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Principles And Pitfalls In Alcohol Toxicity

Intoxication Defense

By Nachman Brautbar, M.D.

Dr. Nachman Brautbar is board-certified in internal medicine, forensic medicine, and nephrology, with a specialization in toxicology. His lists of academic appointments include Associate Professor of Pharmacology and Medicine, and Clinical Professor of Medicine at the University of Southern California, School of Medicine. He specializes in the fields of internal medicine, toxicology, pharmacology, and nephrology. His resume includes membership in 25 national and international scientific societies. Dr. Brautbar is a peer review for the Department of Health & Human Services (A Follow-Up Investigation of the Stability and Predictive Value of Kidney Biomarkers among Participants of Three Earlier ATSDR Health Investigations, 2000), Agency for Toxic Substances and Disease Registry - ATSDR (Malathion, Chemical Technical Summary for Public Health Evidence, Second Edition, 2000). Dr. Brautbar has been on the faculty of the National Judicial College and has lecture to judges on the issue of scientific evidence.

Introduction to Alcohol Abuse Effects
Alcohol abuse effects are a major medical and social problem. Alcohol can be toxic to the brain. Driving or operating automobiles or any other vehicles while under the influence of alcohol is dangerous. Legislation around the country has enacted various rules mandating fines and penalties for driving under the influence of alcohol. In the worker's compensation arena (as in the civil and criminal arena) work related injuries can result from intoxication with alcohol and drugs among others. When a worker is found to have a positive blood test for alcohol, the intoxication defense can be raised. The pharmacology and toxicology of alcohol differ from individual to individual and depends heavily on the forensic toxicology methods used to analyze the blood alcohol levels. There is the potential for errors in the process and as a result, some can be wrongfully convicted.

To assess the forensic analysis of alcohol abuse effects and intoxication, I will review here some important aspects of alcohol pharmacology, toxicology, and the scientific literature.

This article does not address the reasonable use of red wine on social events or daily with meals. This article addresses the unreasonable use (abuse) of alcohol.

Alcohol Absorption
Once ingested, alcohol (ethanol) is absorbed into the blood system and the fluids surrounding various tissue and inside of the cells. The concentration of alcohol in blood and tissue depends on the amount of total body water, since alcohol is soluble in water. Therefore, the weight of an individual is important in the analytical process of alcohol intoxication, since the water body content is a factor of total body weight. As an example if we do an experiment and place 100 ul of 8% alcohol into a container of 10 liters water, we will end up with a final content of alcohol in that container, different from a container with 9.75 liters of water. Once ingested, alcohol is absorbed mainly in the small intestine, and to some extent, in the stomach as well as the colon. A delay in stomach emptying will delay the absorption of the majority of alcohol into the patient's system through the small intestine. This is an important point when assessing the blood alcohol contents (BAC) in relation to an occurrence of an accident since we have to assess BAC relative to time of consumption. BAC is a major tool in assessing alcohol abuse effects.

The amount of alcohol which should have been absorbed normally through the small intestine at a certain point in time, will be significantly delayed if that same individual has a disease of the stomach, or medications or food which prevent the emptying of the stomach alcohol into the small intestine, and therefore delaying the absorption of alcohol from the small intestine. While the absorption of alcohol from the stomach is dependant on food among others, the absorption from the small intestine is rapid, and is not affected by food presence. From the stomach and intestine alcohol will be distributed via the blood to all body organs including the lungs. This is the basis for extrapolating from alcohol breath measurements into blood alcohol content (BAC). The alcohol breath testing is based on a concept that the ratio between the air that we exhale and blood alcohol is 1/2100. This, however, has not reached scientific acceptance, and data showing figures from 1/1500 to 1/3000 have been published in the scientific literature. Therefore, there is an individual variation, which cannot be determined with the methodology utilized today and therefore cannot be simply and routinely applied to breath testing. (3)

Factors Determining Alcohol Absorption

Body Water Alcohol is absorbed into the water of body fluids. The concentration of alcohol within an individual depends on the amount of body water contained in the individual's body. An individual with a total body water which is large will be able to dilute and absorb more alcohol than an individual with a smaller volume of body water. Body water content varies and ranges from 55 to 68%.(1).

