Pneumothorax

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Chapter 67 Pneumothorax

Madison Macht, MD , Michael E. Hanley, MD

1 What are the major etiologic classifications of pneumothoraces?

Pneumothoraces are classified as spontaneous or traumatic:

Spontaneous: Spontaneous pneumothoraces occur without antecedent trauma or other obvious cause. A primary spontaneous pneumothorax occurs in a person without underlying lung disease. Secondary spontaneous pneumothoraces occur as a complication of underlying lung disease.

Traumatic: Traumatic pneumothoraces result from direct or indirect trauma to the chest and are further classified as iatrogenic or noniatrogenic.

2 What are the common causes of pneumothorax in critically ill patients?

Secondary spontaneous pneumothoraces occasionally require admission to the intensive care unit because of acute respiratory failure resulting from the combination of the pneumothorax and underlying lung disease. In addition, secondary spontaneous pneumothoraces may develop in patients with lung disease who are already in the intensive care unit. This occurs more commonly in patients with chronic obstructive lung disease, asthma, interstitial lung disease, necrotizing lung infections, and Pneumocystis jiroveci pneumonia. However, most pneumothoraces that develop in the intensive care unit are due to either antecedent noniatrogenic chest trauma or iatrogenic causes. Box 67-1 lists the common causes of iatrogenic pneumothorax.

3 What measures reduce the risk of iatrogenic pneumothorax in patients receiving positive pressure ventilation?

End-inspiratory plateau pressure should be kept < 35 cm H₂O, and both positive end-expiratory pressure (PEEP) and auto-PEEP levels should be minimized. Approaches that may help achieve these goals include using the following:

Smaller tidal volumes in patients with underlying lung disease

Permissive hypercapnia when high minute ventilation is required

High inspiratory flow rates

In addition, thoracentesis and subclavian or internal jugular venous line insertion should be performed with utmost care (including under ultrasound guidance) in high-risk patients.

4 Describe the clinical manifestations of pneumothoraces

Dyspnea and unilateral chest pain are the most common manifestations of primary spontaneous pneumothorax. Physical examination findings include tachycardia, ipsilateral chest expansion, hyperresonance to percussion, decreased tactile fremitus, and decreased breath sounds on the affected side. The trachea may also be deviated toward the contralateral side. On rare occasions patients with primary pneumothoraces may have no symptoms.

In contrast, most patients in whom secondary spontaneous pneumothoraces develop have preexisting lung pathologic conditions and resultant decreased pulmonary reserve. Therefore their symptoms are often more severe than in those with primary pneumothoraces. Dyspnea occurs in virtually all patients with secondary pneumothoraces and is commonly out of proportion to the size of the pneumothorax. Cyanosis and hypotension are common. Side-to-side differences in the examination of the chest may not be so apparent because many of the physical signs associated with the underlying lung disease are similar to those associated with pneumothoraces.

6 How is the diagnosis of pneumothorax established in critically ill patients?

Chest radiography is the most common tool used to confirm the presence of a pneumothorax. A thin pleural line and the absence of lung parenchymal markings between the pleural line and chest wall adequately support the diagnosis. Upright radiographs are most helpful, as the supine position commonly allows free pleural air to collect anteriorly and avoid detection. Evidence of an increase in the size of the ipsilateral hemithorax, including contralateral shift of the mediastinum and heart, as well as depression of the ipsilateral hemidiaphragm, may be the only radiographic clues to the presence of a pneumothorax in such cases. A wide, deep radiolucency along the costophrenic angle is referred to as the deep sulcus sign and may be the only clue to the presence of a pneumothorax on supine chest radiography. Chest roentgenograms obtained at expiration are often requested, although some data suggest that inspiratory and expiratory films are equally sensitive for the diagnosis. Radiographs taken with the patient in the lateral decubitus position or from the cross-table lateral view may be useful in confirming the diagnosis in select cases. If chest radiographs are nondiagnostic and the patient’s condition is sufficiently stable for transport, computed tomography of the chest may be required to prove the diagnosis.

7 What is the role of ultrasonography in the diagnosis of pneumothorax in critically ill patients?

Ultrasonography has several important advantages in the diagnosis of pneumothoraces in critically ill patients. Pneumothoraces can be detected by ultrasound with certainty at the bedside, without the need for conventional radiography, thus potentially saving time and sparing patients radiation exposure. Other advantages include portability and real-time imaging. These features are especially important when a diagnosis must be made emergently. Large dressings, agitation, significant subcutaneous emphysema, and posterior or mediastinal air collections may decrease the sensitivity of ultrasonography. Several studies have shown that the sensitivity and specificity of ultrasonography for the detection of pneumothorax is greater than 90% in the initial management of trauma patients.

