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: Anaesthesia
[{'content': 'A 27 year old male patient is referred for resection of pheochromocytoma. Which of the following medications should the patient be taking prior to surgery \nSelect and explain. \nA. Propranolol, B. Labetalol, C. Phenoxybenzamine, D. Hydralazine', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Phenoxybenzamine is non selective alpha antagonist, which prevents vasoconstriction. If\xa0patient receives beta blocker without alpha blockade, he will experience alpha mediated vasoconstriction that would result in very high blood pressure.', 'role': 'assistant'}]