forensics lecture 2- alcohol

Question 1

what is alcohol?

Answer 1

-Ethyl alcohol (ethanol) is clear, colourless and miscible with water.
-It contains by products and additives which give it colour and flavour.
-Alcohol is produced by fermentation from grapes/ cereal grains

Question 2

what is the pathway of absorption and distribution of alcohol?

Answer 2

mouth –> oesophagus –> stomach and small intestine –> circulatory system –> brain, kidneys, lungs and liver

Question 2

what are the factors affecting the rate of absorption?

Answer 2

-Quantity
-Concentration
-Contact time in GIT
-Food
-Stomach emptying

Question 2

what is the distribution of alcohol like?

Answer 2

-Rapid
-Distribution to all organs and body compartments in proportion to that compartments water content.
-Most organs and fluids are in constant equilibrium with blood.

Question 3

how does alcohol get eliminated from the body?

Answer 3

Metabolism - > 90%

Ethanol –> acetaldehyde –> Carbon dioxide + water

This reduces BAC by approximately 15mg/100ml - 18mg/100ml / Hour (0.015 - 0.018 % / Hour)

Question 4

what are the effects of alcohol dehydrogenase and aldehyde dehydrogenase?

Answer 4

CH3CH2OH + NAD+ –> CH3CHO + NADH+
alcohol dehydrogenase

CH3CHO + NAD+ + H2O –> CH3COO- + NADH+
aldehyde dehydrogenase

Question 5

what is road traffic act 1988?

Answer 5

An Act to consolidate certain enactments relating to road traffic with amendments to give effect to recommendations of the Law Commission and the Scottish Law Commission.

Question 6

what are the different sections of the road traffic act 1988?

Answer 6

Section 4(1) - driving a motor vehicle whilst unfit through drink or drugs

Section 4(2) - being in charge of a motor vehicle whilst unfit through drink or drugs

Section 5(1)(a) - driving a motor vehicle after consuming so much alcohol that the proportion in breath, blood or urine exceeds the prescribed limits.

Question 7

what are the legal limits of alcohol of England, Wales and Northern Ireland?

Answer 7

-80 mg / 100 ml in blood
-35 µg / 100 ml in breath
-107 mg / 100 ml in urine

Question 8

what are the legal limits of alcohol in Scotland?

Answer 8

-50 mg / 100 ml in blood
-22 µg / 100 ml in breath
-67 mg / 100 ml in urine

Question 9

what are the ways to analyse alcohol?

Answer 9

Electrochemical fuel cell breathalysers

Infrared optical sensor breathalysers

Dual sensor breathalysers: Both electrochemical and infrared.

Gas Chromatography

Question 10

what are the blood alcohol levels effects?

Answer 10

Under 50 Not obvious, talkative
50 - 100 Slurred speech, Bravado, some co-ordination loss
100 - 150 Marked loss of gait, possible nausea
150 - 200 Nausea, Non co-operative, total loss of interest
200 - 300 Probable coma
300 - 400 Coma, Impaired respiration
400+ Death may ensue from respiratory paralysis

Question 11

what is he blood alcohol concentration?

Answer 11

Rapid equilibration across the blood brain barrier. Most accurate measurement of alcohol concentration affecting the brain.

Question 12

what is the urine alcohol concentration?

Answer 12

Urine alcohol only provides a mean value over the period of excretion.

found by blood alcohol (mg/100ml) x 1.3 = urine alcohol in microg / 100ml

Question 13

what is the breath alcohol concentration?

Answer 13

Breath alcohol is in equilibrium with that in the blood, although in a very small concentration of about 1:2300.

found by doing the blood alcohol (mg/100 ml) / 2300 = breath alcohol (microg / 100ml)

Question 14

what does ADH do?

Answer 14

ADH in the presence of it’s coenzyme oxidises alcohol.
The reduced coenzyme can be measured calorimetrically or spectrophotometrically.

Question 15

how do you calculate the blood alcohol concentration t hours after tmax

Answer 15

Cmax – (t x elimination rate)

Average: 18 mg/100mL/hour in blood
(Breath equivalent = 7.8 micrograms/100 mL/hour)

Variation between individuals
Range: 9 – 27 mg/100mL/hour in blood
(Breath 3.9 – 11.7 micrograms/100 mL/hour)

Heavy drinkers tend to have an increased rate from the average value.

Question 16

what is an example of finding the blood alcohol concentration?

Answer 16

e.g. Cmax is 120 mg/100 ml blood at 6 pm, At 10pm t = 4 hours,
Average metabolism = 18mg/100ml/hour
Concentration at 10 pm will be
120 – (4 x 18) = 120-72 = 48 mg/100 ml blood

Slow metabolisers = 120 – (4 x 9) = 84mg/100ml
Fast metabolisers = 120 – (4 x 27) = 12mg/100ml
Range : 12 – 84mg/100ml

Question 17

how do you calculate when someone will be below the limit?

Answer 17

Alcohol level found in blood sample is 160 mg/100 mL
How long would it take the driver to be below the limit to drive in Scotland?
Alcohol level must fall from 160 mg/100 mL to 50 mg/100 mL,
i.e. decrease of 110 mg/100 mL

Time required = 110/18 = 6.11 hours (average value)
Range Low (fast metabolisers) = 110/27 = 4.07 hours
Range High (slow metabolisers) = 110/9 = 12.2 hours

Question 18

what is cytochrome p450 in the oxidative pathways of alcohol metabolism?

Answer 18

MEOS – Microsomal enzyme oxidising system
Free radicals – damage tissue

Question 19

what is the relationship between genetics and ADH?

Answer 19

ADH – Number of isozymes with different structural, physical and chemical properties
Fast and slow metabolisers

Question 20

what is pharmacokinetics?

Answer 20

Zero order kinetics - clearance is zero order with respect to ethanol.
Cleared at a constant rate regardless of concentration.
Also depends on liver size and body mass