Alcohol Metabolism and Forensic Testing
Injury Classification
Injuries are often classified based on severity and type:
Cases with Craniocerebral Injury: These are due to direct collision of a portion of the vehicle on the head or, more frequently, the impact of the head against the ground or other obstacle. They have high mortality.
Cases with Severe Skeletal Lesions of the Trunk: Characterized by the absence of visceral injuries. Most are caused by motor vehicles, whose large kinetic energy and relatively light weight cause their action to be absorbed by the skeleton.
Cases with Severe Fractures of the Head, Trunk, and Limbs, Accompanied by Alterations of Multiple Organs: This category comprises injuries from animal-drawn vehicles, high-mass motor vehicles, and rail accidents.
Special Cases: Those in which death occurs late due to infectious or hemorrhagic complications.
Alcohol Metabolism
Absorption: Alcohol is a liquid fuel from the fermentation of sugary substances, starch, and cellulose. It is the active component of alcoholic or spirituous beverages. Alcohol absorption occurs primarily via the gastrointestinal tract. Absorption through the mouth and colon are very small and negligible.
Factors that Modify Absorption:
- The presence of food in the stomach results in lower alcohol levels.
- The alcoholic beverage: Beverages that are between 10-30 degrees are absorbed more rapidly than beer or wine. Very high alcohol drinks delay gastric emptying.
- The manner of drinking the beverage: The same amount consumed quickly will produce a greater Blood Alcohol Concentration (BAC) than if consumed in multiple sips. Alcohol is absorbed into the bloodstream between 30 and 60 minutes after ingestion.
Alcohol Distribution and Elimination
Distribution: In the bloodstream, alcohol is distributed throughout the body since it is hydrophilic.
Elimination: Most alcohol is metabolized by the enzyme alcohol dehydrogenase and the peroxidase-catalase system. A small amount of the absorbed alcohol is eliminated unchanged in urine, exhaled air, etc.
The Blood Alcohol Curve
The blood alcohol curve is a representation that reflects the evolution of the concentration of alcohol in the blood over the time period following ingestion until total catabolism (destruction and disposal). The curve consists of three parts:
- A rapidly ascending phase, corresponding to the absorption phase. This part is completed in 30-60 minutes after alcohol ingestion if the subject is fasting, extending (up to 2 hours) if food has been consumed.
- A peak or plateau (distribution equilibrium): Distribution of alcohol in the body is characterized by the blood alcohol concentration stabilizing during this phase.
- A slowly descending line (elimination): Represents the disappearance of ethanol from blood, its duration being proportional to the amount of alcohol ingested.
Alcohol in Exhaled Air: Evaluation and Correlation
The ratio between the concentration of alcohol in arterial blood and exhaled air is 2280:1. This ratio means that the amount of alcohol in 2280 mL of exhaled alveolar air is the same as that in 1 mL of blood.
Variables Affecting Breath Alcohol Determination: The correlation between the concentrations of ethanol in air and blood samples is consistently observed when the subject is in the elimination phase. When you perform two measurements in exhaled air and the second is lower than the first, the subject is in the elimination phase.