USMLE Step 2 CK Pulmonology Questions: Pulmonary Embolism, Severe Asthma and Tension Pneumothorax

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Pulmonary emergencies on USMLE Step 2 CK test whether you choose the right diagnostic test and recognize when a patient needs immediate intervention. Try these three questions, then open each explanation.

Question 1: Sudden shortness of breath after hip surgery

A 54-year-old woman develops sudden shortness of breath and right-sided pleuritic chest pain 5 days after a total hip replacement. Pulse is 112/min, respirations are 24/min, blood pressure is 128/80 mm Hg, and oxygen saturation is 89% on room air. The lungs are clear. Her serum creatinine is normal, and she has no history of contrast allergy. Which of the following is the most appropriate next step to confirm the diagnosis?

A. D-dimer level
B. Lower extremity compression ultrasonography
C. CT pulmonary angiography
D. Ventilation-perfusion scan
E. Transthoracic echocardiography

Correct answer: C. CT pulmonary angiography

This patient has a high clinical probability of pulmonary embolism (recent major orthopedic surgery, sudden dyspnea, pleuritic pain, tachycardia, hypoxemia). With normal kidney function and no contrast allergy, the test of choice is CT pulmonary angiography. If suspicion is high and bleeding risk is low, empiric anticoagulation can be started while waiting for imaging.

Why the other options are wrong:

  • D-dimer is useful only to rule out PE in low-probability patients; it is often elevated after surgery.
  • Leg ultrasonography can support the diagnosis if positive but cannot exclude PE.
  • V/Q scan is preferred when CT contrast must be avoided (renal failure, contrast allergy, sometimes pregnancy).
  • Echocardiography can show right heart strain but does not confirm PE; it is mainly used in unstable patients who cannot go to CT.

Question 2: An asthma attack with a “normal” PaCO2

A 24-year-old man with asthma has had increasing shortness of breath for 2 days. He has received three nebulized albuterol and ipratropium treatments and intravenous methylprednisolone. He is now drowsy and can speak only one or two words at a time. Breath sounds are barely audible, with almost no wheezing. Arterial blood gas on oxygen shows pH 7.32, PaCO2 47 mm Hg and PaO2 62 mm Hg. Which of the following is the most appropriate next step?

A. Discharge home with an oral steroid taper
B. Add montelukast
C. Add inhaled salmeterol
D. Chest physiotherapy
E. Endotracheal intubation and mechanical ventilation

Correct answer: E. Endotracheal intubation and mechanical ventilation

During an asthma attack, patients hyperventilate, so the PaCO2 should be low. A normal or rising PaCO2 means the patient is tiring and heading toward respiratory failure. Other danger signs here are drowsiness, inability to speak and a “silent chest” (too little airflow to make a wheeze). This patient needs intubation and mechanical ventilation. IV magnesium sulfate may also be given in severe exacerbations.

Why the other options are wrong:

  • Discharge would be dangerous for a patient with impending respiratory failure.
  • Montelukast is a controller medication with no role in acute rescue.
  • Salmeterol is a long-acting controller and is not used for acute attacks.
  • Chest physiotherapy does not help acute bronchospasm.

Question 3: Hypotension and absent breath sounds after a car crash

A 30-year-old man is brought to the emergency department after a high-speed motor vehicle collision. He is in severe respiratory distress. Blood pressure is 76/40 mm Hg and pulse is 136/min. Breath sounds are absent on the left side, the left chest is hyperresonant to percussion, the trachea is shifted to the right, and the neck veins are distended. Which of the following is the most appropriate next step?

A. Chest x-ray
B. Needle decompression or finger thoracostomy of the left chest
C. CT scan of the chest
D. Pericardiocentesis
E. Intravenous fluids and observation

Correct answer: B. Needle decompression or finger thoracostomy of the left chest

This is a tension pneumothorax: hypotension, absent breath sounds, hyperresonance, tracheal deviation away from the affected side and distended neck veins. It is a clinical diagnosis. Do not wait for imaging. Treat immediately with needle decompression (or finger thoracostomy), followed by chest tube placement.

Why the other options are wrong:

  • Chest x-ray delays life-saving treatment in an unstable patient.
  • CT scan is never appropriate for an unstable patient with a clinical tension pneumothorax.
  • Pericardiocentesis treats cardiac tamponade, which also causes hypotension and JVD but with normal breath sounds and no tracheal shift.
  • Fluids alone will not relieve the obstructed venous return.

Key takeaways

  • High-probability PE with normal kidneys: CT pulmonary angiography (D-dimer only for low probability).
  • Asthma attack with normal or rising PaCO2, drowsiness or a silent chest = impending respiratory failure: intubate.
  • Tension pneumothorax is a clinical diagnosis: decompress immediately, then place a chest tube.

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Written and reviewed by Dr. Ray Makar, MD, dermatologist with 20 years of clinical practice. Last reviewed: October 2026. For exam preparation only, not medical advice.

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