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Blood alcohol concentration

blood alcohol concentration (GB)

Designation (BAK) for the amount of alcohol contained in venous blood, expressed in milligrams per gram or per thousand (1 per thousand = 1 g alcohol in 1 kg blood or 1 mg/g). It is measured in serum (blood without blood cells and coagulation factors) and converted to blood content. The enzyme ADH (alcohol dehydrogenase) is used to determine the blood alcohol content. In 1922, the Swedish chemist Prof. Erik Widmark (1889-1945) developed the "Widmark's formula", named after him, for the determination of BAK. In addition to Widmark's formula, there are other calculation methods (Seidel, Ullrich, Watson), also named after the "inventors", which take into account body weight and sex as well as body length and age. The Widmark formula is used as a basis for electronic BAK determination devices.

Using Widmark's formula, the blood alcohol content can be calculated with an accuracy of plus/minus 0.1 per thousand: c = A / (r * G)

  • c: blood alcohol content in per mille
  • A: alcohol ingested in grams
  • r: Distribution factor in the body (water in the body) = 0.7 for men and 0.6 for women
  • G: body weight in kilograms

Since alcohol is only water-soluble, it is not distributed in the bones and fatty tissue, so this body mass is not available. The factor is lower for women, as they have a higher body fat percentage on average. Men should also assume a correspondingly lower weight G if they are overweight, as body fat is not conducive to either distribution or alcohol reduction.

Amount of alcohol absorbed in grams = V * e * p
To calculate the mass of alcohol (A) in a liquid (beer, wine, spirits), the volume (V) of the beverage measured in decilitres must be multiplied by the alcoholic strength by volume (e) and the density (specific gravity) of alcohol (p = 0,8 kg/l or 0,08 g/cl). For a litre of wine (100 cl) of 12 % vol. alcoholic strength by volume, the 12 cl of alcohol present in this case corresponds to a weight of 96 g. Three glasses of cognac of 4 cl each give 12 cl of cognac (slightly less than "one eighth"), which, at 40% vol. of alcohol, gives 4.8 cl of alcohol weighing 38.4 g. To calculate the blood alcohol concentration, therefore, the quantity of the drink in cl must be multiplied by the alcohol content in vol% and then by 0.08. Two calculation examples:

A man with 85 kg and a woman with 70 kg enjoy three eighths of wine each (0.375 l = 37.5 cl) with 12% vol alcohol content: 37.5 * 12 * 0.08 = 36 g alcohol

reduced body weight = body weight in kg * distribution factor:
Man with 85 kg: 0.7 * 85 = 59.5 kg
Woman with 70 kg: 0.6 * 70 = 42.0 kg

Alcohol level = alcohol / reduced body weight
Man 36 g / 59.5 kg = 0.60‰ - best assumption 0.38‰
Woman 36 g / 42.0 kg = 0.86‰ - best guess 0.59‰

Any alcohol degradation is not taken into account in the first value. Neither does the fact that 10% and 30% (on average 20%) can be deducted from the quantity, as the alcohol is not completely absorbed by the body. Assuming these 20% as well as a reduction of 0.1‰ each, the "best assumption" results.

The alcohol consumed passes from the stomach (20%) and small intestine (80%) first into the bloodstream and then into body tissue (absorption). The distribution depends on the amount of blood (approx. 5 to 7l) and the body size or body surface area, the more extensive, the better the alcohol is distributed. However, as already mentioned, fatty tissue cannot absorb alcohol. This is why alcohol is distributed more in a tall, lean person and there is relatively less alcohol concentration in the blood compared to a small, fat person. The absorption process is relatively slow and, depending on the stomach contents, is not completed until one to two hours after the end of drinking. This amount is also known as residual alcohol.

The liver is the only organ that can break down the alcohol up to 90%, the rest is excreted via the kidneys with urine or sweat. The organ begins to break down alcohol at the earliest 15 minutes "after the first sip" and continues to do so in a linear fashion, independently of further consumption. The more someone is accustomed to alcohol, the higher the elimination rate. The human body breaks down 0.1 to 0.2‰ per hour. A thumb formula: Half a liter of beer (5% vol) or an eighth of wine (12% vol) with ~12 mg alcohol each will be eliminated in one to two hours. A faster breakdown of the residual alcohol is not possible through coffee consumption, increased exercise or sleep. See further information under Health.

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