Blood alcohol content
Blood alcohol content | |
---|---|
Synonyms | Blood alcohol concentration, blood ethanol concentration, blood alcohol level, blood alcohol |
LOINC | 5639-0, 5640-8, 15120-9, 56478-1 |
Blood alcohol content (BAC), also called blood alcohol concentration or blood alcohol level, is a measurement of
Effects by alcohol level
At BAC 0.01–0.05%, people may experience mild relaxation and reduced social inhibition, along with impaired judgment and coordination. At BAC 0.06–0.20%, effects can include emotional swings, impaired vision, hearing, speech, and motor skills. The NIAAA defines the term "binge drinking" as a pattern of drinking that brings a person's blood alcohol concentration (BAC) to 0.08 grams percent or above.[5]
Beginning at a BAC greater than 0.2%, people may experience urinary incontinence, vomiting, and symptoms of alcohol intoxication. At a BAC greater than 0.3%, people may experience total loss of consciousness and show signs of severe alcohol intoxication. A BAC of 0.4% or higher is potentially fatal and can result in a coma or respiratory failure.[6][7] The magnitude of sensory impairment may vary in people of differing weights.[8]
Estimation
Direct measurement
Blood samples for BAC analysis are typically obtained by taking a venous blood sample from the arm. A variety of methods exist for determining blood-alcohol concentration in a blood sample.
By breathalyzer
The amount of alcohol on the breath can be measured, without requiring drawing blood, by blowing into a breathalyzer, resulting in a breath alcohol content (BrAC). The BrAC specifically correlates with the concentration of alcohol in arterial blood, satisfying the equation BACarterial = BrAC × 2251 ± 46. Its correlation with the standard BAC found by drawing venous blood is less strong.[12] Jurisdictions vary in the statutory conversion factor from BrAC to BAC, from 2000 to 2400. Many factors may affect the accuracy of a breathalyzer test,[13] but they are the most common method for measuring alcohol concentrations in most jurisdictions.[14]
By intake
Blood alcohol content can be estimated by a model developed by Swedish professor Erik Widmark in the 1920s.
where:
- EBAC is the estimated blood alcohol concentration (in g/L)
- A is the mass of alcohol consumed (g).
- T is the amount time during which alcohol was present in the blood (usually time since consumption began), in hours.
- β is the rate at which alcohol is eliminated, averaging around 0.15 g/L/hr
- Vd is the volume of distribution (L); typically body weight (kg) multiplied by 0.71 L/kg for men and 0.58 L/kg for women
Examples:
- A 80 kg man drinks 2 US standard drinks (3 oz) of 40% ABV vodka, containing 14 grams of ethanol each (28 g total). After two hours:
- A 70 kg woman drinks 63 g of 40% ABV vodka, containing 21 grams of ethanol. After two hours:
The volume of distribution Vd contributes about 15% of the uncertainty to Widmark's equation[20] and has been the subject of much research. It corresponds to the volume of the blood in the body.[15] In his research, Widmark used units of mass (g/kg) for EBAC, thus he calculated the apparent mass of distribution Md or mass of blood in kilograms. He fitted an equation of the body weight W in kg, finding an average rho-factor of 0.68 for men and 0.55 for women. This ρm has units of dose per body weight (g/kg) divided by concentration (g/kg) and is therefore dimensionless. However, modern calculations use weight/volume concentrations (g/L) for EBAC, so Widmark's rho-factors must be adjusted for the density of blood, 1.055 g/mL. This has units of dose per body weight (g/kg) divided by concentration (g/L blood) - calculation gives values of 0.64 L/kg for men and 0.52 L/kg for women, lower than the original.
