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Indications

The indications for thoracentesis are relatively broad and include diagnostic and therapeutic clinical management.[3] The procedural aim is to evacuate persistent small-to-moderate pleural effusions to prevent superinfection or drain symptomatic moderate-to-large effusions. The procedure is typically performed when pleural fluid is detectable on imaging, with subsequent analysis of the fluid’s chemical, microbiological, and cytological properties to guide further clinical management.[4]

Diagnostic Indications for Thoracentesis

When thoracentesis is indicated for diagnosis, the Light criteria are instrumental in distinguishing between exudates and transudates. The analysis of pleural aspirate should routinely include a Gram stain, differential cell count, culture, cytology, protein levels, l-lactate dehydrogenase, and pH. Additional tests, such as tuberculosis (TB) screening, should be considered based on individual patient risk factors and regional prevalence. Typically, diagnostic thoracentesis extracts a small volume (20-30 mL) of accumulated fluid. Diagnostic indications for thoracentesis include:

Therapeutic Indications for Thoracentesis

A therapeutic thoracentesis is performed when the fluid volume is causing significant clinical symptoms. Typically, therapeutic thoracentesis removes a large volume (liters) of accumulated fluid. A small sample of a large-volume thoracentesis should be sent for analysis when the etiology effusion is unknown or may have changed. Therapeutic indications for thoracentesis include:

Conditions in Which Thoracentesis May Be Diagnostic and Therapeutic

Pneumonia and parapneumonic effusion

Parapneumonic effusion, an accumulation of exudative fluid in the pleural space during acute pulmonary infection, is observed in approximately 40% of patients hospitalized with bacterial pneumonia and 20% with viral or Mycoplasma pneumonia. The presence of a parapneumonic effusion increases both morbidity and mortality risks, necessitating appropriate management to improve patient outcomes.[5]

The initial stage of parapneumonic effusion, often called the exudative stage, is characterized by the simple accumulation of fluid in the pleural cavity. During this phase, imaging typically reveals a free-flowing effusion. Therapeutic thoracentesis is recommended when the effusion exceeds minimal size, defined as a thickness more significant than 10 mm but less than half of the hemithorax.[6]

If left untreated or if the infection overwhelms the immune response, the parapneumonic effusion may progress to the fibropurulent stage. At this stage, the pleural fluid generally exhibits a low pH (<7.20), low glucose levels (<60 mg/dL), elevated lactate dehydrogenase, and may become loculated. This stage often signifies microbial invasion, although cultures may be negative in up to 40% of cases.[7] Parapneumonic effusion in the fibropurulent stage is considered ‘complicated,’ as antibiotic therapy alone is insufficient. Drainage through a chest tube or surgical intervention is necessary for resolution, regardless of the effusion’s size. Empyema, a type of complicated pleural effusion, is identified by the presence of pus in the pleural space or positive Gram stain or culture results from the fluid. Treatment of empyema is similar to that of other complicated effusions.

In cases of community-acquired pneumonia requiring hospitalization, 5.5% to 7.2% of patients will develop a complicated pleural effusion or empyema.[8] Patients with a complicated pleural effusion or empyema have a higher mortality rate, and significantly so if drainage is delayed.[9] Chest tube placement is advised for effusions occupying more than 50% of the hemithorax. If these effusions are not adequately drained, they may progress to an organized or cortical stage, where fibroblasts infiltrate the pleural fluid, forming a thick visceral pleural peel and preventing lung expansion.[10] In such cases, video-assisted thoracoscopic surgery or a full thoracotomy with decortication may be required to allow lung reexpansion.[11]

Thoracentesis can diagnose and manage other conditions associated with pleural effusions. These conditions include, but are not limited to: