Hypoxaemia after inhalation of 50% nitrous oxide and oxygen.

We have investigated, in volunteers, the effect of inhaling 50% nitrous oxide in oxygen on subsequent oxygenation. Subjects breathed either 50% nitrous oxide in oxygen or 50% nitrogen in oxygen during hyperventilation and normal ventilation. Arterial oxygen saturation and end-expired oxygen concentrations were lower after 50% nitrous oxide in oxygen than after the other mixture with both patterns of ventilation and were lowest after hyperventilation with 50% nitrous oxide in oxygen.