Pneumothorax

Author: Dr Michael Hanley University of Colorado Denver 2008-07-28
Pneumothorax or "Collapsed Lung"

INTRODUCTION

A pneumothorax exists when air or another gas is introduced into the pleural space within the chest, causing the lung to collapse away from the chest wall. To visualize this, it’s important to understand that the lungs are each located in their own chamber within the chest (thorax). Each chamber is termed a hemithorax. The outer surface of each lung and the inner surface of the chest wall are lined with a very thin, continuous membrane called the pleura or pleural membrane. That portion of the membrane covering the lung is called the visceral pleura and the portion covering the inner chest wall is the parietal pleura. The pleural space is the potential space that exists between each of these surfaces. It normally contains about five to seven ml of fluid. Under normal conditions the pleural space is quite small as the outer surface of the lung is in contact with the inner surface of the chest wall and the volume of the space is determined by the amount of fluid in it. However, the surface of the lung is not tethered to the inner surface of the chest wall and will fall away from the chest wall if something collects within the pleural space. When air or another gas is introduced into the space it causes the lung to collapse away from the chest wall; this is a pneumothorax. Some pneumothoraces are small and can resolve themselves with minimal treatment and close observation. Large pneumothoraces, however, are life-threatening and require emergency medical attention.

LAY TERMS USED TO DESCRIBE A PNEUMOTHORAX

Health care providers will occasionally refer to a pneumothorax as a “collapsed lung” when talking with patients. This term is misleading however as other pathological processes may also cause the lung to collapse and are also referred to as a “collapsed lung.” The most common of these result from obstruction of a larger airway. Airway obstruction is common, especially in patients hospitalized on mechanical ventilators or with pulmonary (lung) infections, and can occur from mucus, tumor, aspirated (inhaled or sucked in) foreign body, and other viscous material. It can also occur if a lung mass or lymph nodes compress an airway. If the airway is completely obstructed, the air in the portion of the lung furthest away from the obstruction slowly gets absorbed into the blood stream and surrounding tissues, causing the lung to collapse.

It is important to clarify what a health care provider means if the term “collapsed lung’ is used, as the treatment for the condition differs dramatically depending on the cause. If airway obstruction is present, management may include a procedure to open the airway such as bronchoscopy. Treatment of pneumothorax on the other hand requires evacuation of the air or gas from the pleural space.

CAUSES OF A PNEUMOTHORAX

Air may enter the pleural space by one of two mechanisms. The air may originate from within the lung itself and enter the space if the surface of the lung ruptures. This may occur if the lung is injured by penetrating trauma such as a stab or gun shot wound, due to sudden increases in air pressure within the airways and air sacs in the lungs as might occur during violent coughing, vomiting, or retching, or due to trauma to airways. Air may also enter the pleural space directly from the atmosphere due to injuries to the chest wall.

TYPES OF PNEUMOTHORAX

Pneumothoraces are classified as either spontaneous or traumatic. Spontaneous pneumothoraces occur without any obvious cause or preceding trauma. They may be either primary or secondary depending on the clinical setting in which they occur. A primary spontaneous pneumothorax occurs in a patient without known lung disease. Secondary spontaneous pneumothoraces occur in patients with known lung disease and are a complication of the underlying lung pathology. Traumatic pneumothoraces result from either direct on indirect trauma to the chest. The trauma may be either penetrating or blunt trauma or trauma resulting from positive pressure ventilation (barotrauma). Traumatic pneumothoraces are further classified as either iatrogenic or non-iatrogenic. Iatrogenic means that the condition results from a medical procedure or treatment.

A tension pneumothorax occurs when the pressure of the air in the pleural space is increased and remains greater than atmospheric pressure throughout much if not all of the respiratory cycle (inspiration and expiration). The increased pressure within the pleural space shifts the mediastinum (the middle portion of the chest that contains amongst other things the heart, aorta, inferior vena cava, trachea, major bronchi, and esophagus) toward the opposite hemithorax and displaces the diaphragm inferiorly, toward the abdomen . Tension pneumothoraces typically result from a “ball-valve” mechanism within an airway that allows continued entry of gas into the pleural space but limits emptying of gas from the space. The physiologic changes that accompany a tension pneumothorax frequently result in profoundly low blood oxygen levels (hypoxemia) and shock. Death may occur quickly if the pneumothorax is unrecognized and untreated.

