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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 159th Avenue
Omaha, NE 68118
Email:
mdcorbett@tconl.com
Website:
http://www.tconl.com/~corbett |
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"BAC Tracker software has caused me to change the way in
which I report alcohol use in medico-legal reports" --
Dr. Edward Ogden, Victoria,
Australia.
