Do they sedate you for a thoracentesis?

Chest Radiograph

Because pleural fluid is denser than air-filled lung, a free-flowing effusion will first accumulate in the most dependent parts of the thoracic cavity: the subpulmonic space and the lateral costophrenic sulcus. Pleural effusions are usually visible on an upright chest radiograph if 200 to 250 mL of fluid is present. A lateral radiograph may reveal an effusion of 50 to 75 mL.

The earliest recognized sign of a pleural effusion on an upright chest radiograph is blunting of the lateral costophrenic angle, which may be seen on either the frontal or the lateral view [Fig. 9.2]. With a larger free-flowing effusion, the pleural fluid appears as a meniscus that curves downward toward the mediastinum in the frontal view and appears “lowest” midway through the thoracic cavity on the lateral view [Fig. 9.3]. The presence of air from pneumothorax or abscess may alter the appearance of the meniscus to more of a straight line [air-fluid level].

Occasionally, up to 1000 mL of fluid collects in the subpulmonic space and causes neither blunting of the costophrenic angle nor a meniscus appearance on the upright radiograph. This is called asubpulmonic effusion [Fig. 9.4]. This should be suspected if the hemidiaphragm is elevated and the hemidiaphragm dome peaks more laterally than expected on the upright frontal radiograph.

Pleural effusions are challenging to identify on chest radiograph in the supine patient, and even a significant amount of fluid may not be appreciated. If the effusion is large enough, a diffuse haziness may be appreciated [Fig. 9.5]. Other findings include apical capping, obliteration of the hemidiaphragm, partial opacification of a hemithorax, and a widened minor fissure.

Obtaining bilateral decubitus radiographs when a pleural effusion is seen or suspected will confirm the presence of a free-flowing effusion and allow for visualization of loculations, contained abscesses, infiltrates, or masses. With the side of the effusion down, a simple pleural effusion will follow gravity and layer between the floating lung and the chest wall [Fig. 9.6]. A lateral decubitus view on the opposite side draws the fluid toward the mediastinum and allows further visualization of the lung parenchyma.

With a diseased or scarred lung, tissue adhesions can trap pleural fluid within the parietal, visceral, or interlobar surfaces. Because these adhesions anchor the fluid, loculated effusions are often described as “D-shaped” [Fig. 9.7]. Fluid loculated in the fissures assumes a lenticular shape.

In the case of a massive pleural effusion, the entire hemithorax is opacified [Fig. 9.8]. On such films, identification of mediastinal shift is a key to identifying the underlying disease process. In the absence of a diseased lung or mediastinum, large fluid collections push the mediastinum contralaterally. When the mediastinum is shifted toward the effusion, the lungs and main stem bronchi are diseased, obstructed, or both. When the mediastinum is fixed midline, it is likely invaded by tumor.

B. MATERIALS AND PREPARATION

1.

Thoracentesis kit: Become familiar with the kit available. All are based on a catheter-over-needle design.

Create your own kit.

Sterile tray, sterile drapes, prep kit, sterile 4 × 4 gauze, sterile dressing, sterile gown, gloves, and mask

Anesthesia—10 to 20 ml Luer–Lock syringe; 25-gauge needles for infiltration; 1.5- to 2-inch, 22-gauge needle for infiltration; 10 ml 1% lidocaine with 1:1,000,000 epinephrine for local anesthetic

Needle insertion/collection—0- to 60 ml Luer–Lock syringe for aspiration, needle catheter [depending on technique chosen]: 2-inch, 20- to 22-gauge needle, over-the-needle catheter [16- to 20-gauge needle]; scalpel [used during needle catheter technique only]; 3-way stopcock; 2 curved clamps, intravenous pressure tubing, collection container, 500- to 1000-ml vacuum bottle

Specimen tubes—one plain tube, one EDTA tube, iced blood gas syringe

Culture tubes—both aerobic and anaerobic, 50-ml plain tube for cytology; one heparin tube

Interpretation of Results

First take a look at the fluid [Table 218.1]. Food particles in the fluid suggests an esophageal perforation; black fluid suggests anAspergillus infection. Milky fluid indicates a chylothorax or pseudochylothorax, whereas bile-staining suggests a biliary fistula [cholothorax]. Anchovy paste suggests an amoebic abscess; a putrid odor suggests anaerobic empyema.

If etiology is not determined by the appearance of the fluid, the next important distinction is whether the fluid is a transudate [unbalanced hydrostatic forces] or an exudate [“leaks in the system or a damaged system”]. If the lactate dehydrogenase [LDH] levels inthe fluid and the pleural fluid/serum ratios for LDH and protein are all normal [these are the Light criteria; seeTable 218.2], the fluid is a transudate and further studies are unlikely to give useful information. Light criteria are 99.5% sensitive for diagnosing exudative effusion; they differentiate exudative from transudative effusions in 93 to 96% of cases. In the absence of known serum levels, simply knowing pleural fluid protein [≥30g/L] and LDH levels [>0.45 of upper limit of normal serum level] is useful. These values have a 92% concordance with the Light criteria [Murphy]. A recent systematic review found that a pleural cholesterol level greater than 55 mg/dL, a pleural to serum cholesterol ratio greater than 0.3, or a pleural LDH level greater than200 IU or U/L were among the most specific findings for diagnosing exudate [Wilcox et al., 2014].

Most transudates are from congestive heart failure, with the rest associated with hypoalbuminemia, hepatic hydrothorax, hydronephrosis, pulmonary embolism, peritoneal dialysis, or trapped lung. Occasionally, pleural effusions that appear to be due to congestive heart failure may be classified as an exudate using traditional measures of LDH and total protein, particularly if the patient has been treated with diuretics. In this case, the use of a serum–pleural effusion albumin gradient [SEAG] can be useful. A serum–pleural effusion albumin gradient of greater than 1.2 g/dL will classify the pleural effusion as transudative, and less than 1.2 g/dL as exudative [Roth and colleagues, 1990]. One diagnostic approach is to send some of the fluid for protein, pH, LDH measurement, and possibly aerobic and anaerobic culture and sensitivities while storing the remaining fluid for the other tests if the fluid proves to be an exudate [Fig. 218.4]. Causes of exudates include cancer, pneumonia, trauma, tuberculosis, pulmonary embolism, pancreatitis, rheumatoid arthritis, and systemic lupus erythematosus. Up to 50% of patients with a pulmonary malignancy will have neoplastic cells in the pleural fluid, so sending exudates for cytology is important. Low pH [