photo by Billy Wilson Photography
Breath/blood alcohol concentration (BAC) also known as blood alcohol level and blood ethanol concentration is the amount of alcohol in a person’s breath or bloodstream. Typically this measurement is converted to a percentage such as 0.10 percent, this shows that 1/10 of a percent of a person’s blood is alcohol. Since alcohol in the bloodstream travels directly to the brain, cognitive activities are usually affected. This results in high risk of injuries such as the risk of vehicle crash when a person drives under the influence of alcohol.
Current there are several different units in use around the world to define BAC. Each of these is defined as either a mass of alcohol per mass of blood or mass of alcohol per volume of blood.1 millilitre of blood is almost equivalent to 1.06 grams of blood. As a result, units by volume are similar but not identical to units by mass. In the United States, concentration unit of 1percent w/v or 1 g per 100 ml is commonly used. This should never be confused with the amount of alcohol measured on the breath using devices such as the Breathalyzer. The concentration of alcohol measured on the breath is generally accepted as proportional to the amount of alcohol in the blood at a rate of 1:2100.
For purposes of enforcing the law, blood alcohol level is used to define intoxication and offers a rough measure of impairment. Though the degree of impairment may vary among individuals with similar blood alcohol content, it can be measured objectively. This makes it legally enforceable and difficult to contest in court. In most countries, the law prohibits operation of heavy machinery or motor vehicles above prescribed levels of blood alcohol content. In addition operation of aircrafts and boats is also regulated.
Breath alcohol testing assumes that the test is post-absorptive. This means that the absorption of alcohol in the subject’s body is incomplete. If the subject is still absorbing alcohol, the body has not yet attained a state of equilibrium where the concentration of alcohol is uniform throughout the body. Many forensic alcohol experts reject test results during this period as the amounts of alcohol in the breath do not accurately reflect a true concentration in the blood.
When a person drinks alcohol, it is absorbed throughout the gastrointestinal tract, however absorption occurs more slowly in the stomach compared to the small and large intestine. As a result alcohol consumed with food is absorbed slower since it spends more time in the stomach. The alcohol passes to the liver where it undergoes metabolism before entering the bloodstream and travelling to the brain.
Studies have found that the effects of alcohol affects many critical cognitive functions such as driving .This includes eye-hand coordination, information processing and decision making. Though it is not yet fully understood to what extent any of these functions contribute to driving, evidence from controlled case studies of drivers involved in crashes indicate that at BACs above 0.08 percent, the risk of a crash increases sharply.
At blood alcohol level 0.02 -0.039 percent, a person experiences slight euphoria, feels relaxed but no loss of coordination occurs. When the concentration reaches 0.06-0.099 percent, there is slight impairment of motor coordination and loss of judgment. At 0.160-0.199 percent nausea and dysphoria dominate. If the alcohol concentration goes above 0.3 percent, alcohol poisoning, loss of consciousness and coma may occur. Death may also occur due to respiratory arrest.