Toxicology in Motor Vehicle Accidents

In all fatal motor vehicle accidents, a complete toxicologic screen for alcohol and drugs, and in certain circumstances carbon monoxide, should be performed on both drivers and passengers. Tests for alcohol alone are not sufficient. Drugs tested for should include alcohol; carbon monoxide; acid, basic, and neutral drugs. Marijuana testing is optional. In select cases, analysis for opiates is indicated.

In 1999, 38% of traffic fatalities were alcohol related compared with 49% in 1989.12 The intoxication (blood alcohol of 0.10 g/dL or greater) rates for

Figure 9.14 Brake pedal with imprint of sole of shoe.

drivers in fatal crashes were: 17% passenger cars, 20% light trucks, 28% motorcycles, and 1% for large trucks.

At least 10-15% of drivers involved in automobile accidents will be under the influence of other drugs, either illicit or prescribed.1 Whether a drug is a cause of an accident, either wholly or in part, can be decided only by individual analysis of a case. Drug testing on passengers is recommended for two reasons — first, a "passenger" occasionally turns out to have been the driver; second, the presence of a drug or alcohol in a passenger often reflects the toxicologic status of the driver.

Often victims of motor vehicle accidents do not die immediately and are transported to a hospital. Here, intravenous fluids are started and massive blood transfusions begun. Prior to instituting a transfusion, blood is virtually always drawn for type and cross matching. Unused blood for this purpose is retained in the blood bank for at least 7 d. Thus, it is usually possible to obtain original, pre-transfusion blood for toxicologic analysis within 1 week of admission to a hospital.

If, in spite of the transfusions and medical attention, the victim dies within a few hours of admission, toxicologic screens should still be performed on blood and vitreous fluid removed at autopsy. In spite of massive transfusions, we have been able to document elevated or intoxicating levels of alcohol in the blood in many people. This is because alcohol, being water soluble, distributes itself throughout the body of a drinker. When he is then transfused, the alcohol diffuses back into the blood from water in the tissue in an attempt to equalize the concentrations. Vitreous is valuable in that it reflects alcohol and drug levels 1-2 h prior to death and is essentially unaffected by the transfusions.

Carbon monoxide levels should be performed in most motor vehicle deaths, since occasionally death might be caused by, or the accident precipitated by, acute carbon monoxide poisoning. The source of the carbon monoxide is usually a defective exhaust system in the vehicle.17

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