Pre-oxygenation is done to?

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 breathing/ventilation 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 ml/min).* 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.