Porth's Essentials of Pathophysiology, 4e

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Disorders of Ventilation and Gas Exchange

C h a p t e r 2 3

Pneumothorax Pneumothorax refers to the presence of air in the pleural space. Pneumothorax causes partial or com- plete collapse of the affected lung. Pneumothorax can occur without an obvious cause or injury (i.e., spontaneous pneumothorax) or as a result of direct injury to the chest or major airways (i.e., traumatic pneumothorax). 7,8 Tension pneumothorax describes a life-threatening condition in which increased pressure within the pleural cavity impairs both respiratory and cardiac function. Spontaneous Pneumothorax. Spontaneous pneumo- thorax is hypothesized to occur due to the rupture of an air-filled bleb, or blister, on the surface of the lung. 8,10,13,14 Rupture of these blebs allows atmospheric air from the airways to enter the pleural cavity (Fig. 23-1). Because alveolar pressure normally is greater than pleural pres- sure, air flows from the alveoli into the pleural space, causing the involved portion of the lung to collapse as a result of its own recoil. Air continues to flow into the pleural space until a pressure gradient no longer exists or the decline in lung size causes the leak to seal. Spontaneous pneumothoraces can be divided into primary and secondary pneumothoraces. 8,13,14 Primary pneumothorax occurs in otherwise healthy persons, whereas secondary pneumothorax occurs in persons with underlying lung disease. In primary spontaneous pneumothorax, the blebs usually are located at the top of the lungs. The condi- tion is seen in persons who are tall and thin. It has been suggested that the difference in pleural pressure from the top to the bottom of the lung is greater in tall persons and that this difference in pressure may contribute to the development of blebs. Smoking is another factor that has been associated with primary spontaneous pneu- mothorax. Inflammation of the small airways related

transudates have none of these features. Because mea- surements of LDH are easily obtained from a sample of pleural fluid, it is a useful marker for diagnosis of exu- dative pleural disorders. Conditions that produce exu- dative pleural effusions are bacterial pneumonia, viral infection, pulmonary infarction, and malignancies. Empyema refers to an infection in the pleural cav- ity that results in exudate containing glucose, proteins, leukocytes, and debris from dead cells and tissue. 3 The infection may be caused by invasion from an adjacent bacterial pneumonia or a subdiaphragmatic infection, by rupture of a lung abscess into the pleural space, or by trauma. Chylothorax is the effusion of lymph in the thoracic cavity. 12 Chyle, a milky fluid containing chylomicrons, is found in the lymph fluid drained by lacteals in the villi of the small intestine. The thoracic duct transports chyle to the central circulation. Chylothorax results from trauma, inflammation, or malignant infiltration obstructing chyle transport from the thoracic duct into the central circula- tion. It is the most common cause of pleural effusion in the fetus and neonate, resulting from congenital malforma- tion of the thoracic duct or lymph channels. Chylothorax also can occur as a complication of intrathoracic surgical procedures and use of the great veins for total parenteral nutrition and hemodynamic monitoring. Hemothorax is the presence of blood in the pleural cavity. Bleeding may arise from chest injury, a complica- tion of chest surgery, malignancies, or rupture of a great vessel such as an aortic aneurysm. It is usually diagnosed by the presence of blood in the pleural fluid. Hemothorax usually requires drainage, and if the bleeding continues, surgery to control the bleeding may be required. The manifestations of pleural effusion vary with the cause. 7,8,10,11 Fluid in the pleural cavity acts as a space- occupying mass, causing a decrease in lung expansion on the affected side that is proportional to the amount of fluid collected. Characteristic signs of pleural effusion are dullness to percussion and diminished breath sounds. Hypoxemia may occur because of decreased surface area for diffusion and usually is corrected with supple- mental oxygen. Dyspnea, the most common symptom, occurs when fluid in the pleural cavity compresses the lung, resulting in increased effort or rate of breathing. Pleuritic pain usually occurs only when inflammation is present, although constant discomfort may be felt with large effusions. Diagnosis of pleural effusion is based on chest radio- graphs, chest ultrasonography, and computed tomogra- phy (CT). 8 Thoracentesis (aspiration of fluid from the pleural space) can be used to obtain a sample of pleural fluid for diagnosis. The treatment of pleural effusion is directed at the cause of the disorder. 8 With large effu- sions, thoracentesis may be used to remove fluid from the intrapleural space and allow for reexpansion of the lung. A palliative method used for treatment of pleural effusions caused by a malignancy is the injection of a sclerosing agent into the pleural cavity. This method of treatment causes obliteration of the pleural space and prevents the reaccumulation of fluid. Chest tube drain- age may be necessary in cases of continued effusion.

Ruptured bleb

Parietal pleura

Visceral pleura

Pleural space

Air

FIGURE 23-1. Mechanism for development of spontaneous pneumothorax, in which an air-filled bleb on the surface of the lung ruptures, allowing atmospheric air from the airways to enter the pleural space.