Laboratory Evaluation of a New Evidential Breath-Alcohol Analyser Designed for Mobile Testing – the Evidenzer

Abstract

The Evidenzer is a new kind of forensic breath-alcohol analyser, designed for use both at a police station (stationary) and also in a police vehicle (mobile) at the roadside. In this paper we report the accuracy and precision of the Evidenzer, determined under controlled laboratory conditions. The results were compared with a well-established breath-alcohol instrument (Intoxilyzer 5000S) and also with the concentration of alcohol in venous blood. Twenty healthy volunteers (10 men and 10 women) consumed ethanol (0.4 g/kg) in 15 minutes starting two to three hours after their last meal. Venous blood and breath were obtained for determination of ethanol at 15-30 minute intervals for up to four hours post-dosing. There was a good overall agreement between the two breath-alcohol instruments and the mean bias was only 0.003 mg/L (95% limits of agreement of -0.016 to 0.023 mg/L). The standard deviation (SD) of measuring ethanol in breath was about the same for both instruments, being 0.006 mg/L, and this corresponds to a relative precision or coefficient of variation (CV) of 4.7%. When the Evidenzer was used to analyse ethanol vapour (0.50 mg/L) generated from a wet-bath simulator, i.e. in-vitro conditions, the coefficient of variation was 0.7% indicating high analytical precision. The concentration of ethanol in venous blood and breath were highly correlated (r=0.95) although systematic differences existed depending on time after drinking when comparisons were made. Both breath-alcohol instruments gave results higher than venous blood alcohol in tests made at 15 minutes after the end of drinking whereas at all later times the venous blood-alcohol concentration was higher than the breath instrument readings. These observations can be explained by the time necessary for ethanol to equilibrate between arterial blood and tissue water and by the resulting arterial-venous differences. The time-course of alcohol concentration in arterial blood runs closer to the breath-alcohol concentration rather than the venous blood draining the forearm muscle tissue. The new Evidenzer instrument was easy to operate and gave accurate and precise results compared with Intoxilyzer 5000S.