Etiology and Pathogenesis

Pleural effusions are the result of an imbalance of hydrostatic and oncotic pressures between the blood in the pulmonary capillary bed and fluid in the pleural space, an alteration in permeability of the pleural membranes, or inadequate uptake by the lymphatic system. Pleural effusions can be divided into transudates and exudates. Exudative effusions occur from pleural inflammation or lymphatic flow obstruction. Transudative effusions occur when there is an imbalance between the formation and reabsorption of pleural fluid. Pleural fluid analysis determines whether the effusion is transudative or exudative. Because exudative effusions result from inflammation of the pleural membranes and leaky capillaries, large molecules such as cholesterol, lactate dehydrogenase (LDH), and proteins enter the pleural space. Conversely, the protein, LDH, and cholesterol levels in transudates are low because the filtration properties of the pleural membranes are not altered.

Typically, small amounts of protein are filtered into the pleural space and are readily absorbed by the parietal pleura via the lymphatic system. If increased amounts of protein enter the pleural space, especially when accompanied by increased capillary permeability (e.g., in pneumonia), the lymphatic system cannot absorb the excessive protein, and an exudative pleural effusion forms. The most common cause of exudative pleural effusions in children is bacterial pneumonia. Additional causes include connective tissue diseases, metastatic intrathoracic malignancy, subdiaphragmatic abscess, and aspiration pneumonitis. Transudative effusions in children are typically associated with overhydration, atelectasis, nephrotic syndrome, and congestive left heart failure. Correcting the oncotic and hydrostatic pressures usually results in resolution of a transudate; drainage of the fluid is only needed for immediate symptomatic relief.

An exudative pleural effusion that is associated with pneumonia is referred to as a parapneumonic effusion. Parapneumonic effusions result from the spread of inflammatory cells and infecting organisms into the pleural space. Initially, the pleurae become inflamed, and the leakage of proteins and leukocytes into the pleural space forms the effusion. Initially, the fluid is sterile with a low leukocyte count. As a parapneumonic effusion progresses and bacteria leak into the pleural space, the pleural fluid becomes purulent, and the effusion is referred to as an empyema, occurring in approximately 0.6% of childhood pneumonia. Loculations (parietal–visceral pleural adhesions) and septations (fibrous strands) form within parapneumonic effusions as the pleural fluid exudate thickens and deposition of fibrin occurs within the pleural space.

The risk of a child developing an empyema increases in certain underlying diseases, such as immunodeficiencies, malignancy, Down syndrome, congenital heart disease, tuberculosis, and cystic fibrosis (CF). Streptococcus pneumoniae remains the most common pathogen causing parapneumonic effusions. Community-acquired methicillin-resistant Staphylococcus aureus is an increasingly common cause of both parapneumonic effusions and empyemas. Empyemas can also be caused by the rupture of lung abscesses into the pleural space; by bacteria entering the pleural space from trauma, thoracic surgery, mediastinitis; or through the spread of intraabdominal abscesses. Complications associated with parapneumonic effusions and empyemas are infrequent in children but include bronchopleural fistula, lung abscess, and empyema necessitatis (perforation through the chest wall). Boys and girls are affected equally by empyemas, and the morbidity and mortality are highest in children younger than 2 years of age.

Clinical Presentation

The size of the effusion, the underlying cause, and when in the course a child presents all determine the clinical presentation. Children with small pleural effusions may be asymptomatic. As the effusion enlarges, it limits lung inflation, causing a decrease in vital capacity. Furthermore, if present, pleural inflammation is associated with dyspnea, chest tightness, and chest pain that is exaggerated by deep breathing, coughing, and straining; all of these further limit full lung expansion. The pain, resulting from stretching of parietal pleura nerve fibers, is often described as a dull ache that worsens with inspiration. The pain is often localized over the chest wall and is referred to the shoulder or the back. Often the child will attempt to decrease the pain by lying on the affected side in an attempt to splint it during breathing.

On physical examination, a child with a significant pleural effusion can appear ill but is rarely toxic appearing. Most children are tachypneic with shallow breathing to minimize the pain. It is important to look for signs and symptoms of underlying conditions that predispose to the development of pleural effusions. If the child has an empyema, he or she is usually febrile with a cough and malaise. If a child is being appropriately treated for pneumonia and is not improving within 48 hours, a parapneumonic effusion must be suspected. A malignant effusion must be suspected in a child with an effusion accompanied by a mediastinal mass or lymphadenopathy. A history of recurrent serious bacterial infections, failure to thrive, or chronic diarrhea is suggestive of a primary immunodeficiency.

