This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
In acute exacerbations of COPD, noninvasive positive pressure ventilation (NIPPV) is initiated when 
Select and explain. 
A. Paco2 >45 mmHg, B. PaO2 <80 mmHg, C. FEV1 <30, D. FEV1/FVC <0.7
A: Paco2 >45 mmHg
Answer: A: Paco2 >45 mmHg 
Explanation: In acute exacerbations of COPD, noninvasive positive pressure ventilation (NIPPV) is initiated in patients with respiratory failure, which is defined as Paco2 > 45 mmHg, This results in a significant reduction in moality rate, need for intubation, complications of therapy, and hospital length of stay.Ref: Harrison 19e pg: 1707