The elimination rate from the blood, β, is perhaps the more important parameter, contributing 60% of the uncertainty to Widmark's equation.[20] Similarly to ρ, its value depends on the units used for blood.[19] β varies 58% by occasion and 42% between subjects; it is thus difficult to determine β precisely, and more practical to use a mean and a range of values. The mean values for 164 men and 156 women were 0.148 g/L/h and 0.156 g/L/h respectively. Although statistically significant, the difference between sexes is small compared to the overall uncertainty, so Jones recommends using the value 0.15 for the mean and the range 0.10 - 0.25 g/L/h for forensic purposes, for all subjects.[23] Explanations for the gender difference are quite varied and include liver size, secondary effects of the volume of distribution, and sex-specific hormones.[24] Elaborating on the secondary effects, zero-order kinetics are not an adequate model for ethanol elimination; the elimination rate is better described by Michaelis–Menten kinetics. M-M kinetics are approximately zero-order above a BAC of 0.15-0.20 g/L, but below this value alcohol is eliminated more slowly and the elimination rate more closely follows first-order kinetics. This change in behavior was not noticed by Widmark because he could not analyze low BAC levels.[19] A 2023 study using a more complex two-compartment model with M-M elimination kinetics, with data from 60 men and 12 women, found statistically small effects of gender on maximal elimination rate and excluded them from the final model. Eating food in proximity to drinking increases elimination rate significantly.[25]
In terms of fluid ounces of alcohol consumed and weight in pounds, Widmark's formula can be simply approximated as[15]
for a man or
for a woman, where EBAC and β factors are given as g/dL (% BAC), such as a β factor of 0.0015% BAC per hour.[15]
By standard drinks
The examples above define a standard drink as 0.6
Drinks | Sex | Body weight | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
40 kg 90 lb |
45 kg 100 lb |
55 kg 120 lb |
64 kg 140 lb |
73 kg 160 lb |
82 kg 180 lb |
91 kg 200 lb |
100 kg 220 lb |
109 kg 240 lb | ||
1 | Male | – | 0.04 | 0.03 | 0.03 | 0.02 | 0.02 | 0.02 | 0.02 | 0.02 |
Female | 0.05 | 0.05 | 0.04 | 0.03 | 0.03 | 0.03 | 0.02 | 0.02 | 0.02 | |
2 | Male | – | 0.08 | 0.06 | 0.05 | 0.05 | 0.04 | 0.04 | 0.03 | 0.03 |
Female | 0.10 | 0.09 | 0.08 | 0.07 | 0.06 | 0.05 | 0.05 | 0.04 | 0.04 | |
3 | Male | – | 0.11 | 0.09 | 0.08 | 0.07 | 0.06 | 0.06 | 0.05 | 0.05 |
Female | 0.15 | 0.14 | 0.11 | 0.10 | 0.09 | 0.08 | 0.07 | 0.06 | 0.06 | |
4 | Male | – | 0.15 | 0.12 | 0.11 | 0.09 | 0.08 | 0.08 | 0.07 | 0.06 |
Female | 0.20 | 0.18 | 0.15 | 0.13 | 0.11 | 0.10 | 0.09 | 0.08 | 0.08 | |
5 | Male | – | 0.19 | 0.16 | 0.13 | 0.12 | 0.11 | 0.09 | 0.09 | 0.08 |
Female | 0.25 | 0.23 | 0.19 | 0.16 | 0.14 | 0.13 | 0.11 | 0.10 | 0.09 | |
6 | Male | – | 0.23 | 0.19 | 0.16 | 0.14 | 0.13 | 0.11 | 0.10 | 0.09 |
Female | 0.30 | 0.27 | 0.23 | 0.19 | 0.17 | 0.15 | 0.14 | 0.12 | 0.11 | |
7 | Male | – | 0.26 | 0.22 | 0.19 | 0.16 | 0.15 | 0.13 | 0.12 | 0.11 |
Female | 0.35 | 0.32 | 0.27 | 0.23 | 0.20 | 0.18 | 0.16 | 0.14 | 0.13 | |
8 | Male | – | 0.30 | 0.25 | 0.21 | 0.19 | 0.17 | 0.15 | 0.14 | 0.13 |
Female | 0.40 | 0.36 | 0.30 | 0.26 | 0.23 | 0.20 | 0.18 | 0.17 | 0.15 | |
9 | Male | – | 0.34 | 0.28 | 0.24 | 0.21 | 0.19 | 0.17 | 0.15 | 0.14 |
Female | 0.45 | 0.41 | 0.34 | 0.29 | 0.26 | 0.23 | 0.20 | 0.19 | 0.17 | |
10 | Male | – | 0.38 | 0.31 | 0.27 | 0.23 | 0.21 | 0.19 | 0.17 | 0.16 |
Female | 0.51 | 0.45 | 0.38 | 0.32 | 0.28 | 0.25 | 0.23 | 0.21 | 0.19 | |
Subtract approximately 0.01 every 40 minutes after drinking. |
By training
If individuals are asked to estimate their BAC, then given accurate feedback via a breathalyzer, and this procedure is repeated a number of times during a drinking session, studies show that these individuals can learn to discriminate their BAC, to within a mean error of 9 mg/100 mL (0.009% BAC).[27] The ability is robust to different types of alcohol, different drink quantities, and drinks with unknown levels of alcohol. Trained individuals can even drink alcoholic drinks so as to adjust or maintain their BAC at a desired level.[28] Training the ability does not appear to require any information or procedure besides breathalyzer feedback, although most studies have provided information such as intoxication symptoms at different BAC levels. Subjects continue to retain the ability one month after training.[29]
Post-mortem
