This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
[{'content': 'A 64 year old hypertensive obsese female was undergoing surgery for fracture femur under general anaesthesia. Intra-operatively her end-tidal carbon dioxide decreased to 20 from 40 mm of Hg, followed by hypotension and oxygen saturation of 85%. What could be the most probable cause? \nSelect and explain. \nA. Fat embolism, B. Hypovolemia, C. Bronchospasm, D. Myocardial infarction', 'role': 'user'}, {'content': 'Answer: A \nExplanation: "Arterial blood gas analysis reveals hypoxemia and hypocapnia, with subsequent metabolic acidosis in severe\xa0pulmonary embolism. During anaesthesia, end tidal CO2 concentration may fall dramatically because of increased\xa0dead space and reduced cardiac output". _________\xa0Anesthesia & Intensive care\n\nNote : Fat embolism can present as pulmonary embolism when an extensive fat embolism of lung is present.', 'role': 'assistant'}]