• Thoracentesis is performed with insertion of a needle or a catheter into the pleural space, which allows for removal of pleural fluid.

• Pleural effusions are defined as the accumulation of fluid in the pleural space that exceeds 10 to 20 mL and results from the overproduction of fluid or disruption in fluid reabsorption.¹

• Thoracentesis is not used to verify the presence of pleural effusion. Diagnosis of pleural effusion is made via clinical examination, patient symptoms, and diagnostic techniques. A number of techniques can demonstrate pleural effusion with varying levels of sensitivity. Percussion requires a minimum of 300 to 400 mL for identification of a pleural effusion, whereas a standard chest radiography requires 200 to 300 mL. Lateral decubitus radiographs can be used to recognize smaller fluid amounts and highlight whether present fluid is free flowing. Ultrasound scan, computed tomography (CT) scan, and magnetic resonance imaging (MRI) technology can detect 100 mL of fluid with 100% sensitivity.¹ Therefore, initial diagnosis of pleural effusion should use imaging techniques such as chest radiographs, ultrasound scans, CT scans, or MRI combined with patient symptoms and clinical examination findings.

• Diagnostic thoracentesis is indicated for differential diagnosis for patients with pleural effusion of unknown etiology. A diagnostic thoracentesis may be repeated if initial results fail to yield a diagnosis.

• Therapeutic thoracentesis is indicated to relieve the symptoms (e.g., dyspnea, cough, hypoxemia, or chest pain) caused by a pleural effusion.

• Pleural effusions are classified as either transudative or exudative effusions.

• Exudative effusions indicate a local etiology (e.g., pulmonary embolus, infection), whereas transudative effusions usually are associated with systemic etiologies (e.g., heart failure).

• Samples of pleural fluid are analyzed and assist in distinguishing between exudative and transudative etiologies of effusion. Results of laboratory tests on pleural fluid alone do not establish a diagnosis; instead the laboratory results must be correlated with the clinical findings and serum laboratory results.

• Exudative pleural effusions meet one of the following criteria¹:

• A transudative pleural effusion is considered when none of the exudative criteria is met and is usually associated with systemic etiologies (e.g., heart failure), whereas exudative effusions indicate a local etiology (e.g., pulmonary embolus, infection, open heart surgery).

• Relative contraindications for thoracentesis include the following:

^• Ultrasound scan–guided thoracentesis is thought to reduce complications, especially when used in the last four patient groups listed in the relative contraindications list.3,4

• Complications commonly associated with thoracentesis include:

• Recent studies have shown a reduction in complications with ultrasound scan–guided technique, especially when used in the last four patient groups listed in the relative contraindications list.4–6

• Pneumothorax is the most common postthoracentesis complication with a reported incidence rate between 3% and 30%.¹¹

• Hemorrhagic complications are more likely to occur in elderly patients because of tortuosity of vessels.⁸

• Hypotension can occur as part of the vasovagal reaction during or hours after the procedure. If it occurs during the procedure, cessation of the procedure and atropine instillation may be necessary. If hypotension occurs after the procedure, it is likely the result of fluid shifting from pleural effusion reaccumulation. In this situation, the patient is likely to respond to fluid resuscitation.¹¹

• Development of cough generally initiates toward the end of the procedure and should result in procedure cessation.

• Reexpansion pulmonary edema is thought to occur from overdraining of fluid too quickly. Limitation of this complication may be accomplished by minimizing fluid removal to 1000 mL,¹¹ but at least one study found no correlation with drainage of up to 2000 mL as long as the patient was symptom free during the procedure.⁵

Diagnostic Thoracentesis