8 What findings on ultrasound suggest the presence of a pneumothorax?

Sonographic findings suggestive of a pneumothorax include absence of lung sliding and comet tail artifacts. Lung sliding refers to the normal horizontal back-and-forth movement of the visceral pleura as it slides over the parietal pleura during the respiratory cycle. Comet tail artifacts, also called “B-lines,” are echogenic raylike shadows that radiate from the visceral-parietal pleural interface and extend to the bottom of the ultrasound screen. False-positive results have been reported in patients with bullous emphysema and pleural adhesions.

The presence of these findings excludes a pneumothorax. For this reason, ultrasound may be especially valuable as a quick, safe, and reliable method of excluding this diagnosis in emergent situations (such as when a tension pneumothorax may be the cause of a clinically unstable patient) or after invasive procedures that may be complicated by a pneumothorax (such as thoracentesis or central venous catheter placement).

9 Describe the treatment of a pneumothorax in critically ill patients

Tube thoracostomy should be performed in almost all secondary spontaneous or noniatrogenic, traumatic pneumothoraces, especially if mechanical ventilation is required. Proper positioning of the thoracostomy tube is important in obtaining complete evacuation of pleural air. The tube should be directed to an anterior-apical position. For isolated pneumothoraces a 20 F to 24 F thoracostomy tube is frequently adequate. However, if an associated pleural effusion or hemothorax is present, 32 F to 36 F tubes are usually preferred. Tube thoracostomy should also be performed for all iatrogenic pneumothoraces because of positive pressure ventilation. Other forms of iatrogenic pneumothorax require tube thoracostomy only if the pneumothorax:

Is large (> 40%)

Is associated with significant symptoms or arterial blood gas abnormalities

Progressively enlarges

Does not respond to simple aspiration

Occurs in a patient requiring positive pressure ventilation

Pleural air resorbs at a rate of approximately 1.5% per day. Because nitrogen is the largest component of the atmosphere and is not metabolized, the usual partial pressure gradient between pleural air and the pulmonary capillary blood is small. Decreasing the nitrogen content by increasing inhaled oxygen content may therefore hasten pleural air resorption. For this reason patients who are treated conservatively with observation alone should at minimum be given high levels of supplemental oxygen.

10 Does the development of a pneumothorax portend a worse prognosis for patients with acute respiratory distress syndrome (ARDS)?

Not necessarily. The association of pneumothorax and other air leaks (i.e., extrusion of any air outside the tracheobronchial tree) with mortality was studied in 725 patients with ARDS in the late 1990s. The 30-day mortality rate for patients in whom a pneumothorax developed was 46% compared with 40% in patients without pneumothorax (P = 0.35). Similarly, the 30-day mortality rate for patients with any type of air leak was 45.5% compared with 39.0% for patients without air leaks (P = 0.28).

However, it should be pointed out that both groups of patients received ventilation with higher tidal volumes than are currently recommended for ARDS (mean 11.4 ± 3 mL/kg in those without pneumothorax and 11.7 ± 3.3 mL/kg in those without). It is not known whether the same results would be observed in the era of lower tidal volumes and lung-protective ventilator strategies.

11 What are the potential physiologic consequences of a bronchopleural fistula (BPF) in patients receiving mechanical ventilation?

The potential consequences of a BPF are highlighted in Box 67-2. It should be emphasized, however, that BPFs are extremely well tolerated by most patients.

Box 67-2 Physiologic Consequences of a Bronchopleural Fistula in Patients Receiving Mechanical Ventilation

Inability to maintain adequate alveolar ventilation through loss of effective tidal volume

Inappropriate cycling of the ventilator

Incomplete lung reexpansion

Inability to apply PEEP

12 Describe the initial management of a BPF

BPFs are managed by minimizing the flow of air through the fistula while maintaining complete evacuation of the pleural space. This is primarily accomplished in spontaneously breathing patients (negative-pressure ventilation) by altering the level of suction applied to the pleural space. The optimal amount of suction must be determined on an individual basis.

