When water-soluble gases such as anesthetic agent N2O (nitrous oxide) are breathed in large quantities they can be dissolved in body fluids rapidly.
This leads to a temporary increase[clarification needed] in both the concentrations and partial pressures of oxygen and carbon dioxide in the alveoli.
[1][4] When a patient is recovering from N2O anaesthesia, large quantities of this gas cross from the blood into the alveoli (down its concentration gradient) and so for a short period of time, the O2 and CO2 in the alveoli are diluted by this gas.
[5] Nonetheless, this effect only lasts a couple of minutes and hypoxia can be avoided by increasing the fractional inspired oxygen concentration when recovering from N2O administration.
[6] It is for this reason that Entonox, a 50:50 gaseous mixture of nitrous oxide and oxygen, is suitable for use by para-medical staff such as ambulance officers: it provides sufficient nitrous oxide for pain relief with sufficient oxygen to avoid hypoxia.