DIAGNOSIS

The most common symptoms of a pneumothorax include chest pain and shortness of breath. There may be absent or diminished breath sounds on the side of the chest occupied by the pneumothorax and patients may have a bluish discoloration of the skin (cyanosis). Laboratory testing reveals a low arterial blood oxygen level. These findings are non-specific however. A chest x-ray is required to confirm the diagnosis and demonstrates a collection of air in the space between the outer edge of the lung and the internal surface of the chest wall. Occasionally the pneumothorax is not readily visible on a routine chest x-ray and diagnosis requires computed tomography (CT) of the chest. This most commonly occurs if the pneumothorax is small, in bedridden patients who cannot sit upright, and when patients have bullous emphysema (a type of lung disease frequently associated with tobacco use).

RISK FACTORS FOR PNEUMOTHORAX

Primary spontaneous pneumothoraces are thought to occur due to the rupture of cysts that lie just below the surface of the lung. These large blisters (blebs) may be either congenital in nature or result from airway inflammation. Several factors are associated with an increased risk of this form of pneumothorax. These include a family history of primary spontaneous pneumothorax, a tall, thin body habitus (especially in men between the ages of 10 and 30), and a history of smoking tobacco products. Smoking increases the risk of primary spontaneous pneumothorax by 20 fold and does so in a dose dependent fashion; that is, the more you smoke, the greater your risk of pneumothorax.

By definition, secondary spontaneous pneumothoraces occur in the setting of underlying lung disease and are a complication of those conditions. Secondary spontaneous pneumothoraces have been associated with a great many different types of lung diseases. Most of these are chronic in nature. The more common conditions that have been associated with this type of pneumothorax include Chronic Obstructive Pulmonary Disease (COPD, which includes emphysema and chronic bronchitis), asthma, cystic fibrosis, pulmonary infarction, granulomatous diseases such as tuberculosis and sarcoidosis, and interstitial lung disease. COPD is the most common chronic lung disease associated with pneumothorax. In some older clinical series, nearly two thirds of cases of secondary spontaneous pneumothorax occurred in patients with COPD. The risk of pneumothorax in COPD increases with the severity of lung dysfunction as measured by pulmonary function tests. The highest risk occurs in COPD patients with a forced expiratory volume in one second (FEV1) of less than 1 liter (FEV1, a commonly used measure of lung function, is a marker of the severity of some lung diseases).

Occasionally, a secondary spontaneous pneumothorax will complicate an acute lung process, such as a necrotizing pneumonia or lung abscess. The most common example of this is Pneumocystis jirovecii pneumonia. This form of pneumonia, which was previously termed Pneumocystis carinii pneumonia or PCP, is common in patients infected with the human immunodeficiency virus (HIV) who have advanced to AIDS. It also occurs less commonly in other patients suffering from immune suppression. The infection is characterized by the acute development of lung cysts which may enlarge and rupture, resulting in a pneumothorax.

TREATMENT

Management of a pneumothorax focuses on both immediate treatment to eliminate the pneumothorax and stabilize the patient as well as strategies to prevent recurrence.

Immediate treatment depends on the size and clinical significance of the pneumothorax. Air in the pleural space slowly gets reabsorbed from the space into the surrounding tissue and blood vessels. Typically, the rate of reabsorption is quite low; about 1.25% of the volume of air is reabsorbed per day. However, if no additional air is introduced into the space, a pneumothorax will eventually resolve without treatment. Small pneumothoraces (comprising less than 15% of the volume of the hemithorax) that are not associated with symptoms in otherwise healthy patients (no underlying lung disease) may therefore be treated with observation and administration of high concentrations of supplemental oxygen. The role of supplemental oxygen in this setting is primarily to increase the rate of reabsorption of the pneumothorax. Eighty percent of the gas in air (and therefore the pneumothorax) is nitrogen. Administration of high concentrations of oxygen lowers the partial pressure of nitrogen in the tissues surrounding the pneumothorax, creating a higher pressure gradient for that gas and increasing its rate of reabsorption. The rate of adsorption of pleural air increases four to sixfold if high flow oxygen is administered.

A repeat chest x-ray should be obtained in 12-24 hours for any pneumothorax treated by simple observation and oxygen to determine if the pneumothorax is stable in size. If the pneumothorax is unchanged in size or smaller, no additional treatment is required. If the pneumothorax is larger, it should be evacuated by inserting a chest tube (a catheter placed into the pleural space) through the chest wall. The chest x-ray should be obtained sooner if patients undergoing observation and oxygen therapy become symptomatic.

