Pediatric Respiratory Medicine || Abnormalities of the Pleural Space

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P A R T 12STRUCTURAL AND MECHANICAL ABNORMALITIES

CHAPTER68 Abnormalities of the Pleural SpaceDanna Tauber and Daniel V. Schidlow

The pleural space is a cavity surrounded by two membranes. The visceral pleura covers the entire surface of the lung, and the parietal pleura covers the inner surface of the chest wall, mediastinum, and diaphragm. The two membranes meet at the hilar root of the lung. The normal pleural space is approximately 18 µm wide at its least dependent point and widens to about 20 µm in the dependent regions. 1 Under normal conditions, the pleural space contains 0.1 to 0.2 mL/kg of fl uid with a protein concentration of less than 1.5 g/dL that fl ows down gravity-dependent gradients. 2,3 The pleural membranes and the space they defi ne play an integral func-tion in respiration. The pleura allows for mechanical coupling of the lung and chest wall throughout the respiratory cycle, providing support to the lung tissue while allowing the lung to move extensively in relation to the chest wall. The anatomy and structure of the pleural space are essential to an under-standing of its function and abnormalities.

EMBRYOLOGY AND ANATOMY

By the third week of gestation, the pleural, pericardial, and peritoneal spaces begin to develop. All of these cavities are lined by visceral and parietal membranes made up of meso-thelial cells. As the lung develops, the lung buds invaginate into the visceral pleura and become invested in this layer. The mesothelial cells can be fl at, cuboidal, or columnar in shape. They have microvilli projections on their free surface. Meso-

thelial cells are capable of multiple functions, including active transport of small particles, 4 secretion and organization of components of the extracellular matrix such as collagen, elastin, and connective tissue glycoproteins, 5 secretion of neutrophil and monocyte chemotactic factors, 6 phagocytosis of particles, 7 and production of fi brinolytic and procoagulant factors. 8

Stomata are 2- to 12-µm openings between mesothelial cells of the parietal pleura. 2 These stomata communicate the pleural space and lymphatics, allowing for clearance of large particles and blood cells. 9 The fl uid fl ows into lacunae, spider-like submesothelial collecting lymphatics, which drain into intercostal lymphatics. From there, fl uid drains into mediastinal, parasternal, and periaortic nodes, subsequently into the thoracic duct, and ultimately into the systemic venous system 2 (Fig. 68-1).

The parietal pleural is fed by the intercostal arteries. The visceral pleura is supplied by the bronchial circulation and is drained by the pulmonary veins. 10,11 Because the pulmonary venous system is a low-pressure system, the perfusion pres-sure is lower in the visceral pleura. 10 The parietal pleura has sensory nerve fi bers supplied by intercostal and phrenic nerves, whereas the visceral pleura has no sensory nerve innervation.

PHYSIOLOGY OF THE PLEURAL SPACE

Pressure in the pleural space is subatmospheric. Gases do not accumulate in the pleural space because the sum of all partial pressures of gases in venous blood and tissue is lower than that of atmospheric or alveolar gas. There is a 60-mm Hg pressure gradient that maintains dissolved gases in the venous blood and promotes absorption of gases from the pleural space.

The small amount of fl uid contained within the pleural space is the result of a dynamic balance between fl uid fi ltered from subpleural capillaries into the intrapleural space and removal of fl uid from the space via lymphatics. Suffi cient fl uid must remain in the pleural space to provide lubrication for the lungs to move but not so much as to uncouple the mechanical forces of the chest wall and the lung. 12

Starling forces across both the parietal and visceral mem-branes favor fi ltration of fl uid out of the capillaries and into the interstitial spaces. 4 Fluid then fi lters from the interstitial spaces into the pleural space because the pleural liquid pres-sure is subatmospheric and therefore lower than interstitial pressure. 4,12,13 Fluid, cells, and protein are then removed

TEACHING POINTS

● The pleura allows for mechanical coupling of the lung and chest wall throughout the respiratory cycle.

● Pleural fl uid accumulates in the pleural space either by an increase in fl uid production or by obstructed fl uid drainage.

● Pleural effusions can present with dyspnea, cough, pain, tachypnea, and diminished breath sounds.

● Treatment of purulent effusions includes antibiotics, anti-biotics plus chest tube drainage, chest tube drainage plus fi brinolytic therapy, and early debridement by video-assisted thoracoscopic surgery (VATS).

