A pneumothorax is a collection of air outside the lung but within the pleural cavity. It occurs when air accumulates between the parietal and visceral pleura inside the chest. The air accumulation can apply pressure on the lung and make it collapse. That is why a pneumothorax is commonly referred to as a "collapsed lung." There are two types of pneumothorax: traumatic and atraumatic. The two subtypes of atraumatic pneumothorax are primary and secondary. A primary spontaneous pneumothorax (PSP) occurs automatically without a known eliciting event, while a secondary spontaneous pneumothorax (SSP) occurs subsequent to an underlying pulmonary disease. A traumatic pneumothorax can be the result of blunt or penetrating trauma. Pneumothoraces can be even further classified as simple, tension, or open. A simple pneumothorax does not shift the mediastinal structures as does a tension pneumothorax. An open pneumothorax also is known as a "sucking" chest wound.
The etiology of air is usually from disruption of the tracheobronchial tree. This disruption can be caused by a traumatic event or rupture of a bleb.
The incidence of PSP in the United States is 7 per 100,000 men and 1 per 100,000 women per year. The majority of recurrence occurs within the first year, and incidence ranges widely from 25% to 50%. Recurrence rate is highest over the first 30 days.
The leading cause of iatrogenic pneumothorax is transthoracic needle aspiration (usually for biopsies) and the second leading cause is central venous catheterization. Other possible causes are not as frequent including positive pressure ventilation and thoracentesis.
The pressure gradient inside the thorax changes with a pneumothorax. Normally the pressure of the pleural space is negative when compared to atmospheric pressure. When there is communication between the alveoli and the pleural space, air fills this space changing the gradient. A tension pneumothorax occurs when this communication becomes a one-way valve without any outflow from the pleural space. The pressure in the pleural space increases causing hypoxia, mediastinal shift, and can compromise venous return as well. Clinical presentation of a pneumothorax can range anywhere from asymptomatic to chest pain and shortness of breath. A tension pneumothorax can cause severe hypotension (obstructive shock) and even death. Beck's triad describes symptoms commonly associated with tension pneumothorax. The three components of Beck's triad are: distended neck veins, distant heart sounds, and hypotension. Other symptoms include tachypnea, dyspnea, tachycardia, and hypoxia.
On examination, breath sounds may be diminished and percussion hyperresonant on the affected side. Some traumatic pneumothoraces are associated with subcutaneous emphysema. Pneumothorax may be difficult to diagnose from physical exam especially in a noisy trauma bay. However, it is essential to make the diagnosis of tension pneumothorax on physical exam. Beck's triad of distended neck veins, distant heart sounds and hypotension help in making this diagnosis. A late finding associated with tension pneumothorax includes tracheal deviation away from the affected side.
Chest radiography, ultrasonography, or CT can be used for diagnosis, although diagnosis from a chest x-ray is more common. Radiographic findings of 2.5 cm air space are equivalent to a 30% pneumothorax. Occult pneumothoraces may be diagnosed by CT but are usually clinically insignificant. The extended focused abdominal sonography for trauma (E-FAST) exam has been a more recent diagnostic tool for pneumothorax. The diagnosis on ultrasound is usually made by the absence of lung sliding, the absence of comet-tails artifact, and the presence of a lung point. Unfortunately, this diagnostic method is very operator dependent and sensitivity, and specificity can vary. In skilled hands, ultrasonography has up to a 94% sensitivity and 100% specificity (better than chest x-ray). If a patient is hemodynamically unstable with a suspected tension pneumothorax, intervention is not withheld to await imaging. Needle decompression can be performed if the patient is hemodynamically unstable with a convincing history and physical exam indicating tension pneumothorax.
Management depends on the clinical scenario. For patients who have associated symptoms and are showing signs of instability, needle decompression is the treatment of a pneumothorax. This usually is performed with a 14- to 16-guage and 4.5 cm in length angiocatheter just superior to the rib in the second intercostal space in the midclavicular line. After needle decompression or for stable pneumothoraces, the treatment is the insertion of a thoracostomy tube. This usually is placed above the rib in the fifth intercostal space anterior to the midaxillary line. The size of thoracostomy tube usually ranges depending on the patient's height and weight and whether there is an associated hemothorax. Open "sucking" chest wounds are treated initially with a three-sided occlusive dressing. Further treatment may require tube thoracostomy and/or chest wall defect repair. An asymptomatic small pneumothorax usually can be observed with oxygen via nasal cannula administration and repeat chest radiography. Air can reabsorb from the pleural space at a rate of 1.5%/day. Using supplemental oxygen can increase this reabsorption rate. By increasing the fraction of inspired oxygen concentration, the nitrogen of atmospheric air is displaced changing the pressure gradient between the air in the pleural space and the capillaries. Pneumothorax on chest radiography approximately 25% or larger usually needs treatment with a thoracostomy tube even if the patient is asymptomatic.
Patients with spontaneous, persistent (> 3 days with adequate thoracostomy tube positioning), or recurrent pneumothorax should undergo a video-assisted thoracic surgery (VATS) and pleurodesis. A mechanical pleurodesis with bleb/bullectomy decreases the recurrence rate of pneumothorax to < 5%. Options for mechanical pleurodesis include stripping of the parietal pleura versus using an abrasive "scratchpad" or dry gauze. A chemical pleurodesis is an option in patients who may not tolerate a mechanical pleurodesis. Options for chemical pleurodesis include talc, tetracycline, doxycycline, or minocycline which are all irritants to the pleural lining.
Do not let a chest radiograph or CT scan delay treatment with needle decompression or thoracostomy tube if the patient is clinically unstable, i.e. tension pneumothorax.
Worsening subcutaneous emphysema can be associated with malposition of a chest tube and repositioning with a new chest tube is recommended. A chest tube should never be reinserted as this can increase the patient's risk for empyema.
An untreated pneumothorax is a contraindication for flying or scuba diving. If air transport is required, then a thoracostomy tube should be placed before transport.
If there is a persistent or recurrent pneumothorax despite treatment with thoracostomy tube, these patients need specialty consultations for a possible video-assisted thoracoscopic surgery (VATS) with or without pleurodesis or thoracotomy.
If the patient is discharged from the hospital after a resolved pneumothorax, recommendations should be made for no flying or scuba diving for a minimum of two weeks. Patients with known history of spontaneous pneumothorax should not be medically cleared for occupations involving flying or scuba diving.
The management of a pneumothorax is often done by the emergency department physician. In some cases, the disorder may be managed by the ICU staff and the thoracic surgeon. The care of patients who have a chest tube is done by the nurse. All nurses who manage patients with a chest tube should know how a chest drain functions. Patients need to be examined every shift and the patency of the chest tube is important. Patients with small pneumothorax can be observed if they have no symptoms. If discharged the patient should be seen within 24 hours.
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