CHAPTER 27 Spontaneous Pneumothorax
The term pneumothorax was first coined by Jean Marc Gaspard Itard1 in 1803, when he called attention to five cases in which free air was found in the thorax after trauma. Derived from the Greek words pneuma (air) and thorakos (breastplate or chest), it is an apt description for the accumulation of air in the pleural space that leads to partial or total collapse of the affected lung. The clinical features of pneumothorax were first described in 1819 by René Laennec,2 who postulated the relationship to preexisting blebs and unprovoked rupture and, hence, the term spontaneous pneumothorax. This pathophysiologic mechanism was confirmed by Kjærgaard3 in later decades. Today, the classification of pneumothoraces is based on clinical presentation and underlying lung disease. Multiple management strategies range from simple evacuation of air from the pleural space to potential prevention of future pneumothoraces.
EPIDEMIOLOGY
Spontaneous pneumothorax (SP) may be termed either a primary or secondary event, dependent on underlying lung disease. Primary spontaneous pneumothorax (PSP) typically occurs in young patients with localized blebs but otherwise normal lungs. Secondary spontaneous pneumothorax (SSP) occurs in patients with marked structural lung disease and directly contributes to SP. Approximately 20,000 new cases of PSP are diagnosed annually in the United States,4 with an estimated economic impact of $130 million per year due to lost wages. The annual estimated incidence of PSP is between 7.4 and 18 cases per 100,000 population among men and 1.2 and 6 cases per 100,000 population among women.4 Patients prone to PSP are usually tall and thin and between 10 and 30 years of age.5 A significant factor is cigarette smoking, which can increase the risk of PSP by a factor as high as 20.6
SSP develops as a complication of underlying lung disease, most commonly chronic obstructive pulmonary disease (COPD).7 The annual incidence of SSP is approximately 6.3 cases per 100,000 population among men and 2 cases per 100,000 population among women.4 The peak incidence occurs between the ages of 60 and 65 years.5
ETIOLOGY
PSP manifests without forewarning signs or symptoms and is most likely due to rupture of a subpleural bleb. This premise is based on cumulative results of patients undergoing computed tomography (CT), which demonstrated subpleural blebs in as many as 80%.8,9 Surgical experience confirmed the presence of bullae in more than 75% of patients who underwent video-assisted thoracoscopic surgery and thoracotomy.10–12 After the first episode of PSP, recurrence varies, ranging from 16% to 54%. Most studies indicate an average of 30%.13,14 Most recurrences develop between 6 months and 2 years after the initial episode.13 Men who are tall and with a smoking history are at the greatest risk of recurrence. Counseling for smoking cessation should be strongly encouraged.13 After the second episode of PSP, the likelihood of recurrence increases markedly and can reach as high as 83%.7,14
CLINICAL PRESENTATION
PSP typically manifests with sudden pleuritic chest pain and dyspnea.6,15 Classic findings on physical examination include diminished breath sounds, hyperresonance, and fremitus; however, patients with small pneumothoraces may have normal findings on physical examination. Most patients with PSP are stable. This is primarily due to their young age and otherwise normal lung function. Patients with SSP are more likely to present with respiratory distress, a result of respiratory compromise caused by SP superimposed on preexisting lung disease.12 Whereas tension SP is unusual, indicators include tachycardia, cyanosis, and hypotension.
IMAGING
Chest radiography is the most common diagnostic tool for SP. A thin pleural line can be identified that has been displaced from the chest wall. A small SP may be difficult to identify on plain radiography; an expiratory view may prove more beneficial in determining the presence of SP. Frequently, attempts are made to measure the size of the SP as a percentage of the hemithorax it occupies, although this method is typically inaccurate.16,17 On occasion, a giant bulla can mimic a pneumothorax. Subtle lines demarcate a bulla, which tends to be surrounded by thickened visceral pleura. In addition, a pleural line can frequently be seen with lung markings visible beyond the suspected bulla (double wall sign).18,19
CT is seldom required for routine diagnosis of SP, but it can help differentiate between SP and a giant bulla.17 Controversy exists about the significance of routine chest CT to evaluate for subpleural blebs. Proponents contend that identification of large or multiple subpleural blebs on CT is an indication for early surgical intervention to prevent recurrence.11,20,21 Opponents of this principle argue that management should not be influenced by these findings alone.22,23
MANAGEMENT
Algorithms for the management of SP range from established management protocols to operative intervention. Selected therapies depend on a number of variables: SP size, stability of the patient, symptom complex, initial SP onset or recurrent episode, and presence or absence of structural lung disease.17,24 The principal procedure is evacuation of air from the pleural space (spontaneous resolution versus instrumentation). Additional procedures targeted to prevent future SP episodes should also be considered.
Observation
Small pneumothoraces are those that are less than 3 cm in distance between the apical parietal pleura and the thoracic cupula, with no lateral component. Asymptomatic patients should be managed expectantly24–26 by close monitoring, physical examination, continuous pulse oximetry, and repeated chest radiography within 6 hours. Our practice is to monitor patients in the hospital for a minimum of 24 hours. Even though some patients with stable radiographic features may be discharged from the hospital with follow-up within 12 to 24 hours,24 the potential for catastrophic consequences from a missed tension pneumothorax is a great risk.27 Small pneumothoraces usually resolve without intervention, but recurrence is possible. If chest radiography reveals that the SP is enlarging, immediate intervention is crucial.
Aspiration
Aspiration allows evacuation of pleural air and complete reexpansion of the lung. This technique can be applied even for larger pneumothoraces if the patient is stable. We prefer the Seldinger technique,28,29 which uses a small, single-lumen central line placed over the superior rib edge in the second interspace in the midclavicular line. A three-way stopcock and large syringe are used to aspirate until resistance is felt, usually signifying full lung expansion. Chest radiography is then performed to confirm the findings, and the catheter is removed.25,26,30–34 Commercially prepared kits with one-way valves (Heimlich valve)7 allow air to exit but prevent air entry. These valves can be left in place until full lung expansion is achieved. For more rapid resolution, however, it is our preference to perform tube thoracostomy with a small chest tube. Complications of aspiration, although rare, may include bleeding and possible lung injury. Reported success is higher in resolving PSP (66% to 83%) than for SSP (37%).25,33 SP that does not respond successfully to aspiration requires tube thoracostomy.
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