<prompt> Pre-oxygenation is done to?Increase the oxygen content of FRCDecrease the nitrogen content of FRCBothNone  <response>: Ans. is c i.e. Both Pre-oxygenation Pre-oxygenation is the administration of oxygen to a patient prior to intubation to extend the safe apnea time duration of time following cessation of breathingventilation until critical arterial desaturation occurs. The aim of pre-oxygenation is to increase to oxygen reserve of body which is in the form of functional residual capacity FRC, i.e., the air remaining in the lungs after normal expiration. The oxygen content of the FRC filled with air is 21 i.e., at the end of the expiration oxygen content is 21 in the air of lung. Normal FRC is 2.5 litres, therefore oxygen content is 500 ml 21 of 2.5 litres. Most of the remaining gas is nitrogen. This oxygen content will last only for 2 minutes oxygen consumption is 250 mlmin. By pre-oxygenation, we washout nitrogen denitrogenation with 100 O2 - O2 content of FRC is 2.5 litres 100 - Lasts for 8 to 10 minutes. Pre oxygenation is done for 3 minutes because 99 of denitrogenation nitrogen wash out takes place in 3 minutes. 