Blood alcohol content (BAC) is of obvious importance in a driving under the influence (DUI / DWI) arrest. Where someone is accused of drinking and driving, the blood or breath alcohol level will prove to be some of the most damning – or exonerating – evidence against them.
For those who are arrested for suspicion of drunk driving with a chemical test result that exceeds the legal limit – .08 percent in all 50 states – there are many ways to challenge the accuracy of these tests. A competent DUI / DWI criminal defense lawyer can launch a challenge to chemical test results, and help a driver fight a drunk driving case.
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However, even where it is conceded that the chemical test of the blood, breath or urine sample is accurate, these test results only reveal the subject’s alcohol level at the time of testing, not at the time of driving. It is the condition at the time of driving that is of ultimate concern in DUI / DWI cases; the chemical test is only relevant to the extent that it allows those concerned to look backwards in time and estimate alcohol level at the time of driving.
This is a point that is so important as to be worthy of repeating: Because it is illegal to drive with a BAC that exceeds the legal limit, the chemical test results are ONLY relevant to the extent that they allow those concerned to look backwards in time to determine alcohol levels at the time of driving, NOT at the time of testing. Since there is usually significant delay between the time of driving and the time of testing in a DUI / DWI arrest, this is a critical area of concern.
Many authoritative articles have been written on the subject, most notably those by Kurt Dubowski and A.W. Jones. Because of the variables in the subjects taking the test, such as metabolic rate, as well as variations in conditions, such as stomach contents and drinking patterns, it is exceptionally difficult to look backward in time to pinpoint BAC at an earlier time. This difficulty increases with the passage of time, and becomes increasingly speculative. Obviously, for the DUI / DWI criminal defense attorney whose stock-in-trade is highlighting reasonable doubt as to any element of the criminal case, this becomes increasingly valuable.
Alcohol takes time to be absorbed into the body. When a person drinks alcohol, it goes first into the stomach, and then into the small intestine, which is where most of the absorption takes place. The type of alcohol consumed, as well as the stomach contents prior to and during drinking, will impact the speed at which absorption takes place.
Elimination of alcohol begins immediately; however, the body cannot eliminate alcohol as quickly as it is absorbed. This is how an elevated alcohol level is created in the first place. It is similar to a bathtub that has no stopper but a slow drain – as water flows into the tub, it is draining at the same time, but because it flows in faster than it flows out, the level increases. It is the same with alcohol absorption in the human body.
After drinking stops, absorption continues. This will result in an increasing alcohol level, followed by a peak or plateau. This peak or plateau level is where there is perfect equilibrium – absorption and elimination occur at the same rate, so the alcohol level flattens out and is consistent for a period of time, usually 15 to 45 minutes, depending upon stomach contents and metabolic rate.
After the peak or plateau period, the individual will enter into the pure elimination phase. Here, so long as no additional alcohol is consumed, the alcohol level will steadily decrease at a rate of approximately .02 per hour. This, too, will vary widely from person to person and in situation to situation.
When this is represented graphically, it looks like a bell curve. Even where the chemical test is above the legal limit, it begs the question of where on the curve the subject was at the time of driving. Another issue that frequently comes up in breath testing cases relates to overestimation of true blood alcohol level where breath testing is performed in the absorptive phase (the first half of the bell curve). There is a wealth of scientific literature in the field that demonstrates that breath testing during the absorptive phase overestimates true alcohol levels by at least 40 percent, and by as much as 100 percent.
Alcohol absorption and elimination can be affected greatly by drivers’ metabolic rates, eating patterns, fatigue levels, and many other factors. Typically, a police officer’s roadside investigation is not thorough enough to effectively address these issues. This information is extremely valuable in the hands of a well-trained criminal defense lawyer, who can devastate the prosecutions DUI / DWI case by effective cross-examination on these issues.
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