After fatal accidents, it is common to check the blood alcohol levels of involved persons. However, soon after death, the body begins to putrefy, a biological process which produces ethanol. This can make it difficult to conclusively determine the blood alcohol content in autopsies, particularly in bodies recovered from water.[30][31][32][33] For instance, following the 1975 Moorgate tube crash, the driver's kidneys had a blood alcohol concentration of 80 mg/100 mL, but it could not be established how much of this could be attributed to natural decomposition.[34] Newer research has shown that vitreous (eye) fluid provides an accurate estimate of blood alcohol concentration that is less subject to the effects of decomposition or contamination.[35]
Units of measurement
BAC is generally defined as a fraction of weight of alcohol per volume of blood, with a
Sign | Units | Used in |
---|---|---|
1 percent (%), 1 g%[19] | 1 g/dL = 1 cg/mL = 10 g/L = 1 g/100 mL | US, Australia,[19][37] Canada[38] |
1 per mille (‰)[a] | 1 g/L = 1 mg/mL | Austria, Belgium, France, Germany, Spain,[19] Bulgaria, Czech Republic, Latvia, Lithuania, Netherlands, Poland, Portugal, Romania, Russia, Slovenia, Sweden, Switzerland, Turkey[citation needed] |
1 mg%[19] | 1 mg/dL = 0.01 g/L = 1 mg/100 mL | United Kingdom[40] Ireland, Canada, New Zealand[19] |
It is also possible to use other units, but these have become uncommon. For example, in the 1930s Widmark measured alcohol and blood by mass, and thus reported his concentrations in units of g/kg or mg/g, weight alcohol per weight blood. 1 mL of blood has a mass of approximately 1.055 grams, thus a mass-volume BAC of 1 g/L corresponds to a mass-mass BAC of 0.948 mg/g. Sweden, Denmark, Norway, Finland, Germany, and Switzerland use mass-mass concentrations in their laws,[19] but this distinction is often skipped over in public materials.[41]
In pharmacokinetics, it is common to use the amount of substance, in moles, to quantify the dose. As the molar mass of ethanol is 46.07 g/mol, a BAC of 1 g/L is 21.706 mmol/L.[42]
Legal limits
For purposes of law enforcement, blood alcohol content is used to define intoxication and provides a rough measure of impairment. Although the degree of impairment may vary among individuals with the same blood alcohol content, it can be measured objectively and is therefore legally useful and difficult to contest in court. Most countries forbid operation of motor vehicles and heavy machinery above prescribed levels of blood alcohol content. Operation of boats and aircraft is also regulated. Some jurisdictions also regulate bicycling under the influence. The alcohol level at which a person is considered legally impaired to drive varies by country.
Test assumptions
Extrapolation
Retrograde extrapolation is the mathematical process by which someone's blood alcohol concentration at the time of driving is estimated by projecting backwards from a later chemical test. This involves estimating the absorption and elimination of alcohol in the interim between driving and testing. The rate of elimination in the average person is commonly estimated at 0.015 to 0.020 grams per deciliter per hour (g/dL/h),[43] although again this can vary from person to person and in a given person from one moment to another. Metabolism can be affected by numerous factors, including such things as body temperature, the type of alcoholic beverage consumed, and the amount and type of food consumed.
In an increasing number of states, laws have been enacted to facilitate this speculative task: the blood alcohol content at the time of driving is legally presumed to be the same as when later tested. There are usually time limits put on this presumption, commonly two or three hours, and the defendant is permitted to offer evidence to rebut this presumption.
Forward extrapolation can also be attempted. If the amount of alcohol consumed is known, along with such variables as the weight and sex of the subject and period and rate of consumption, the blood alcohol level can be estimated by extrapolating forward. Although subject to the same infirmities as retrograde extrapolation—guessing based upon averages and unknown variables—this can be relevant in estimating BAC when driving and/or corroborating or contradicting the results of a later chemical test.
Metabolism
Alcohol is absorbed throughout the gastrointestinal tract, but more slowly in the stomach than in the small or large intestine. For this reason, alcohol consumed with food is absorbed more slowly, because it spends a longer time in the stomach.
