Distribution of ethanol between blood and alternative biological specimens in life and after death. Part I: Importance of body water.

Measuring the concentration of ethanol in blood and other biological specimens provides important forensic information whenever alcohol-related crimes and alcohol-related deaths are investigated. A dose-response relationship holds between a person's blood-alcohol concentration (BAC) and the degree of impairment of the central nervous system (CNS): When their BAC reaches 0.3-0.5 g/L, most people feel less inhibited and experience mild euphoria, while heavy drinking resulting in a BAC of 3.0-4.0 g/L is sufficient to cause death by depression of respiratory centers in the brainstem. After the consumption of alcoholic beverages, the ethanol they contain is distributed into the total body water (TBW) compartment without significant binding to plasma proteins or other macro-molecules. When absorption and distribution are complete, the concentrations of ethanol in blood and other body fluids and tissues depend on their relative water contents. Other factors influencing BAC are the dose ingested and the rate of drinking, as well as the person's age, sex, body weight, ethnicity, and degree of adiposity. Concentration-time profiles of ethanol in the blood also depend upon the route of administration (oral or intravenous) and upon whether ingested as a bolus dose or through repetitive drinking over several hours. Factors influencing gastric emptying are also important considerations, such as whether the ethanol was consumed on an empty stomach or after a meal. Blood is the most important biological specimen in forensic casework, because BAC serves as a proxy for the concentration of ethanol influencing the brain. This forensic science review deals with the distribution of ethanol between the blood and the total body water compartment, and the role played by body composition (obesity), which is an important consideration when blood-alcohol calculations are performed.