A Review of BAC Tracker from a Forensic Toxicologist

      "BAC Tracker is a software program that interfaces alcohol kinetics with Microsoft Excel in a very user friendly manner.  You don’t even have to know how to use Excel.  In a nutshell, BAC Tracker streamlines the use of the Widmark Equation to enable calculations of blood alcohol concentration (BAC) either from a knowledge of a measured BAC (retrograde extrapolations) or of the amount of alcohol consumed (anterograde extrapolations).  It is highly flexible since it automatically incorporates five different methods to calculate the Widmark factor ‘r’ (essentially the volume of distribution for ethyl alcohol).  The user need only enter the gender, age, height and weight of the subject with no need to convert the numbers to the metric system.  Similarly, alcohol doses are entered as ounces and percent alcohol by volume; the software converts them to grams of pure alcohol for subsequent calculations.  The alcohol elimination rate (beta value) is selected by the user for both a high and low value, or allowed to run at a default value.

      The most useful aspect of BAC Tracker is the handling of the absorptive phase of the alcohol curve.  The software applies a first-order rate equation to calculate alcohol absorption from a given amount of alcohol in the stomach.  This calculation, in combination with the simultaneous calculation of alcohol elimination by the standard zero-order equation, provides the BAC at any given time following alcohol ingestion. The mathematics of this process can be extremely time consuming when done by hand, and rapidly become quite complicated as the number of drinks increases.  To further complicate the calculations, different drinks and varying time periods for the consumption of each drink are common in actual drinking scenarios.  So also is the need to oftentimes consider, at least for some of the drinks in a lengthy scenario, the presence of food in the stomach.  BAC Tracker readily handles such complications.  The rate constant employed for alcohol absorption is predetermined based on the user’s selection of either an empty or full stomach for each drink.  Thus, BAC Tracker enables complicated calculations that I wouldn’t even consider attempting to do by hand.  The end-product is a tabular and graphical presentation of BAC as a function of time, with the option to show the results on the basis of Widmark’s, Watson’s, and three additional “r-factors”, or as an average of the five factors.   What’s really great is the confidence level in the final result, since the results are computer generated from mathematical relationships, as opposed to hand calculations and the plotting of graphs, which are necessarily subject to occasional human errors.

      BAC Tracker will greatly facilitate the presentation of extrapolated results to the judge and jury, especially when it comes to explaining the origin and degree of uncertainty attendant to such calculations.  I think that expert witnesses involved in litigation arising from alcohol consumption will find BAC Tracker to be very useful.  Educators will likely find BAC Tracker to be a valuable teaching aid that can be used to demonstrate the effect of alcohol dose, alcohol pharmacokinetics, gender, age and physical stature on BAC."

Michael D. Corbett, Ph.D.                                                                                 Consulting Forensic Toxicologist                                                                                     616 South 159^th Avenue                                                                                                Omaha, NE 68118                                                                                                     Email: mdcorbett@tconl.com                                                                              Website: http://www.tconl.com/~corbett