Time A delay of the emptying of the stomach into the small intestine will delay absorption of the majority of the alcohol. Such a delay is important in calculating the peak blood alcohol content (BAC) or extrapolating from a given level. Conditions which may delay the stomach emptying into the intestine such as scarring or spasm of the pylorus (point of connection between the stomach to the small intestine), will delay the absorption of the alcohol from the small intestine as well, and therefore will affect the blood alcohol content curve. In addition to the delaying of the stomach into the small intestine, factors of the amount of alcoholic consumed, the presence of food, the time that the alcohol was ingested, and some other individual parameters such as medication use are important factors in assessing blood alcohol levels and peak alcohol levels.

Metabolism of Alcohol
Addressing alcohol abuse effects requires an understanding of alcohol metabolism.

The liver is the major organ to metabolize and eliminate alcohol. From a pharmacological point of view, the process of metabolism of alcohol is a linear function of time, and it can be affected by increasing the concentration of alcohol in the blood. As a rule of thumb, the mean rate of alcohol elimination is about 100 mg/kg/hr or about 15 mg/100 ml/hr for a 70 kilo person which corresponds to 8-10 cc per hour. What that means is that it takes about 1-1/2 hours to metabolize the alcohol in 1 ounce of 100 proof whisky or in 12 ounces of beer. (1) It is well accepted that the time from the last drink to maximal concentration in blood usually ranges from 30 to 90 minutes. This however may vary between individuals, depending on various physiological conditions. This information is important in assessing whether an individual's arrest or involvement in a collision was while the individual had reached the peak level of blood alcohol content, and was on the rising limb of the curve, or whether the individual was on the down slope of the curve after having reached the peak blood alcohol concentration (1,2).

Applying Breath Alcohol to Blood Alcohol Contents
There are several methods by which breath alcohol is determined.

The BAC Data Master
This instrument analyses breath sample using of infrared absorption in the 3.4 micron infrared band with the raw data being processed by 2 or 3 narrow band filters within this region.

BAC Verifier Data Master
This method is designed primarily to meet the State of Washington requirements for a breath testing device. The Verifier uses the same system to analyze a breath sample, but includes a number of additional technical features which includes a printer, adding a new central processing unit to inhibit electrical interference, changes in the formula used to calculate the presence of acetone in a breath sample. Prior to the use of the Data Master, it was found that while this unit may be able to accurately and precisely measure the ethanol concentration, absolutely no information was obtained as to whether or not the Data Master can specifically measure alcohol (and only alcohol) contained in a human breath sample, and to be able to differentiate from acetone in the exhaled air from the lung. Furthermore, the State performed no test to compare the individuals' breath alcohol sample with a corresponding blood sample taken at or about the same time. Therefore some questions may be raised in regards to 100% reliance on this method only, for forensic purposes. Currently there are several published research papers, peer reviewed, evaluating the capabilities of the BAC Data Master. The papers conclude that when compared to a mechanical simulator the human body has a sizable biological variability, and in any given human breath test there exists a statistically significant possibility of the breath testing devise registering an erroneously high or low result, based on the biological variability of the human subjects.

The infrared method detects other metabolites in exhaled lung air and cannot absolutely distinguish between ethyl alcohol and other metabolites and therefore, has the potential of giving erroneous readings. Several papers have looked into the suitability of the breathalyzers. The overall assessment was that the majority of breath test machines will potentially erroneously detect other metabolites in the exhaled air. For instance, acetone in the exhaled air will be registered by infrared as alcohol and their reliance on breath analysis only for forensic purposes is not sufficient.

The problems with the forensic use of breathing instruments for alcohol determination are that the human being is not and cannot be compared with a standardized test solution. The biological variability from one subject to the next is just too significant to allow for a comparison to a single model.

Extrapolation from Breath Alcohol Testing to Blood Alcohol Levels
The extrapolation from breath alcohol content into blood alcohol content level at the time of accident or arrest is one of the most important steps in the forensic process. While the extrapolation process takes into account simple mathematical extrapolation, it is imperative to understand that in most cases the extrapolation of the amount of blood alcohol concentration to a time other than the time when the specimen of body fluid or breath was taken from the subject is applicable only to the average person in a normal physical condition and may not be relevant otherwise. Current research has shown that there are multiple variables such as blood breath ratio, absorption rates of alcohol, elimination rates of alcohol, and difference in total body water. Accurate and precise extrapolation of evidential breath test results back to the time of driving is not possible using the current available technology (1,3).