● Pneumothorax presents with the sudden onset of chest pain, tachypnea, and dyspnea.

● Treatment of pneumothorax depends on the size, cause, extent of respiratory distress, and presence of underlying lung disease.

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P A R T 12 ■ STRUCTURAL AND MECHANICAL ABNORMALITIES

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from the pleural space by the lymphatics of the parietal pleura via bulk fl ow and not by diffusion or active trans-port. 4,13 There are two essential mechanisms for fl uid accu-mulation in the pleural space: (1) changes in the balance between hydrostatic and oncotic pressures result in increased fl uid production as can changes in the permeability of the capillary membrane or (2) fl uid removal is disturbed by obstruction of the lymphatic drainage (Table 68-1).

CLINICAL MANIFESTATIONS

The severity of presenting signs and symptoms of pleural effusion directly correlates to its size and nature. Small effu-sions rarely cause symptoms. Larger effusions cause dyspnea, dry cough, and orthopnea due to lung compression. Pain results from stretching of the sensory nerve fi bers of the parietal pleura, which worsens with inspiration and can radiate to the chest or shoulder. Breath sounds are diminished over the affected area, as are tactile and voice fremitus. There is increased resonance of the voice (egophony) and dullness to percussion. Larger effusions can cause tachypnea, decreased rib excursion, ipsilateral bulging of the intercostal spaces, and contralateral displacement of the heart and trachea.

A chest radiograph is the fi rst laboratory examination that should be done when considering a diagnosis of pleural effu-sion. With larger effusions, a meniscus is present at the cos-tophrenic angle when the patient is in the upright position. 14 Lateral decubitus fi lms are useful in cases where a “white-

out” is seen to differentiate solid underlying lung collapse or consolidation from pleural effusion. The fl uid “layers out,” allowing abnormalities such as mediastinal masses or lung consolidation to be visualized. Ultrasound and computed tomography (CT) are helpful in differentiating empyema from simple effusions. An ultrasound examination can esti-mate the size of an effusion and can differentiate free from loculated fl uid and can also identify septations in pleural fl uid collections. 15,16 CT scans assist in delineating loculated pleural fl uid and parenchymal lung abnormalities such as a lung abscess, as well as defi ning possible mediastinal pathology or mediastinal tumors. 17,18

DIAGNOSIS

The best method of determining the cause of an effusion is sampling of the fl uid accumulation. Thoracocentesis is impractical if the effusion is small or if the cause is known (i.e., congestive heart failure, nephrotic syndrome, ascites, or peritoneal dialysis). Thoracocentesis may be safely performed when a layer of at least 1 cm of fl uid is present on decubitus fi lms. If no fl uid shift is seen, ultrasound may reveal loculated fl uid and guide thoracocentesis or chest tube insertion. Com-plications of thoracocentesis are pneumothorax, pain, and bleeding due to improper insertion of the needle into the nerve, blood vessel, or lung parenchyma. Intercostal nerve damage, puncture of the liver or spleen, and secondary empyema have been reported. 19-21

Intercostalmicrovessels

Bronchialmicrovessels

LymphaticAlveoli

Pleuralspace

Parietalpleura

Visceralpleura

Figure 68-1 Schema showing normal pleural liquid turnover. The initial microvascular fi ltrate in the parietal and visceral pleura is partly reabsorbed (dashed arrows). The remaining low-protein interstitial liquid fl ows across the leaky pleural mesothelial layers into the pleural space. The pleural liquid exits the pleural space via the parietal pleural lymphatic stomata. (Redrawn from Staub NC, Wiener-Kronish JP, Albertine KH:Transport through the pleura: Physiology of normal liquid and solute exchange in the pleural space. In Chretien J, Bignon J, Hirsch A [eds]: The Pleura in Health and Disease [Lung Biology in Health and Disease, Vol. 30]. New York: Marcel Dekker, 1985, p. 182.)


CHAPTER 68 ■ Abnormalities of the Pleural Space

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Pleural fl uid appearance varies with the cause (Table 68-2). Transudates are serous or straw colored, whereas chylous effusions are milky. There are a number of laboratory studies that should always be performed on the sampled fl uid (Table 68-3). Analysis of the fl uid should fi rst determine if the effusion is transudative or exudative 22 (Table 68-4). Exu-dative effusions arise from infl ammation of the pleural mem-branes or lymphatics resulting in leaky capillary membranes that allow passage of large particles such as proteins. 23 There-fore, exudates have elevated protein, lactic dehydrogenase (LDH), and cholesterol. LDH levels rise as a result of tissue breakdown from infl ammation and thus serves as a marker for infl ammation. Transudates are not associated with infl am-mation, so their protein and LDH levels are low. Additional studies should be performed in cases when certain character-istics of the pleural fl uid are seen (Table 68-5).

