128: Pneumothorax and Pneumomediastinum

Pneumothorax is defined as air in the pleural space and is commonly seen after thoracic surgery. Pneumomediastinum is defined as air in the mediastinum and is quite rare. Despite their differences, the principles used to treat these two conditions are similar. Successful management requires a thorough understanding of the thoracic anatomy and pathophysiologic mechanisms that cause these conditions. Pneumothorax may signal a life-threatening condition, and pneumomediastinum may be a sign of an innocuous problem that requires no treatment. This chapter provides an overview of the incidence, causes, pathophysiology, symptoms, radiologic signs, diagnostic evaluation, and most importantly, the techniques for treatment of both pneumothorax and pneumomediastinum.

Pneumothorax is a collection of air or gas in the pleural space. It is classified into three subtypes: spontaneous, traumatic, and iatrogenic pneumothorax (Table 128-1). A spontaneous pneumothorax is a collection of air or gas in the chest that causes the lung to collapse. It can be further classified as primary (i.e., collapse of lung for no apparent reason) or secondary (i.e., collapse of the lung secondary to underlying pulmonary pathology), as detailed in Table 128-2. The incidence of all types of pneumothoraces is greater in men than in women. For primary pneumothorax, the incidence is 7.4 per 100,000 per year in men and 1.2 per 100,000 in women. Similarly, the incidence of secondary pneumothorax is 6.3 per 100,000 population per year in men and 2.0 per 100,000 in women. More specifically, the incidence is greatest in tall, thin young males.^1,2

A tension pneumothorax occurs as a result of a pulmonary parenchymal or bronchial injury that acts as a one-way valve, permitting air to enter the pleural space but not escape. This causes a decrease in venous return and leads to hemodynamic compromise owing to low preload. Iatrogenic pneumothorax occurs as a consequence of inadvertent puncture of the lung during an invasive procedure.

The lung has an inherent tendency to collapse and the chest wall to expand. Hence the pressure in the pleural space is always negative in relation to atmospheric pressure. The alveolar pressure rises and falls on inspiration and expiration but is always greater than the intrapleural pressure (Fig. 128-1A). Since air flows from an area of higher pressure to an area of lower pressure, when a fistula or air leak or other anomalous communication develops between an alveolus and the pleural space, the air flows down the pressure gradient until an equilibrium is reached or the communication is sealed (see Fig. 128-1B). This condition is known as a pneumothorax. As the lung becomes smaller, the pneumothorax increases in size. The transpulmonary pressure, also known as elastic recoil of the lung, is the difference between alveolar pressure and pleural pressure (Palv–Ppl). When this value equals zero, the lung collapses. The primary physiologic consequence of this process is a decrease in the vital capacity of the lung, a decrease in the partial pressure of oxygen, and if the pressure becomes great enough, compression of the superior vena cava and tension pneumothorax. Young and healthy patients can tolerate these changes fairly well, with minimal changes in vital signs and symptoms, but individuals with underlying lung disease may develop respiratory or hemodynamic distress.

Tension pneumothorax has a far more dangerous outcome. As pressure within the intrapleural space increases, the mediastinum impinges on and compresses the heart and contralateral lung, thus decreasing the venous return (Fig. 128-2). Hypoxia results as the collapsed lung on the affected side and the compressed lung on the contralateral side compromise effective gas exchange. The hypoxia and decreased venous return caused by compression of the relatively thin walls of the superior vena cava and atria impair cardiac function. The decrease in cardiac output results in hypotension and may lead to hemodynamic collapse and death, if untreated.

Causes

A spontaneous primary pneumothorax is commonly caused by rupture of subpleural apical emphysematous blebs, which are more prevalent in tall, thin males. Different mechanisms have been proposed; however, most concur that this process may occur because alveoli are subjected to a greater mean distending pressure over time, leading to subpleural bleb formation. Since pleural pressure is more negative at the apex of the lung than elsewhere, blebs located at the apex are more likely to rupture and cause pneumothorax.

