Estimation of the Level of Blood Alcohol from Analysis of Breath. II. Use of Rebreathed Air

Abstract

Using 31 human subjects, detns. were made of the concn. of alcohol in rebreathed air, finger-tip capillary blood and cubital vein blood, at intervals of 1, 2 and 3 hrs. after ingesting 0.69 to 1.70 g of alcohol per kg. The subject rebreathed 4 times in a polyethylene bag. The observed rebreathed-air blood alcohol ratio was 1:2100, which is the ratio found earlier for alveolar air:blood (Harger, Forney and Barnes J. Lab. Clin. Med., 36:306-18, 1950). For 70 min. after drinking, the alcohol level in venous blood averaged 7.5% below that of capillary blood, with lags of 15 to 22% in 1/5 of the detns. Using capillary blood values for samples taken less than 70 min. after drinking and venous blood values for other time intervals, the deviations between estimated and observed blood alcohol levels of the 93 rebreathed air:blood pairs were: 0 to t 5%, 50; + 6 to 10%, 31; + 11 to 15%, 10; and above 15%, 2. The rebreathed air procedure eliminates the need of a simultaneous detn. of CO2. The following modifications of the Drunkometer for analyzing rebreathed air are described: a compact glass gas- metering pump; ampule storage of the 16 [image] H2SO4, with the ampule serving as the reaction tube; two color standards for reading the end point; and a more stable permanganate solution. Detns. of the rate of loss of alcohol through certain breath containers showed: rubber > polyethylene, 12:1; polyethylene > polyvinyl chloride, 4:1; and polyvinyl chloride > flexible aluminum, 6:1. Anhydrous CaCl2 was found to absorb alcohol efficiently from breath, with recovery of 96-100% on distilling the H2O soln. Ether and aliphatic esters are poorly retained by CaCl2 and may thus be differentiated from alcohol.