TRANSUDATES

A transudate develops from an imbalance of hydrostatic or oncotic pressure. Infl ammation is not present; therefore,

Table 68-1Pathophysiology of Pleural Fluid Accumulation

Effusion Type Mechanism Clinical Diagnosis

Transudate Increased capillary hydrostatic pressure Overhydration, congestive heart failure, venous hypertension, pericarditisDecreased hydrostatic pressure of the interstitial space Trapped lung with chronic pleural space, post-thoracentesis

Decreased plasma oncotic pressure Hypoalbuminemia, nephrotic syndrome, hepatic cirrhosis

Exudate Increased permeability of the capillary membrane Infection—pleural or parenchymal, circulating toxinsConnective tissue disease: systemic lupus erythmatosus, rheumatoid arthritis,

sarcoidosisImpaired/obstructed fl ow Malignancy: lymphoma, leukemia, neuroblastoma, chest wall sarcoma, Wilms

tumor, hepatomaPancreatitisSubphrenic abscessSuperior vena caval syndrome

Increased oncotic pressure of the interstitial space Pulmonary infarction

Chyle Leakage from lymphatic vessels Thoracic duct injury post cardiac surgeryObstruction of lymphatic vessels or vena cava Tumors (i.e., lymphoma)

TuberculosisSarcoidosis

Congenital abnormalities (thoracic duct atresia or abnormal connections)

Trisomy 21, Noonan syndrome, extralobar sequestration, lymphangiomatosis, or lymphangiectasia

Blood Vascular leak Trauma, spontaneous rupture, vascular erosion by neoplasm, hemorrhagic disease

Table 68-2Pleural Fluid Appearance

Fluid Appearance Cause

Grossly purulent fl uid Empyema; rarely pancreatitis, ruptured esophagus

Thick, tan-brown Staphylococcus aureus Putrid Anaerobes Also bloody Group A StreptococcusMilky fl uid ChylothoraxBloody fl uid Hemothorax, traumatic thoracocentesis,

malignancy, tuberculosis, uremia, or empyema due to group A Streptococcus

Yellow-green fl uid, debris Rheumatoid arthritisBlack fl uid Aspergillus niger“Anchovy” brown fl uid Entamoeba histolytica

Table 68-3Laboratory Studies to Be Obtained in All Cases of

Pleural Fluid Accumulation

Specimen Laboratory Study

Pleural fl uid ProteinLactic dehydrogenase (LDH)GlucosepHCholesterolBacterial culture and Gram stainDifferential cell countStaining and culture for acid-fast bacilliAmylase

Serum Complete blood cell countComplete metabolic panel including: LDH Total protein Glucose Albumin BUN/creatinine

Table 68-4Distinguishing Exudate from Transudate

Exudate Fulfi ll at least one of the following criteria: Pleural fl uid/serum lactic dehydrogenase (LDH) > 0.6 Pleural fl uid/serum protein >0.5 Pleural fl uid LDH > 2/3 upper limit of normal serum values Pleural fl uid cholesterol >55 mg/dL

Transudate Fulfi ll none of the above criteria

transudates have a low cellular count and low protein con-centration. Correction of the forces governing pleural fl uid homeostasis will lead to resolution of the transudate; drainage is required only for immediate symptomatic relief. Disorders associated with transudative effusions in children include atelectasis, nephrotic syndrome, left ventricular failure, free peritoneal fl uid, and hypothyroidism.



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Table 68-5Additional Studies to Be Obtained in Specifi c Cases

Effusions Studies

Purulent Blood cultureSputum cultureSerum C-reactive protein

Lymphocytic Fluid cytospin/cytologyFluid triglyceride levelTuberculin skin testEffusion and serum antinuclear antibody, rheumatoid

factor, and complementFungal titers and skin tests

Bloody Fluid hematocritFluid triglyceride levelFluid hemosiderin-laden macrophages

Atelectasis, trapped lung, and upper airway obstruction can cause effusions by generating excessive negative pleural pressure. 13 Parietal pleural pressure becomes more negative when lung separates from parietal pleura or when inspiratory effort against an obstruction increases.

