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
ABG analysis of a patient on ventilator,shows decreased pCO2, normal pO2, pH 7.5; diagnosis is: 
Select and explain. 
A. Respiratory acidosis, B. Metabolic alkalosis, C. Resp alkalosis, D. Metabolic acidosis
C: Resp alkalosis
Answer: C: Resp alkalosis 
Explanation: Answer is C (Respiratory akalosis) : There is alkalosis (pH = 7.5) and CO2 is low (alkalosis). Change in CO2 is inkeeping with change in pH and thus the primary cause is respiratory. The acid base disturbance is thus primary respiratory alkalosis.