Describe the important features of blood alcohol testing
Answers
Blood alcohol content (BAC) is a measurement of alcohol intoxication used for legal or medical purposes. A BAC of 0.10 (0.10% or one tenth of one percent) means that there are 0.10 g of alcohol for every 100 ml of blood which is the same as 21.7 mmol/l. A BAC of 0.0 is sober, while in the United States 0.08 is legally intoxicated, and above that is very impaired. BAC levels above 0.40 are potentially fatal.
Estimation by intake
To calculate estimated peak blood alcohol concentration (EBAC), a variation, including drinking period in hours, of the Widmark formula was used. The formula is:
{\displaystyle EBAC=\left({\frac {0.806\times SD\times 1.2}{BW\times Wt}}-MR\times DP\right)\times 10}
where:
0.806 is a constant for body water in the blood (mean 80.6%),
SD is the number of standard drinks, that being 10 grams of ethanol each,
1.2 is a factor to convert the amount in grams to Swedish standards set by The Swedish National Institute of Public Health,
BW is a body water constant (0.58 for males and 0.49 for females),
Wt is body weight (kilogram),
MR is the metabolism constant (0.015 for males and 0.017 for females) and
DP is the drinking period in hours.
10 converts the result to permillage of alcohol
Regarding metabolism (MR) in the formula; females demonstrated a higher average rate of elimination (mean, 0.017; range, 0.014–0.021 g/210 L) than males (mean, 0.015; range, 0.013–0.017 g/210 L). Female subjects on average had a higher percentage of body fat (mean, 26.0; range, 16.7–36.8%) than males (mean, 18.0; range, 10.2–25.3%). Additionally, men are, on average, heavier than women but it is not strictly accurate to say that the water content of a person alone is responsible for the dissolution of alcohol within the body, because alcohol does dissolve in fatty tissue as well. When it does, a certain amount of alcohol is temporarily taken out of the blood and briefly stored in the fat. For this reason, most calculations of alcohol to body mass simply use the weight of the individual, and not specifically his/her water content. Finally, it is speculated that the bubbles in sparkling wine may speed up alcohol intoxication by helping the alcohol to reach the bloodstream faster.
Examples:
80 kg male drinking 3 standard drinks in two hours:
{\displaystyle EBAC=(0.806\cdot 3\cdot 1.2)/(0.58\cdot 80)-(0.015\cdot 2)=0.032534483\approx 0.033g/dL}
70 kg woman drinking 2.5 standard drinks in two hours:
{\displaystyle EBAC=(0.806\cdot 2.5\cdot 1.2)/(0.49\cdot 70)-(0.017\cdot 2)=0.036495627\approx 0.036g/dL}