In nephrotic syndrome, a decrease in oncotic pressure from hypoalbuminemia coupled with an increase in hydro-static pressure from fl uid overload favors movement of fl uid into the pleural space. 13 The resulting effusions are generally small and bilateral and resolve with correction of the hyper-volemia and protein concentration. Thoracocentesis is indicated with chest or abdominal pain, unilateral or large effusions, fever, or pulmonary infi ltrates. If effusion persists after correction of renal function, thoracocentesis should be performed to evaluate for infection, thromboembolism, or collagen vascular disease. Therapeutic thoracocentesis should be performed with caution because removal of a large amount of fl uid can result in hypotension.

Patients with cardiac disease develop effusions when left atrial or pulmonary capillary wedge pressure is elevated. 23,24 Effusions are usually bilateral; if unilateral, they are typically right sided. 25 Fluid collections that persist for several months can become exudative due to reabsorption of water over protein. 26 In some cases, repeated thoracocentesis or pleurodesis is necessary to control symptomatic effusions that result from refractory heart failure. 27

Free fl uid in the peritoneal cavity can traverse small open-ings in the diaphragm and enter the pleural space. Effusions caused by ascites usually occur on the right side, 28 whereas effusions secondary to dialysis are usually bilateral and small. 13,29 Hypothyroidism has been reported to cause effu-sions as a result of signifi cantly lowered metabolic state. These are often associated with heart failure, pericardial effu-sions, or ascites and respond to thyroid replacement. 30

EXUDATES

Exudative effusions result from infl ammation of the pleura or obstruction of lymphatic fl ow. Infl ammation leads to leakage of fl uid and protein from pleural capillaries and blocks reabsorption of the fl uid by the lymphatic lacunae of the parietal pleura. Diffuse destruction or obstruction of lym-phatic vessels, which occurs in malignancy or granulomatous disease, also can result in pleural fl uid accumulation. The

cause of an exudative effusion is not often evident from the clinical presentation. The diagnosis can be narrowed by the appearance of the fl uid and the principal cell type found in the fl uid (Table 68-6).

NEUTROPHILIC PREDOMINANCE (PURULENT EFFUSION)

Purulent or parapneumonic effusions are a rare but recog-nized complication of bacterial pneumonia. Studies have cited an incidence of 0.4 to 6 cases per 1000 pediatric hos-pital admissions. 31 Empyema is defi ned as the presence of pus in the pleural space. There are three distinct phases of development of an empyema 32 (Table 68-7). Early in the process, in the exudative phase, the fl uid that accumulates is thin and free fl owing, with normal values of glucose, pH, LDH, and a low white blood cell count. In the fi brinopurulent phase, there is a deposition of fi brin in the pleural space leading to septation (fi brous strands) and loculation (parietal-visceral pleural adhesion) of infected fl uid. The white blood cell count increases as the fl uid thickens. The pH and glucose fall as the LDH level rises secondary to the bacterial con-sumption of glucose and release of lactic acid. In the fi nal, organizing phase, fi broblasts invade the cavity, forming a dense peel on both pleural surfaces while the fl uid becomes a thick, gelatinous mass. This visceral pleural peel contracts, leading to compression and trapping of the lung. The pH and glucose levels are extremely low, whereas the LDH is very elevated. This stage has also been referred to as complicated empyema. Further complications are uncommon in children but include bronchopleural fi stula, lung abscess, or even per-foration through the chest wall (empyema necessitatis).

Identifi cation of a causative organism from the pleural fl uid or blood is made diffi cult by the use of antibiotics before the diagnosis of parapneumonic effusion is made. The most frequently recovered pathogens include Streptococcus pneu-moniae, Streptococcus pyogenes, and Staphylococcus aureus. 33 Of these, S. pneumoniae has emerged as the predominant pathogen in childhood empyema. Polymerase chain reaction (PCR) can be used in culture-negative cases and has identi-fi ed a pathogen in 75% of those cases. 34 S. aureus causes a more severe pneumonia and empyema than other pathogens. The increasing incidence of methicillin-resistant S. aureus in the community poses a new challenge to successful treat-ment. Other pathogens include Klebsiella spp, Pseudomonas spp., anaerobic organisms, and viruses. 35

