A 53-year-old man comes to the emergency department due to increasing shortness of breath and right-sided pleuritic chest pain over 10 days. He visited an urgent care center 5 days ago and was diagnosed with pneumonia. The patient received an unknown antibiotic (which he took as prescribed), but it has not helped. He has no other medical problems. He smokes a pack of cigarettes a day and drinks 2 or 3 beers each night. Temperature is 38.7 C (101.6 F), blood pressure is 136/88 mm Hg, pulse is 104/min, and respirations are 18/min. The patient appears comfortable. There is no jugular venous distension. Cardiopulmonary examination shows dullness to percussion over the lower part of the right lung and normal heart sounds. There is no peripheral edema. Chest imaging reveals a large, loculated right pleural fluid collection. Which of the following sets of pleural fluid findings is most likely in this patient?
Parapneumonic effusions | ||
Uncomplicated | Complicated | |
Etiology | Sterile exudate in pleural space | Bacterial invasion of pleural space |
Radiologic | Small to moderate & free flowing | Moderate to large, free flowing |
Pleural fluid characteristics |
|
|
Pleural fluid | Negative | Positive or negative* |
Treatment | Antibiotics | Antibiotics & drainage |
*Gram stain & culture are often falsely negative due to low bacterial count. Both are typically positive in empyema, which represents advanced progression of a complicated effusion. LDH = lactate dehydrogenase; WBC = white blood cell. | ||
Bacterial pneumonia often causes a pleural effusion. Typically, the effusion is small, sterile, free-flowing, and resolves with antibiotics (uncomplicated). However, if bacteria persistently invade the pleural space, a complicated parapneumonic effusion or empyema may develop. Patients with these pleural space infections tend to have continued symptoms (fever, pleuritic pain) despite adequate antibiotics. Chest x-ray often shows loculation (walled-off pleural fluid). Thoracentesis will show an exudative effusion characterized by:
Empyemas are differentiated from complicated parapneumonic effusions by the presence of gross pus or bacteria on Gram stain. Most complicated parapneumonic effusions and all empyemas require drainage (eg, chest tube) in addition to antibiotics.
(Choices B, C, and D) Transudative effusions are marked by low protein (eg, <3 g/dL). Glucose and pH are usually normal. Parapneumonic effusions are exudative (not transudative).
(Choice E) The elevated protein suggests an exudative effusion; however, both the pH and glucose are elevated, which would be unusual with a parapneumonic effusion.
Educational objective:
Complicated parapneumonic effusions and empyemas often present with continued symptoms (fever, pleuritic pain) despite adequate antibiotic coverage for pneumonia. Chest x-ray usually shows loculation, and thoracentesis reveals fluid that is exudative with low glucose (<60 mg/dL) and low pH (<7.2). Most complicated parapneumonic effusions and all empyemas require drainage (eg, chest tube) in addition to antibiotics.