A 67-year-old woman recently discharged after hip surgery presents with shortness of breath and sharp chest pain; dried blood around the mouth, facial cyanosis, SpO2 88%. Suspect

• A. Myocardial infarction
• B. Pneumothorax
• C. Acute pulmonary embolism
• D. Pneumonia

Answer: (C)

Immobilization after surgery markedly raises the risk of a deep vein clot forming and traveling to the lungs, causing a pulmonary embolism. When an embolus blocks a pulmonary artery, it creates a ventilation–perfusion mismatch and significant hypoxemia, which explains the patient’s low SpO2 and facial cyanosis. The sharp, pleuritic chest pain comes from irritation of the lung and pleura where blood flow is disrupted. In the postoperative setting, this combination of sudden shortness of breath, pleuritic chest pain, and hypoxemia is classic for a pulmonary embolism.

Other conditions don’t fit as well: a heart attack often presents with more pressure-like chest pain and different accompanying symptoms; a pneumothorax would typically show unilateral abnormal breath sounds or hyperresonance; pneumonia usually has fever and a slower onset with infectious signs. Because a pulmonary embolism is highly suspected here, prioritize oxygenation and rapid transport for definitive care.