Clinical manifestations of parapneumonic effusions are very similar to those of classic pneumonia—fever, cough, lethargy, malaise, poor appetite, and lower exercise tolerance. However, in the presence of a purulent effusion, the child will appear sicker with pleuritic chest pain and splinting of the affected side. Suspicion for a parapneumonic effusion should be raised in the case of pneumonia that does not respond to traditional treatment within 48 hours. 36

Diagnosis of a parapneumonic effusion is made on chest radiograph. Staging of the effusion can be made with either computed tomography or ultrasound (Fig. 68-2). Recent studies point to the advantages of early ultrasound in diagnos-ing effusions in the fi brinopurulent or organizing phase. Ultra-sound is able to differentiate loculated, septated fl uid from free-fl owing effusions as well as identify a pleural peel. 16 CT



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Table 68-6Categories of Exudative Pleural Effusion

Type Cell Characteristics Cause

Purulent >5000 leukocytes/mm3 Parapneumonic effusionsPancreatitisPerforation of the esophagusPulmonary infarctionPericardial or myocardial injury

Lymphocytic >50% lymphocytes, usually 1000-1500 cells/mm3

TuberculosisMalignancy: lymphoma (predominantly), leukemia, neuroblastoma, chest wall sarcoma, Wilms

tumor, hepatomaUremiaConnective tissue disorder: rheumatoid arthritis, systemic lupus erythematosusFungal infections

Monocytic >20% monocytes, usually <5000 cells/mm3 Viruses: adenovirus, infl uenza, herpes, varicella, measles, and cytomegalovirusMycoplasma pneumomia

Eosinophilic >10% eosinophils Recent pneumothorax or blood in pleural spaceDrugs: dantrolene, nitrofurantoinUremiaFungal infectionsParasitic infections: histoplasmosis, coccidiodomycosis, ascariasis, paragonimiasis,

echinococcosis, amebiasisChylothorax Pleural fl uid triglyceride >110 mg/dL Injury to thoracic duct

Tumors: lymphomaTuberculosisSarcoidosisNeonatal: Trisomy 21, Noonan syndrome, extralobar sequestration, lymphangiomatosis,

lymphangiectasiaHemothorax Fluid hematocrit >50% blood hematocrit Trauma

Erosion of vessels by central venous cathetersPulmonary infarctionMalignancyThrombocytopeniaHemophiliaRupture of bronchopulmonary sequestrationRupture of arteriovenous malformationRupture of intrathoracic vessel

Table 68-7Stages of Purulent Effusion

Phase Characteristics

Exudative Thin, free-fl owing fl uidNormal glucose, pH, LDHLow WBC count

Fibrinopurulent Deposition of fi brin leading to septations and loculations

High WBC countLow pH and glucoseHigh LDH

Organizing Fibroblasts invade, fl uid thickens, dense peel formsExtremely low pH and glucoseExtremely elevated LDH

provides detailed images of the pleural cavity as well as dif-ferentiating empyema from abscess. 17 However, CT may miss multiloculations or septations within fl uid collections. Ultrasound has the additional advantage over CT in that it is portable, involves no radiation, and does not usually require sedation.

Treatment of parapneumonic effusions has been an ongoing focus of debate. Early surgical intervention in the form of video-assisted thoracoscopic surgery (VATS) for debride-ment of the empyema has become more prevalent. Most authors agree that the goals of treatment include elimination

of the empyema, reexpansion of the lung, decreased duration of symptoms, and a shortened length of stay. 37 In all cases, treatment with antibiotics is essential. Most uncomplicated cases will respond to a single agent, such as a second- or third-generation cephalosporin or a beta-lactam antibiotic or a beta-lactamase inhibitor such as ampicillin-sulbactam or ticarcillin-clavulanate at high dose 33 (Table 68-8). Small effu-sions in association with pneumonia can be treated with antibiotics alone. Larger effusions in the early, exudative phase can be treated with intravenous antibiotics plus chest tube drainage. 38,39

Treatment with simple chest tube drainage is insuffi cient for effusions in the later stages, once septations, loculations,

Table 68-8Antibiotic Treatment for Purulent Effusion

Bacteria Antibiotic

Streptonomis pneumoniae Second-generation cephalosporinThird-generation cephalosporinAmpicillin-sulbactamTicarcillin-clavulanate

Staphylococcus aureus OxacillinMethicillin-resistant S. aureus Vancomycin

LinezolidMycoplasma/Chlamydia Erythromycin

Azithromycin



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A

B

C

Liver

D

Liver

E FFigure 68-2 Images of a 4-year-old girl with a cough, fever, and abdominal pain. A and B, Anteroposterior and lateral chest radiographs demonstrating a large pleural effusion on the right with bilateral lower lobe infi ltrates. C and D, Ultrasound images of the same patient demonstrating an inhomogeneous area of consolidation on the right, which is predominantly hypoechoic with scattered mildly echogenic foci. E and F, CT images of the chest, again demonstrating the large consolidation with pleural effusion.



