Arterial blood gases before, during, and after nitrous oxide: Oxygen administration

The use of nitrous oxide as an anesthetic or analgesic agent frequently raises concerns about the possibility of post-inhalational diffusion hypoxemia. We undertook a study in 20 healthy volunteers to determine whether hypoxemia occurs after the self-administration by face mask of a 50:50 mixture of nitrous oxide and oxygen for 15 minutes, followed by breathing room air. Blood gases were measured through an in-dwelling arterial cannula before, during, and after inhalation of the mixture, at time O, five, ten, and 15 minutes, and then 30 seconds, 45 seconds, 21/2 minutes, five, and ten minutes following room air breathing. Ten of the 20 subjects breathed a control gas, a mixture of 50% nitrogen:50% oxygen. No subject demonstrated arterial hypoxemia at any time before, during, or after self-administration of the gas mixture. In the ten subjects who self-administered the control gas there were no significant differences in the PaO₂ values while they breathed either gas at any corresponding sampling time. We conclude that diffusion hypoxia is not seen in normal subjects following self-administration of a mixture of 50:50 nitrous oxide and oxygen.