Pneumothorax and Pneumomediastinum




Introduction



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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



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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




Table 128-1Types of Pneumothoraces




Table 128-2Causes of Secondary Spontaneous Pneumothorax



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.




Pathophysiology



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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.




Figure 128-1


A. Pressure in the intrapleural space is always negative (just below atmospheric pressure) and always lower than in the alveoli of the lung. B. Since air flows from regions of high to low pressure, when there is an anomalous communication between the alveolar tissues and the pleura, air flows down the pressure gradient and collects in the pleural space.





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.




Figure 128-2


Chest x-ray of tension pneumothorax.





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




Management



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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.




Figure 128-3


Chest x-ray of spontaneous pneumothorax.






Surgical Technique



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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.

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Dec 30, 2018 | Posted by in VASCULAR SURGERY | Comments Off on Pneumothorax and Pneumomediastinum
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