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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. Accumulation of pleural fluid is not a specific diagnosis but rather a reflection of an underlying process. In almost all newly discovered pleural effusions, thoracentesis should be performed to aid in the diagnosis and management of the underlying etiology.

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Hippocrates first described thoracentesis in the management of an empyema.1 Thoracentesis was used widely in World War II and the Korean conflict in lieu of a thoracotomy for chest drainage. By the time of the Vietnam War, this practice was replaced by tube thoracostomy. Today, thoracentesis is used in the diagnosis and therapy of pleural effusions, emergent and temporizing treatment of a tension pneumothorax, and the management of small, nontraumatic pneumothoraces.14

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A pleural effusion can be identified clinically and radiologically. Clinically, 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 located in the chest, abdomen, or ipsilateral shoulder. Another common symptom is a cough; its mechanism is unclear. Dyspnea occurs secondary to the space-occupying effect of the fluid and alterations in gas exchange. In extreme cases, pleural effusions can reduce cardiac output. On physical examination, tactile fremitus is absent or attenuated and there is dullness to percussion. Auscultation reveals decreased breath sounds on the involved hemithorax.

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Radiographically, on a posteroanterior (PA) chest radiograph, an effusion can be diagnosed when there is homogeneous opacification in the hemithorax, absent air bronchograms, and clouded vesicular vascular markings. In a cadaveric study, the minimum fluid volume needed to blunt the costophrenic angle was 175 mL.5 More than 500 mL had to be injected into some cadavers to blunt the costophrenic angle.5 In a study on mechanically ventilated patients, ultrasound consistently identified nonloculated pleural effusions when the effusion was at least 500 mL.6 A lateral decubitus film is often necessary and will determine whether the fluid is loculated or free-flowing. It will also be helpful if one of the following signs is present on the PA chest radiograph: a clear costophrenic angle, an elevated hemidiaphragm, a blurred contour of the diaphragmatic dome, or the gastric bubble seen more than 2 cm from the lung border in patients with left-sided pleural effusions.2 If the fluid collection is 10 mm thick on the lateral decubitus film, thoracentesis can most likely be performed using clinical skills to locate the fluid.7 If it is less than 10 mm thick, ultrasound may be needed for localization.3

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The use of ultrasound is no longer limited to Radiologists. With proper training, Emergency Physicians can utilize ultrasound for thoracentesis procedural guidance. The portable AP (anteroposterior) radiograph cannot always reliably distinguish between a pleural effusion, a pneumonia, or atelectasis.8 In these indeterminate cases, ...

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