Because of splinting toward the affected side, the child may appear to have mild scoliosis. There can be ipsilateral bulging of the intercostal spaces and contralateral displacement of the heart and trachea. A pleural friction rub caused by roughened pleural surfaces may be the only physical examination finding early in the course of disease, heard during inspiration and exhalation. As the pleural effusion increases and separates the pleural membranes, the plural rub disappears. Diminished thoracic wall excursion, decreased breath sounds, dullness to percussion, and decreased tactile and vocal fremitus can be observed over the affected area in an older child with a moderate effusion. If pneumonia is present, crackles and rhonchi can also be audible. In infants, the physical signs of an effusion are less noticeable. Breath sounds can be deceptively loud and clear throughout both lungs because of the small lung volume in an infant.

Evaluation and Management

Children with the clinical history and findings suggestive of a pleural effusion should be evaluated with an upright chest radiograph and a lateral decubitus view (Figure 40-2). Performing radiographic examinations with the child in multiple positions helps to demonstrate a shift in the effusion with position changes. These radiographic images can help in making the diagnosis of pleural effusion and in determining the need for thoracocentesis or chest tube placement.

Figure 40-2 Pleural effusion.

Radiographic signs of pleural effusion include a homogenous density overlying the normal markings of the underlying lung, obliteration of the costophrenic angle, the “meniscus sign” or “pleural stripe” (a rim of fluid ascending the lateral chest wall), and possible scoliosis. Infants or children whose radiograph is taken in a recumbent position will not have a meniscus, but instead demonstrate only a denser hemithorax on the affected side. Air-fluid levels within the pleural space suggest the presence of gas-forming organisms, pneumothorax, perforated viscus, or bronchopleural fistula. If there is no shift in the fluid on chest radiograph with a change in position, the effusion is most likely a loculated empyema.

Ultrasonography is useful in confirming the presence of fluid in the pleural space. Additionally, if a child has findings consistent with a parapneumonic effusion, ultrasonography should be undertaken to determine whether loculations are present.

Chest computed tomography (CT) can also be helpful in determining the presence of pleural fluid; however, CT findings do not typically affect management decisions, and they should not be performed routinely in the evaluation of children with pleural effusions. Chest CT can be useful in the evaluation of complicated cases when more detail about the effusion or the underlying lung parenchyma is desired.

When infection is in the differential diagnosis, pleural fluid aspiration via thoracocentesis should be performed if at least 1 cm of fluid is seen on decubitus radiographs to determine the type of effusion (i.e., infectious exudate, empyema, hydrothorax, hemothorax, or chylothorax) before starting therapy (Figure 40-3). Certain laboratory studies should always be performed on the pleural fluid aspirate. Additional laboratory studies should also be obtained during the evaluation of a child with a parapneumonic effusion or empyema (Table 40-1). Microbiologic studies of the pleural fluid can identify a causative organism, and the analysis of pleural fluid is helpful in guiding therapeutic options. Pleural fluid can be obtained through thoracocentesis, aspiration under ultrasonographic guidance, or through video-assisted thoracoscopic surgery (VATS), depending on the presence of loculations or the availability of pediatric surgeons trained in VATS.

Figure 40-3 Pleural fluid aspiration.

Table 40-1 Laboratory Studies Obtained at Time of Pleural Fluid Aspiration

AFB, acid-fast bacilli; CRP, C-reactive protein; LDH, lactic dehydrogenase; PCR, polymerase chain reaction.

There are no definitive management approaches for children with exudative pleural effusions. The aim of treatment is to aspirate the pleural fluid, sterilize the pleural cavity, decrease the duration of symptoms, and ensure full expansion of the lung with return to normal function. Therapeutic options include administration of systemic antibiotics; thoracocentesis; chest tube thoracostomy with or without instillation of fibrinolytic agents; and more invasive techniques, including thoracoscopic surgery (i.e., VATS), mini-thoracotomy, or standard thoracotomy with decortication (removal of fibrinous “peel” from the lungs). Some clinicians have suggested that children with loculated effusions documented on ultrasonography proceed directly to VATS but those with free fluid undergo initial thoracocentesis with administration of systemic antibiotics. Most children improve with antibiotic therapy and simple drainage. However, early, more invasive therapies (i.e., chest tube placement with or without fibrinolytic therapy or VATS) may result in a shorter duration of illness and length of hospital stay.

