Pleural Effusion

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52 Pleural Effusion

Bret A. Nicks, David E. Manthey

Key Points

• Pleural effusion is the manifestation of an underlying disease process.

• The most common cause of pleural effusion in developed countries is congestive heart failure.

• Pulmonary embolism should be considered in patients with pulmonary effusions of uncertain etiology.

• Therapeutic thoracentesis is indicated in the emergency department for relief of acute respiratory or cardiovascular distress.

• Diagnostic thoracentesis should be performed in the emergency department to diagnose immediately life-threatening conditions in toxic-appearing patients.

Epidemiology

Because pleural effusions are harbingers of underlying disease, their precise incidence is difficult to determine. The incidence in the United States is estimated to be at least 1.5 million cases annually.¹ In industrialized countries worldwide, the incidence approaches 320 cases per 100,000 people—with heart failure, bacterial pneumonia, cirrhosis, malignancy, and pulmonary embolism representing the most common causes. The morbidity and mortality associated with pleural effusion are directly related to cause, stage of disease at the time of diagnosis, and biochemical findings in the pleural fluid. Because pleural effusions are manifestations of underlying diseases, age, sex, race, and socioeconomic status reflect the variation in incidence of the causative disease state or disorder.

Pathophysiology

Under normal physiologic conditions, the parietal and visceral pleurae are in close apposition, with only a small potential space between them. This potential space contains a small amount of pleural fluid (1 mL) to minimize friction from continuous movement of the appositional lining. The accumulation of pleural fluid (whether osmotic or hydrostatic in nature) can usually be explained by either increased pleural fluid formation or decreased pleural fluid absorption, or both.

Pleural effusions caused by an increase in pleural fluid formation can be further subdivided into elevation in hydrostatic pressure (e.g., congestive heart failure), decreased colloid osmotic pressure (e.g., cirrhosis, nephrotic syndrome), increased capillary permeability (e.g., infection, neoplasm), passage of fluid through openings in the diaphragm (e.g., ascites), or reduction of pleural space pressure (e.g., atelectasis). An effusion caused by decreased pleural fluid absorption can be qualified further as either lymphatic obstruction or elevation of systemic venous pressure resulting in impaired lymphatic drainage (e.g., superior vena cava syndrome).

The presence of fluid in the normally negative pressure environment of the pleural space has a number of consequences for respiratory physiology. Pleural effusions produce a restrictive ventilatory defect and also decrease total lung capacity, functional residual capacity, and forced vital capacity. They may cause ventilation-perfusion mismatches and, when large enough, compromise cardiac output.²

The classic work of Light et al.³ in 1972 demonstrated that 99% of pleural effusions could be classified into these two general categories, transudative and exudative (Box 52.1). A basic difference is that transudates generally reflect a systemic process whereas exudates usually signify underlying local pleuropulmonary disease.³

Box 52.1 Light Criteria for Classification of Pleural Effusions

In 1972, Light et al.³ developed the currently accepted benchmark for classifying pleural fluid, as follows:

– Pleural fluid protein–to–serum protein ratio > 0.5 : 1

– Pleural fluid lactate dehydrogenase (LDH)–to–serum LDH ratio > 0.6 : 1

– Pleural fluid LDH greater than two thirds the upper limit of normal for serum LDH (a cutoff value of 200 IU/L was used previously)

Pleural fluid is classified as an exudate if it meets any of the aforementioned criteria. Conversely, if all three characteristics are absent, the fluid is classified as a transudate. These researchers achieved a diagnostic sensitivity of 99% and specificity of 98% for classification of an exudate.

Presenting Signs and Symptoms

In many cases, pleural effusions are asymptomatic when discovered. Physical findings of pleural effusions are unlikely to be manifested until an effusion exceeds 300 mL. Dyspnea, the most common symptom associated with pleural effusion, is related more to distortion of the diaphragm and chest wall during respiration than to hypoxemia. Less commonly, symptoms of pleural effusions consist of a mild, nonproductive cough and chest pain. Pleuritic chest pain indicates inflammation of the parietal pleura because the visceral pleura is not innervated. In many patients, drainage of pleural fluid alleviates the symptoms despite limited improvement in gas exchange. Findings on lung examination such as decreased breath sounds, dullness to percussion, pleural friction rub, egophony, and reduced tactile fremitus have all been described.^1,² Auscultation alone can miss up to 600 mL of fluid in the lung.⁴^–⁶

The emergency physician should assess for the cause of the effusion. If a patient complains of fever, weight loss, and a progressively worsening cough with associated dyspnea, an oncologic or infectious cause is likely. Constant chest wall pain may reflect chest wall invasion by bronchogenic carcinoma or malignant mesothelioma. Pleuritic chest pain suggests either pulmonary embolism or an inflammatory pleural process. An effusion can mimic the classic symptoms of acute coronary syndrome, such as chest pain, dyspnea, and shoulder pain (Box 52.2).

