A 65-year-old man comes to the clinic complaining of progressively worsening dyspnea over the last 2 months. His past medical history is significant for hypertension, type 2 diabetes mellitus, and myocardial infarction 2 years ago. His temperature is 36.7 C (98 F), blood pressure is 156/96 mm Hg, pulse is 65/min, and respirations are 18/min. Physical examination shows bilateral 2+ pitting edema in the lower extremities up to the knees. Hepatojugular reflux is present. The point of maximal impulse is displaced downward and to the left. There is a 2/6 soft and blowing systolic murmur at the apex. Breath sounds are diminished at the right base. Serum protein level is 6.5 g/dL and serum lactate dehydrogenase is 320 U/L. After taking a chest radiograph, the physician suspects pleural effusion on the right and decides to perform diagnostic thoracocentesis. Which of the following findings on pleural fluid analysis would be most consistent with this patient's condition?
Common causes of pleural effusions | |
Transudate | Exudate |
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This patient's presentation is most consistent with congestive heart failure (CHF). CHF commonly causes transudative effusions. However, 25% of effusions can meet exudative criteria if the patient has received aggressive diuretics prior to thoracentesis. These effusions are usually bilateral (61%) but can be unilateral on either the right (27%) or left (12%) side. The elevated pressure from left ventricular end diastole and the left atrium transmits back to the alveolar capillaries to increase hydrostatic pressure. This leads to fluid movement across the visceral pleura into the pleural space. Light's criteria can distinguish transudate from exudate. Exudates generally have the following characteristics:
Normal pleural fluid pH is approximately 7.60. Transudative fluid is usually due to systemic factors (eg, increased hydrostatic pressure or hypoalbuminemia) and has a pleural fluid pH of 7.4-7.55. Exudate is usually due to inflammation with a pleural fluid pH of 7.30-7.45. Pleural fluid pH <7.30 (with normal arterial pH and low pleural glucose) is usually due to increased acid production by pleural fluid cells and bacteria (eg, empyema) or decreased hydrogen ion efflux from the pleural space (eg, pleuritis, tumor, pleural fibrosis).
(Choice A) Glucose level <60 mg/dL or pleural fluid/serum glucose ratio <0.5 is usually seen in complicated parapneumonic effusion, malignancy, tuberculosis, or rheumatoid arthritis. Transudates and all other exudative effusions usually have pleural fluid glucose similar to blood glucose concentration.
(Choice B) High pleural fluid amylase level is typically due to pancreatitis-associated effusion or esophageal rupture (from saliva).
(Choices C and E) Pleural LDH of 210 U/L would give a pleural/serum LDH ratio >0.6. Pleural protein of 5.0 g/dL would give a pleural/serum protein ratio >0.5. Both of these are found in exudative effusion, which is less likely in this patient with new-onset and untreated CHF.
Educational objective:
Congestive heart failure commonly causes transudative effusions (bilateral 61%, unilateral right-sided 27%, and unilateral left-sided 12%). Normal pleural fluid pH is 7.60. Transudative fluid usually has a pleural fluid pH of 7.4-7.55.