This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2017, Subject name: Anaesthesia
Time required for pre-oxygenation before tracheal intubation 
Select and explain. 
A. 3 min, B. 5 min, C. 2 min, D. 1 min
A: 3 min
Answer: A: 3 min 
Explanation: Preoxygenation before intubation : Process of replacing nitrogen in the lungs with oxygen. Preoxygenation with tidal volume breathing of 3 mins is required before tracheal intubation. This delays the onset of critical hypoxia during the period of apnea by 5-8 minutes.