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 (<7.2) can indicate a complicated parapneumonic effusion, which may require chest tube drainage. SeeTable 218.2 for potentially useful tests and their significance.

COMPLICATIONS

The most common major complication of thoracentesis is pneumothorax. Other potential complications include laceration of an intercostal neurovascular bundle and subsequent hemothorax, inadvertent puncture of subdiaphragmatic organs (e.g., liver, spleen), and local infection or pain. Patients may also experience transient hypoxia associated with thoracentesis. Finally, hypotension or pulmonary edema can occur if too much fluid is removed too quickly. In an adult-sized patient, no more than 1000 to 1500 mL of fluid should be removed at a time. In children, one should avoid taking off more than a few hundred milliliters at one time.

Pleural Effusion and Thoracentesis

Simple pleural fluid appears as an anechoic (black) space between the parietal and visceral pleura. On 2D imaging, atelectatic lung may be visible as hypoechoic tissue, often triangular in shape, moving within the pleural fluid (Videos 23.10 and23.11

Ultrasonography is more sensitive than chest radiograph but less sensitive thancomputed tomography (CT) for detecting pleural effusion.22,23 Pleural effusion volume may be estimated using several formulas, the simplest of which involves multiplying the distance between the pleural surfaces by a constant.24,25 Estimates are likely more accurate when the patient is upright.

The sonographic appearance of pleural fluid can help characterize the nature of an effusion; ultrasound is superior to CT for characterizing the internal structure of pleural effusions and may be more useful for following evolution over time.26,27 Echogenic material within an effusion may indicate septations in a complex exudative process28,29 (Videos 23.13 and23.14

Ultrasound guidance improves the success rate and safety of thoracentesis.32,33Static guidance refers to preprocedure imaging to mark the insertion site, ideally immediately before and with the patient in the same position as during the procedure.Dynamic guidance is used to direct needle movement in real time. In either technique, the needle insertion site should be selected to maximize the depth of pleural fluid, avoid lung and other structures, and allow the needle to pass over the top of a rib to avoid the intercostal neurovascular bundle. The sonographer should note the limits of downward excursion of the lung and upward excursion of the diaphragm during respiration to avoid injury to this structure. If using static guidance, the operator should hold the transducer at the anticipated angle of needle insertion and note the distance from skin to pleural fluid and the depth of pleural fluid. The depth of fluid indicating a safe volume for thoracentesis depends on the skill level of the operator and the patient’s clinical circumstances. British Thoracic Society guidelines suggest a minimum of 10 mm of pleural fluid depth, although other authors suggest 20 mm.34,35 Dynamic guidance may be required for very small or loculated pleural effusions and should be performed by operators with appropriate experience.

Thoracentesis

Thoracentesis is performed as a therapeutic or diagnostic procedure. The site for insertion of a needle or catheter into the chest is commonly selected by chest percussion. Increasing evidence suggests that real-time ultrasonography should guide thoracentesis to decrease risks of puncturing intrathoracic and intra-abdominal organs. No absolute contraindications exist for thoracentesis, although caution is advised in performing the procedure in the settings of bleeding diatheses, small volumes of pleural fluid, skin infections near the thoracentesis site, and positive pressure ventilation.

Therapeutic thoracentesis removes pleural fluid to improve dyspnea for patients with large effusions. The presence of a free-flowing effusion without loculations and radiographic evidence of shift of mediastinal structures away from the effusion identify patients likely to respond to therapeutic thoracentesis. A small-gauge catheter is inserted through the intercostal space into the pleural space with removal of fluid by a vacuum bottle or gravity system. Thoracentesis performed by repeatedly drawing aliquots of fluid out of the chest with a syringe can create a large degree of intrapleural negative pressure and remove pleural fluid beyond the ability of the lung to expand against the chest wall, which risks re-expansion pulmonary edema.

Diagnostic thoracentesis is performed when the etiology of a pleural effusion remains uncertain after an initial clinical evaluation. Patients who present with clearcut evidence of conditions known to cause incidental pleural effusions, such as congestive heart failure, do not require a diagnostic thoracentesis. Thoracentesis should be performed if patients do not experience resolution of the effusion after treatment of the primary condition.