Another risk factor for pneumothorax is smoking. Smoking increases the risk of spontaneous pneumothorax by 20-fold in men and by nearly 10-fold in women, as compared with similar risks in nonsmokers.⁵

The goal of treatment of pneumothorax is to remove air from the pleural space and prevent recurrence. Management depends on the symptoms and the radiologic size of the pneumothorax. Small, asymptomatic pneumothoraces may be followed with chest radiographs alone (Fig. 128-3). For larger pneumothoraces with more severe clinical symptoms and/or iatrogenic etiology, a chest tube should be inserted to protect the pleural space. If the cause is spontaneous, careful follow-up can be chosen.

We prefer surgical intervention when there is persistent air leak (>3 days), large air leak (>expiratory 4⁶), failure of lung reexpansion, and in cases of recurrent spontaneous pneumothorax.⁷ Other indications for surgery include a space problem with air leak or occupations that predispose to pneumothorax, such as a pilot or scuba diver. Once the decision to proceed with surgery has been made, several different approaches can be taken, either by open, or by video-assisted thoracoscopic surgery (VATS) or robotic techniques. The latter is preferred by most surgeons because it affords the use of minimally invasive techniques, which can be particularly important when operating on patients with benign disease.⁸ However, newer techniques for thoracotomy have made this approach less painful with reduced morbidity. For example, open procedures can be performed using posterolateral muscle-sparing, rib-sparing, and nerve-sparing approaches.^9,10 In addition, because this pathology requires access mainly to the upper hemithorax, axillary thoracotomy is also an option. Since VATS is by far the most common operation used for these patients, we will review the operative steps.

Minimally Invasive Techniques: Video-Assisted Thoracoscopy and Robotic Surgery

The goal of any operation in a patient with a recurrent pneumothorax is to prevent the patient from developing another symptomatic pneumothorax. Thus the conduct of the operation depends on the cause of the pneumothorax. If the patient has one large bleb, it should be resected and the staple line is buttressed with material and a sealant is also applied. Although one may not be able to prevent other parts of the lung from rupturing, the main goal is to prevent significant collapse and thus eliminate the risk of tension pneumothorax as well as shortness of breath. However, even when these goals are met, some patients still will have the sensation of an acute onset of chest pain postoperatively, and this probably signifies a small perforation in the lung. If the pleurodesis is successful, the lung will stay inflated, and the chest roentgenogram should be normal. To achieve these goals, some form of pleurodesis is usually needed. In this regard, we prefer to combine chemical with mechanical pleurodesis. In patients who have had more than one spontaneous pneumothorax every intraoperative technique should be applied to prevent further ones. This includes trying to identify the source of the air leak and removing or stapling it closed, maximizing this staple line from leaking by using buttressing material and a sealant and promoting apposition by performing a parietal pleurectomy and adding chemical pleurodesis in selected patients.

Preoperative Care

Patients should have a chest CT scan and pulmonary function testing performed before surgery. A CT scan is ordered to assess the number and severity of blebs, if any, and to ensure there are no indeterminate pulmonary nodules. In older patients with emphysema and hypercapnia, surgery would be ill-advised if numerous large blebs are found on CT scan. These patients should be managed with a chest tube and bedside sclerotherapy. This chapter, however, focuses on the more common phenomenon of a young patient with recurrent pneumothorax. We prefer to use an epidural, even when performing a VATS procedure because the need for pleurectomy as well as mechanical and chemical pleurodesis causes it to be more painful than a VATS wedge resection.