Measuring and Determining Impairment in Alcohol Cases
Alcohol abuse effects are commonly associated with brain process impairment. Alcohol affects the motor and cognitive performance. The effects of alcohol are not uniform, and impairment varies across different types of behavioral functions. Two areas of functioning that are sensitive to alcohol impairment and assessed in field sobriety tests, are those of speech and vestibular functioning.

Reaction - TimeSince alcohol is a general central nervous system depressant, it affects a wide range of functions. Some of the most basic performance tasks which were studied in relation to alcohol are reaction time parity. Interestingly enough the majority of studies have shown no effects or minimal effects on reaction time (2,3). All studies have shown that alcohol affects the tracking performance time, and that there is significant evidence of impaired tracking performance with blood alcohol content above 50 mg/100 ml. (4,5,6,7) Therefore, simple reaction time would not be the test to assess whether an individual is impaired by alcohol or not. Dual task performance is sensitive to the affects of alcohol, and has been shown to be impaired (8) Accident statistics consistently show that crash risk in the increased significantly when BACs are above 40 mg/100 ml. Several studies with automobile simulators have shown that risk taking is affected only at very high levels of alcohol described as 106 mg/100 ml (9).

Speech - Speech production requires fine motor control, timing and coordination of the lips, tongue and vocal cords, and may be a sensitive index of impairment resulting from alcohol intoxication. Therefore, one of the common tests is having the subjects recite the alphabet at a fast rate of speed. The problem with the use of speech as a parameter of intoxication is interference from the affect of stress, fatigue and other factors on the speech control, and the lack of baseline speech in the same individual by evaluable speech is affected at levels of alcohol already over 100 mg/100 ml (2,3,5,6).

Vestibular - The affects of alcohol on the vestibular system are demonstrated in measurements which evaluate the ocular motor control. One of these is the eye movements called nystagmus (jerkiness). One of the tests is measuring the eye movements when the head is placed in a sideways position, and it is called Positional Alcohol Nystagmus (PAN). Positional Alcohol Nystagmus I (PAN I) is measurements of eye movements to the right side when the right side of the head is down, then to the left when the left side of the head is down. This occurs during peak BACs beginning at around 40 mg/100 ml (10). Positional Alcohol Nystagmus II (PAN II) typically is observed between 5-10 hours after drinking, and it is characterized by nystagmus in the opposite direction, compared to Positional Alcohol Nystagmus I (11). Both types of PAN are produced by the toxic effects of alcohol on the vestibular system. The literature has shown that the faster the rate of drinking, the faster PAN I appears (12). Another type of nystagmus is Horizontal Gaze Nystagmus (HGN). This is a nystagmus which is jerkiness in eye movements as the gaze is directed to the side when the head is in the upright position. Typically HGN is observed when the blood alcohol contents reach 80 mg/100 ml (13). The Horizontal Gaze Nystagmus appears to be pharmacologically specific to alcohol and therefore should be used to differentiate from the toxic effects of other mind altering drugs and chemicals. (14) Several studies have shown that alcohol leads to an increase in the sway, appearing in drinkers at BACs of 30-50 mg/100 ml (15,16,17,18) Postural control is sensitive, but other factors not related to alcohol must be taken into account such as physical difficulties with walking, pain in the joints or the ankles, physical deformation of the feet and effects of prescription medications.

The Importance of Individual Differences in the Assessment of Blood Alcohol
In the process of extrapolation and interpretation of alcohol data, one must remember that there are individual differences which may play a role in the assessment of blood alcohol contents. There is a large difference between patients and their sensitivity to alcohol impairment, such as drinking habits. Those who use alcohol more often and in larger amounts, develop tolerance to the impairing effects of alcohol, and develop an acquired decrease in the level of impairment. The scientific literature has described greater impairment in light drinkers compared to heavier drinkers (19, 20, 21). Additionally studies have documented an increase in impairment at low levels of alcohol in patients with coexisting neurological and psychological factors.

The Role of Alcohol Consumption
Initially, there is a stimulant effect which precedes the sedative effect. Due to the individual physiological differences it is difficult to predict when the stimulant effect of alcohol will take place and the BACs at which this will occur. Stimulant effects have been shown in some at blood alcohol concentrations as low as 20-30 mg/100 ml, and may persist on the rising limb well over 100 mg/100 ml. (2) The sedative effects of alcohol have been shown to present at peak BACs of 60-80 mg/100 ml. Research has shown that alcohol related impairment is greater on the ascending (uprising) limb of the curve compared to the descending limb of the BAC curve (2). (Ascending limb is the BAC from the time of consumption to the peak level. Descending limb is from the peak levels going down secondary to the metabolism and elimination of alcohol).

