You may see questions on the Physician Assistant Exam about conditions that affect the pleura. You will need to review the evaluation and management of pleural effusions, the pneumothorax, and pleurisy.
Fluid around the lungs: Pleural effusion
Normally, the pleura is an empty space; a pleural effusion is simply fluid that occupies that space. Pleural effusions can be unilateral or bilateral.
In evaluating pleural effusions, a thoracentesis helps you determine the etiology. The fluid is sent for LDH, protein, Gram stain and culture, cell count with differential, cytology, glucose, and pH tests.
Measuring protein and LDH: Transudative and exudative pleural effusions
Light’s criteria say that if an effusion meets any one of three characteristics, then it meets criteria to be an exudate:
The ratio of pleural fluid total protein to serum total protein is > 0.5.
The ratio of pleural fluid LDH level to serum LDH level is > 0.6.
The pleural LDH is > 2/3 the value of the total LDH.
An exudative pleural effusion (caused by local factors) can be caused by pneumonia, a malignancy, or connective tissue disease, such as rheumatoid arthritis. Rheumatoid arthritis can also cause the pleural fluid glucose to be very low. A pneumonia, empyema (pus in the pleural space), connective tissue diseases, and malignancy can also present with a very low pleural fluid pH (usually less than 7.3).
A transudative effusion (caused by systemic factors) is an effusion where the ratio of pleural fluid protein to serum protein level is < 0.5. Common causes include congestive heart failure, kidney disease, and cirrhosis.
A pulmonary embolism can be associated with either a transudative or exudative effusion.
Considering types of fluid in the pleural space
Here are the types of fluid you may find in the pleural space:
A hemothorax is blood in the pleural space. This can occur after a trauma or interventional procedure.
A chylothorax occurs when lymphatic fluid is in the pleural space. This usually results from a leak in the thoracic duct. Causes include trauma and lymphoma.
An empyema is pus in the pleural space. It fits all of Light’s criteria. In addition, the pH may be low. The culture and Gram stain are usually positive also. Sometimes the fluid is so fibrin-rich that a chest tube — with or without a lysing agent such as streptokinase — is used to try to make the fluid amenable to drainage. Sometimes surgical intervention, such as a thoracotomy, is needed.
Pneumothorax
A pneumothorax is air that occupies the pleural space. You should know about the following types of pneumothoraces:
A primary spontaneous pneumothorax happens just like that — spontaneously, not precipitated by a traumatic event. It can occur in the absence of documented lung disease. This type of pneumothorax typically happens to men, usually between their teenage years and their early 30s. These men tend to have tall and thin builds. There’s usually no history of underlying lung disease with a primary pneumothorax.
A secondary spontaneous pneumothorax usually occurs in people who have a smoking history and documented emphysema. If blebs (large blisters filled with serous fluid) or bullae are present, they can spontaneously rupture.
A traumatic pneumothorax means the patient has a hole in his or her chest. Knife wounds and rib fractures are common causes.
In a tension pneumothorax, the pneumothorax results in hypoxia and low blood pressure. This is a medical emergency because it can lead to cardiac arrest. Any type of pneumothorax could conceivably develop into a tension pneumothorax, which can be a result of a motor vehicle accident, trauma, or barotrauma.
The tension pneumothorax is potentially fatal if not diagnosed and treated early. In a tension pneumothorax, an air leak continues to put more air in the pleural space. Basically, air is able to get in but can’t get out. The trapped air can affect the function of the heart and other organs in the thoracic space as they’re in essence squeezed.
This can affect venous return, and hypotension can result. Symptoms include chest pain, shortness of breath, and rarely, abdominal pain.
On physical exam, the person with tension pneumothorax can be tachycardic, hypotensive, and/or hypoxemic. On lung examination, you find absent breath sounds over the collapsed lung. In addition, there can be tracheal deviation and a mediastinal shift to the opposite side. Note that tracheal deviation can be an inconsistent finding.
You need to get the air out of the pleural space rapidly. How do you do that? By placing a large-gauge needle in the second intercostal space at the midclavicular line. This is a temporizing measure, but it allows the built-up air to escape.
How can you determine who needs a chest tube? It depends on the size of the pneumothorax. On a normal chest radiograph, the lung markings should extend to the periphery. With a pneumothorax, you can often see where the lung markings are in comparison to a normal chest radiograph. If the pneumothorax is small, you can watch it; if it’s a larger pneumothorax, then a chest tube may be needed.
Pleurisy
Pleurisy is pain due to inflammation in the pleural space. Pleurisy is most commonly caused by a viral process. The treatment is supportive, but pain medication may be prescribed. With pleurisy, you need to make sure that the person can take a deep breath; if not, he or she is at increased risk for a superimposed bacterial infection.