Updating the widmark equation
Recently, however, the National Academies of Science (NAS), in their report Strengthening Forensic Science in the United States: A Path Forward, recognized that “methods for measuring the level of blood alcohol in an individual..do so only within a confidence interval of possible values.” By continuing to report BAC results as a single numerical value without accounting for the uncertainty associated with the metabolic process and calculations precludes objective interpretation of, and testimony concerning, the result which interferes with the quest for truth in the courtroom and the jury’s ability to execute justice.In the last few months, courts have recognized this and have decided blood and breath test results without a measure of uncertainty are inadmissible under Evidence Rules (ER) 702 and ER 403.To allow the test value into evidence without stating a confidence level violates ER 403.The probative value of this evidence is substantially outweighed by its prejudicial value.Many jurisdictions have imposed statutory law defining alcohol intoxication as having a blood alcohol concentration (BAC) of 0.080g/dl or greater.Because of this, forensic toxicologists are frequently faced with the question “What was the BAC of the defendant at the time he/she was operating the vehicle?
Higher ethanol concentrations in the gastrointestinal tract cause a greater concentration gradient and therefore hasten the rate of absorption. Peak blood-alcohol levels can vary between different types of alcoholic beverages. As fat constitutes a higher proportion of the body weight in women than in men, the resultant volume of distribution of ethanol in women is lower than that of men. D., Page 251-252, Harcourt Brace Jovanovich, Philadelphia (1992)). Widmark, Principles & Applications of Medicalegal Alcohol Determinations (Scitran, Santa Barbara, CA, trans.)(Biomedical Pubs.: Davis, CA 1981). Watson published the following values for "r" in Prediction of Blood Alcohol Concentration in Human Subjects: Updating the Widmark Equation, 42:7 J. Therefore this court holds that the result of the blood test in this case is not admissible under ER 403 in the absence of a scientifically determined confidence level.The question many toxicologists now ask is “How can a measure of uncertainty be included with extrapolated BAC results?Ethanol is absorbed primarily in the small intestine. Dubowski, Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects, J. This is consistent with the higher standard of reasonable doubt.Although there is some absorption from the stomach, it is significantly slower than that from the intestine.