July 29, 1974

Oxygen Therapy Masks

Author Affiliations

Westminster Hospital London

JAMA. 1974;229(5):521. doi:10.1001/jama.1974.03230430015011

To the Editor.—  I was interested to read the paper by Friedman et al (228:474, 1974) on the evaluation of air-entraining oxygen masks. I, too, have searched for a method of evaluating these devices and agree that it is futile to attempt sampling within the barrel using an oxygen analyzer. My solution to this problem1,2 utilizes the mathematical theory of the O2/ CO2 diagram. In principle, it assesses what comes out of the patient from which the inspired oxygen concentration can be determined with certainty. My studies have shown that Ventimasks perform within the manufacturers' tolerance, ie, ±1% for 24% and 28%, and ±2% for 35% and 40%. I tried some time ago to employ plastic bags as described by Friedman et al and found that even the minute back pressure of this technique interferes with the performance of Ventimasks, causing less air entrainment and hence a