SC6: Special Considerations

Myriad medical texts describe the medical consequences of acute and chronic ethanol use. The purpose of this discussion is to describe the history and use of assessments of ethanol induced impairment, primarily in a legal context. Some of the principles described may, however, be extrapolated from the legal to the medical setting. Throughout this chapter, the terms ethanol and alcohol are used interchangeably to retain the forensic, legislative, and medical contexts in which the terms are utilized.

Numerous well designed laboratory studies assessing alcohol induced impairment have been published. However, application of study results to actual cases of possible driving impairment or over service of alcohol in a drinking establishment may be inaccurate without an understanding of the origin of laws governing these activities. Although the intoxicating effects of ethanol have been known for centuries, the advent of mechanized transportation spawned increased public and legal scrutiny. Concern was expressed over the potential adverse safety implications of driving while intoxicated, not just for the impaired driver, but also for other persons (passengers, other drivers, pedestrians) and property. Although railroads had regulations against the operation of equipment while intoxicated dating back to the 19th century, the first arrest for drunk driving in an automobile was that of a London taxicab driver in 1897.²⁰ The realization that alcohol intoxicated motor vehicle operators were a public health issue worthy of legal scrutiny soon followed, and legislation was enacted to combat “drunken driving,” with New York being the first US state to enact such a law in 1910.²⁰

In early laws, “drunken driving” was poorly defined and relied heavily on observable signs of gross intoxication. Attempts at legislative clarification of language resulted in terms that were nearly as nebulous, such as “alcohol impaired” and “under the influence.” Prior to the landmark works in Sweden by Widmark and in the United States by Heise, evaluations of driver impairment were predominantly based on the “expert” testimony of an evaluating physician and the arresting police officer, as well as behaviors reported by witnesses. These evaluations were observational rather than scientifically based, and such nonsystematic and nonobjective testimony was often dubious and frequently plagued by exaggeration of behaviors (eg, staggering gait, incoherent speech).

The development of analytical technology capable of measuring the concentration of alcohol in blood gave rise to the idea that diagnosis of intoxication might be assisted by an objective chemical test result. The theory behind this idea being simply, the higher the blood alcohol concentration (BAC), the more drinks the individual must have consumed and therefore, the greater the degree of impairment. It was, therefore, reasoned that there may also exist a legally punishable limit of alcohol in blood or other biological matrix. Although the assignment of a specific clinical effect to a given BAC is not rigorously applicable to evaluation of an individual case, the general trends when examined across a population formed the foundation of many modern driving while intoxicated (DWI) laws.

Despite centuries’ worth of knowledge of the effects of alcohol and decades of efforts to articulate drunk driving standards, a single universal definition of “alcohol intoxicated” still does not exist. A typical medical definition may focus on altered mental status, ataxia, or the ability to care for oneself, whereas the focus of a legal definition may be on the ability to safely operate a motor vehicle or whether the patron of a bar or restaurant should be served additional alcohol. A lay public definition may include parts of both.

Although alcohol intoxication may be an important factor in a nearly infinite number of settings, two of the most common legal circumstances involving toxicology consultation for alcohol-related issues are (a) alcohol impaired operation of a motor vehicle and (b) so-called “dram-shop” cases when an already intoxicated individual is served alcohol. Discussion of alcohol use in the workplace and abstinence monitoring are beyond the scope of this discussion.

With the advent of analytical measurements capable of quantitatively determining BAC and the increasing public awareness of the dangers associated with drinking and driving, legislation based on BAC began to appear. Although the initial laws did not define the specific BAC that established illegality in the operation of a motor vehicle, they did allow for the use of BAC results as supportive evidence of intoxication. The first states to incorporate BAC into drunk-driving statutes were Indiana and Maine, which did so in 1939.²⁷ The approach taken by the Indiana legislature resulted in a three-tiered statute, which stated that a BAC of less than 50 mg/dL was considered presumptive evidence of no intoxication, a BAC between 50 and 100 mg/dL was considered supportive evidence of intoxicated driving, and a BAC of greater than 150 mg/dL was considered prima facie (ie, obvious and evident without proof) evidence of guilt. From a legal perspective, prima facie evidence shifts the burden of proof from the accuser having to substantiate the charge to the defense to rebut the allegation. It is this legal perspective from which the so-called “per se” standards are derived—that is, an individual whose BAC exceeds a predetermined concentration is guilty “per se” of driving while impaired by alcohol, even without any other evidence of intoxication or impairment.

