“Rising Blood Level Alcohol” Defense

miranda_rightsWhat matters ultimately in a DUI case is the alcohol concentration at the time of driving rather than at the time of the alcohol test. The law presumes if the alcohol test occurs within three hours of driving, the driver is presumed to have a .08% or more by weight of alcohol in his/her blood at the time of driving IF the person had at the time of the test a .08% or more by weight of alcohol in his/her blood.

DUI defense attorneys therefore want to use the rising blood level alcohol defense: the driver’s blood level alcohol was under .08 at the time of driving but, between the DUI stop to the time of the breath or blood test at the station, rose to the level of .08% or higher (with the caveat that the DUI defense attorney does not concede the validity of the alcohol test result itself).

Absorption of alcohol

Thus, the analysis of time and the absorption of alcohol are critical elements in a DUI case.

Ingestion of alcohol does not immediately impact a person’s brain. Impairment takes time. Alcohol does not impair a driver until its effects impact the brain. To reach the brain, alcohol must be absorbed through the stomach and small intestine into the blood. This absorption will be complete when equilibrium exists (the same amount of blood alcohol exists in all parts of the body).   The absorption of alcohol varies from person to person, and is affected by food in a person’s body. Typically, after a person consumes alcohol, the presence of alcohol can be detected as early as five minutes after the drink. Absorption, however, is not complete for 45 minutes to 2 hours after consumption and may be delayed for additional time by food in the gastro intestinal tract.

Absorption is different between individuals and in general, between men and women. In fact, the same person can experience different rates of absorption.

Elimination of alcohol

Once absorbed, alcohol is eliminated by the liver. The rate of elimination varies from person to person. This elimination is also called “burn off.” Prosecution experts in alcohol cases presume that the “average person” burns off or eliminates alcohol at the rate of .15% to .20% per hour.

The prosecution assumes that at the time of testing, a driver has fully absorbed the alcohol and thus, the driver’s blood alcohol was “falling” at the time of testing. The reason that the prosecution presumes that the driver had reached absorption and thus had a falling blood alcohol level at the time of testing is that such a presumption then allows the prosecution to posit that at the time of driving (the critical moment for blood alcohol), the driver’s blood alcohol reading was HIGHER than at the time of the test.

The defense in a DUI case wants to show that at the time of testing, the driver was still absorbing alcohol because in such a case, the blood alcohol reading will then be artificially elevated and skewed.

“Retrograde extrapolation”

The prosecution will try to use a pseudo scientific formula, “retrograde extrapolation,” to calculate the driver’s blood alcohol at the time of driving based on the test result. “Retrograde extrapolation” is nothing more than an estimate, rather than a scientific certainty, of what the driver’s blood alcohol was at the time of driving. It is fraught with error because, as in other areas of DUI testing, it involves assumptions that often are not true.

However, DUI defense attorneys should demonstrate the many fallacies of “retrograde extrapolation.” First, as indicated above, “retrograde extrapolation” depends on the assumption that absorption of alcohol is complete. It further presumes that alcohol levels rise (and fall) in a steady, linear manner. It further assumes that the elimination of alcohol from the body is steady, as well as the same, for all individuals.

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