1. 
   

   What are the indications for performing a thoracentesis?

   
   
2. 
   

   What steps should be taken to reduce the likelihood of complications?

   
   
3. 
   

   What diagnostic criteria differentiate the three types of pleural effusions, namely, transudates, exudatives, and empyema?

Physicians or other providers perform an estimated 173,000 thoracenteses in the United States every year. In general, the procedure is usually safe and well tolerated. However, when iatrogenic pneumothorax does occur, chest tube insertion may be required for up to 50% of the patients with an increased average length of stay of approximately four days. This complication not only incurs substantial increase in cost, but also increases morbidity and mortality.

Pleural effusions develop secondarily to systemic changes (transudates) or to local causes (exudates). Systemic causes that lead to the formation and absorption of pleural fluid most commonly include left ventricular heart failure, pulmonary embolism, cirrhosis, and renal disease. Acute pancreatitis may cause a left-sided pleural effusion. Pleural effusions commonly occur after abdominal surgery due to the porous diaphragm and are usually benign. Renal diseases that can cause pleural effusion include the nephrotic syndrome and urinothorax from hydronephrosis. Myxedema and cerebrospinal fluid leak to the pleura are other causes of transudates.

Local causes (exudates) are most commonly bacterial pneumonia, viral infection, malignancy, and pulmonary embolism. Approximately 40% of patients with community-acquired pneumonia will develop pleural effusions, and approximately 10% of these will be complicated parapneumonic effusions or empyema. Parapneumonic effusions start out as sterile, reactive effusions and can rapidly progress to loculated empyema in immunocompromised patients or when there is a delay in administration of appropriate antibiotics. Other infectious causes include viral or fungal disease and tuberculosis. Failure to identify those patients with empyema or significant inflammation necessitating pleural drainage can result in trapped lung. Pancreatic pseudocyst, intraabdominal abscess, post–coronary artery bypass grafting or cardiac contusion, pericardial disease, drug-induced pleuritis, rheumatologic disease, uremia, and gynecologic disorders may also cause exudates.

The most common causes of malignant pleural effusions in descending order of frequency are lung cancer, breast cancer, and lymphoma. In a patient with a prior history of asbestos exposure, mesothelioma should be suspected, especially if the pleural effusion is grossly hemorrhagic. While dullness to percussion and reduced tactile fremitus are valuable findings to help identify a pleural effusion (positive likelihood ratio [LR+], 8.7 and 5.7, respectively)1, the physical examination is usually not helpful in diagnosing the cause of the pleural effusion. If a patient has yellow, dystrophic nails, chronic peripheral edema, and chronic exudative effusions, the yellow nail syndrome should be suspected (Moldonado, and Ryu, 2009).

Thoracentesis is performed for diagnostic or therapeutic purposes. The strict indications for thoracentesis are the presence of pleural fluid of unknown etiology where the physician cannot initiate care prior to diagnosis, and severe dyspnea. The first step is to determine whether there is fluid by radiographic imaging. On chest X-ray (CXR), a pleural effusion will characteristically push the heart to the opposite side. If, however, the opacified space does not shift the heart, it is possible that the patient has significant atelectasis as the cause. A lateral decubitus film should reveal whether there is free flowing fluid, and should be ordered to document free flow in most patients prior to thoracentesis procedure. If there is doubt, ultrasonography can identify solid from liquid pleural effusions with 98% accuracy when combined with CXR. Computed tomography (CT) imaging may be indicated prior to definitive drainage in some instances, and CT-PE protocol imaging should be performed if pulmonary embolism is suspected (See Chapters 107: Basic Chest Radiography and 108: Advanced Cardiothoracic Imaging).

For some patients, initiating treatment directed at the systemic cause (congestive heart disease, kidney disease, and cirrhosis) may be most appropriate. However, a diagnostic thoracentesis should be performed if the patient has an unexplained pleural effusion or fails to respond to treatment

In the setting of pneumonia, clinical judgment is neither sensitive nor specific in distinguishing between those patients who will require complete drainage of the pleural space due to empyema or significant inflammation. Hence, there are specific indications for a diagnostic thoracentesis as follows:

• Effusions > 1 cm in depth on a lateral decubitus chest film
  
• Increasing effusions despite appropriate antibiotic treatment
  
• Persistent unilateral effusion with persistent fever and tachycardia despite appropriate antibiotic treatment
  
• Imaging findings—pleural-based opacity with an abnormal contour on CXR or thickened parietal pleura on CT—that raise the possibility of a loculated effusion or empyema.

Therapeutic indications are usually for symptomatic relief. Most of the volume a pleural effusion occupies is by distending the diaphragm, thereby causing dyspnea. A therapeutic thoracentesis of a large pleural effusion will decrease intrathoracic volume.

It is usually prudent to perform a diagnostic thoracentesis prior to putting in a chest tube, but in situations with a very high likelihood of hemothorax such as trauma or when the lung has a large pleural effusion more than 50% of the thorax, this step may be bypassed.

Contraindications to thoracentesis include a hemodynamically unstable patient who cannot be positioned properly due to severe tachypnea or hypotension and skin infection over the proposed entry site. Relative contraindications include a coagulopathy that increases the risk of bleeding. While there is little data to support a platelet count threshold, in practice a platelet count of greater than 50,000/mm3 is generally accepted as the safe level. For patients receiving antiplatelet therapy (eg, aspirin or clopidogrel), some authorities suggest that those agents should be discontinued five days prior to thoracentesis procedure, but recent expert opinion based guidelines by the American College of Radiology state that no waiting time is necessary. Similarly, an INR of <1.5 is used as a cutoff for safely performing thoracentesis, but little data to supports this cutoff. Some studies suggest that thoracentesis can be safely performed in fully anticoagulated patients.

Notable complications from the procedure itself have been reported in the following order of decreasing frequency: pneumothorax (3–30%), infection, hemorrhage, hypotension due to a vasovagal response, reexpansion pulmonary edema, and injury to liver or spleen (Table 117-1).