Early drunk-driving standards established in the Uniform Vehicle Code made reference to a BAC at which there was “no doubt of obvious intoxication”; this BAC was defined as 150 mg/dL. However, by 1960, as data regarding alcohol related motor vehicle crashes became available, most (but not all) states adopted a more rigorous per se BAC driving standard of 100 mg/dL.²⁷ This reduction in the per se legal BAC for a DWI charge was supported by powerful medical and political groups, including the American Medical Association (AMA). Interestingly, the AMA recom­mendation also noted that some persons were “under the influence” or impaired in their ability to safely operate a motor vehicle at BACs of 50 to 100 mg/dL. Despite newer drinking and driving laws defined on the basis of an objective chemical test, many state laws still contained older vague language such as “intoxicated,” “visibly intoxicated,” and “obviously intoxicated,” which forced legislators to define more clearly and objectively.

In 2000, the National Highway Traffic Safety Administration (NHTSA) reported that of 41,471 motor vehicle fatalities, 38.4% were alcohol related; this corresponded to an average of one alcohol-related traffic fatality every 31 minutes.⁵⁴ Although the NHTSA statistical methods likely overestimated the number of actual fatalities involved in alcohol-related crashes, there is little argument that alcohol use increases crash risk. Epidemiological assessments demonstrate that the probability of causing an alcohol-related motor vehicle crash increases slightly at a breath alcohol concentration (BrAC) of 50 mg/dL. The risk of causing a crash is increased by roughly four-fold at a BrAC of 80 mg/dL, seven-fold at a BrAC of 100 mg/dL, and 25-fold at a BrAC of 150 mg/dL.^4,27 In 1994, a successful campaign vigorously supported by the AMA and Mothers Against Drunk Driving (MADD) encouraged all the states in the United States to lower the BAC used to define per se intoxicated driving to 80 mg/dL.²⁰ Although all states technically have the right to set drunk-driving statutes at their discretion, the anti–drunk-driving political lobby was successful in convincing the US government to require a minimum legal drinking age of 21 years and a mandatory per se BAC statute of 80 mg/dL in order to receive federal highway funding.²⁰ Consequently, as of July 2004, all states in the United States, the District of Columbia, and Puerto Rico conform with federal recommendations defining a BAC of 80 mg/dL as a violation of motor vehicle code. Lower per se BACs are applied to interstate commercial drivers (40 mg/dL) and pilots of aircraft (40 mg/dL, with no alcohol consumed within 8 hours prior to acting as pilot in command), as well as minors (10–20 mg/dL, depending on the state and 20–50 mg/dL in some European countries). Additionally, some states in the United States, such as Colorado, have lower per se statutes for the slightly lesser charge of driving while ability impaired (DWAI), which may be invoked when a driver’s BAC is between 50 and 80 mg/dL.

Laws addressing per se driving under the influence (DUI) limits are based on ethanol concentrations measured in whole blood. BrAC limits (which are arithmetically linked to BAC) are also frequently specified in per se statutes. As such, the use of appropriately conducted breath alcohol measurements eliminates the need to collect a blood specimen from a suspect. Per se limits, as described above, apply to the ability to safely accomplish specifically defined tasks such as driving an automobile or flying an aircraft. It is, however, imperative to understand that per se BACs do not define drunkenness or alcohol intoxication in nondriving situations, and their use in circumstances not involving motor vehicle operation is generally inappropriate.

The legal significance of a per se limit is that there is no requirement for behavioral evidence of intoxication, as long as the measured BAC exceeds that established by the legislature. Since their enactment, numerous legal arguments have challenged the constitutionality of per se drunk-driving laws. Issues including a lack of due process through application of the “void for vagueness” doctrine, reliability of breath testing results, and the distinction between blood alcohol and breath alcohol have all formed bases for legal challenges to per se laws.²⁰ However, despite such challenges, the courts have consistently upheld the laws.

Accurate measurement of ethanol concentration in various biological matrices can be done using a number of analytical techniques. Historically, Widmark used wet chemical oxidation, using potassium dichromate and excess sulfuric acid followed by iodometric titration of the remaining amount of oxidizing agent. Although this method is effective, it is laborious and lacks specificity if other volatiles (eg, methanol, acetone, ether) are present, because they are also oxidized, giving a falsely elevated ethanol result. Such wet chemical methods are obsolete and no longer used in forensic and clinical laboratories.

