This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Surgery
[{'content': 'An abnormal ventilation-perfusion ratio (Qs/Qr) in the postoperative patient has been associated with \nSelect and explain. \nA. Pulmonary thromboembolism, B. Lower abdominal surgery, C. Starvation, D. The upright position', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Abnormalities of ventilation-perfusion ratio result from the shunting of blood to a hypo ventilated lung or from the ventilation of hypo perfused regions of lung tissue. When this imbalance is extreme, as following massive pulmonary thromboembolism, the effect is life-threatening hypoxemia. Other common predisposing factors in the postoperative patient that contribute to this maldistribution include the assumption of a supine position, thoracic and upper abdominal incisions, obesity, atelectasis, and reduced cardiac output.', 'role': 'assistant'}]