Differential Diagnosis and Medical Decision Making

A pleural effusion is frequently identified during evaluation of the underlying chief complaint of the patient. Because the etiology of pleural effusion is myriad, a thorough history and physical examination may narrow the differential diagnosis substantially. Box 52.3 lists the common causes of pleural effusion. Frequently, effusion is identified on physical examination or with basic chest radiography, but additional imaging modalities, including radiography, ultrasonography, and computed tomography (CT), may identify the cause and provide additional insight about the effusion.^1,^3,⁶

Facts and Formulas

Auscultation alone can miss effusions of up to 600 mL.

Effusions of approximately 400 mL are routinely visible on upright chest radiographs.

Bedside ultrasonography is effective for visualizing and characterizing effusions.

Ultrasound-guided thoracentesis should be performed when available.

Diagnostic Considerations

Radiography

Erect posteroanterior and lateral chest radiographs are still the most important initial tools in the diagnosis of a pleural effusion. On upright and lateral decubitus films, loss of the costophrenic angle is seen. With increasing size of the pleural effusion, the hemidiaphragm is obscured (Fig. 52.1), and a mass effect with shift of the mediastinum away from the affected side is noted. If a film is taken with the patient supine, one may see only a nonspecific haze over the affected hemithorax because the fluid layers posteriorly. To confirm that the fluid is free flowing, lateral decubitus films with the affected side down are often obtained. With very large effusions, the affected side may remain opacified, thus rendering the decubitus film unhelpful. In adults the minimum amount of fluid required for identification of effusion on an upright film is approximately 400 mL, whereas lateral decubitus films (with the affected side down) may detect as little as 50 mL of fluid. A lateral decubitus film with the affected side up may facilitate evaluation of the underlying lung for atelectasis, a mass, or infiltrates along the lateral portion of the lung.^5,⁶

Fig. 52.1 Large parapneumonic effusion on an upright chest radiograph.

Mediastinal shift contralateral to the effusion (observed with effusions > 1000 mL) with concomitant displacement of the trachea is an important clue to obstruction of a lobar bronchus by an endobronchial lesion, possibly because of malignancy or, less commonly, obstruction by a foreign body.

Subpulmonic effusions are an uncommon manifestation of pleural effusions seen when fluid accumulates between the lower lung lobe and diaphragm. The fluid collection may mimic an elevated hemidiaphragm in upright imaging (Fig. 52.2). Upward of 400 mL of fluid can collect in the subpulmonic region before the posterior costophrenic sinus is filled. Evidence of an elevated hemidiaphragm with steep lateral peaks, obscured pulmonary vessels below the level of the diaphragm on a lateral projection, or a flat appearance of the posterior aspect of the hemidiaphragm on a lateral projection is suggestive of a subpulmonic effusion.⁶

Fig. 52.2 A subpulmonic effusion may mimic the surface of the diaphragm without blunting the costophrenic angle.

Ultrasonography

Ultrasonography is effective for visualizing an effusion and determining whether the fluid is free flowing or loculated (Fig. 52.3).⁷^–⁹ In a prospective study, Piccoli et al.⁸ compared ultrasonography, physical examination, and radiography in patients with suspected effusions. Findings on physical examination and radiography were in agreement 76% of the time, with a kappa value of 0.52. When compared with chest ultrasonography, physical examination showed a sensitivity of 69% and a specificity of 77%. Ultrasonography may help distinguish a large solid chest mass from an effusion and can be used to guide thoracentesis. Ramnath et al.¹⁰ suggested early use of ultrasonography to identify complicated effusions (loculations or organization) because patients whose effusions were treated aggressively by decortication had significantly shorter hospital stays than did those whose effusions were treated with tube thoracostomy alone. The same study showed that in children with effusions but no ultrasonographic evidence of organization, outcomes in those receiving treatment consisting of intravenous antibiotics and drainage were similar to outcomes in those undergoing aggressive treatment such as thoracoscopy or decortication. The major advantage of ultrasonography over conventional radiography is its ability to differentiate between solid and liquid components, thereby assisting in identification of pleural fluid loculations.