Intraoperative Care

After the induction of general anesthesia, bronchoscopy is performed. A double-lumen endotracheal tube is placed as well as appropriate lines. The patient is positioned with operative side up, and all indwelling chest tubes are removed. Three standard VATS incisions are made. These incisions should be placed in a triangle to permit complete inspection and access to all areas of the chest. The apical segment of the upper lobe and the superior segment of the lower lobe are examined carefully. Even if a bleb cannot be located, we prefer to excise a wedge of the upper lobe and a small part of the lower lobe by using an endoscopic stapler that is buttressed with pericardial strips (Bovine Pericardial Strips, Synovis Surgical Innovations, St. Paul, MN) (Fig. 128-4). The recurrence rate after VATS by means of endoscopic stapler is less than 5%.⁹ These strips help to create adhesions. A complete pleurectomy from the mammary artery to the vertebral bodies is performed. It extends from the top of the chest to the diaphragm. The pleura is scraped by attaching a Bovie scratch pad to the end of a long, curved VATS ringed forceps (Fig. 128-5). This technique creates a pleural edge that can be grasped. A blunt instrument, such as a Kittner dissector, a finger to start, and then a sucker (Ethicon Endo-Surgery, Cincinnati, OH) are used to slowly remove the entire pleura. If the pleura is grasped with a long, curved VATS ringed forceps, it can be twisted and rotated, and this helps the operator to perform a complete pleurectomy quickly, usually in 15 to 25 minutes (Fig. 128-6). After the pleurectomy is completed, we prefer to add a chemical pleurodesis as well. We do not use talc in these young patients because of some of its potential side effects. The intrapleural injection of talc has resulted in acute respiratory distress syndrome in some patients treated for malignant pleural effusion. In addition, extensive pleural thickening with calcifications can develop many years after intrapleural talc,¹¹ causing restriction of pulmonary function. Instead we use 500-mg doxycycline in 250-mL normal saline. The intrapleural injection of a tetracycline derivative decreases the recurrence rate for pneumothorax. In a prospective, randomized study of 229 patients with spontaneous pneumothorax, for example, the recurrence rate was 25% in the group treated with intrapleural tetracycline compared with 41% in the control group.¹² Thus we add this to our intraoperative technique. This fluid is instilled in the chest for 10 minutes and then evacuated. Two chest tubes are placed through two more anterior incisions (the most inferior port used for the camera and the most anterior port). We prefer to place two soft 24 F drains. One tube is placed anteroapically, and the other is placed posteroapically.

Postoperative Care

The chest tubes are placed on suction for a few days unless there is an air leak. Although we have written extensively about the benefits of the setting chest tubes to water seal, this applies to patients with an air leak. In patients, often with large and expansive chests, the lungs have difficulty filling this space, and thus we prefer suction. The epidural is removed on postoperative day 2 (or 3), and the patient can be discharged home on day 3 or 4. We usually send the patient home for a week or two with the anterior apical tube in place on a Heimlich valve or, more recently, connected to an Atrium Express (Atrium Medical Corporation, Hudson, NH) device. The patient returns to the outpatient clinic 1 to 2 weeks later. If the device shows no air leak and the radiograph shows no or only a minor pneumothorax, the chest tube is removed. If there is a large pneumothorax that is new, we prefer suction for another few days to help promote visceral–pleural to parietal–pleural apposition. Even if an air leak is present, the tubes can be removed safely if there is no new pneumothorax or subcutaneous emphysema.¹³

Complications

Chest tube insertion may result in empyema (1%–3%), lung parenchyma perforation (0.2%–0.6%), diaphragmatic perforation (0.4%), and subcutaneous placement (0.6%). In an analysis of 126 chest tube placements by pulmonologists at a teaching hospital, the complication rate was 11%; however, 10 of the 14 reported complications were related to clotting, kinking, or dislodgment of the chest tube.¹⁴

The most common short-term complication of VATS for a recurrent pneumothorax is an air leak. As described earlier, the initial treatment should be water seal, and if it persists, then outpatient management with an Atrium device is preferred. Persistent air leak commonly occurs in patients with secondary pneumothoraces. Pain is another common complaint after VATS, despite the fact that the ribs are not spread. The pain is usually secondary to impingement of the intercostal nerve. The best management is prevention. We do not use a trocar for the camera or for any of the ports. The trocar can be slipped over the camera once it is introduced into the chest. Pain can lead to inadequate ventilation of the lungs, thus promoting the incidence of atelectasis and pneumonia. Most patients have minimal postoperative discomfort; however, analgesics may be required to achieve adequate control of pain once the epidural is removed.

