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Review Question - QID 216748

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QID 216748 (Type "216748" in App Search)
A 65-year-old man presents to the emergency department with worsening shortness of breath. His exercise tolerance has decreased over the past 3 months. He was previously walking up to a mile a day but now cannot take more than 10 steps without having to catch his breath. He has a longstanding history of hypertension and hyperlipidemia for which he takes amlodipine, chlorthalidone, and atorvastatin. He is a former smoker with a 40-pack-year history. The patient’s temperature is 98.6°F (37.0°C), blood pressure is 154/90 mmHg, pulse is 90/min, respirations are 24/min, and oxygen saturation on room air is 87%. Physical exam reveals a fatigued-appearing man with increased work of breathing. Breath sounds are diminished over the bilateral lung bases and chest radiograph reveals bilateral fluid collections at the lung bases. The patient’s NT-proBNP is 1,500 pg/mL (reference: <125 pg/mL). If a thoracentesis is performed, which of the following sets of findings, shown in Figure A, would be expected?
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  • A

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This patient with worsening dyspnea and exercise intolerance in the setting of multiple cardiac comorbidities, elevated NT-proBNP, and bilateral fluid collections at the lung bases most likely has a pleural effusion secondary to an acute heart failure exacerbation. Pleural effusions due to heart failure are transudative, presenting with fluid LDH ≤2/3 of upper limit of normal, fluid/serum LDH ratio ≤0.6, and fluid/serum total protein ratio ≤0.5.

Pleural effusions are characterized by accumulation of fluid in the pleural cavity, which is a potential space that lies between the visceral and parietal pleura that line the lungs. Pleural effusions are caused by an imbalance between hydrostatic and oncotic forces in the capillaries and interstitium. Increased hydrostatic forces in the capillaries, such as those caused by states of fluid overload (e.g., heart failure), or reduced oncotic forces in the capillaries (e.g., cirrhosis, nephrotic syndrome) result in transudative effusions in which fluid spills out of the capillaries. In contrast, inflammatory states (e.g., tuberculous lung disease, malignancy) result in leakage of protein-containing fluid around capillary cells, causing exudative effusions. Transudative and exudative effusions can be distinguished by the Light criteria, where analysis of pleural fluid reveals fluid LDH ≤2/3 of upper limit of normal, fluid/serum LDH ratio ≤0.6, and fluid/serum total protein ratio ≤0.5 in transudative processes. If any single criterion is violated, the effusion is exudative.

D’Agostino and Edens describe the physiology of pleural effusions, including a discussion of the Light criteria for classifying effusions as transudative or exudative.

Figure A shows the answer choices. (LDH = lactate dehydrogenase.)

Incorrect Answers:
Answer 2: Fluid LDH of 70 U/L, fluid total protein of 4.1 g/dL, serum LDH of 150 g/dL, and serum total protein of 6.9 g/dL fails to satisfy the fluid/serum total protein ratio of ≤0.5 criterion, making this an exudative effusion.

Answer 3: Fluid LDH of 140 U/L, fluid total protein of 2.9 g/dL, serum LDH of 200 g/dL, and serum total protein of 7.4 g/dL fails to satisfy the fluid/serum LDH ratio of ≤0.6 criterion, making this an exudative effusion.

Answer 4: Fluid LDH of 200 U/L, fluid total protein of 2.8 g/dL, serum LDH of 350 g/dL, and serum total protein of 7.1 g/dL fails to satisfy the fluid LDH ≤2/3 of upper limit of normal, making this an exudative effusion.

Answer 5: Fluid LDH of 90 U/L, fluid total protein of 3.1 g/dL, serum LDH of 180 g/dL, and serum total protein of 5.6 g/dL fails to satisfy the fluid/serum total protein ratio of ≤0.5 criterion, making this an exudative effusion.

Bullet Summary:
Pleural effusions can be classified as transudative or exudative using the Light criteria, with pleural fluid analysis of fluid LDH ≤2/3 of upper limit of normal, fluid/serum LDH ratio ≤0.6, and fluid/serum total protein ratio ≤0.5 denoting a transudative effusion.

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