Alcohol abuse effects are therefore measurable and relatively easy to assess given the basic data at time of consumption and amount of consumption.

Field Sobriety Tests
Field sobriety tests which include the walk and turn, one leg stand and horizontal gaze nystagmus test have been shown in the literature to detect impairment in field testing. Essentially, these are screening tests only which detect impairment, and must be followed by some other parameters of blood alcohol content directly or via extrapolation. Horizontal gaze nystagmus is more reliable at predicting blood alcohol content than the walk and turn and the one leg test. Field sobriety testing is relevant to blood alcohol levels of 80-100 mg/100 ml. At lower levels more studies are needed. Therefore at levels lower than 80 mg/100 ml field sobriety tests will not be helpful. Furthermore, the field sobriety test must take into account factors such as prescription medications, orthopedic leg and back disease and arthritis.

Determination of Alcohol in Blood Samples
The forensic toxicology evaluation of alcohol abuse effects requires blood alcohol samples. When blood samples are analyzed for forensic purposes, civil or criminal, a standard procedure is to make duplicate determinations. The concentration of blood alcohol should be reported with the confidence limits such as 95% or 99%. (22) Therefore, it is imperative that in clinical chemical laboratories, the calibration of standards test by biological specimens along with the unknowns be done and kept on record for forensic evidence (23). In some cases the results have been thrown out of court due to the absence of the raw standardization data. The analysis done by clinical lab (such as a hospital lab) and a certified forensic lab are different. Forensic laboratories receive samples of whole blood which are commonly hemolyzed, and often contain clots, where clinical laboratories receive plasma or serum. The content of water in these specimens is not the same, and therefore, the results of analyzing alcohol at the clinical laboratory should not be used for forensic analysis of driving while under the influence or work related accidents without an appropriate correction for the difference between whole blood and plasma or serum (the amount of water in specimens with a mean value of 91.8 whole plasma/serum and the 80.1% for whole blood). (24,25). From experimental studies (26) a plasma/blood ratio of 1.22 to 1 corresponds to the mean plus 2 standard deviation, and this higher conversion factor should be used in forensic work, instead of a mean value of 1.14/1. This approach gives a more conservative estimate of blood alcohol content to be used in criminal litigation. For example, a blood alcohol concentration of 0.10, will be 0.114 in plasma or serum, and a level of 0.50 in blood would equal 0.57 in plasma or serum. This difference may be significant in some cases, and should not be missed.

Quality Assurance of Alcohol Testing
Several important factors should be controlled for quality assurance. The specimens used should be gently inverted a few times immediately after collection to increase mixing in the solution of the chemical preservatives sodium fluoride to inhibit the activity of various enzymes and microorganisms and yeast. Since these organisms can produce alcohol in the test tube from the blood glucose, and therefore may give a higher level of alcohol in the test tube as opposed to in the body. There should also be an anticoagulant to prevent blood clotting. The test tube should be labeled with the person's name, date and sampling, and the name of the person that took the sample. The vacutainer tubes containing blood should be sealed in such a way as to prevent unauthorized handling or tampering, and special adhesive paper strips should be used. The blood specimen should be carefully inspected when they arrive in the laboratory, and documentation in writing must be made in regards to the seal on the package, as well as the individual tubes whether they are intact, or whether they contain blood clots, or whether they are diluted with other liquids. The same information on the vacutainer tube should be compared with other documentation to ensure the name, date and time. Gas chromatography, which is the most common method of blood alcohol analysis, requires special standard and routine attention. The chromatography peaks should be well documented and well identified, and marked for any unidentified peaks on the gas schematogram. Daily calibration and measurements of known standards must be done and documented by the measuring laboratory. The rate of lost alcohol during storage needs to be established under refrigerated conditions (+4 degrees Celsius), and also when specimens are kept deeply frozen. The chromatographic tracing and the evidence corroborating the analytical results as well as calibration plots and calculation should be kept and stored safely. Furthermore, the laboratory must be accredited for making forensic toxicological analysis. If these steps are not followed there is a great likelihood that the alcohol results can be found unreliable or inadmissible.