Gas flow across a BPF in patients with mechanical ventilation is also influenced by peak inspiratory and mean airway pressures. Management in this setting includes measures that minimize alveolar distention and minute ventilation. This is accomplished by minimizing PEEP, tidal volume, inspiratory time, and the number of mechanically delivered breaths per minute. Permissive hypercapnia should be considered if not contraindicated. Mechanical ventilation should be discontinued as soon as possible.

13 How is a persistent BPF managed?

Most BPFs close spontaneously once the underlying lung injury improves and positive pressure ventilation is discontinued. However, if a BPF in a patient no longer receiving positive pressure ventilation does not close after 5 to 7 days of chest tube drainage, or if adequate ventilation cannot be maintained because of the size of the air leak, suturing or resection of the fistula with scarification of the pleura by either thoracoscopy or open thoracotomy should be considered. The decision to perform this procedure should include a consideration of the operative risk to the patient. Prolonged chest tube drainage, intrabronchial bronchoscopic instillation of materials (e.g., Gelfoam or tissue adhesives such as cyanoacrylate-based or fibrin glues) designed to occlude the fistula, differential lung ventilation, or synchronized chest tube occlusion should be considered in patients whose operative risk is increased by significant underlying lung disease or other medical problems.

14 What is reexpansion pulmonary edema?

Reexpansion pulmonary edema involves the development of unilateral pulmonary edema after reexpansion of a collapsed lung. The risk and severity of reexpansion pulmonary edema appear to be related to the duration of the pneumothorax, as well as the magnitude of negative pressure applied to the pleural space to reexpand the lung. The exact incidence of reexpansion pulmonary edema after treatment of pneumothoraces in humans is unknown, but it is rare. The mortality of reexpansion pulmonary edema can be as high as 10% to 20%.

15 How can the risk of reexpansion pulmonary edema be minimized?

The risk can be minimized by withholding pleural suction during the immediate treatment of pneumothoraces of either unknown duration or duration greater than 3 days. If the pneumothorax is not completely evacuated after 24 to 48 hours of water seal, or if significant respiratory compromise requires more rapid evacuation, low levels of negative pressure (< 20 cm H₂O) should be applied to the pleural space. Nonetheless, reexpansion pulmonary edema has been reported even under these conditions.

16 What is a tension pneumothorax?

A tension pneumothorax occurs when the pressure within a pneumothorax is greater than atmospheric pressure throughout expiration and often during inspiration. Tension pneumothoraces generally result from a one-way valve phenomenon and most frequently occur in patients receiving positive pressure ventilation. They are a medical emergency that may rapidly lead to death if not recognized and treated expeditiously.

17 Describe the treatment for a tension pneumothorax

Time should not be wasted pursuing radiographic confirmation if a clinician suspects the diagnosis of tension pneumothorax in a hemodynamically unstable patient. The patient should be immediately given 100% oxygen and the pneumothorax evacuated. This is best accomplished by emergent placement of a tube thoracostomy. If the diagnosis is in question, or if a tube thoracostomy is not readily available, an alternative approach includes insertion into the pleural space of a large-bore needle attached by a three-way stopcock to a 50-mL syringe partially filled with sterile saline solution. The needle is inserted under sterile conditions through the second anterior intercostal space in the midclavicular line while the patient is supine. After the needle has been inserted, the plunger is withdrawn from the syringe. The presence of a pneumothorax is confirmed if air bubbles up through the saline solution. If a pneumothorax is present, the needle should be left in place until air ceases to bubble through the saline solution, and a tube thoracostomy is performed. If air does not bubble up into the syringe, a pneumothorax is not present and the needle may be removed.

Controversy

18 Should a tube thoracostomy be removed immediately in patients receiving positive pressure ventilation once the air leak has resolved and the lung is completely reexpanded?

The tube thoracostomy is no longer required to evacuate air after the BPF has closed and all air has been evacuated. At this point, the chest tube is only a potential source of infection, both at its insertion site and in the pleural space.

Patients can be closely monitored and chest tubes reinserted if a pneumothorax recurs.

Routine insertion of a prophylactic tube thoracostomy is not indicated in patients receiving mechanical ventilation.

Risk of a recurrent pneumothorax remains high in patients receiving mechanical ventilation, especially if they have ARDS or a necrotic lung process.

Many pneumothoraces in patients receiving mechanical ventilation present under tension. Tension pneumothoraces are associated with a higher mortality, especially if delay occurs in diagnosis or treatment.

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