Pneumothorax

51 Pneumothorax



David E. Manthey, Bret A. Nicks



image      Key Points




• Primary pneumothoraces (spontaneous or traumatic) occur in patients without clinically apparent lung disease.


• Chronic obstructive pulmonary disease is the most common cause of secondary pneumothorax.


• Physical examination may miss a pneumothorax occupying up to 27% of lung volume.


• Standard posteroanterior and lateral chest radiographs are the only routine examination needed because expiratory films add little to diagnostic accuracy.


• Ultrasound’s lung point sign has an overall sensitivity of 66% and a specificity of 100%.


• Treatment of pneumothorax is based on its cause, size and stability, symptoms, and the presence or absence of underlying lung disease. Treatment options include observation, catheter aspiration, and tube thoracostomy.



Epidemiology


Primary spontaneous pneumothorax occurs at a rate of 10 to 18 cases per 100,000 population per year in men and 5 cases per 100,000 in women. It has a peak incidence in young adults (20 to 30 years).


Secondary pneumothoraces make up one third of spontaneous pneumothoraces and occur with underlying pulmonary disease. Of note, chronic obstructive pulmonary disease (COPD) is the most common cause of secondary spontaneous pneumothorax. Recurrences are common, so prevention of recurrence is indicated after the first episode.


Patients with a spontaneous pneumothorax have a 30% recurrence rate within 2 years after air evacuation only; patients who have experienced two pneumothoraces have about an 80% chance of a recurrent pneumothorax.



Pathophysiology



Pneumothorax


The pleural space lies between the parietal and visceral pleura and is normally negatively pressured at −5 mm Hg with fluctuations of 6 to 8 mm Hg between inspiration and expiration. With loss of the normal negative pressure, the affected lung collapses. Primary spontaneous pneumothorax occurs when a subpleural bleb, most commonly in the lung apex, ruptures into the pleural space. In secondary spontaneous pneumothorax, rupture of the visceral pleura and alveolar barrier is most commonly due to the underlying pulmonary disease process.



Open Pneumothorax


Open chest wounds become symptomatic when the diameter of the chest wall defect approaches two thirds the size of the trachea. At this point, air preferentially enters the pleural cavity during inspiration (negative intrathoracic pressure) via the chest wall defect instead of the trachea, which leaves the lungs without oxygenation or ventilation.



Tension Pneumothorax


Tension pneumothorax occurs when a one-way valve develops in the injured lung and allows entry of air into the pleural space during inspiration without being able to escape during expiration. Tension physiology occurs when the increased intrathoracic pressure (15 to 20 mm Hg) limits the return of venous blood flow from the body to the right heart and compresses the great vessels and pericardium. Compression of the affected lung causes hypoxia and arterial constriction, which shunts blood flow mostly to the contralateral lung and decreases the magnitude of preload to the left atrium.



Presenting Signs and Symptoms



Pneumothorax


Classically, the symptoms of primary spontaneous pneumothorax are a sudden onset of ipsilateral, pleuritic chest pain and associated dyspnea. The pain typically begins at rest and is worsened with deep inspiration. It may eventually become a dull persistent ache that does not vary with respiration. Profound dyspnea is rare in the absence of tension pneumothorax or underlying parenchymal disease. Sinus tachycardia is the most common physical finding, with other classic signs such as decreased breath sounds, hyperresonance to percussion, unilateral enlargement of the hemithorax, absence of tactile fremitus, and decreased excursion volumes occurring less frequently. Symptoms may resolve in 24 hours without resolution of the pneumothorax. Many patients (45%) may delay seeking medical care for 48 hours. The severity of symptoms does not necessarily correlate with the size of the pneumothorax.


The ability of auscultation to detect hemothorax, pneumothorax, or hemopneumothorax associated with penetrating trauma had a sensitivity of 58%, a specificity of 98%, and a positive predictive value of 98% in one study.1 Auscultation can miss up to 600 mL of hemothorax, a pneumothorax occupying up to 28% of lung volume, and a combined hemopneumothorax of up to 800 mL and 28%.1 Physical examination alone is not sensitive enough to exclude the diagnosis of pneumothorax.