Blood Alcohol Levels
Alcohol abuse effects are determined daily by law enforcement, health care workers, and forensic toxicologists. The key factor is blood alcohol levels. The peak blood alcohol concentration after drinking, as well as the time of reaching the peak varies widely from person to person, and depends on many factors (3,2,1,27). The concentration of alcohol in body fluid tissues after reaching a calibration depends on the water contents, and the ratio of blood flow to tissue perfusion, as well as various other time elements (28).

Experiments in healthy male volunteers who drank 0.68 gr/kg as whisky in 20 minutes after an overnight fast, showed blood alcohol peak reaching maximum at 1 hour, measuring blood alcohol and 45 minutes measuring breath alcohol. At the same time saliva alcohol reached a maximum within half an hour, and urine alcohol reached maximum excretion within 2 hours (29). What these data demonstrate is several factors such as blood circulation will affect the rate and time of alcohol to the kidney, lung and brain.

Alcohol induced impairment in occasional drinkers has been shown as follows at a BAC of 10 to 30 mg/100 ml, slight changes in performance and behavior can be demonstrated with highly specialized tests. Between 30-60 mg/100 ml, most people experience euphoria, becoming more talkative and sociable, at a BAC between 60-100 mg/100 ml, a marked euphoria and excitement is often reported with partial or complete loss of inhibitions, and in some individual's judgment and control are seriously impaired. The elimination of alcohol from blood was studied by Widmark (30).

The rate of elimination of alcohol from the blood in moderate drinkers falls within the range of 10-20 mg/100 ml per hour with a mean value of about 15 mg/100 ml per hour. Higher values have been described in drinking drivers and in alcoholics undergoing detoxification. In order to use the Widmark model we must assume that the error factor is known, and that absorption and distribution of alcohol are complete at the time of sampling blood. This assumption is not always applicable. Commonly the sampling of blood alcohol levels can be at the rising limb of the blood alcohol content. When calculating blood alcohol content from the dose consumed, one must assume that the systemic availability is 100%, and that complete absorption and distribution of alcohol in the body water has occurred, and at the time of sampling of blood the distribution and absorption reached a steady state. The individual variation was recently estimated at 20%. (31) Food in the stomach before drinking retards the absorption of alcohol and the peak BAC, and slows the initial effects compared with drinking the same dose on an empty stomach (32,33) Studies in volunteers, showed that 9 subjects who consumed 0.3 grams alcohol per kilograms either on an empty stomach, overnight fast, or exactly 1 hour after eating a protein rich breakfast had a large inter individual variations in peak BACs. For instance, those who were fasting reached maximum peak at 45 minutes to 1 hour, while those who were not fasting and were fed reached a significantly less elevated BAC (average of 20 mg/100 ml, as compared to an average of 40 mg/100 ml in the fasting volunteers) (34). What is also interesting in those studies is that food intake not only lowered the BAC peak, but also increased the rate of metabolism of ethanol (33). The calculation and extrapolation of BAC becomes difficult, especially when small doses of alcohol are consumed after a meal, since the food in the stomach influences the bioavailability of alcohol and reduces it.

Post Mortem Determination of Alcohol
On many occasions the forensic toxicologist has to provide an opinion whether a certain event was the result of alcohol abuse effects. Many times this will involve accidents or injuries where one party or more have died. Alcohol contents of body fluids are of major importance in the forensic toxicologist's analysis in the criminal arena and commonly in the worker's compensation arena. The interpretation of the analytical results obtained from autopsy material has difficulties as a result of lack of homogeneity of blood samples, microbial alcohol production post mortem, alcohol diffusion from gastric residue and contaminated airways, and the lack of or unreliability of information on the clinical condition of the person immediately prior to death. At the same time, post mortem analysis allows the ability to measure other body fluids for alcohol content, which are usually not accessible otherwise. Nevertheless, interpretation of post mortem alcohol must take into the account the totality of the available information. A single autopsy blood alcohol level is uninterpretable without concurrent vitreous humour and urine alcohol levels, as well as information gleaned from the scene of the accident. Human plasma contains approximately 10-15% more water than whole blood. Therefore, it can be expected that the plasma alcohol content is approximately 10-15% higher than the corresponding whole blood concentrations. These facts must be taken into account when analyzing post mortem and comparing to pre-mortem hospital samples of serum or plasma analysis of alcohol.

