Rising Blood Alcohol Levels
The prosecution in drunk driving cases always assumes that the absorptive phase of alcohol ingestion is completed before the time of testing - that is, that the DUI defendant was in the postabsorptive stage when he was tested on the breath machine. Thus the argument is made that the blood-alcohol concentration was falling at the time of testing - and, therefore, that the level was higher at the time of driving.
This assumption is fallacious for a number of reasons, such as food ingestion, pattern of drinking, and individual blood/breath partition ratio. The simple fact is that the DUI suspect may still be absorbing alcohol into his system when he is tested. In other words, his BAC may be rising- and the reading, therefore, maybe higher than the actual BAC at the time of driving.
In a recent study, researchers found that absorption continued for an average of 50 minutes after cessation of drinking. Tests taken with Intoxilyzer models 4011A, 4O11AS, and 5000 consistently overestimated the blood-alcohol levels during this time period when compared to analyzed blood samples. Giguiere and Simpson, Medicolegal Alcohol Determination: In Vivo Blood/ Breath Ratios as a Function of Time, Proceedings of the 27th Meeting of the International Association of Forensic Toxicologists 494 (October 1990).
A Las Vegas DUI lawyer should always determine from his client what the exact drinking pattern was on the night in question. In terms of a possible rising BAC defense, particular attention should be paid to what ingestion of alcohol took place in the one hour or so before the client began to drive (or, in an appropriate case, during the driving). Most DUI detentions occur within 15 minutes of the client entering the car; the blood-alcohol test commonly takes place an hour or so after this. Thus in most drunk driving cases the arrestee who had
one for the road is still absorbing alcohol at the time of the test - and even an accurate test result will he higher than the actual blood-alcohol concentration at the time of driving. Even if the suspect is not still absorbing alcohol into his system, his test BAC will almost certainly be higher than his driving BAC.
The mentioned 50-minute absorption period is, of course, an average; the actual period can vary from a half-hour to as long as three hours (see 5.1), and this can be extended by recent ingestion of food. Consequently, counsel representing a DUI client should not discount the possibility of a rising BAC curve even when the test was administered two or three hours after the driving.
Is the defendant in a DUI trial entitled to have the jury instructed as to his theory of a rising blood-alcohol level? This would certainly seem appropriate, and this was the holding in State v. Drown, 532 A.2d 575 (Vt. 1987). The defendant in that case established during cross-examination of the prosecution's expert that her level at the time of driving could have been as low as .085 percent, as opposed to the tested level of .147 percent. The trial judge refused the requested instruction, reasoning that it was only one of many possible theories. However, the appellate court reversed the conviction because
the court below failed to instruct on the defense theory, a substantial issue that was arguably supported by the evidence.
The claim that the DUI defendant's BAC was falling can, perhaps, be turned against the prosecution. One scientific study has concluded that impairment is greater during the rising phase of the BAC curve than during the falling. Nicholson, et al., Variability in Behavioral Impairment Involved in the Rising and Falling BAC Curve, Journal of Studies on Alcohol 349 (July 1992).