In alveoli gas exchange , if a second vapour is also administered along with N2O, the percentage of the second gas is also increased due to the shrinking of the alveoli as a result of the speedy uptake of N2O by blood.
Diffusion in Alveoli
During reversal of anaesthesia, a similar phenomenon is observed in reverse. Maximum diffusion of N20 occurs in the first 5-10 minutes of recovery, faster than the uptake of N2, as a result, hypoxic mixtures are present in the alveoli. This should be taken care of by administering oxygen. This is how diffusion in alveoli happens.
Also we see for diffusion in alveoli , the closed gas spaces may increase in size in the middle ear and pneumoencephalus (non-compliant spaces); bowels, pneumothorax or pneumoperitoneum, a gas embolus and retina after intravitral injections (compliant spaces). This is due to change in volume secondary to transfer of nitrous oxide into these spaces due to its faster diffusibility than nitrogen.