Thoracentesis

Thoracentesis is a medical procedure used to take fluid or air out of the space around the lungs. Doctors do this to help diagnose or treat certain health problems. During the procedure, a thin tube, called a cannula, is carefully placed into the chest after a local numbing medicine is applied.

This procedure was first done by Morrill Wyman in 1850 and later described by Henry Ingersoll Bowditch in 1852. Today, doctors often use ultrasound to guide the procedure, which helps make it safer and reduces the chance of problems.

The exact spot where the tube is placed can vary, but it is usually in the area between the ribs on the side of the chest, depending on what the doctor recommends. This careful approach helps ensure the procedure is done safely and effectively.

Indications

This procedure is used when fluid builds up in the chest outside the lung without a clear reason. Looking at this fluid can help doctors understand what’s wrong more than 90% of the time. If there’s a lot of fluid, removing it can also make the patient more comfortable and help the lung work better.

The most common reasons for fluid to collect in the chest are cancer, congestive heart failure, pneumonia, and recent surgery. In places where tuberculosis is common, it can also cause fluid to collect.

When the heart or lungs are struggling because of air (pneumothorax), fluid (pleural fluid), or blood (hemothorax) outside the lung, doctors usually use a different method called tube thoracostomy instead.

Contraindications

Sometimes, doctors might decide not to do a thoracentesis, which is a procedure to remove fluid from the chest area. This can happen if the patient is not cooperative or has certain health conditions that make the procedure risky. For example, if there is a problem with blood clotting that can’t be fixed, doctors might choose not to do the procedure.

Other reasons include if there is a certain lung condition at the spot where the procedure would be done, if the patient is using special breathing support machines, or if they only have one working lung. Even though some advice suggests not removing too much fluid to prevent complications, this guideline isn’t always clear because the amount of fluid removed doesn’t always lead to problems.

Complications

When doctors perform a thoracentesis, there can be some risks. Major risks include pneumothorax (which happens in 3 to 30% of cases), hemopneumothorax, hemorrhage, low blood pressure, and reexpansion pulmonary edema.

Smaller risks are having no fluid come out, small bruises under the skin, feeling anxious, shortness of breath, and coughing after large amounts of fluid are removed. Using ultrasound to guide the needle can help lower these risks.

Follow-up imaging

In the past, doctors often took a chest X-ray after the procedure to check for pneumothorax. But now, because ultrasound is commonly used to guide the procedure, this may not be needed for people who are feeling fine and not on a breathing machine.

Interpretation of pleural fluid analysis

Doctors have several ways to find out why fluid builds up around the lungs. First, they decide if the fluid is a transudate or an exudate. An exudate happens when fluid leaks from blood vessels into areas that are inflamed or damaged. It can come from infections, inflammation, cancer, or other issues. A transudate happens when fluid builds up because of problems like heart failure or kidney disease.

They also check the fluid for things like amylase, glucose, pH, triglycerides, and cholesterol. These tests can help find clues about conditions such as pancreatitis, infections, cancer, or ruptures in the esophagus. Counting the cells in the fluid and testing for bacteria can also help doctors understand what might be causing the fluid to collect. Looking at the cells under a microscope can sometimes show if cancer is present.

Main article: Light's criteria

See also: Light's criteria

An exudate is defined as pleural fluid to serum total protein ratio of more than 0.5, pleural fluid to serum LDH ratio > 0.6, and absolute pleural fluid LDH > 200 IU or > 2⁄3 of the normal.

An exudate is defined as pleural fluid that filters from the circulatory system into lesions or areas of inflammation. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as blood. In the case of blood it will contain some or all plasma proteins, white blood cells, platelets and (in the case of local vascular damage) red blood cells.

Exudate

• hemorrhage
• Infection
• Inflammation
• Malignancy
• Iatrogenic
• Connective tissue disease
• Endocrine disorders
• Lymphatic disorders vs Constrictive pericarditis

Transudate

• Congestive heart failure
• Nephrotic syndrome
• Hypoalbuminemia
• Cirrhosis
• Atelectasis
• Trapped lung
• Peritoneal dialysis
• Superior vena cava obstruction

Amylase

A high amylase level (twice the serum level or the absolute value is greater than 160 Somogy units) in the pleural fluid is indicative of either acute or chronic pancreatitis, pancreatic pseudocyst that has dissected or ruptured into the pleural space, cancer or esophageal rupture.

Glucose

Glucose is considered low if pleural fluid value is less than 50% of normal serum value. The differential diagnosis for this is:

• rheumatoid effusion. The levels are characteristically low (<15 mg/dL).
• lupus effusion
• bacterial empyema
• malignancy
• tuberculosis
• esophageal rupture (Boerhaave syndrome)

pH

Normal pleural fluid pH is approximately 7.60. A pleural fluid pH below 7.30 with normal arterial blood pH has the same differential diagnosis as low pleural fluid glucose.

Triglyceride and cholesterol

Chylothorax (fluid from lymph vessels leaking into the pleural cavity) may be identified by determining triglyceride and cholesterol levels, which are relatively high in lymph. A triglyceride level over 110 mg/dl and the presence of chylomicrons indicate a chylous effusion. The appearance is generally milky but can be serous.

The main cause for chylothorax is rupture of the thoracic duct, most frequently as a result of trauma or malignancy (such as lymphoma).

Cell count and differential

The number of white blood cells can give an indication of infection. The specific subtypes can also give clues as to the type on infection. The amount of red blood cells are an obvious sign of bleeding.

Cultures and stains

If the effusion is caused by infection, microbiological culture may yield the infectious organism responsible for the infection, sometimes before other cultures (e.g. blood cultures and sputum cultures) become positive. A Gram stain may give a rough indication of the causative organism. A Ziehl–Neelsen stain may identify tuberculosis or other mycobacterial diseases.

Cytology

Cytology is an important tool in identifying effusions due to malignancy. The most common causes for pleural fluid are lung cancer, metastasis from elsewhere and pleural mesothelioma. The latter often presents with an effusion. Normal cytology results do not reliably rule out malignancy, but make the diagnosis more unlikely.