The forensic toxicologist is one of the experts who will address key issues. While the autopsy is performed by the coroner, the forensic toxicologist, who is a medical doctor, with expertise in clinical medicine and toxicology will have to address these factors in the death cases of alcohol abuse effects.

Post Mortem Vitreous Alcohol
Analysis of vitreous humour is useful to corroborate the post mortem blood alcohol and assist in assessing and extrapolating to anti-mortem intoxication from post mortem alcohol production. Vitreous alcohol can also serve as an alternative sample if a satisfactory post mortem blood sample is unavailable or contaminated. In most cases the specimen is easily obtained, and can be sampled without a full autopsy. Vitreous alcohol is also important, because studies have shown post mortem putrification does not contribute to the alcohol levels measured in the vitreous. There have been various formulas including a simple conversion factor to predict blood alcohol content from vitreous humour alcohol content, but these do not take into account the uncertainty of the prediction for an individual subject. From a forensic viewpoint, it is unreasonable to give an estimate of the mean BAC based on VH AC without providing the data with 95% of confidence interval (which is a measure of the degree of confidence attached to the estimate in an individual case) (35,36,37) Blood has lower water content than vitreous so the expectation is that the blood vitreous alcohol ratio will be less than 1. In cases where the ratio of blood to vitreous humour alcohol concentration exceeds 1, the most likely explanation is that death occurred before diffusion equilibrium had been obtained, and this observation may be of forensic significance (38). It is also reasonable to assume that ethanol may diffuse into or out of the vitreous post mortem. The chemical constituents of embalming fluids may diffuse into the vitreous humour after a body has been embalmed (39,40).

Urinary Alcohol
Bladder urine alcohol does not necessarily reflect the blood alcohol concentration existing at the time of death. Several studies have shown that a BAC of 80 mg/100 ml was predicted with 95% certainty by a UAC of 204 mg/100 ml, and similarly a BAC of 150 mg/100 ml, by a UAC of 291 mg/100 ml. Because the prediction interval is very wide, the autopsy UAC is of limited value in predicting an unknown BAC. Furthermore, an autopsy UAC should not be translated into a presumed BAC for legal purposes. It is possible to make a conservative estimate of the BAC existing during the time the urine was being produced and accumulated in the bladder by dividing the observed autopsy UAC by 1.35. The use of urine alcohol collected post mortem is not practical for forensic purposes.

Practical Approach to Estimation of Blood Alcohol Concentration

Examples
The estimation of blood alcohol concentration must be based on sufficient information. Among the most important parameters are body weight, concentration and number of alcoholic beverages consumed, and length of the drinking. Other factors which will affect the rate of absorption from the gastrointestinal tract will further affect the final BAC curve. Approximation of the time when the alcohol was consumed may be of crucial importance. It is also important to determine if the subject's BAC was on the ascending or descending limb.

Example 1
A person weighing 150 pounds will reach a BAC of 0.025% upon complete absorption of one 12 ounce beer (4% alcohol), or 1 ounce of 100 proof (50% alcohol). The amount of alcohol is the same in both beverages. Should the person weigh more or less than 150 pounds, or the alcohol beverage concentration be less or greater than 50% the BAC will be lower or higher. A formula has been established to calculate the BAC as follows: 150 divided by A times B divided by 50 times C times 0.025% equals D, whereby: A is body weight, B percent of alcoholic beverage, C number of 1 ounce drinks ( a number of ounces), D level obtained upon completion absorption. 150/A x B/50 x C x 0.0251 = D (1). For example, the BAC of a man weighing 200 pounds upon complete absorption of five 12 ounce beers using the equation gives us the blood alcohol concentration of 0.09%. The elimination rate of alcohol has been established to be linear. This allows us to calculate alcohol level by extrapolation. Back calculation is only accurate in the elimination phase of the alcohol curve, and it does not apply to the absorption phase. (Ascending limb to a certain extent).

Example 2
The equation for the extrapolation is BAC plus dissipation rate times numbers of hours elapsed. Based on this, if the person was drinking from 8:00 p.m. to 10:00 p.m., and was involved in an accident at 11:30 p.m., the blood sample drawn at 1:30 a.m. revealed a BAC of 0.07%. Since the dissipation factor is different from person to person, three calculations can be made using a higher dissipation level of 0.02, lower dissipation level of .015 and medium dissipation level of 0.018. According to this formula the BAC calculated based on elimination factor of 0.015, 0.018, and 0.02 will bring the results of 0.100, 0.106 and 0.11 mg/100 ml. BAC - (Dissipation rate x number of hours after first drink) (1).