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or pleural peels have been identifi ed. Other options include the instillation of fi brinolytics into the pleural cavity or surgi-cal decortications through VATS or open thoracotomy. Fibri-nolytics degrade fi brin and allow better drainage of the pleural space with the chest tube and antibiotics. Urokinase and streptokinase seem to be effective, with success rates of 60% to 90%. 40-45

Early surgical debridement of the pleural cavity via VATS has been used with increasing frequency and success. Two trocars (one for the video equipment, the other for surgical tools) are inserted through two small incisions in the chest wall. Under direct visualization, loculations are broken down and pus is drained from the pleural cavity. This method of treatment is associated with a shorter length of stay, shorter duration of fever, fewer days with a chest tube, lower failure rates, and lower complication rates. 46-50 Open thoracotomy has been the defi nitive treatment for empyema over the past century. 51,52 Pus is evacuated from the cavity, and the pleural peel is resected or stripped of all fi brous tissue. The incision is larger, and issues with postoperative pain and cosmesis are signifi cant. Published studies comparing the different treat-

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H

ment options are retrospective reviews, and therefore diffi -cult to interpret and lack suffi cient data regarding the stage of effusion before treatment. There is no consensus, and the decision to proceed to VATS versus treatment with fi brino-lytics is left to the practitioner. A treatment algorithm has been proposed by some authors 33,36 (Fig. 68-3).

In addition to purulent effusions there are other categories of exudative effusions. For a complete list and their causes, please refer to Table 68-6.

PNEUMOTHORAX

Pneumothorax is defi ned as the abnormal collection of air in the pleural space outside of the lung. Air can enter the pleural space by a leak in either the visceral or parietal pleura. Pneu-mothorax can be categorized as spontaneous or traumatic. Traumatic pneumothorax occurs as the result of blunt or penetrating trauma to the chest wall or an injury from a diagnostic or therapeutic procedure. Spontaneous pneumo-thorax occurs without identifi ed trauma and can be further subdivided into primary and secondary. In primary pneumo-

Figure 68-2, cont’d G and H, Images from VATS demonstrating a thick, visceral peel with septations.

Clinical suspicion forparapneumonic effusion

Ultrasound or CT scan

Pneumonia with treatmentfailure after 48 hours

Fibrinopurulentor organized

Medical Surgical

Chest tube plusfibrinolytics and

antibiotics

VATS or openthoracotomy

Patient improved: afebrile, normal oxygen saturationRemove chest tubeStop intravenous antibioticsTreat with oral antibiotics for 1-4 weeksFollow up with radiograph

Exudate

Fibrinolysis Chest tubeplus antibiotics

Chest radiograph

Pleural effusion

Figure 68-3 Treatment algorithm for parapneumonic effusion. VATS, video assisted thorascopic surgery.



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Table 68-9Causes of Pneumothorax

Type of Pneumothrax Cause

Traumatic Penetrating or blunt chest traumaIatrogenic Mechanical ventilation (barotrauma)

Central vein catheterizationProcedures on airways: intubation, endoscopy,

transbronchial biopsyLaparoscopic proceduresPercutaneous biopsies

Primary spontaneous Aesthenic body habitusIdiopathicCocaine or marijuana inhalation

Secondary spontaneous Airway disease: asthma, cystic fi brosisPostinfection: measles, Pneumocystis carinii,

tuberculosis, necrotizing pneumonia or abscess, parasitic (ecchinococcal)

Interstitial lung disease: sarcoidosisLangerhans cell granulomatosisConnective tissue disease: Marfan, Ehlers-

Danlos, rheumatoid arthritis, systemic lupus erythematosus, polymyositis, dermatomyositis