Open Pneumothorax


Patients with an open pneumothorax have significant dyspnea and a history of a penetrating wound to the thorax. Physical examination will reveal a chest wound that produces an audible, sucking air movement sound on inspiration and may bubble on expiration. Findings of a pneumothorax will also be present.



Tension Pneumothorax


Patients with tension pneumothorax exhibit extreme dyspnea, hypotension, and cyanosis. Physical findings are hyperresonance, hyperinflation, absence of breath sounds on the affected side, and deviation of the trachea (at the sternal notch) away from the affected side. Tachycardia is often present and is defined as a pulse greater than 120 beats/min. Patients with tachycardia should undergo immediate tube thoracostomy (or needle thoracostomy if a chest tube is not immediately available) without waiting for a confirmatory radiograph.



Secondary Pneumothoraces


Patients with pneumothoraces secondary to underlying lung disease may experience extreme dyspnea as a result of deflation of one lung and limited capacity and function of the remaining lung. Classically, symptoms do not resolve without intervention. Because of the underlying lung disease (most commonly COPD), lung findings may be abnormal, with hyperinflation and decreased lung sounds being noted.



Diagnostic Testing and Medical Decision Making (Table 51.1)



Radiography


The primary evaluation tool is the standard posteroanterior chest radiograph to look for loss of lung markings in the periphery and a pleural line that runs parallel to the chest wall but does not extend outside the chest cavity. A lateral radiograph contributes to the diagnosis in 14% of cases.2 There is no evidence that an expiratory radiograph adds any value even with small apical pneumothoraces.3 The sensitivity for flat anteroposterior chest radiography, versus computed tomography (CT) as the “gold standard,” has been found to be 75.5% (95% confidence interval [CI], 61.7% to 86.2%), and the specificity is 100% (95% CI, 97.1% to 100%).4


Table 51.1 Differential Diagnosis of Pneumothorax



























Pulmonary embolism Perform a risk stratification based on the Wells or Charlotte criteria.
If the result of stratification is not low probability or the D-dimer test result is positive, proceed to computed tomography–pulmonary angiography.
A chest radiograph may show infarcted lung.
Pleurisy Look for an underlying disease process (connective tissue, pneumonia).
Pleura-based diseases (pneumonia, tumor, effusion) often have radiographic findings.
Pneumonia Chest radiography will be helpful.
Clinical examination and the history may suggest pneumonia because of cough (uncommon with pneumothorax), upper respiratory symptoms, fever, or immunosuppression.
Pericarditis Look for an underlying disease process.
Check the electrocardiogram (ECG) for classic but not common PR-segment depression and/or widespread ST-segment elevation.
Does position affect the pain (less with leaning forward, more with lying back)?
Consider ultrasonography to diagnose effusion.
Myocardial infarction Assess for appropriate risk factors.
Evaluate with an ECG and cardiac marker measurements if suspicious.
ECG findings associated with a pneumothorax include axis deviation, decreased voltage, and T-wave inversion.
Aortic dissection Interscapular back pain with a tearing sensation is typical.
Check the chest radiograph for a widened mediastinum, apical capping, left-sided pleural effusion, blurring of the aortic knob, or displacement of the trachea or esophagus to the anatomic right.
Consider checking bilateral arm pressures.
Look for a neurologic deficit or end-organ ischemia.
Musculoskeletal pain Is the pain reproducible with palpation and use of the muscle group?
Does the patient have a history consistent with muscle injury?
Are the findings on chest radiography and ECG normal?
Pneumomediastinum Is subcutaneous emphysema present on physical examination?
Is mediastinal, pericardiac, or prevertebral air found on the chest radiograph?
Does it typically occur during a Valsalva maneuver or exertion?

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Jun 14, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Pneumothorax

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