. Without drainage, 30 to 40% of these cases become empyema, which requires surgery.

But malignant effusions are the toughest. After a single thoracentesis, half of them come back within 30 days. That’s why doctors don’t just drain and wait. They go straight to prevention.

Two main options exist: pleurodesis and indwelling pleural catheters. Pleurodesis means irritating the pleural space with talc or chemicals so the lung sticks to the chest wall. Talc works in 70 to 90% of cases. But it’s painful-60 to 80% of patients need strong pain meds afterward. It also requires hospital stays of 5 to 7 days.

Indwelling pleural catheters are changing the game. A thin tube stays in place for weeks. You drain fluid at home, usually once or twice a week. Success rates hit 85 to 90% after six months. Patients go home the same day. Hospital stays drop from 7.2 days to just 2.1. And for people with advanced cancer, it means more control, less pain, and better quality of life.

For post-surgery effusions-common after heart bypass-most resolve on their own. But if more than 500 mL drains daily for three days straight, doctors will keep a chest tube in longer. With that approach, recurrence drops to just 5%.

What Doctors Are Doing Differently Now

Also, doctors now avoid chemical pleurodesis for non-cancer cases. There’s no proof it works for heart failure or infection-related effusions. It just adds risk.

The move toward personalized care is powerful. For lung cancer patients, talc pleurodesis works better than for breast cancer. For those with poor lung function, indwelling catheters are safer. Yale Medicine’s data shows recurrence for malignant effusions dropped from 50% to 15% when treatment matched the cancer type and patient’s overall health.

Even survival rates are improving. Between 2010 and 2020, five-year survival for people with malignant pleural effusion jumped from 10% to 25%. That’s thanks to better targeted therapies, earlier diagnosis, and smarter drainage strategies.

What You Should Know If You’re Diagnosed

• Is this transudative or exudative? That tells us what to look for next.
• Was ultrasound used during the procedure? If not, ask why.
• What’s the plan to prevent it from coming back? Drainage alone isn’t enough.

Don’t let a simple fluid buildup be ignored. It’s often the first warning sign of something serious. But with the right tests and treatment, you can breathe easier-and stay that way.