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Difficulty: EasyCardiovascular System

A 64-year-old woman presents to the emergency department with a 3-day history of progressively worsening shortness of breath and a dry cough. She has a 35-pack-year smoking history and a history of an anterior myocardial infarction 4 years ago. On physical examination, her blood pressure is 155/90 mmHg, heart rate is 102/min, and respiratory rate is 22/min. Oxygen saturation is 89% on room air. Lung auscultation reveals diffuse expiratory wheezes bilaterally and prolonged expiration. Cardiac auscultation reveals a regular rhythm with an audible S3 gallop. She has 2+ pitting edema in both lower extremities. Which of the following laboratory findings is most useful to differentiate the primary cause of this patient's respiratory symptoms from a chronic obstructive pulmonary disease (COPD) exacerbation?

  1. Elevated serum B-type natriuretic peptide levelAnswer
  2. B
    Increased arterial partial pressure of carbon dioxide
  3. C
    Elevated serum procalcitonin level
  4. D
    Decreased arterial partial pressure of oxygen
  5. E
    Elevated peripheral blood eosinophil count

Answer

Elevated serum B-type natriuretic peptide level
B-type natriuretic peptide (BNP) is a neurohormone synthesized and released by the ventricular myocardium in response to increased wall tension and stretch, which occur in states of volume overload. In patients presenting with acute dyspnea and wheezing who have risk factors for both pulmonary and cardiac disease, an elevated BNP level is highly sensitive and specific for establishing a diagnosis of acute decompensated heart failure. It effectively differentiates cardiogenic pulmonary edema (which can cause wheezing, often termed 'cardiac asthma') from a primary chronic obstructive pulmonary disease (COPD) exacerbation.

Step-by-Step Solution

1
Identify the overlapping clinical features in the presentation.
The patient has wheezing, dyspnea, and a smoking history (suggesting COPD), but also has an S3 gallop, peripheral edema, and a history of myocardial infarction (suggesting heart failure).
Recognizing that 'cardiac asthma' (wheezing due to pulmonary edema) can perfectly mimic a COPD exacerbation is essential for selecting the correct diagnostic path.
2
Evaluate which laboratory marker isolates the cardiac etiology.
Select B-type natriuretic peptide (BNP).
BNP is released from ventricular myocytes directly in response to volume expansion and pressure overload, distinguishing cardiogenic pulmonary edema from primary pulmonary disease.

Key Concept

Differentiating acute decompensated heart failure from COPD exacerbation using B-type natriuretic peptide (BNP).
Estimated Time:45s
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Topics

Cardiovascular System

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