An outpatient pulmonary clinic evaluates a 69-year-old man for progressively worsening fat… — USMLE Step 2 CK

An outpatient pulmonary clinic evaluates a 69-year-old man for progressively worsening fatigue and bilateral ankle swelling over the last two months. He has a known diagnosis of chronic obstructive pulmonary disease (COPD). The patient reports no recent increase in cough or changes in sputum character. His current daily medications are inhaled tiotropium and formoterol.

Vital signs are:
Blood pressure: 130/82 mmHg
Heart rate: 88/min
Respiratory rate: 18/min
Oxygen saturation: 87% on room air

Physical examination reveals distension of the jugular veins to 8 cm above the sternal angle and 2+ pitting edema in the lower extremities bilaterally. Cardiac auscultation identifies a loud pulmonic component of the second heart sound ( $P_2$ ) with no murmurs. Pulmonary auscultation reveals globally diminished breath sounds without adventitious sounds.

Laboratory and diagnostic data on room air:

Parameter	Value
Hematocrit	57%
pH	7.37
$PaCO_2$	50 mmHg
$PaO_2$	54 mmHg
$HCO_3^-$	28 mEq/L

Which of the following interventions is most likely to improve this patient's long-term survival?

Continuous supplemental oxygen therapyAnswer
B
Oral furosemide
C
Prophylactic oral azithromycin
D
Oral sodium bicarbonate
E
Addition of an inhaled corticosteroid

Answer

Continuous supplemental oxygen therapy

The patient has chronic obstructive pulmonary disease (COPD) complicated by severe resting hypoxemia (

PaO_2

≤ 55 mmHg or

SaO_2

≤ 88%) and cor pulmonale (right heart failure). In patients with severe resting hypoxemia, long-term continuous supplemental oxygen therapy is the primary intervention proven to reduce hypoxic pulmonary vasoconstriction, lower pulmonary artery pressures, and significantly improve mortality. Other criteria for oxygen therapy include a

PaO_2

between 56-59 mmHg if there is evidence of cor pulmonale or a hematocrit > 55%.

Step-by-Step Solution

Analyze the patient's clinical presentation and laboratory data.

The patient has severe COPD with resting hypoxemia (

PaO_2

of 54 mmHg,

SaO_2

87%) and clear signs of cor pulmonale (right heart failure with JVD, lower extremity edema, loud

P_2

, and compensatory polycythemia).

Identifying the specific pathophysiologic state (cor pulmonale secondary to chronic hypoxemia) is necessary to determine the appropriate disease-modifying treatment.

Determine the intervention with the greatest mortality benefit for this specific condition.

Long-term continuous supplemental oxygen therapy is identified as the intervention that improves survival.

In patients with severe resting hypoxemia, oxygen therapy reduces hypoxic pulmonary vasoconstriction, thereby decreasing pulmonary hypertension, improving right ventricular function, and significantly improving mortality.

Key Concept

In patients with chronic obstructive pulmonary disease (COPD) complicated by severe resting hypoxemia (

PaO_2

≤ 55 mmHg or

SaO_2

≤ 88%) or cor pulmonale, long-term continuous supplemental oxygen therapy is the primary intervention proven to prolong survival.

Estimated Time:1m 0s

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