A 75-year-old man with a history of hypertension and peptic ulcer disease presents with dyspnea on exertion

 A 75-year-old man with a history of hypertension and peptic ulcer disease presents with dyspnea on exertion to the emergency department (ED). He notes black-colored stools for the past 2 weeks. His initial examination is notable for conjunctival pallor, clear lung fields without rales, wheezing, or rhonchi, as well as tachycardia with a regular rhythm, normal s1 and s2, and without murmurs, rubs, or gallops. Initial laboratory workup reveals a hemoglobin of 5.5 g/dL, reduced from a baseline of 12 g/dL on routine outpatient laboratory testing from 3 months prior. His basic metabolic panel, arterial blood gas (ABG), and lactateare all within normal limits. A chest radiograph (CXR) is normal.

What is the mechanism of this man’s dyspnea on exertion?

A. Decreased cardiac output

B. Decreased oxygen delivery

C. Decreased systemic vascular resistance

D. High-output heart failure

E. Pulmonary edema

Answer:

The correct answer is: B. Decreased oxygen delivery. 

Discussion

This patient is likely suffering from an upper gastrointestinal (GI) bleed, as evidenced by melena, new anemia, and history of peptic ulcer disease. His presenting symptom of dyspnea on exertion is secondary to decreased oxygen delivery to tissues. Delivery of oxygen to tissues is dictated by cardiac output and the oxygen content of blood. The major determinant of oxygen-carrying capacity in blood is the hemoglobin concentration. His examination and testing do not support a diagnosis of heart failure or pulmonary edema. High-output heart failure may develop in the setting of chronic anemia; however, his known hemoglobin 3 months prior was normal.