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': 'A patient with salicylic acid poisoning has the following arterial blood gas analysis report: pH is 7.12 , PCO2 is 18 mm Hg HCO3– is 12 mmol/L. The resulting acid-base abnormality can be best labelled \nSelect and explain. \nA. Metabolic acidosis with respiratory alkalosis, B. Metabolic acidosis with respiratory acidosis, C. Respiratory acidosis with metabolic alkalosis, D. Metabolic acidosis', 'role': 'user'}, {'content': "Answer: A \nExplanation: First step\n\nDetermine whether it is acidosis or alkalosis\nLow pH (7.2) means that it is acidosis\n\nSecond step\n\nObserve HCO3-/ CO2 to determine the cause of acidosis or a decrease in pH\nDecreased PCO2 means respiratory alkalosis\nDecreased HCO3- means metabolic acidosis\nThe abnormality which is in sync with the change in pH, i.e., the abnormality which is causing acidosis is decreased HCO3- So, the primary abnormality in the case is metabolic acidosis\n\nThird step\n\nThe third step requires determining whether the patient's compensation is appropriate or not.\nRefer to the table\nChange in HCO3- →12 mmol / L\nExpected change in PCO2 → 1.25 x 12 mmol =15 for 12 mmol change in HCO3-\n\xa0(PaCO2 is expected to decrease 1.25 mm Hg for each mmol/L decrease in HCO3-)\nThus, the decrease in PCO2 is more than the expected. This suggests that there must be coexisting respiratory alkalosis, which causes more than the expected decrease in PCO2.", 'role': 'assistant'}]