Determination of ethanol

Ethyl alcohol (ethanol, C ₂ H ₅ OH) has a sedative-hypnotic effect. When taken orally, ethanol, like methanol, ethylene glycol and other alcohols, is easily absorbed from the stomach (20%) and small intestine (80%) due to its low molecular weight and lipid solubility. The rate of absorption depends on the concentration: for example, in the stomach it is maximum at a concentration of approximately 30%. Ethanol vapors can be easily absorbed in the lungs. After taking ethanol on an empty stomach, the maximum concentration in the blood is achieved after 30 minutes. The presence of food in the intestine delays absorption. The distribution of ethanol in the tissues of the body occurs quickly and evenly. More than 90% of the ingested ethanol is oxidized in the liver, the rest is excreted through the lungs and kidneys (within 7-12 hours). The amount of alcohol oxidized per unit of time is approximately proportional to body weight or liver. An adult can metabolize 7-10 g (0.15-0.22 mol) of ethanol per hour.

Ethanol metabolism occurs mainly in the liver with the participation of two enzyme systems: alcohol dehydrogenase and the microsomal ethanol-oxidizing system (MEOS).

The major pathway of ethanol metabolism involves alcohol dehydrogenase, a Zn ²⁺ -containing cytosolic enzyme that catalyzes the conversion of alcohol to acetaldehyde. This enzyme is found primarily in the liver, but is also present in other organs (e.g., the brain and stomach). In men, a significant amount of ethanol is metabolized by gastric alcohol dehydrogenase. MEOS includes mixed-function oxidases. An intermediate product of ethanol metabolism involving MEOS is also acetaldehyde.

It is believed that at blood alcohol concentrations below 100 mg% (22 nmol/l) its oxidation is carried out predominantly by alcohol dehydrogenase, whereas at higher concentrations MEOS begins to play a more significant role. At present, it has not been proven that chronic alcohol consumption increases alcohol dehydrogenase activity, but it has been reliably established that MEOS activity increases. More than 90% of acetaldehyde formed from ethanol is oxidized in the liver to acetate with the participation of mitochondrial aldehyde dehydrogenase. Both reactions of ethanol conversion are NAD-dependent. NAD deficiency due to its consumption during alcohol intoxication can block aerobic metabolism and limit the conversion of the end product of carbohydrate and amino acid glycolysis - lactic acid. Lactate accumulates in the blood, causing metabolic acidosis.

The mechanism of action of alcohol on the central nervous system is unknown. However, it has been established that non-physiological concentrations of ethanol inhibit ion pumps responsible for the generation of electrical nerve impulses. As a result, alcohol suppresses the functions of the central nervous system, similar to other anesthetics. With alcohol intoxication, typical effects of an overdose of a sedative-hypnotic drug develop along with cardiovascular effects (vasodilation, tachycardia) and gastrointestinal irritation. The relationship between the concentration of ethanol in the blood and the clinical manifestations of intoxication is presented in Table 11-2. The lethal dose of ethanol with a single intake is from 4 to 12 g per 1 kg of body weight (on average, 300 ml of 96% ethanol in the absence of tolerance to it). Alcoholic coma develops when the concentration of ethanol in the blood is above 500 mg%, and death - above 2000 mg%.

The relationship between the concentration of ethanol in the blood and urine and clinical manifestations of intoxication

Ethanol concentration, mg%		Stage of alcohol intoxication	Clinical manifestations
Blood	Urine
10-50	10-70	Sober state	Weak impact on most people
40-100	30-140	Euphoria	Decreased self-control and reaction time (by 20%)
100-200	75-300	Excitation	Impaired coordination, loss of critical judgment, increased reaction time (by 100%)
200-300	300-400	Confusion	Disorientation, slurred speech, sensory disturbances, memory loss
300-400	400-500	Stupor	Impaired ability to stand or walk
More than 500	More than 600	Coma	Respiratory failure, all reflexes are suppressed
More than 2000	More than 2400	Death	Respiratory paralysis

Unsteadiness of gait, slurred speech, and difficulty performing simple tasks become apparent at plasma ethanol concentrations of approximately 80 mg%. For this reason, in a number of countries, this value serves as the threshold for prohibiting driving. Driving skill is impaired even at lower ethanol concentrations.

When determining the concentration of ethanol in blood serum, it should be borne in mind that it is 10-35% higher than in blood. When using the method for determining ethanol with alcohol dehydrogenase, other alcohols (e.g., isopropanol) can serve as substrates and cause interference, which leads to false positive results.

The degree of intoxication depends on three factors: the concentration of ethanol in the blood, the rate of increase in alcohol levels, and the time during which the elevated level of ethanol in the blood remains. The nature of consumption, the condition of the gastrointestinal mucosa, and the presence of drugs in the body also affect the degree of intoxication.

To assess the level of ethanol in the blood, the following rules must be used.

• The peak concentration of alcohol in the blood is reached 0.5-3 hours after taking the last dose.
• Every 30 g of vodka, glass of wine or 330 ml of beer increases the concentration of ethanol in the blood by 15-25 mg%.
• Women metabolize alcohol faster than men, and its concentration in the blood is 35-45% higher; during the premenstrual period, the concentration of ethanol in the blood increases faster and to a greater extent.
• Taking oral contraceptives increases the concentration of ethanol in the blood and increases the duration of intoxication.
• The concentration of ethanol in urine does not correlate well with its level in the blood, so it cannot be used to assess the degree of intoxication.
• In elderly people, intoxication develops faster than in young people.

The breath tests currently used to determine alcohol have their own characteristics and limitations. The concentration of ethanol in exhaled air is approximately 0.05% of the concentration in the blood, i.e. 0.04 mg% (0.04 mg/l) with a concentration in the blood of 80 mg% (800 mg/l), which is sufficient for its detection by breath tests.

Time to detect ethanol with breath tests

Type of alcohol	Dose, ml	Detection time, h
Vodka 40°	50	1.5
Vodka 40°	100	3.5
Vodka 40°	200	7
Vodka 40°	250	9
Vodka 40°	500	18
Cognac	100	4
Champagne	100	1
Cognac and champagne	150	5
Port	200	3.5
Port	300	4
Port	400	5
Beer 6°	500	0.75
Beer below 3.4°	500	Not defined

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