A chest tube drain should be considered for any of the following pleural fluid findings suggestive of a complicated empyema: frank pus or positive gram stain, pH below 7.0, LDH level above 1000 IU/dL, or glucose level below 40 mg/dL. Additionally, children who have effusions that are enlarging or compromising respiratory function require chest tube insertion and drainage of the pleural effusion.

Supportive care for children with parapneumonic effusions and empyema includes antipyretics, adequate analgesia with nonsteroidal antiinflammatory agents, and early mobilization. Sedatives and analgesics that can cause central respiratory depression should be used cautiously with close monitoring of respiratory status. Intravenous (IV) fluids should be administered if the child refuses oral intake or is unable to drink.

All children with a parapneumonic effusion or empyema should be treated with antibiotics. In mild cases, this can include broad-spectrum oral antibiotics and close observation with chest radiographs on an outpatient basis. Children with empyema should be hospitalized and treated with IV antibiotics in doses adequate to ensure pleural penetration. The choice of antibiotic coverage should be based on the suspected causative organism. Most clinicians agree on continuing IV antibiotic therapy as long as the child is febrile; however, the duration of IV antibiotic therapy after resolution of fever is controversial. Some clinicians continue IV antibiotics for 48 hours after the patient becomes afebrile or after the chest drain is removed; others continue IV therapy for up to 2 weeks.

For both medical and surgical options, the chest tube can be removed when the patient is clinically improved and the chest tube drainage has slowed. Evidence of clinical resolution includes the following: absence of fever, overall sense of well-being, improved chest radiograph and ultrasound appearance, and decrease in white blood cell count and acute-phase reactants.

With appropriate therapy, children with parapneumonic effusions should clinically improve within the first few days of treatment. Those with empyema typically have more protracted courses. If a child with chest tube drain remains febrile or tachypneic and aeration does not improve, the chest tube may be obstructed or fail to drain because of the development of loculations.

Children with a pleural effusion should have a follow-up chest radiograph 1 to 2 months after discharge from the hospital. These children should continue to be followed until they have recovered completely and their chest radiographs have returned to near normal. This usually occurs by 3 to 6 months but may take as long as 16 months. Patients can have residual dullness to percussion and decreased breath sounds over the affected areas related to pleural thickening.

Despite the marked abnormalities at the time of presentation, the majority of children make a complete recovery. Long-term follow-up studies suggest that fewer than 10% of children have residual symptoms. Patients with residual restrictive abnormalities in lung function are usually asymptomatic and have normal exercise tolerance.

Etiology and Pathogenesis

A pneumothorax can be classified as spontaneous, traumatic, or catamenial. Spontaneous pneumothorax is the most common type that occurs in children. Traumatic pneumothorax is caused by blunt or penetrating trauma to the chest, by injury from a diagnostic or therapeutic procedure (i.e., subclavian line placement, thoracocentesis, or transbronchial biopsy), or as a consequence of mechanical ventilation. Catamenial pneumothorax (thoracic endometriosis) is a rare disorder that occurs exclusively in women of reproductive age who present with a spontaneous pneumothorax within 24 to 48 hours of the onset of menstruation. The mechanism is uncertain, but this type of pneumothorax is thought to result from the passage of intraabdominal air through diaphragmatic defects. Spontaneous pneumothorax, which occurs in the absence of identified trauma, is subdivided into primary and secondary types.

Clinical Presentation

The clinical presentation of a pneumothorax depends on the extent of lung collapse and the amount of underlying lung disease. The most common presenting symptom is acute chest pain, which is typically sharp or stabbing and may be preceded by a popping sensation. The pain is diffuse on the affected side with radiation to the ipsilateral shoulder. Dyspnea, cyanosis, tachypnea, and tachycardia are often seen.

Physical examination findings include decreased chest excursion, diminished breath sounds, and hyperresonant percussion on the affected side. The larynx, trachea, and heart can be shifted toward the contralateral side, especially in tension pneumothorax. It may be difficult to diagnose a pneumothorax in infancy because the symptoms and physical signs can be difficult to recognize.

Evaluation and Management

The diagnosis of a pneumothorax is verified radiographically (see Figure 40-4). Lateral and anteroposterior views of the chest can confirm the presence of intrapleural air that appears to outline the visceral pleura. Expiratory views accentuate the contrast between lung markings and the hyperlucency of the air in the pleural space. The trachea and mediastinum shift away from the pneumothorax, especially in the case of a tension pneumothorax. However, if both lungs are poorly compliant, as in patients with CF or respiratory distress syndrome, the unaffected lung may not collapse easily, and the shift may not occur.

