Infectious Pleural Effusion

Infectious pleural effusion continuously threatens health worldwide, and despite medical advances, the condition can lead to serious complications with fatality rates reaching up to 20%, rising even higher in elderly patients with underlying conditions.

Table of contents

• What is infectious pleural effusion?
• Stages of development
• Causes and bacteria
• Symptoms
• Diagnosis
• Treatment approaches
• Prognosis and complications

What is infectious pleural effusion?

Infectious pleural effusion is a condition where excess fluid builds up in the space around the lungs due to an infection. The pleura are thin membranes that line the lungs and the inside of the chest cavity. Normally, a small amount of fluid exists between these layers to help the lungs move smoothly when breathing. However, when an infection occurs in the lung tissue, such as pneumonia or lung abscess, fluid can accumulate in this space^[2][11].

Any fluid buildup that happens alongside an infectious process in the lung is called a parapneumonic effusion. When this condition worsens and bacteria can be found in the fluid, or when the fluid becomes pus, it is called empyema^[2][11].

This condition affects approximately 80,000 adults in the United States and United Kingdom each year, with medical costs reaching around USD 500 million. Pleural effusion related to pneumonia is particularly common, as 40% of patients admitted with pneumonia develop fluid around their lungs^[2][4].

Stages of development

From a medical standpoint, infectious pleural effusion develops through three distinct stages^[2]:

1. Exudative stage: This is the early phase when watery fluid begins to accumulate in response to infection.
2. Fibrin exudation and pus formation stage: During this phase, the fluid becomes thicker as proteins and inflammatory cells collect, and pus may form.
3. Organization stage: In the final stage, the fluid can become thick or hardened, and scar tissue may develop, making treatment more difficult.

Causes and bacteria

Infectious pleural effusion develops when bacteria or other germs cause an infection in the lungs that spreads to the pleural space. The most common cause is bacterial pneumonia. Different types of bacteria can be responsible, including Staphylococci, Pneumococci, and Haemophilus influenzae^[18].

In areas where tuberculosis is common, this infection is another important cause of infectious pleural effusion^[18]. Viral infections, especially those caused by coxsackieviruses or echoviruses, can also lead to this condition^[18].

An important point is that the bacteria causing infection in the pleural space may differ from those causing the lung infection itself. This is why analyzing the fluid and identifying the specific bacteria is very important for proper treatment^[2].

Symptoms

People with infectious pleural effusion may experience various symptoms, though some may have no symptoms at all in the early stages^[1]. Common symptoms include:

• Chest pain: This pain typically becomes worse when coughing or taking deep breaths. It is called pleuritic chest pain and happens because the inflamed pleural layers rub against each other^[1][18].
• Shortness of breath: The excess fluid around the lungs makes it harder for them to expand fully, causing difficulty breathing. This symptom may worsen when lying down^[1][20].
• Cough: A persistent cough is common, and if the underlying cause is pneumonia, the cough may produce thick, yellow, or dark mucus^[1][18].
• Fever: When the fluid becomes infected, fever often develops^[7].

Additional symptoms related to the underlying pneumonia or lung infection may include a general feeling of being unwell, called malaise, and tiredness. Some people may feel anxious or experience a sensation of suffocation, especially if the fluid buildup is large^[1].

Diagnosis

Doctors diagnose infectious pleural effusion through a combination of medical history, physical examination, imaging tests, and fluid analysis^[6].

During the physical exam, the doctor listens to the lungs with a stethoscope to check for abnormal sounds and may gently tap the chest wall to detect fluid^[1]. A chest X-ray is often the first imaging test used to confirm the presence of fluid^[1][9]. Other imaging tests may include ultrasound or computed tomography (CT) scans, which provide more detailed pictures^[4][9].

The most important diagnostic step is thoracentesis, a procedure where a thin needle is inserted between the ribs into the pleural space to remove fluid for testing. This procedure serves both diagnostic and treatment purposes^[6][9].

The removed fluid undergoes several tests to determine its characteristics and identify the cause. Doctors classify the fluid as either protein-poor and watery (transudative) or protein-rich (exudative). Infectious pleural effusion typically produces exudative fluid^[1][9].

Laboratory testing of the fluid includes checking for bacteria through cultures and examining it under a microscope. When bacteria are found or the fluid contains pus, this confirms an infectious process^[2]. The fluid may also be tested for chemical markers and cell counts that help determine the severity of the infection.

In some cases, doctors may recommend a pleural biopsy, where a small tissue sample is taken from the pleural lining. This is particularly useful when tuberculosis or other specific infections are suspected^[9].

Treatment approaches

Treatment of infectious pleural effusion has two main goals: eliminating the infection and draining the excess fluid^[2]. The foundation of treatment includes antibiotic therapy and sufficient drainage^[2][11].

Antibiotic treatment

Antibiotics are essential to fight the bacterial infection causing the pleural effusion. The choice of antibiotic depends on the specific bacteria identified or suspected. Treatment typically continues for several weeks^[12].

Drainage procedures

Removing the infected fluid is critical for recovery. Several methods can be used^[10][11]:

• Thoracentesis: This procedure uses a needle to remove fluid and can provide immediate relief from breathing difficulties^[9][10].
• Chest tube drainage: For larger amounts of fluid or more complicated cases, a flexible plastic tube called a chest tube is inserted between the ribs. This tube remains in place to allow continuous drainage^[10][11].

Enzymatic therapy

When the fluid becomes thick or contains fibrin that makes drainage difficult, doctors may use enzymes delivered through the chest tube. Research has shown that using tissue plasminogen activator (TPA) and deoxyribonuclease (DNase) together can help break down thick fluid and improve drainage^[2][12]. These medications are typically given twice daily through the chest tube, left in the pleural cavity for one hour, and then drained.

Surgical treatment

When medical treatment fails to resolve the infection or drain the fluid effectively, surgery may be necessary^[2][11]. Surgical options include:

• Thoracoscopy: A minimally invasive procedure where a small camera and instruments are inserted through small incisions to remove infected fluid and break up thick deposits.
• Pleural decortication: A more extensive surgery to remove thick, hardened tissue that has formed around the lung, allowing it to expand properly again.

Surgery is particularly important when conservative treatment fails or when complications develop^[11][12].

Prognosis and complications

Most patients with infectious pleural effusion have a relatively good prognosis when the condition is diagnosed and treated promptly^[2]. However, serious complications can occur in some cases.

The overall fatality rate for pleural cavity infections reaches up to 20%. For elderly people with underlying diseases, this rate can climb to 30%^[2][3].

Poor outcomes can be related to several factors including the patient’s overall health condition, delayed diagnosis, improper selection of antibiotics, or bacteria that are resistant to antibiotics^[2].

The key to better outcomes is early evaluation and proper staging of the disease. Prompt drainage when needed can prevent prolonged hospital stays and reduce the need for more invasive procedures later^[11].