A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
Eight hours after undergoing successful cholecystectomy, a 65-year-old man with scoliosis complains of shortness of breath. Respirations are 28/min and pulse oximetry on room air shows an oxygen saturation of 85%. Physical examination shows kyphotic deformation of the thorax. Cardiopulmonary examination shows intercostal retractions and diminished breath sounds on the left side. There is trace pedal edema bilaterally. An x-ray of the chest shows bilateral fluffy infiltrates, and the cardiac silhouette is shifted slightly to the left side. Which of the following is the most likely explanation for this patient's hypoxia?
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A
Collapsed alveoliCorrect. Postoperative atelectasis (collapsed alveoli) is the most common cause of early postoperative hypoxia, especially with kyphoscoliosis and upper abdominal surgery, and produces ipsilateral mediastinal shift.
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B
Embolus in the pulmonary arteryIncorrect. Pulmonary embolism presents with sudden dyspnea and pleuritic pain but typically has a normal CXR — not fluffy infiltrates with mediastinal shift toward the affected side.
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C
Fluid in the pleural spaceIncorrect. A pleural effusion blunts costophrenic angles but causes mediastinal shift away from the affected side, not toward it.
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D
Air trapped in the pleural spaceIncorrect. A pneumothorax shows a lucent zone without lung markings and also shifts the mediastinum away from the affected side.
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E
Aspirated gastric contentsIncorrect. Aspiration pneumonitis would more typically produce focal infiltrates in dependent lung segments rather than diffuse bilateral fluffy infiltrates with ipsilateral mediastinal shift, and is less common than postoperative atelectasis after upper abdominal surgery in a kyphoscoliotic patient.
↑ Tap an answer to reveal the reasoning
Answer: A. An elderly patient with kyphoscoliosis who develops postoperative hypoxia after upper abdominal surgery, with diminished breath sounds, intercostal retractions, ipsilateral mediastinal shift on chest x-ray, and bilateral fluffy infiltrates has postoperative atelectasis — collapse of alveoli. This is the most common cause of postoperative fever and hypoxia in the first 24–48 hours. Kyphoscoliosis (restrictive chest wall) and abdominal surgery (splinting from pain, decreased diaphragmatic excursion) are major risk factors.
Volume loss from alveolar collapse causes the ipsilateral mediastinum (cardiac silhouette) to shift toward the affected side, distinguishing it from a pleural effusion or pneumothorax which would push the mediastinum away. The fluffy infiltrates reflect retained secretions and atelectatic lung. Treatment is incentive spirometry, ambulation, adequate pain control, and chest physiotherapy.
Pulmonary embolism typically presents with sudden dyspnea, pleuritic pain, and tachycardia, often with a normal CXR or Westermark sign — not lobar collapse. Pleural effusion (fluid in pleural space) blunts costophrenic angles and pushes the mediastinum away from the affected side. Pneumothorax (air in pleural space) appears as a lucent zone without lung markings and also pushes the mediastinum away.
**Why each option:**
**A.** Correct. Postoperative atelectasis (collapsed alveoli) is the most common cause of early postoperative hypoxia, especially with kyphoscoliosis and upper abdominal surgery, and produces ipsilateral mediastinal shift.
**B.** Pulmonary embolism presents with sudden dyspnea and pleuritic pain but typically has a normal CXR — not fluffy infiltrates with mediastinal shift toward the affected side.
**C.** A pleural effusion blunts costophrenic angles but causes mediastinal shift away from the affected side, not toward it.
**D.** A pneumothorax shows a lucent zone without lung markings and also shifts the mediastinum away from the affected side.