Although history (cough, dyspnea, or pleuritic chest pain) and physical findings (dullness to percussion, decreased breath sounds, and decreased vocal fremitus) suggest that an effusion is present, chest radiography or ultrasonic examination is essential to confirm the clinical suspicion. Thoracentesis can be performed for diagnostic or therapeutic reasons. When done for diagnostic reasons, the procedure should be performed whenever possible before any treatment has been given to avoid confusion in interpretation [5]. Analysis of pleural fluid has been shown to yield clinically useful information in more than 90% of cases [2]. The four most common diagnoses for symptomatic and asymptomatic pleural effusions are malignancy, congestive heart failure, parapneumonia, and postoperative sympathetic effusions. A diagnostic algorithm for evaluation of a pleural effusion of unknown etiology is presented in Figure 10.1. In patients whose pleural effusion remains undiagnosed after thoracentesis and closed pleural biopsy, thoracoscopy should be considered for visualization of the pleura and directed biopsy. Thoracoscopy has provided a positive diagnosis in more than 80% of patients with recurrent pleural effusions that are not diagnosed by repeated thoracentesis, pleural biopsy, or bronchoscopy.

Therapeutic thoracentesis is indicated to remove fluid or air that is causing cardiopulmonary embarrassment or to relieve severe symptoms. Definitive drainage of the pleural space with a thoracostomy tube must be done for a tension pneumothorax (PTX) and should be considered for a PTX that is slowly enlarging, any size PTX in the mechanically ventilated patient, hemothorax, or the instillation of a sclerosing agent after drainage of a recurrent malignant pleural effusion.

Absolute contraindications to performing a thoracentesis are an uncooperative patient, the inability to identify the top of the rib clearly under the percutaneous puncture site, a lack of expertise in performing the procedure, and the presence of a coagulation abnormality that cannot be corrected. Relative
contraindications to a thoracentesis include entry into an area where known bullous lung disease exists, a patient who is on positive end-expiratory pressure, and a patient who has only one “functioning” lung (the other having been surgically removed or that has severe disease limiting its gas exchange function). In these settings, it may be safest to perform the thoracentesis under ultrasonic guidance.

A number of prospective studies have documented that complications associated with the procedure are not infrequent [1,2]. The overall complication rate has been reported to be as high as 50% to 78%, and can be further categorized as major (15% to 19%) or minor (31% to 63%) [2,3]. Complication rates appear to be inversely related to experience level of the operator; the more experienced, the fewer the complications [6]. Although death due to the procedure is infrequently reported, complications may be life threatening [1].

Major complications include PTX, hemopneumothorax, hemorrhage, hypotension, and reexpansion pulmonary edema. The reported incidence of PTX varies between 3% and 30% [1,2,3,6,7], with up to one-third to one-half of those with demonstrated PTX requiring subsequent intervention. Various investigators have reported associations between PTX and underlying lung disease (chronic obstructive pulmonary disease, prior thoracic radiation, prior thoracic surgery, or lung cancer) [8,9], needle size and technique [3,8], number of passes required to obtain a sample [8], aspiration of air during the procedure, experience level of the operator [1,3,6], use of a vacuum bottle [9], size of the effusion [2,8], and mechanical ventilation versus spontaneously breathing patients. Some of the above-mentioned studies report directly contradictory findings compared to other similar studies. This is most apparent in the reported association between PTX and therapeutic thoracentesis [3,8], which was not supported by subsequent large prospective trials [8,9]. The most likely explanation for this discrepancy in the literature concerning the presumed increased risk for PTX for therapeutic over diagnostic procedures is the generally lower experience level of the operator in the first group. Small sample sizes also limit the generalization of reported findings to allow for the delineation of a clear risk profile for the development of a PTX due to thoracentesis. The presence of
baseline lung disease, low experience level of the operator with the procedure, and the use of positive-pressure mechanical ventilation appear for now to be the best-established risk factors in the literature. Further research involving more patients is needed.

Although PTX is most commonly due to laceration of lung parenchyma, room air may enter the pleural space if the thoracentesis needle is open to room air when a spontaneously breathing patient takes a deep breath. (Intrapleural pressure is subatmospheric.) The PTX may be small and asymptomatic, resolving spontaneously, or large and associated with respiratory compromise, requiring chest tube drainage. Hemorrhage can occur from laceration of an intercostal artery or inadvertent puncture of the liver or spleen even if coagulation studies are normal. The risk of intercostal artery laceration is greatest in the elderly because of increased tortuosity of their vessels. This last complication is potentially lethal, and open thoracotomy may be required to control the bleeding.

Hypotension may occur during the procedure (as part of a vasovagal reaction or tension PTX) or hours after the procedure (most likely due to reaccumulation of fluid into the pleural space or the pulmonary parenchyma from the intravascular space). Hypotension in the latter settings responds to volume expansion; it can usually be prevented by limiting pleural fluid drainage to 1.5 L or less. Other major complications are rare, and include implantation of tumor along the needle tract of a previously performed thoracentesis, venous and cerebral air embolism (so-called pleural shock) [10,11], and inadvertent placement of a sheared-off catheter into the pleural space [1].

Minor complications include dry tap or insufficient fluid, pain, subcutaneous hematoma or seroma, anxiety, dyspnea, and cough [2]. Reported rates for these minor complications range from 16% to 63% and depend on the method used to perform the procedure, with higher rates associated with the catheter-through-needle technique [2,3]. Dry tap and insufficient fluid are technical problems, and they expose the patient to increased risk of morbidity because of the need to perform a repeat thoracentesis. Under these circumstances, it is recommended that the procedure be repeated under direct sonographic guidance. Pain may originate from parietal pleural nerve endings from inadequate local anesthesia, inadvertent scraping of rib periosteum, or piercing an intercostal nerve during a misdirected needle thrust.