Alcohol is removed from the bloodstream by a combination of metabolism, excretion, and evaporation. Alcohol is metabolized mainly by the group of six enzymes collectively called alcohol dehydrogenase. These convert the ethanol into acetaldehyde (an intermediate more toxic than ethanol). The enzyme acetaldehyde dehydrogenase then converts the acetaldehyde into non-toxic acetic acid.
Many physiologically active materials are removed from the bloodstream (whether by metabolism or excretion) at a rate proportional to the current concentration, so that they exhibit exponential decay with a characteristic half-life (see pharmacokinetics). This is not true for alcohol, however. Typical doses of alcohol actually saturate the enzymes' capacity, so that alcohol is removed from the bloodstream at an approximately constant rate. This rate varies considerably between individuals. Another sex-based difference is in the elimination of alcohol. For females, the concentration of alcohol in breast milk produced during lactation is closely correlated to the individual's blood alcohol content.[46] People under 25, women,[47] or people with liver disease may process alcohol more slowly. Falsely high BAC readings may be seen in patients with kidney or liver disease or failure.[citation needed]
Such persons also have impaired acetaldehyde dehydrogenase, which causes acetaldehyde levels to peak higher, producing more severe
Currently, the only known substance that can increase the rate of alcohol metabolism is fructose. The effect can vary significantly from person to person, but a 100 g dose of fructose has been shown to increase alcohol metabolism by an average of 80%. Fructose also increases false positives of high BAC readings in anyone with proteinuria and hematuria, due to kidney-liver metabolism.[48]
The peak of blood alcohol level (or concentration of alcohol) is reduced after a large meal.[44]
Highest levels
There have been reported cases of blood alcohol content higher than 1%:
- In 1982, a 24-year-old woman was admitted to the UCLA emergency room with a serum alcohol content of 1.51%, corresponding to a blood alcohol content of 1.33%. She was alert and oriented to person and place and survived.[49] Serum alcohol concentration is not equal to nor calculated in the same way as blood alcohol content.[50]
- In 1984, a 30-year-old man survived a blood alcohol concentration of 1.5% after vigorous medical intervention that included dialysis and intravenous therapy with fructose.[51]
- In 1995, a man from Wrocław, Poland, caused a car accident near his hometown. He had a blood alcohol content of 1.48%; he was tested five times, with each test returning the same reading. He died a few days later of injuries from the accident.[52]
- In 2004, an unidentified Taiwanese woman died of alcohol intoxication after immersion for twelve hours in a bathtub filled with 40% ethanol. Her blood alcohol content was 1.35%. It was believed that she had immersed herself as a response to the SARS epidemic.[53]
- In South Africa, a man driving a Queenstown in Eastern Cape. His blood had an alcohol content of 1.6%. Also in the vehicle were five boys and a woman, who were also arrested.[54][dubious]
- On 26 October 2012, a man from Gmina Olszewo-Borki, Poland, who died in a car accident, recorded a blood alcohol content of 2.23%; however, the blood sample was collected from a wound and thus possibly contaminated.[52]
- On 26 July 2013 a 30-year-old man from Alfredówka, Poland, was found by Municipal Police Patrol from Nowa Dęba lying in the ditch along the road in Tarnowska Wola. At the hospital, it was recorded that the man had a blood alcohol content of 1.374%. The man survived.[55][56]
Notes
References
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When food is ingested, the pyloric valve at the bottom of the stomach will close in order to hold food in the stomach for digestion and thus keep the alcohol from reaching the small intestine. The larger the meal and closer in time to drinking, the lower the peak of alcohol concentration; some studies indicate up to a 20% reduction in peak blood alcohol level.
Stress causes the stomach to empty directly into the small intestine, where alcohol is absorbed even faster.
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General and cited references
- Carnegie Library of Pittsburgh. Science and Technology Department. The Handy Science Answer Book. Pittsburgh: The Carnegie Library, 1997. ISBN 978-0-7876-1013-5.
- Perham, Nick; Moore, Simon C.; Shepherd, Jonathan; Cusens, Bryany (2007). "Identifying drunkenness in the night-time economy". Addiction. 102 (3): 377–80. PMID 17298644.
- Taylor, L., and S. Oberman. Drunk Driving Defense, 6th edition. New York: Aspen Law and Business, 2006. ISBN 978-0-7355-5429-0.