Larger pneumothoraces, especially when associated with significant symptoms, and secondary spontaneous pneumothoraces, tension pneumothoraces, and iatrogenic pneumothoraces due to mechanical ventilation should be immediately evacuated with a chest tube. Most spontaneous secondary pneumothoraces are not well tolerated by patients due to the pre-existent respiratory compromise associated with their underlying lung disease. In addition, the risk of rapid deterioration should the pneumothorax enlarge is greater in these patients. Tension pneumothoraces represent true medical emergencies requiring prompt intervention. Aggressive care of pneumothoraces in patients receiving mechanical ventilation is warranted due to the risk of progression to a tension pneumothorax.

Additional management of symptomatic pneumothoraces includes supportive care such as oxygen for hypoxemia and analgesics (pain relievers) for chest pain.

Both primary and secondary spontaneous pneumothoraces may recur after treatment. The rate of recurrence is unclear, but is higher for secondary compared to primary pneumothoraces and ranges from 28-52%. The risk of recurrence increases with each subsequent pneumothorax and appears to decrease with time. Most recurrences occur in the first year following a pneumothorax, however, the risk remains elevated for many years. Strategies to prevent recurrence focus on obliterating the pleural space; the procedures to accomplish this are termed pleural sclerosis or pleurodesis. They create inflammation of the pleural surfaces and subsequent permanent fusion of the surfaces through scarring. Multiple techniques to achieve this have been developed including both surgical and non-surgical approaches. Surgical techniques include both open thoracotomy and video-assisted thoracoscopy (VATS). The latter consists of either mechanical or chemical scarification of the space through a videoscope inserted into the pleural space through a small incision in the chest wall. The videoscope facilitates direct visualization of the pleural surface. This allows the operator to 1) remove or ablate with stapling or laser therapy any blebs and bullae that may be present and 2) either instill medications called sclerosants through the scope that will cause pleural inflammation or pass instruments through the scope that can be used to directly injure the pleural membrane and subsequently cause inflammation. The key is that the operator can perform these procedures under direct visualization. Open thoracotomy is a surgical procedure in which the surgeon gains access to the pleural space by making an incision in the chest wall. Open thoracotomy also allows visualization of to the pleural space but requires a much larger incision tah does VATS. Both procedures are performed under general anesthesia but the morbidity, mortality and duration of hospitalization following open thoracotomy are greater.

Non-surgical approaches to obliterate the pleural space consist of instillation of sclerosants directly into the pleural space through a large bore chest tube. The sclerosant is allowed to dwell for four to six hours and then is drained out through the same tube. A variety of medications have been recommended as sclerosants. These include talc slurry, tetracycline derivatives (tetracycline, doxycycline and monocycline), quinacrine, and bleomycin. Of these, talc and tetracyclines are the most efficacious. Although talc is likely more effective than the tetracyclines, there are higher risks of side effects. Potential complications include the adult respiratory distress syndrome (ARDS), chronic pleuritis and subsequent restrictive lung disease, and concerns regarding contamination of talc with asbestos. However, case reports of these complications are quite rare and talc remains the preferred sclerosant of many physicians, especially for patients with limited life expectancy.

Several controversies exist regarding the use of these techniques to prevent recurrence of a pneumothorax. The first regards whether the preferred approach is surgical or non-surgical. Studies demonstrate that the surgical approaches are more effective. Recurrence rates after VATS pleurodesis are about 1%, while those following talc and tetracycline pleurodesis are 10% and from 9-25%, respectively. However, the surgical approaches are associated with more morbidity, some mortality, and may not be well tolerated by patients with limited pulmonary reserve due to severe underlying lung disease. Although there is not 100% consensus, surgical approaches are likely preferred for most patients. Non-surgical chemical pleurodesis should be reserved for patients who refuse surgery or are poor operative candidates.

The second controversy regards the timing of pleurodesis. Although spontaneous pneumothoraces recur with some regularity, many patients (the majority in most studies involving first events) never recur. Is it rational to perform pleurodesis on all patients to prevent recurrence in some? Decisions regarding the timing of pleurodesis must be individualized and should include consideration of the likelihood of recurrence, the potential clinical consequences of recurrence (how well will the patient tolerate a recurrence prior to treatment of it), and the risk of pleurodesis. Most primary spontaneous pneumothoraces are well tolerated. There is no reliable method to predict which patients with primary spontaneous pneumothorax will suffer a recurrence, however the risk increases with each recurrence. For these reasons most physicians do not recommend pleurodesis for primary spontaneous pneumothorax until after the first recurrence or if the patient’s occupation or avocation places the patient at increased risk from a pneumothorax. In contrast, the potential clinical consequence of a secondary spontaneous pneumothorax is greater due to the limited pulmonary reserve of these patients. Pleurodesis should likely be performed after the first occurrence in these patients, with more urgency for patients with more advanced lung disease.