Diagnostic thoracentesis is performed by inserting a small-gauge needle attached to a syringe or a catheter into the pleural space. Sufficient fluid is obtained to send for hematologic, cytologic, and microbiologic studies (Table 1). The specific studies ordered vary on the basis of the patient's clinical presentation and suspected cause of the effusion.

Table 1. Routine tests for initial pleural fluid analysis

Complications of thoracentesis are listed in Table 2. With proper technique and ultrasonographic guidance, the procedure is well tolerated with rare instances of life-threatening problems. Patients managed in the intensive care unit with positive pressure ventilation have a low risk pneumothorax from thoracentesis, but the pneumothorax may be a tension pneumothorax when it does occur. Chest radiographs are not needed after thoracentesis unless patients develop signs of intrathoracic complications.

Table 2. Complications of thoracentesis

Thoracentesis

Thoracentesis is often the first step in both the diagnosis and treatment of MPEs from breast disease. It is not definitive, however, because the mean recurrence interval is within 4.2 days, and the overall recurrence rate is 98% within 30 days.3 In the case of MPE, thoracentesis is more useful as a diagnostic technique because there is no mechanism to prevent recurrence of fluid accumulation or continued drainage. Despite its short therapeutic duration, a thoracentesis not only confirms the cause of the effusion but also can usually ascertain whether the fluid can be removed and whether the lung is able to reexpand. Drainage of up to as much as 1 to 2 L at the initial thoracentesis is warranted. Although the sudden evacuation of more than 1.5 L of pleural fluid of a chronically collapsed lung has been associated with unilateral reexpansion pulmonary edema,46 this complication is rare.47,48 Large volume thoracentesis may be better tolerated if allowed to drain slowly or drain to gravity rather than rapid evacuation with suction. In practice, we terminate the procedure at the onset of excessive coughing and pleuritic chest pain. Any residual fluid is aspirated at a later date. Repeated thoracentesis is reserved for those with acute life-threatening problems, patients who are waiting on the effects of systemic chemotherapy, and those who are poor operative risks (Karnofsky score <30%).49 Repeated thoracentesis has the potential risks of inducing hypoproteinemia, empyema, pneumothorax, and can produce intrathoracic loculations of pleural fluid. Although chemical pleurodesis can theoretically be administered after thoracentesis with a needle or a small-caliber drainage catheter, it is generally more effective when done with VATS drainage with sclerosant insufflation or tube thoracostomy.

Thoracentesis

Thoracentesis derives its greatest practical application in the evaluation of pleural effusion samples for cells and noncellular elements.58–60 As with BAL fluid examination, a number of specific analyses typically are performed. If collected after hours, the sterile thoracentesis fluid can be stored unfixed at 4°C for processing the next day. The aliquoted thoracentesis fluid specimens are distributed to the appropriate laboratory for analysis (e.g., microbiology, chemistry, hematology). Chemical determinations of glucose, amylase, lactate dehydrogenase, and other analytes are compared with cellular composition determined by cytopathology evaluation. The cytocentrifuge or Millipore filter also can be evaluated cytopathologically for the presence of malignant neoplasm. Rapid stains for microorganisms can be performed as indicated.

Contraindications

Thoracentesis has no absolute contraindications, but several relative contraindications exist. If a very small volume of fluid is present, the risk of pneumothorax is great, making the procedure relatively contraindicated. Overlying skin infection makes likely the possibility of introduction of microorganisms into the pleural space. An uncorrected coagulopathy is a relative contraindication, but generally thoracentesis can be safely performed in this situation using a small needle and careful technique. An uncooperative patient greatly increases the risks to underlying thoracic structures, making sedation and analgesia a frequent necessity in pediatric patients. Positive pressure ventilation increases the risk of pneumothorax and subsequent tension pneumothorax.

Thoracentesis

Thoracentesis, first described in 1852, is a procedure used to remove fluid or air from the pleural space. In pediatric patients, thoracentesis is most frequently indicated as a diagnostic procedure. Pleural effusions in children are most commonly the result of an infectious process (50% to 70% parapneumonic effusions), with congestive heart failure (5% to 15%) and malignancy being less common causes.1 Many other conditions may, rarely, cause pleural effusions in children (Box 15-2).