Truncation of Breath Alcohol Measurements and Its Effect on Peak Concentrations

Abstract

An intra-subject comparative study was performed using breath analysis to assess the forensic implications of data truncation on peak blood alcohol concentrations (Cmax). Accordingly, several other forensically relevant pharmacokinetic parameters associated with Cmax were investigated, including the time-to-peak (Tmax), plateau (PLAT) duration, and the rise in blood alcohol concentration (BAC) following the end of drinking (EOD). The study consisted of three drinking sessions, nine subjects per session, with drinking intervals of 30, 90, and 180 minutes, and ethanol doses of 1.0, 1.1, and 1.6 g/kg, respectively. Three-digit breath measurements were collected in duplicate at 10, 30, 45, 60, 75, 90, 105, 120, 135, 195, and 255 minutes following EOD using a fuel-cell based breath instrument (Intox ECIR®). Breath results were then computed using two different data treatment methods. The first method averaged duplicate three-digit breath measurements and reported results to the third digit. The second method used the lower of the two duplicate measurements and reported results to the truncated second digit. The results of the two data treatment methods were then compared using general statistics and alcohol concentration-time profiles. The overall rise in BAC following EOD for three-digit results was 0.009 g/210L with a range of 0.000–0.030 g/210L (standard deviation 0.008 g/210L). When breath measurements where truncated, 25 of the 27 subjects had a rise in BAC of 0.02 g/210L or less. In total, 6 subjects had no rise in BAC following the EOD when evaluating the three-digit results. In contrast, when BAC results were truncated, 11 subjects exhibited no increase in BAC following EOD. The overall Tmax was reduced from 41 minutes to 26 minutes, and overall PLAT durations were extended from 22 to 39 minutes, when the breath measurements were truncated.