Fig. 52.3 Upright bedside ultrasonogram of a large pleural effusion.

Computed Tomography

CT is rarely needed to diagnose a pleural effusion but may identify an underlying mass. In adults the presence of parietal pleural thickening on contrast-enhanced CT is a specific but insensitive indicator of an exudate. Cross-sectional imaging more clearly distinguishes anatomic compartments such as the pleural space from lung parenchyma (Fig. 52.4). Chest CT is likely to be valuable in making management decisions for complicated effusions because it can distinguish empyema from lung abscess, detect pleural masses, outline loculated fluid collections, and identify additional problems such as contusions, blebs, and infiltrates.⁶

Fig. 52.4 A pleural effusion (arrow) seen on chest computed tomography.

Pleural Fluid Analysis

Ideally, evaluation of a pleural effusion should begin with diagnostic thoracentesis and proceed to classification of the pleural fluid as either a transudate or an exudate. The currently accepted benchmark for classifying pleural fluid, developed by Light et al.,³ is shown in Box 52.1. A number of later studies used modifications of the Light criteria but had poorer diagnostic accuracy.¹¹

Normal pleural fluid pH has been estimated to be approximately 7.64. A pH below 7.30 suggests the presence of an inflammatory or infiltrative process,¹² such as parapneumonic effusion, empyema, malignancy, connective tissue disease, tuberculosis, or esophageal rupture. According to the current American College of Chest Physicians consensus statement on the treatment of parapneumonic effusions, pH is the preferred pleural fluid chemistry test for classifying the category of a parapneumonic effusion for subsequent management (Box 52.4).^13,¹⁴ Additional testing considerations for pleural fluid include cholesterol, glucose, amylase, and adenosine deaminase.^11,^13,¹⁴

Red Flags

Failure to establish a working differential diagnosis or identify the underlying cause

Failure to initiate prompt source management for an underlying infectious cause

Failure to identify and manage tension physiology caused by large effusions on an emergency basis

Treatment

Acute medical management of pleural effusions is based on both therapeutic and diagnostic considerations. In the emergency department (ED), therapeutic thoracentesis is indicated for relief of acute respiratory or cardiovascular distress. Diagnostic thoracentesis should be used in the ED to diagnose immediately life-threatening conditions in toxic-appearing patients. Circumstances outside these situations should not necessitate emergency thoracentesis, but appropriate monitoring and further medical management are essential. Table 52.1 summarizes findings dictating the appropriateness of intervention.¹³

Table 52.1 Management of Patients with Parapneumonic Effusions

Approach to Unilateral Pleural Effusion

Thoracentesis should be performed for new and unexplained pleural effusions when sufficient fluid is present to allow a safe procedure. Conventional wisdom holds that if a 10-mm layer of fluid is visible on a radiograph, sufficient fluid is present for thoracentesis to be successful. Treatment of the underlying disorder is generally all that is required for effusions caused by renal, cardiac, or rheumatologic diseases.

Approach to Pleural Effusion Associated with Malignancy

Malignancy-induced pleural effusions should undergo therapeutic thoracentesis as needed. If effusions are undiagnosed, cytologic evaluation is required for patients with oncologic risks. Completion of evaluation may require CT assessment and subsequent tissue biopsy.

Approach to Parapneumonic Pleural Effusions

Parapneumonic effusion and empyema are treated initially with empiric antibiotics according to the patient’s age and the probable organisms and sensitivities commonly present in the community. Parapneumonic effusion usually progresses through three stages. The exudative stage is associated with capillary leak during the first 3 days; the fibrinopurulent stage is associated with bacterial invasion of the pleura between days 3 and 7; and the organizational stage is characterized by fibroblast growth, occurring for 2 to 3 weeks, if the effusion is not treated properly. Lack of early diagnosis and drainage of empyema, especially in younger children, may worsen the course of disease. In a hospitalized patient with a complicated parapneumonic effusion, antibiotics are administered intravenously and a thoracostomy tube is left in place until the patient is afebrile and improving clinically. Oral antibiotics are frequently continued for weeks after these procedures.^1,¹³

Priority Actions

Identify the cause of the pleural effusion.

