Retrograde Extrapolation in Los Angeles DUI Cases

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A more recent study of the validity of retrograde extrapolation in DUI investigations concludes that the process is a "dubious practice." Jones, et al., Peak Blood-Alcohol Concentration and the Time of Its Occurrence After Rapid Drinking on an Empty Stomach, 36(2) Journal of Forensic Sciences 376 (1991). In that study, researchers had a group of men aged 20 to 60 fast overnight and then consume either a shot of whiskey or a "screwdriver" cocktail. Subsequent blood analysis indicated that maximum blood-alcohol concentration among the cocktail drinkers was reached within 15 minutes of consumption. Among the whiskey drinkers, however, peak concentration was reached much later and varied considerably: 72 percent of the men reached peak BACs within 45 minutes, and 95 percent within 75 minutes.

The scientists noted that patterns of alcohol absorption vary widely among individuals and may depend on such factors as "the drinking pattern, the type of beverage consumed, the fed or fasted state, the nature (liquid or solid) and composition (fat, protein, or carbohydrate) of foodstuff in the stomach, the anatomy of the gastrointestinal canal, and the mental state of the subject."

See also a study entitled Physiological Variations in Blood Ethanol Measurements During the Post-Absorptive State, 30(5) Journal of the Forensic Science Society 273 (1990), where blood alcohol concentrations varied erratically even when measured at three to five minute intervals.

There is an expensive but very effective way of demonstrating for the jury in a Los Angeles DUI trial the fallacies of retrograde extrapolation and uniform or "average" rates of absorption and elimination: Have the DUI defendant tested by a recognized blood-alcohol expert. The expert can administer a known quantity of alcohol to the defendant, then test him every five minutes or so on a breath machine. The resulting data - illustrated perhaps on a graph - will reflect anything but the predictable and linear curve presumed by the prosecution.

Should the Los Angeles DUI lawyer encounter the argument that such tests are not relevant to conditions at the time of the arrest, consider having the defense expert read and testify concerning an article that appeared in the British journal of Clinical Pharmacology. Finch, Kendall and Mitchard, An Assessment of Gastric Emptying by Breathalyser, British Journal of Clinical Pharmacology 233 (1974). (See also O'Neil, Williams, and Dubowski, Variability in Blood Alcohol Concentrations: Implications for Estimating Individual Results, 44(2) Journal of Studies on Alcohol 222 (1983)). This article found that the ethanol concentration time curve was very reproducible for any given individual - that is, the DUI defense expert's tests will closely replicate conditions at the time of testing by the officer. In fact, testing a DUI defendant in a manner in which he serves as his own control is considerably more effective - and relevant - than comparing him to some fictional "average" person.

This method can also be effectively used in a Los Angeles DUI trial in estimating the actual blood-alcohol level at the time of driving based on testimony of the defendant and/or witnesses as to actual observed alcohol consumption.

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