Pulmonology — USMLE Step 3 Practice
Pulmonary medicine on USMLE Step 3 includes obstructive and restrictive lung diseases, acute respiratory failure, pulmonary embolism, and pneumonia management. Interpreting ABGs, PFTs, and chest imaging is consistently tested.
Frequently Asked Questions
What is the Wells criteria used for on USMLE Step 3?
The Wells criteria estimate the pre-test probability of pulmonary embolism. Low probability patients can be ruled out with a D-dimer; high probability patients require CT pulmonary angiography (CTPA). CTPA is the gold standard imaging test for PE.
How do you differentiate obstructive from restrictive lung disease on PFTs?
Obstructive disease (COPD, asthma) shows reduced FEV1/FVC ratio (<0.70) with preserved or increased TLC. Restrictive disease (pulmonary fibrosis, sarcoidosis) shows normal or elevated FEV1/FVC ratio with reduced TLC. A reduced DLCO suggests emphysema (obstructive) or fibrosis (restrictive).
What ABG pattern indicates type II respiratory failure?
Type II (hypercapnic) respiratory failure shows elevated PaCO2 (>45 mmHg) with low PaO2 (<60 mmHg). Common causes include COPD exacerbation, neuromuscular weakness, and obesity hypoventilation. Non-invasive positive pressure ventilation (BiPAP) is first-line for COPD exacerbations with hypercapnia.
What is the first-line management of a COPD exacerbation?
COPD exacerbations are managed with short-acting bronchodilators (albuterol + ipratropium), systemic corticosteroids (prednisone 40 mg x 5 days), and antibiotics if there is purulent sputum or increased dyspnea. NIV (BiPAP) is indicated for moderate-severe exacerbations with respiratory acidosis.
Which pneumonia pathogens are tested most on Step 3?
Community-acquired pneumonia caused by Streptococcus pneumoniae (lobar consolidation, rust-colored sputum) and atypical pathogens (Mycoplasma — walking pneumonia in young patients; Legionella — hyponatremia + GI symptoms in hotel/hospital water exposure) are high-yield. Treatment: fluoroquinolone monotherapy or beta-lactam + macrolide for CAP.
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