Therapeutic thoracentesis is recommended for symptomatic patients.

Assess respiratory status before and after any intervention.

Inform patients about the complications associated with pleural effusions and thoracentesis.

Thoracentesis: the Ideal Approach

Thoracentesis is an elective procedure requiring informed consent. Sterile technique and procedural experience lower the incidence of complications.

Drainage of a pleural effusion is indicated for the following reasons:

• Diagnostic fluid or cellular analysis

• Therapeutic relief of symptomatic dyspnea

• Evaluation of complicated parapneumonic effusions or empyema

Positioning

Ideally for thoracentesis, the patient should sit on the edge of the bed, lean forward slightly, and rest on an adjustable table. If the patient cannot sit up because of hemodynamic status, mental status, or the presence of tubes and indwelling lines, thoracentesis can be performed with the patient supine. In this case, the patient should turn onto the side with the effusion and move to position the back at the edge of the bed.

Procedural Approach

Diagnostic thoracentesis is used to determine the cause of a pleural effusion, and therapeutic thoracentesis is performed to relieve symptoms of respiratory distress. Therapeutic thoracentesis may be repeated if indicated, but more definitive therapy such as sclerosis is usually needed to treat recurrent symptomatic pleural effusions. If more than 1.0 to 1.5 L of fluid is removed at one time, reexpansion pulmonary edema (RPE) and postthoracentesis shock should be anticipated in the postprocedural period. Supplemental oxygen should be provided because postthoracentesis decreases in arterial oxygenation have been reported. The magnitude and duration of this decline roughly correlate with the amount of fluid removed. If removal of a large volume of fluid is anticipated, concurrent fluid resuscitation should be considered to blunt postthoracentesis shock. Depending on the causative process, reaccumulation of pleural fluid may occur.

After appropriate positioning, the patient is prepared in standard sterile fashion. The effusion can be identified along the posterior infrascapular line by either clinical examination (auscultation and percussion) or bedside ultrasonography. Ultrasonography is recommended because it identifies not only the level of effusion but also the subdiaphragmatic organs that should be avoided and the depth of the fluid pocket.^7,⁸ As the angiocatheter is advanced, the neurovascular bundles located on the inferior aspect of the ribs should be avoided. Aspiration of fluid can continue until enough fluid is obtained for diagnostic purposes or therapeutic relief.

Needle thoracentesis is adequate for both diagnostic evaluation and therapeutic management of most parapneumonic pleural effusions. When the effusion has progressed to the fibrinopurulent or organizational stage, needle thoracentesis is often inadequate. Thoracoscopy offers the advantages of visual evaluation of the pleura, direct tissue sampling, and therapeutic intervention such as dissecting loculations and pleurodesis. Appropriate consultation for medical thoracoscopy and video-assisted thoracoscopy is indicated in these circumstances.

Documentation

Identify the size and location of the effusion.

Consider the cause and duration of the effusion.

Discuss the appropriate intervention and associated risks.

Assess respiratory function before and after any intervention.

Document repeated physical examination and vital signs during the postprocedural period.

Ensure appropriate outpatient follow-up or inpatient evaluation.

Contraindications

Procedural contraindications to pleurocentesis or thoracostomy are listed in Box 52.5. Absolute contraindications include coagulopathy, known adhesions, and a history of pleurodesis. If the patient is symptomatic and coagulopathic, correction of coagulopathy and ultrasonographic guidance are recommended to minimize bleeding risks. Pleurodesis, or the introduction of a chemical or medication (talc, tetracycline, or bleomycin sulfate) into the chest cavity, triggers an inflammatory reaction over the surface of the lung and inside the chest cavity that causes the pleurae to adhere to each other and prevents or reduces further accumulation of pleural fluid. Thoracentesis should be avoided in patients at increased risk for adverse reactions as a result of unstable angina or arrhythmia or known medical noncompliance, including lack of established outpatient care. Relative contraindications include mechanical ventilation because of an increased risk for lung collapse and difficulty with positioning. In intubated patients, use of ultrasonography or CT for thoracentesis or postponing the procedure is recommended if the indication is not urgent. Patients with known bullous lung disease are at increased risk for postprocedural pneumothorax. Placement of the thoracentesis needle through a concurrent chest wall infection should be avoided because the pleural space may become seeded. A postprocedure radiograph should always be obtained to assess for pneumothorax.^13,¹⁵