Malignancy: lymphoma, metastasisAspiration: foreign body, otherCatamenial pneumothoraxCongenital malformations

thorax, there is no identifi able lung disease that would lead to air leak. Many patients with primary pneumothorax have apical blebs of unknown etiology that are often diagnosed at the time of surgery or on CT examination. 53 Secondary pneu-mothorax occurs as a complication of underlying lung disease such as cystic fi brosis. The incidence of primary spontaneous pneumothorax is highest between 15 and 34 years of age. 54 The incidence of secondary spontaneous pneumothorax is highest later in life due to its association with chronic obstructive lung disease. Primary spontaneous pneu-mothorax typically occurs in tall, asthenic patients and more commonly in males in both the adult and pediatric popula-tions. 55,56 Smoking increases the risk of pneumothorax. 57 A complete list of causes of pneumothorax is listed in Table 68-9.

Two causative mechanisms for pneumothorax have been proposed. The fi rst mechanism suggests that large increases in transpulmonary pressure cause alveolar distention and high-pressure gradients cause the alveolus to rupture. Super-fi cial alveoli can form subpleural blebs that rupture directly into the pleural space. In the second mechanism, direct injury to the visceral pleura secondary to underlying lung disease leads to pneumothorax. A tension pneumothorax develops when air enters the pleural space during inspiration but cannot exit during exhalation. This will lead to collapse of the affected lung and shift of the mediastium away from the affected side.

The cardinal manifestation of pneumothorax is the sudden onset of chest pain. Other common clinical manifestations include tachypnea, dyspnea, tachycardia, and cyanosis. The severity of symptoms depends on the volume of air in the pleural space, rapidity of onset, and the degree of respiratory compromise before the occurrence of the pneumothorax, which is infl uenced by the presence of underlying lung

disease. Pain can range from localized acute retrosternal pain to overwhelming pleuritic pain as well as ipsilateral shoulder pain. Physical examination fi ndings include decreased breath sounds, decreased thoracic excursion, and hyperresonant per-cussion on the affected side. In cases of tension pneumotho-rax with shift of the mediastinum, the trachea will be displaced, as will the point of maximal cardiac impulse. Sub-cutaneous emphysema results from air moving to areas of lower resistance and can reach the neck, upper extremities, abdominal wall, and peritoneum. In cases where the pneu-mothorax is small, the patient will frequently be asymptom-atic and it is usually an incidental fi nding on radiograph.

Diagnosis of a pneumothorax is accomplished with a chest radiograph. Anteroposterior and lateral views reveal the char-acteristic fi ndings of air in the pleural space outlining the visceral pleura (pleural line) and hyperlucency and attenua-tion of vascular and lung markings on the affected side. CT of the chest is helpful to detect bullae and blebs in patients with recurrent pneumothorax and in cases where the radio-graph is inconclusive. 58,59 Arterial blood gas measurements should be obtained in cases of respiratory distress. Hypox-emia occurs due to collapse and poor ventilation. Hypercap-nia is not usually seen in cases of pneumothorax without underlying chronic lung disease. 53 In cases of severe tension pneumothorax with mediastinal shift and cardiac displace-ment and rotation, an electrocardiogram can reveal changes in the amplitude of the QRS complex and the cardiac axis.

Treatment depends on the size and cause of the pneumo-thorax, the extent of respiratory distress, and the presence of underlying lung disease. The goals of treatment are removal of air from the pleural space and prevention of recurrence. 53,60 Treatment can range from observation and supplemental oxygen to simple needle aspiration or chest tube to pleurode-sis and, in some cases, more invasive surgery. Information on pediatric spontaneous pneumothorax is limited and manage-ment guidelines are based on published adult data.

Observation. In the case of a small pneumothorax (<15% of the involved hemithorax) when the patient is asymptom-atic, simple observation can be instituted. 61,62 In a younger child, hospitalization is recommended. In the older child, observation may be done on an outpatient basis.

Supplemental oxygen. The rate of resorption of air from the pleural space is increased with the use of supplemental oxygen. 63 The increased alveolar oxygen tension creates a large gradient between capillary and pleural gas partial pres-sure of nitrogen, resulting in faster reabsorption of intrapleu-ral air. Use of 100% oxygen via a nonrebreathing facemask has been suggested with a minimal fl ow rate of 15 L/min.

