Thoracentesis is a term derived from the Greek meaning “to pierce the chest.” It is used today to refer to the removal of air or fluid from the thoracic cavity. Hippocrates first described thoracentesis in the management of an empyema.1 Thoracentesis was widely used in World War II and the Korean conflict in lieu of a thoracotomy for chest drainage. This practice was replaced by tube thoracostomy by the time of the Vietnam War. Thoracentesis is used today in the diagnosis and therapy of pleural effusions, as an emergent and temporizing treatment of a tension pneumothorax, and in the management of small nontraumatic pneumothoraces.1-4 Thoracentesis is generally indicated to aid in the evaluation and management of the underlying etiology in newly discovered pleural effusions. Accumulation of pleural fluid is not a specific diagnosis but rather a reflection of an underlying process.
A pleural effusion may be identified clinically and radiologically. The patient may develop pain related to irritation of the parietal pleura, compromised pulmonary mechanics, or interference with gas exchange.3 The pain may be in the abdomen, chest, or ipsilateral shoulder. Cough is a common presenting symptom, although its mechanism is unclear. Dyspnea occurs secondary to the space-occupying effect of the fluid and alterations in gas exchange. Pleural effusions can reduce cardiac output in extreme cases. Physical examination findings will depend on the size and location of the pleural effusion. Tactile fremitus may be absent or attenuated. There may be dullness to percussion. Auscultation may reveal decreased breath sounds over the involved hemithorax.
Radiographic diagnosis of pleural effusions may be made by a posteroanterior (PA) chest radiograph when there is homogeneous opacification in the hemithorax, absent air bronchograms, and clouded vesicular vascular markings.5 The minimum fluid volume injected into cadavers to blunt the costophrenic angle was between 175 and 500 mL.6 Chest computed tomography (CT) scan will provide details of the pleural effusion, associated findings, location, and size. Several studies support the routine use of ultrasound (US) to identify pleural effusions and to guide the thoracentesis procedure.
A lateral decubitus film is often necessary and will determine whether the fluid is loculated or free-flowing if CT scan and US are not available. It will be helpful if one of the following signs are present on the PA chest radiograph: blurred contour of the diaphragmatic dome, clear costophrenic angle, elevated hemidiaphragm, or the gastric bubble seen more than 2 cm from the lung border in patients with left-sided pleural effusions.2 US may be necessary in localizing effusions that are < 10 mm thick on the lateral decubitus film.7
The use of US can aid in the localization of pleural effusions that may be small or missed on plain chest films or distinguish between interpretations as possible pneumonia or atelectasis.8 Pleural fluid can be identified on US as a black hypoechoic area that appears darker than the surrounding diaphragm, liver, and lung.