At the end of anaesthesia after discontinuation of nitrous oxide and removal of endotracheal tube, 100% oxygen is administered to the patient to prevent:

Ans. is 'a' i.e. Diffusion hypoxiaRef K.D.T. 5th/e page 337, 4th/ep346N2O has low blood solubility. So when N2O is discontinued after prolonged anaesthesia, due to its low blood solubility it rapidly diffuses into the alveoli and dilutes the alveolar air. This causes excess of N2O in alveoli so the partial pressure of oxygen in the alveoli is reduced.This results in hypoxia and it is known as diffusion hypoxiaIf the cardiac reserve is normal diffusion hypoxia is not of much significance but if cardiac reserve is low, diffusion hypoxia can be very dangerous.Prevention: -It can be prevented by continuing 100% 02 inhalation for a few minutes after discontinuing N2ONote: Diffusion hypoxia is not significant with other anaesthetics because they are administered at very low concentrations (2 - 4%) and so they cannot dilute alveolar air by more than 1-2%