Needle aspiration. Evacuation of air is required for symp-tomatic patients where the pneumothorax has been identi-fi ed to occupy more than 15% of the involved hemithorax. Simple aspiration is done via a large-bore intravenous catheter connected to a large syringe with a three-way stopcock. Air is withdrawn manually until no more can be aspirated. If air continues to be aspirated, this indicates a persistent air leak and a tube thoracostomy should be performed. If no further air can be aspirated, the stopcock is closed and the catheter is secured to the chest wall. A chest radiograph should be performed after 4 hours of observation and if adequate lung reexpansion is seen, the catheter can be removed and the patient observed. Published success rates vary and depend on



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whether the pneumothorax is primary or secondary. 60 The recent ACCP guidelines did not support simple needle aspi-ration in any clinical circumstance. 64

Thoracostomy tube. This is indicated for patients who have large pneumothoraces, are clinically stable or unstable or who have recurrent spontaneous pneumothorax. 64 This involves the use of a one-way Heimlich valve or water seal device to prevent reaccumulation of air. In the ACCP guide-lines, half of the group recommended clamping of the tube 4 hours after the last evidence of an air leak. A repeat chest radiograph should be taken 5 to 12 hours after the last evi-dence of an air leak in preparation for removal of the tube.

Pleurodesis. This involves injection of a sclerosis agent such as talc, tetracycline, doxycycline, autologous blood patches, or fi brin glue at the time of thoracostomy tube place-ment. This method is less favorable than surgical intervention for persistent air leak. 65 Mechanical pleurodesis by direct abrasion with gauze, or laser or chemical pleurodesis with talc or doxycycline at the time of surgery has support in the lit-erature to prevent recurrence. 64

Surgical intervention. This involves stapling or oversewing ruptured blebs (bullectomy) or tears in the visceral pleura

and resection of abnormal lung tissue. Mechanical and chemi-cal pleurodesis can also be done with bullectomy. This can be done via VATS, minithoracotomy, or open thoracotomy, although many physicians prefer VATS. Surgery is indicated to treat persistent air leaks and to prevent recurrence. Surgery is recommended at the time of the fi rst occurrence of a sec-ondary spontaneous pneumothorax 65 and at the second occurrence of a primary spontaneous pneumothorax. 66

Data regarding prognosis after spontaneous pneumothorax in children are limited. One reported series showed a 37% incidence of recurrent spontaneous pneumothorax. 67 In pediatric patients undergoing surgical management, the reported risk of recurrence was 6% to 9%. 68,69 A recent study 70 evaluated primary versus delayed surgery for pediat-ric patients with primary spontaneous pneumothorax. The authors found that patients who had VATS-directed bullec-tomy and pleurodesis at the fi rst presentation of spontaneous pneumothorax had a 29% recurrence rate compared with 0% in the group of patients undergoing VATS on the second occurrence.

SUGGESTED READINGS

Agostoni E, D’Angelo E: Pleural liquid pressure. J Appl Physiol 71:393-403, 1991.

Balfour-Lynn IM, Abrahamson E, Cohen G, et al: BTS guidelines for the management of pleural infection in children. Thorax 60(suppl 1):l-21, 2005.

Baumann MH: Management of spontaneous pneumothorax. Clin Chest Med 27:369-381, 2006.

Gates RL, Hogan M, Weinstein S, Arca MJ: Drainage, fi brinolytics or surgery: A comparison of treatment options in pediatric empyema. J Pediatr Surg 39:1638-1642, 2004.

Hiliard TN, Henderson AJ, Langton Hewer SC: Management of parapneumonic effusion and empyema. Arch Dis Child 88:915-917, 2003.

Lewis RA, Fegin RD: Current issues in the diagnosis and manage-ment of pediatric empyema. Semin Pediatr Infect Dis 13:280-288, 2002.

Light RW, Macgregor MI, Luchsinger PC, Ball WC Jr: Pleural effu-sions: The diagnostic separation of transudates and exudates. Ann Intern Med 77:507-513, 1972.

Sahn SA: State of the art. The pleura. Am Rev Respir Dis 138:184-234, 1988.

Shaw KS, Prasil P, Nguyen LT, Laberge JM: Pediatric spontaneous pneumothorax. Semin Pediatr Surg 12:55-61, 2003.

Wang NS: Anatomy of the pleura. Clin Chest Med 19:229-240, 1998.

REFERENCESThe references for this chapter can be found at www.pedrespmedtext.com.


Pediatric Respiratory Medicine || Abnormalities of the Pleural Space

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