Recurrence of the pneumothorax is the most frequent and frustrating complication of primary spontaneous pneumothoraces; it occurs in up to 25% to 54% of untreated patients, and most recurrences occur within the first year of the first pneumothorax.^15,16 After VATS, however, the incidence is much less. After a second pneumothorax, the risk of having a third increases by more than 50%.¹⁷ Hemorrhage related to VATS is uncommon. Arrhythmia, which is common after many thoracic procedures, should be managed as described in Chapter 8.

Pneumomediastinum (also known as mediastinal emphysema) is defined as air in the mediastinum. It occurs in approximately 1 per 10,000 hospital admissions per year in adults and in 2.5 per 1000 live births per year.¹⁸ It is generally a benign, self-limited condition. Very few, if any, reports of fatal outcomes in patients with spontaneous pneumomediastinum in the absence of underlying disease exist in the recent literature. These data are in sharp contrast to tension pneumomediastinum, which often results in fatality unless there is immediate surgical intervention.

Pneumomediastinum can be caused by air that originates in the pharynx, the tracheobronchial tree, or the esophagus. Excessive intraalveolar pressure, from a Valsalva type maneuver for example, can lead to rupture of perivascular alveoli (Fig. 128-7). Air escapes into the perivascular connective tissue and subsequently dissects into the mediastinum. From there, the air may dissect superiorly into the visceral, retropharyngeal, and subcutaneous spaces of the neck. From the neck, the subcutaneous compartment is continuous throughout the body; thus air can diffuse widely. Mediastinal air also can pass inferiorly into the retroperitoneum and other extraperitoneal compartments. It even can enter the pericardium and cause pneumopericardium. A study by Clements et al.¹⁹ showed that 85% of patients developed pneumomediastinum after esophageal procedures. When it dissects throughout the body, it usually stops at the level of the inguinal ligament. If the mediastinal pressure rises abruptly, or if decompression is not sufficient, the mediastinal parietal pleura also may rupture, causing pneumothorax (in 10%–18% of patients). Table 128-3 lists the common causes of pneumomediastinum. Mihos et al.²⁰ have described sports that commonly lead to pneumomediastinum include scuba diving, basketball, and soccer.

A more serious variant of pneumomediastinum, termed tension pneumomediastinum (or malignant by some), often mimics cardiac tamponade and should be treated immediately with cervical mediastinoscopy.²³ It arises from interference of air in the lung and mediastinum, causing compression of pulmonary and mediastinal vessels and interference with respiration by the splinting action of air in the interstitial tissue of the lung. If unrelieved, it may progress to pulmonary edema and circulatory failure.

The signs and symptoms of pneumomediastinum vary from asymptomatic to severe chest pain below the sternum that may radiate to the neck and arms. Common presentation includes chest pain, subcutaneous emphysema, cough, and neck swelling.²⁴ The pain may be exacerbated by breathing or swallowing. On examination, subcutaneous air is present in approximately 50% of cases. Hamman sign (i.e., precordial crunching noise synchronous with heartbeat and often accentuated during expiration)²⁵ is also commonly present. Tension pneumomediastinum is characterized by dyspnea, cyanosis, engorged neck veins, and hypotension.

The diagnosis of pneumomediastinum can be confirmed with a chest x-ray that reveals streaky gas densities along the fascial planes of the mediastinum (Fig. 128-8). This is most clearly demonstrated on the lateral view. Once diagnosed, a thorough workup is needed to ensure that no life-threatening causes have been missed. An upper gastrointestinal swallow and a contrast chest CT scan, bronchoscopy, and esophagoscopy can be performed depending on the index of suspicion. These are all usually normal. VATS also has been recommended but, in our opinion, is rarely necessary.²⁶

