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: Medicine
[{'content': 'Arterial blood gas analysis of a patient reveals-pH 7.2, HCO3 36 mmol/L pCO2 60 mm of Hg. The abnormality is - \nSelect and explain. \nA. Respiratory acidosis with metabolic alkalosis, B. Respiratory acidosis, C. Respiratory alkalosis with, D. Respiratory acidosis with metabolic acidosis', 'role': 'user'}, {'content': "Answer: A \nExplanation: In this patient\npH\xa0→ decreased (acidosis) N → 7.4\nHCO3-\xa0→\xa0Increased (N → 24 mm\xa0Hg ± 2)\nPCO2\xa0→ Increased (N → 40 Hg ± 2 )\nFirst step\n\nDetermine whether it is acidosis or alkalosis\nDecreased pH (7.2) suggests acidosis.\n\nSecond step\n\nobserve HCO3-/PCO2 to determine the cause of acidosis or alkalosis\nPCO2 is increased which indicates respiratory acidosis.\nHCO3- is increased which indicates metabolic alkalosis\nThe abnormality which is in sync with the change in pH is increased pCO2 i.e., increased pCO2 is responsible for decreased pH or acidosis So the primary abnormality in this case is respiratory acidosis.\n\nThird step\n\nThis step requires determining whether the patient's compensation is appropriate\xa0\nChange in PCO2\xa0→ 20 mm Hg. (N — 40, observed 60)\nExpected change in HCO3-\xa0→ 2 mmol/L for 20 mm Hg change in PCO2\n(For every 10 mm increase in PCO2, HCO3- increases to 1 mmol/L)\nSo the expected value of HCO3-\xa0→ 26 mmol/L\nBut the observed value of HCO3-\xa0→ 36 mmol/L\nThis suggests that some other abnormality other than respiratory acidosis exists which has increased the HCO3- value to more than expected.\nA disorder which increases the HCO3- concentration is metabolic alkalosis\nThus this is a case of mixed disorder, where respiratory acidosis and metabolic alkalosis exist together.", 'role': 'assistant'}]