Thoracentesis is the evacuation of fluid or air from the pleural space. This discussion is limited to the evacuation of fluid (effusion) from the pleural space in patients who have not suffered traumatic injuries. In the setting of trauma, appropriate surgical consultation should be obtained and tube thoracostomy performed to evacuate the presumed hemothorax and assess for ongoing blood loss.

The indications for thoracentesis can be either therapeutic, to remove fluid that is causing pain or respiratory distress, or diagnostic, to determine the cause of the pleural effusion. The diagnosis of pleural effusion should be established by clinical examination and chest radiograph or ultrasonography. Lateral decubitus films or ultrasonography is useful in identifying small effusions and determining whether the pleural fluid is free-flowing or loculated.

The following are relative contraindications to thoracentesis:

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  Uncooperative patient (consider procedural sedation)

  
  
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  Skin infection at the site of needle or catheter insertion

  
  
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  Thrombocytopenia, bleeding or clotting disorder, disseminated intravascular coagulation

  
  
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  Small collection of fluid or pleural adhesions (increased danger of causing iatrogenic pneumothorax; consider doing the procedure under ultrasound (US) guidance)

The pleural space is the potential space that exists between the visceral and parietal pleura in the lung. Normally, there is only a small amount (15 mL) of fluid in this space. Pleural fluid can accumulate when there is a systemic change in the forces that govern fluid production and drainage. Effusions can be classified as transudates (ultrafiltrates of plasma with a low protein concentration) or exudates (due to increased capillary permeability and the resulting accumulation of larger molecules). Common causes of transudative effusions in children are congestive heart failure, nephrotic syndrome, cirrhosis, and hypoalbuminemia. Exudative pleural effusions are usually caused by pneumonia (parapneumonic effusion), empyema, connective tissue disease, malignancy, pancreatitis, trauma, or pulmonary infarction.

Virtually all hospitals carry a commercially or locally made kit that contains most of the equipment needed for thoracentesis (Table 198-1). Some kits may contain small, flexible percutaneous catheters (“pigtail catheters”), which may be left in place after thoracentesis to permit continued drainage of fluid.