Example 3
A man weighing 220 pounds started drinking at 5:00 p.m. and continued to drink until 1:00 a.m. During this time he neglected to eat any food. During the course of the evening he consumed seven 16 ounce beers, and ten 1 ounce shots of whisky 86 proof. At 3:00 a.m. he was involved in an automobile accident. At 4:00 a.m. a blood sample was drawn for alcohol content. The question is, how do we calculate the BAC at the time the blood was drawn. First of all we will calculate the BAC from beers which should be calculated at a body weight of 220 pounds, 150 divided by 220 times 4 divided by 50 times 112 times 0.025% which is 0.153% from beer, and from whisky 150 divided by 220 times 43 divided by 50 times 10 times 0.025% equals 0.147, total BAC from beer and whisky is 0.3% using the formula 150/a x B/150 x C x 0.025 = D. The elapsed time between the first drink which was at 5:00 p.m. and the blood sample was drawn at 4:00 a.m. is 11 hours. The amount of alcohol dissipated during this time is estimated at a range of dissipation rate of 0.300 minus 0.165 which equals 0.135 or alternatively 0.300 minus 0.198 which equals 0.102% or 0.300 minus 0.22 which equals 0.08%. (One has to use the low, high and average dissipation rate, because it is individualized and unknown for a given individual, and therefore BAC dissipation using the average dissipation rate is desirable). The formula here is: BAC - (Dissipation rate x number of hours elapsed), which is 0.3 - 0.165+0.135%. The median figure of 0.135% is the reasonable one.

Example 4
A person is found dead on the job, while falling off a ladder. He was found to have a BAC of 0.25%. The weight is 130 and the testimony is that the person was drinking for three hours and fell off the ladder 3 hours after leaving the bar. The formula to use here is taken from Winer (1).

A = UW x R x CT/018.
W = 130 lbs x 454 g/pound = 59020 g.
R = 0.55
CT - 0.25% = 0.0025.
A = 101.4 ml of 100% alcohol.

Then we must take into account that the drinking took 3 hours and another 3 hours after drinking, total of 6 hours dissipation. Therefore the amount of alcohol dissipates using a medium 0.018 rate is 0.018% x 0.108%. We must again use the formula A = W x R x CT/0.8 = 59020 x 0.55 x 0.00108/0.8 which equals 43.8 ml of 100% alcohol. Therefore the total amount of alcohol consumed was 145.2 ml of 100% alcohol. If we want to express this in lay language of whisky, 100 proof: 4.84 oz/0.50 = 9.68 oz of 50% which equals 10 shots.

Example 5
A worker is involved in a car collision on the job. This happened at 3:30 AM and a breath test was performed at 4:30 AM and showed a calculated BAC of 0.20%. The worker claimed that he was not intoxicated and the breath test was incorrect. The sobriety field toxicity test was positive. The worker testified that he consumed 6 beers from 7:00 PM to 10:00 Pm (3 hours) and then 4 beers from 12:00 PM to 2:00 AM (2 hours). He testified that he had nothing to eat and his weight was 170 pounds. How many beers did he consume? 150/A x B/50 x C x 0.0251 -= D. D = 0.212%. Taking into account the dissipation rate and time, he reached a BAC of 0.124%. This demonstrates that the breath test may not always be accurate, and blood testing is the most reliable.

Example 6
A worker who gets involved in a car accident on the job and is found to have a BAC of 0.22, 2.5 hours after the accident. He was a light drinker. Information is given that he was drinking 2.5 hours prior to his collision. What this tells us is that he was on the descending side of the curve which allows us to back extrapolate the BAC levels at 0.018% per hour. The collision occurred 2.5 hours prior to the obtaining of the blood sample. Therefore, at 0.018% x 2.5 hours, he was at 0.22 - 0.045 which is 0.175 which is legally intoxicated and from forensic toxicology, impaired for a light drinker.

In any case where alcohol abuse effects must be evaluated, the forensic toxicologist will take into account all the factors described in this paper.

[Updated Manuscript Pending]

The author wishes to thank A.R. Badel for her efforts in transcribing this manuscript.

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