| When air or fluid enters the pleural space, it: 1) separates the visceral pleura from the parietal pleura, thus disrupting the negative pressure that prevents the lungs from collapsing at the end of exhalation, and 2) compresses the lung. If only a small amount of air or fluid is present, it may be reabsorbed without intervention. However, if large enough, the fluid or air compromises normal respiration and must be evacuated from the pleural space. PNEUMOTHORAX Air in the pleural space is called a pneumothorax, which can be classified as spontaneous or traumatic. Dyspnea and chest pain are the most common symptoms of pneumothorax. Decreased breath sounds and lack of movement on the affected side may also be observed. SPONTANEOUS PNEUMOTHORAX Spontaneous pneumothorax is usually caused by the rupture of a small bleb (enlarged air sac) on the lung’s surface (figure 8). It typically occurs in tall, thin men who smoke where mechanical stresses at the apex (top) of the lung weaken the lung tissue. It may also result as a complication of pre-existing lung disease that weakens the lung, making it more prone to rupture. Common causes include chronic obstructive pulmonary disease, cystic fibrosis, necrotizing pneumonia and AIDS patients with Pneumocytis carinii infection. TRAUMATIC PNEUMOTHORAX Traumatic pneumothorax may result from: 1) Internal trauma, such as rib fracture, where the rib punctures the lung (figure 9). If there is no opening to the outside of the chest wall, it is called a closed pneumothorax. 2) External trauma, such as a stab wound or bullet wound, that penetrates the chest wall and may puncture the lung (figure 10). This is called an open pneumothorax or a sucking chest wound. 3) Invasive or therapeutic procedures, such as transthoracic needle aspiration, subclavian needle stick or thoracentesis, that inadvertently puncture the lung. This is called iatrogenic pneumothorax. The use of positive end-expiratory pressure (PEEP) with mechanical ventilation can also result in iatrogenic pneumothorax, particularly in patients with acute respiratory distress syndrome (ARDS) where the lung tissue is weakened. TENSION PNEUMOTHORAX Tension pneumothorax occurs when air accumulates in the pleural space more rapidly than it can be evacuated. Pressure builds up which not only collapses the lung, but can also shift the mediastinum and severely impede venous return and cardiac output (figure 11). A tension pneumothorax quickly becomes life-threatening and must be relieved promptly. Signs/symptoms of tension pneumothorax include: rapid, labored respirations; tachycardia; cyanosis; hypoxemia; and sudden chest pain that extends to the shoulders. In a mechanically ventilated patient, the high inspiratory pressure alarm may also sound. Tracheal deviation (the trachea is skewed away from the side of the tension pneumothorax) signifies that a mediastinal shift has occurred and is an ominous sign. PLEURAL EFFUSION Fluid in the pleural space is called pleural effusion. The fluid may be lymph (chylothorax), pus (empyema), blood (hemothorax), or non-specific serous fluid. The mechanism of distress in pleural effusion is direct compression of lung tissue; the fluid occupies space the lung would usually fill (figure 12). On examination, you would detect muffled or absent breath sounds and dullness to percussion. HEMOTHORAX Hemothorax is defined as the presence of blood in the pleural space. This is caused primarily by chest trauma where virtually every blood vessel in the chest can bleed into the pleural space. Iatrogenic hemothorax may occur, mostly as a complication of a central venous catheter placement. CARDIAC TAMPONADE Blood may also accumulate in the mediastinum, specifically the pericardial sac, after cardiac surgery. Accumulation of fluid around the heart can cause cardiac tamponade. Because it compresses the heart and interferes with venous return, it can be life-threatening. Signs reflect the decreased venous return: cardiac output drops severely, jugular veins distend, pulmonary artery (PA) pressures increase, central venous pressure (CVP) increases, and blood pressure falls. These are ominous signs and require immediate emergency actions. |
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CHEST DRAINAGE AS A THERAPEUTIC INTERVENTION
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Thoracic System Pathology
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