Question

During your first day on the job as an anesthesiologist at Vail summit medical center (altitude=3,350 m, pressure=70,000 Pa), you think back to CHEM 452 and realize that the usual 75% N2O / 25% O2 mixture in an anesthetic is not going to work at the high altitude since that recipe is formulated for sea level. Find the proportions of the two gases to use at Vail such that the partial pressure of oxygen at Vail is equal to the partial pressure of O2 that is attained at sea level with a 75/25 mixture. Note that the patient always breathes gas at approximately ambient pressure.

Answer 1

Solution :-

At the sea level atmospheric pressure is 101325 Pa

therefore when the ratio is 75/25 N2O and O2

then partial pressure of the O2 is 101325 Pa * 25 / 100 = 25331 Pa

Therefore now to attain the same pressure at the altitude 3350 m and total pressure 70000 Pa

lets calculate the percent of the O2

(25331 Pa / 70000 Pa )*100% = 36.2 %

Therefore the percent of the O2 = 36.2 %

now lets find the percent of the N2O

% N2O = 100 % - % O2

           = 100 % - 36.2 %

           = 63.8 % N2O

Therefore the ration of the two gases needed is 63.8 % N2O / 36.2 % O2

or 63.8 / 36.2 = 1.74