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Interpretation of Measured Alcohol Levels


The determination of blood ethanol concentration in a deceased pilot is an important part of the accident investigation. The finding of an elevated blood alcohol level in such a case may have significant implications, both medico-legal and social. It is therefore important to ensure that the finding of an elevated blood alcohol concentration is valid.

It is known that micro-organisms involved in the process of putrefaction after death can produce alcohol, usually a mixture of ethanol and other volatile substances. This process occurs when a body is not refrigerated soon after death and is hastened by environmental conditions such as high temperatures and when the body has been traumatised.

Older methods of analysis could not distinguish between ethanol and mixtures of other volatile compounds. Current methodology (gas chromatography) can isolate ethanol and identify other substances.

There is a range of specimens in which ethanol can be measured. Their suitability for analysis can be determined by microbiological studies although this would not be routinely performed in most laboratories.

Medico-legal and forensic implications are associated with a 'blood alcohol concentration'.49 It therefore seems most useful to measure the ethanol level in a specimen of blood, but this may not always be available depending on the state of the body. Vitreous is the next specimen of choice, and valid conclusions regarding the ingestion of alcohol can usually be made based on the results of its analysis.

Urine analysis may also be helpful, particularly in conjunction with blood and vitreous. Comparison of levels of these three specimens is probably the ideal means of interpreting blood alcohol concentrations. If none of these specimens is available, resort can be made to other organ and tissue samples but there are difficulties in both methodology and interpretation of results relating any alcohol present to ingested ethanol.

Ethanol in gastric contents generally indicates recent ingestion, but the rapid absorption of ethanol and post-mortem diffusion from the stomach may limit the usefulness of analysis of gastric contents.

The presence of volatile compounds in addition to ethanol (seen by gas chromatography methods) may suggest post-mortem production by micro-organisms but also needs to be interpreted cautiously.

It is possible to measure parameters which are associated with or indicate ethanol consumption. These are qualitative only and do not enable the blood ethanol concentration to be calculated or estimated. They have applications in a clinical setting where they address the issue of alcohol consumption in previous days. This is not usually the main issue in a fatal aviation accident investigation, where the "bottle to throttle" rule applies, and the issue is what factors were influencing the pilot's capacity to fly the aircraft. Two of these measurements, ethyl glucuronide and the 5-HTOL: 5-HIAA may have some application in the future of fatal aviation accident investigation but they are not currently performed routinely.

Type: Research and Analysis Report
Publication date: 12 October 2005
ISBN: 1 921092 21 1
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Last update 07 April 2014
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