Pneumothorax occurs when the parietal or visceral pleura is breached and the pleural space is exposed to positive atmospheric pressure. Normally the pressure in the pleural space is negative or subatmospheric compared to atmospheric pressure; this negative pressure is required to maintain lung inflation. When either pleura is breached, air enters the pleural space, and the lung or a portion of it collapses. Types of pneumothorax include simple, traumatic, and tension pneumothorax.
A simple, or spontaneous, pneumothorax occurs when air enters the pleural space through a breach of either the parietal or visceral pleura. Most commonly this occurs as air enters the pleural space through the rupture of a bleb or a bronchopleural fistula. A spon-taneous pneumothorax may occur in an apparently healthy per-son in the absence of trauma due to rupture of an air-filled bleb, or blister, on the surface of the lung, allowing air from the airways to enter the pleural cavity. It may be associated with diffuse in-terstitial lung disease and severe emphysema.
Traumatic pneumothorax occurs when air escapes from a lacera-tion in the lung itself and enters the pleural space or enters the pleural space through a wound in the chest wall. It can occur with blunt trauma (eg, rib fractures) or penetrating chest trauma. It may also occur from abdominal trauma (eg, stab wounds or gun-shot wounds to the abdomen) and from diaphragmatic tears. Traumatic pneumothorax may occur with invasive thoracic pro-cedures (ie, thoracentesis, transbronchial lung biopsy, insertion of a subclavian line) in which the pleura is inadvertently punc-tured, or with barotrauma from mechanical ventilation.
Traumatic pneumothorax resulting from major injury to the chest is often accompanied by hemothorax (collection of blood in the pleural space resulting from torn intercostal vessels, lacer-ations of the great vessels, and lacerations of the lungs). Often both blood and air are found in the chest cavity (hemopneu-mothorax) after major trauma. Chest surgery can cause what is classified as a traumatic pneumothorax as a result of the entry into the pleural space and the accumulation of air and fluid in the pleural space.
Open pneumothorax is one form of traumatic pneumothorax. It occurs when a wound in the chest wall is large enough to allow air to pass freely in and out of the thoracic cavity with each at-tempted respiration. Because the rush of air through the hole in the chest wall produces a sucking sound, such injuries are termed sucking chest wounds. In such patients, not only does the lung collapse, but the structures of the mediastinum (heart and great vessels) also shift toward the uninjured side with each inspiration and in the opposite direction with expiration. This is termed me-diastinal flutter or swing, and it produces serious circulatory problems.
The signs and symptoms associated with pneumothorax depend on its size and cause. Pain is usually sudden and may be pleuritic. The patient may have only minimal respiratory distress with slight chest discomfort and tachypnea with a small simple or un-complicated pneumothorax. If the pneumothorax is large and the lung collapses totally, acute respiratory distress occurs. The pa-tient is anxious, has dyspnea and air hunger, has increased use of the accessory muscles, and may develop central cyanosis from se-vere hypoxemia. Severe chest pain may occur, accompanied by tachypnea, decreased movement of the affected side of the tho-rax, a tympanic sound on percussion of the chest wall, and de-creased or absent breath sounds and tactile fremitus on the affected side.
Medical management of pneumothorax depends on its cause and severity. The goal of treatment is to evacuate the air or blood from the pleural space. A small chest tube (28 French) is inserted near the second intercostal space; this space is used because it is the thinnest part of the chest wall, minimizes the danger of contact-ing the thoracic nerve, and leaves a less visible scar. If the patient also has a hemothorax, a large-diameter chest tube (32 French or greater) is inserted, usually in the fourth or fifth intercostal space at the midaxillary line. The tube is directed posteriorly to drain the fluid and air. Once the chest tube or tubes are inserted and suction is applied (usually to 20 mm Hg suction), effective de-compression of the pleural cavity (drainage of blood or air) occurs.
If an excessive amount of blood enters the chest tube in a rel-atively short period, an autotransfusion may be needed. This technique involves taking the patient’s own blood that has been drained from the chest, filtering it, and then transfusing it back into the patient’s vascular system.
In such an emergency, anything may be used that is large enough to fill the chest wound—a towel, a handkerchief, or the heel of the hand. If conscious, the patient is instructed to in-hale and strain against a closed glottis. This action assists in re-expanding the lung and ejecting the air from the thorax. In the hospital, the opening is plugged by sealing it with gauze impreg-nated with petrolatum. A pressure dressing is applied. Usually, a chest tube connected to water-seal drainage is inserted to permit air and fluid to drain. Antibiotics usually are prescribed to com-bat infection from contamination.
The severity of open pneumothorax depends on the amount and rate of thoracic bleeding and the amount of air in the pleural space. The pleural cavity can be decompressed by needle aspira-tion (thoracentesis) or chest tube drainage of the blood or air. The lung is then able to re-expand and resume the function of gas ex-change. As a rule of thumb, the chest wall is opened surgically (thoracotomy) when more than 1,500 mL of blood is aspirated initially by thoracentesis (or is the initial chest tube output) or when chest tube output continues at greater than 200 mL/hour. The urgency with which the blood must be removed is deter-mined by the respiratory compromise. An emergency thoracot-omy may also be performed in the emergency department if there is suggested cardiovascular injury secondary to chest or penetrat-ing trauma.
A tension pneumothorax occurs when air is drawn into the pleural space from a lacerated lung or through a small hole in the chest wall. It may be a complication of other types of pneumo-thorax. In contrast to open pneumothorax, the air that enters the chest cavity with each inspiration is trapped; it cannot be expelled during expiration through the air passages or the hole in the chest wall. In effect, a one-way valve or ball valve mechanism occurs where air enters the pleural space but cannot escape. With each breath, tension (positive pressure) is increased within the affected pleural space. This causes the lung to collapse and the heart, the great vessels, and the trachea to shift toward the unaffected side of the chest (mediastinal shift). Both respiration and circulatory function are compromised because of the increased intrathoracic pressure. The increased intrathoracic pressure decreases venous return to the heart, causing decreased cardiac output and impair-ment of peripheral circulation. In extreme cases, the pulse may be undetectable—this is known as pulseless electrical activity.
The clinical picture is one of air hunger, agitation, increasing hy-poxemia, central cyanosis, hypotension, tachycardia, and profuse diaphoresis. A comparison of open and tension pneumothorax is shown in Figure 23-9.
If a tension pneumothorax is suspected, the patient should im-mediately be given a high concentration of supplemental oxygen to treat the hypoxemia, and pulse oximetry should be used to monitor oxygen saturation.
In an emergency situation, a tension pneumothorax can be de-compressed or quickly converted to a simple pneumothorax by inserting a large-bore needle (14-gauge) at the second intercostal space, midclavicular line on the affected side. This relieves the pressure and vents the positive pressure to the external environ-ment. A chest tube is then inserted and connected to suction to remove the remaining air and fluid, re-establish the negative pressure, and re-expand the lung. If the lung re-expands and air leakage from the lung parenchyma stops, further drainage may be unnecessary. If a prolonged air leak continues despite chest tube drainage to underwater seal, surgery may be necessary to close the leak.
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