Often, it is necessary to differentiate a pneumothorax from localized or generalized emphysema, emphysematous blebs, cystic formations (e.g., congenital lobar emphysema), diaphragmatic hernia, compensatory overexpansion with contralateral atelectasis, and gaseous distension of the stomach, which radiographically can mimic air in the pleural space. In most cases, a chest CT or contrast studies differentiate these conditions.

If a patient has significant respiratory distress, an arterial blood gas analysis should be done. Hypoxemia can occur because of alveolar hypoventilation, ventilation/perfusion mismatch, and intrapulmonary shunt. Hypercapnia is usually not present unless the child has underlying lung disease.

Treatment varies with the extent of lung collapse, cause of the collapse, extent of respiratory distress, and severity of underlying lung disease. Therapies are aimed at removal of air from the pleural space and prevention of recurrence. In addition to treating the air leak, the aggressive treatment of underlying pulmonary disease, when present, is essential. A small (<5% of the involved hemithorax) or moderate-sized pneumothorax in an otherwise healthy child can resolve spontaneously, usually within 1 week. These children can be observed in an outpatient setting if serial chest radiographs are obtained and emergency care is available if needed. However, if there is more than a 5% collapse or if the pneumothorax is recurrent or under tension, hospitalization is usually warranted. Analgesia should be used to decrease the pleural pain.

If the communication between the alveoli and pleural space is eliminated, the air in the pleural space is gradually reabsorbed. Administration of 100% supplemental oxygen can hasten the rate of pleural air absorption. Oxygen replaces nitrogen in the extrapulmonary air, allowing for enhanced gas absorption and resolution of the pneumothorax.

The aspiration of pleural air via a needle thoracostomy is necessary for pneumothoraces that occupy more than 15% of the involved hemithorax; if a tension pneumothorax is suspected; or if the child has severe dyspnea, hypoxemia, or significant pain (see Figure 40-4). Needle aspiration is associated with a recurrence risk of 20% to 50%; therefore, close follow-up is required. If a child has failed a needle aspiration, has a large pneumothorax, or is having recurrent spontaneous pneumothoraces, a thoracostomy tube should be placed; pigtail catheters are frequently used. A water seal device or one-way Heimlich valve should be used to prevent reaccumulation of the air.

Surgical intervention in the treatment of spontaneous pneumothorax is controversial. However, good evidence suggests that surgery is warranted to treat persistent air leaks and to prevent recurrence. Surgery for a pneumothorax involves stapling or oversewing ruptured blebs or tears in the visceral pleura and resection of abnormal lung tissue. This procedure is done via VATS, mini-thoracotomy, or open thoracotomy. Repair by VATS is associated with less morbidity than that related to traditional open thoracotomy.

Chemical pleurodesis (intrapleural instillation of a sclerosing agent) can be performed during chest tube placement or at the time of surgery to induce the formation of strong adhesions between the lung and chest wall and decrease the risk of recurrence. Sclerosing agents include talc, tetracycline, doxycycline, fibrin glue, or autologous blood patches. Most studies in adults do not support the use of chemical pleurodesis through a chest tube unless there is a persistent air leak and a patient refuses surgery or a contraindication to surgery exists. Mechanical pleurodesis, accomplished by directly stripping and abrading the pleura with gauze during surgery, leaves inflamed intrapleural surfaces that heal with sealing adhesions.

Information about the prognosis after a spontaneous pneumothorax in children is based on adult patients, in whom there is a substantial recurrence risk. The majority of recurrences develop within 1 year of the initial event, after which the risk decreases. Activities such as deep sea diving and flying in small, unpressurized aircraft are associated with increased risk of pneumothorax and should be avoided in individuals who did not undergo pleurodesis.

Future Directions

Despite the improvement in the technology available for diagnosing and treating pleural effusions in children, management remains controversial. This is particularly true in children with parapneumonic effusions or empyema because there is no consensus on the role of medical versus surgical management, and there is no consensus on whether surgery should be the initial treatment of choice or reserved for failed medical management. Although there have been a few prospective, randomized controlled trials comparing the various treatment options, additional trials are necessary before standards based on high-quality evidence for the treatment of pleural effusions in children can be developed.

As with pleural effusions, much of the information about pediatric spontaneous pneumothoraces is limited, and most of the published therapeutic guidelines are based on adult data. Thus, although indications for conservative therapy in children with pneumothoraces are fairly well accepted, the criteria for specific drainage procedures remain controversial. Further studies evaluating the role of surgical management options and outcomes are needed for children with pneumothoraces.