The treatment of tension pneumomediastinum, most commonly seen in neonates on ventilators,²⁷ often requires urgent evacuation of air from the mediastinum.²⁶ This can be achieved by incisions into the subcutaneous tissues or, less commonly, by a cervical mediastinoscopy.²³ Moore et al. used a tube to drain subcutaneous air through a subxiphoid incision in neonates. The dissection is carried out bluntly along the entire length of the sternum, exposing the anterior mediastinum and the pericardium.²⁶ Other incisions also have been used for this purpose, such as the transverse suprasternal with or without full sternotomy, infraclavicular,²⁸ and tracheostomy.²⁹

The aim of management of pneumomediastinum is to ensure that a serious underlying cause is not missed. Common causes of pneumomediastinum include asthma exacerbation, emesis, and idiopathic.²⁴ Most patients with a pneumomediastinum do not require surgical intervention, and in most cases, the condition resolves without intervention.^30,31 A study by Mihos et al. evaluated the treatment course of 25 cases of pneumomediastinum resulting from sports accidents. All patients were treated by observation alone. Complete resorption of the pneumomediastinum occurred in 3 to 8 days in all patients, and hospital stay ranged from 2 to 6 days (mean 3.8 days).^20,24 This experience has led some to avoid the expensive battery of usually normal diagnostic tests. Perhaps in the hemodynamically stable patient observation alone is safe as well as cost-effective.

However, once the need for surgery has been decided, the underlying cause of the pneumomediastinum dictates the surgical approach. If the cause is a ruptured bleb, the previously described approach for pneumothorax should be followed as indicated. If the cause is a perforated esophagus, the location of the tear can be revealed on upper gastrointestinal barium swallow. A posterolateral thoracotomy is performed ipsilateral to the infected effusion. Thus the empyema can be treated and the esophagus repaired. If the tear is limited to the mediastinum and does not drain into a pleural space, surgical intervention may not be needed because the tear is contained. However, if surgery is chosen, the side opposite the aortic arch (usually the right) offers better exposure and greater access to the entire length of the intrathoracic esophagus.

The goal of the operation is to drain the empyema, decorticate the lung to control the pleural space, and if possible, identify and repair the esophageal tear. Importantly, the latter is the least important goal because if there is no distal obstruction, no cancer, and no foreign body, the tear will heal on its own if there is adequate drainage of the infected surrounding space. Patients who have esophageal perforation due to instrumentation or a penetrating injury have a better prognosis than those with spontaneous perforation largely because of earlier diagnosis in the former group.³² We prefer to identify the tear and close it primarily if the chest is entered within 48 to 72 hours of the injury, depending on the quality of the tissue. Primary repair alone is never enough. The suture line must be reinforced to reduce the risk of esophageal leaks, mediastinitis, and sepsis by buttressing with a pedicled flap.³³ We prefer an intercostal flap that should be harvested before chest retraction.⁹ Other options include a diaphragmatic patch, although this has the potential to introduce infection in the subphrenic space. A pericardial fat pad is another option, but its blood supply is not reliable. A pleural flap also can be used, but it is often too thin. The postoperative care depends on the underlying cause and the treatment strategy chosen.

Recurrence of spontaneous untreated pneumomediastinum is rare, although it has been reported in a few smaller series. Abolnik et al.³⁴ reported a recurrence incidence of 2 in 25 patients over a 2-year period. While the physiologic mechanism of recurrence has not yet been elucidated, some attribute recurrence from a pulmonary cause to a congenital weakness of the alveolar wall.³⁵

To prevent recurrent pneumothorax, surgery must remove the source of the leak; typically a few blebs at the apex of the lung or a rare secondary site (e.g., apical portion of the superior segment). If the site of the pneumothorax is identified and removed, mechanical or chemical pleurodesis is unnecessary. Alternatively, if pleurodesis is performed without removing the source of the pneumothorax, subsequent pneumothoraces may present as basilar air collections (because effective basilar pleurodesis is unlikely with a functioning diaphragm), and these can be difficult to manage with tube thoracostomy or even thoracoscopy.