Enzymatic ethanol assays based on alcohol dehydrogenase (ADH) are commonly used, especially in high-throughput laboratories. The oxidation conditions of enzymatic methods are milder than wet chemical methods, and acetone, which was the most troublesome interference with wet chemical methods, is not oxidized by ADH. Interferences by other aliphatic low-molecular-weight alcohols such as methanol and isopropanol are known to occur with ADH isolated from humans and other animals; this interference is reduced by using yeast-derived ADH, which shows greater selectivity for ethanol.^28,51 Specific enzymatic methods used for ethanol analysis in body fluids include enzyme multiplied immunoassay technique (EMIT), fluorescence polarization immunoassay (FPIA), and radiative energy attenuation (REA), which is related to FPIA (Chap. 6). Comparative study of ethanol determination by REA and gas chromatography shows excellent agreement in precision and accuracy between the two techniques.¹¹ Both high serum lactate and elevated lactate dehydrogenase concentrations interfere with ADH based methods of ethanol analysis, including providing false positive results in serum specimens from alcohol-free patients.^2,36

The greater selectivity for ethanol of gas chromatographic (GC) methods make this technique the mainstay for quantitative analysis in most forensic laboratories. Typically, the GC method involves head space sampling (HS-GC), which capitalizes on the volatility of ethanol, eliminates some potential interferences, and shortens run time. Samples to be run by HS-GC are first diluted (typically 1:5 or 1:10) with an aqueous solution of internal standard. This mixture is then sealed in a crimp-top vial with a rubber septum and gently heated to 122° to 140°F (50°–60°C) for 30 to 60 minutes in order to achieve equilibrium of volatiles between the gas and liquid phases. The vapor is then sampled with a syringe by puncturing the rubber septum and the withdrawn vapor injected into the instrument. Heating the sample for too long at a high temperature can result in oxidation from oxyhemoglobin.⁴³ This problem may be solved by the addition of sodium azide or sodium dithionite to block the oxidation or simply reducing the equilibrium temperature to 104° to 122°F (40–50°C).⁴³ Once chromatographic separation is achieved, various detection methods, including flame ionization (FID), electron capture (EC), and electrochemical sensing may be used (Chap. 6). Dual detection (eg, FID and EC) can also be useful in circumstances where a larger number of volatiles may need to be screened.⁴⁴

As ethanol distributes based on total body water, the water content of the matrix will affect the amount of ethanol present in a given volume or mass of biological sample. A common circumstance in which this is observed is in the difference between a whole blood ethanol determination and a plasma or serum ethanol determination. The water content of serum and plasma is 10% to 12% higher than whole blood, meaning that serum or plasma ethanol concentrations will be correspondingly higher than whole blood concentrations. Clinical laboratories most often use serum and plasma for analysis, whereas per se DUI statutes are written in terms of whole blood. Therefore, if a comparison is to be made between a serum or plasma analytical result and a legal standard, the result must be converted to an approximated whole blood ethanol concentration. Experimentally determined serum-to-whole blood ethanol ratios range from 1.12 to 1.17, whereas plasma-to-whole blood ethanol ratios range from 1.10 to 1.35.³⁷ Typically, a ratio of 1.16 is used for this conversion, and no significant difference appears to exist between the serum-to-whole blood and plasma-to-whole blood ratios.⁵⁴ Ratios between whole blood and other biological matrices such as urine, saliva, cerebrospinal fluid, vitreous humor, brain, liver, kidney, and bone marrow are published, and a table listing these ratios and the sources from which they are derived is available.¹⁰

Breath testing is commonly performed to assess BAC because of its relative simplicity and lack of invasiveness in its collection when compared with urine or blood. The analytical basis for sampling exhaled breath is that, at equilibrium, alcohol in expired air is present at a predictable ratio with blood. The gas exchange process in the lungs is complex, with significant theoretical variability.³⁴ In the United States, a blood-to-breath alcohol ratio of 2100:1 is commonly used in calibration of breath alcohol testing devices, although experimental evidence suggests that the ratio is actually closer to 2300:1.¹⁵ As such, a systematic underestimation of BAC is expected when breath alcohol results are converted to blood alcohol results. Several studies have documented this underestimation with data from suspected impaired drivers and evidential breath alcohol testing instruments.^18,23 In 1983, Britain adopted a legal limit in breath of 35 μg/100 mL, which corresponds to a blood alcohol of 80 mg/dL, using a 2300:1 blood-to-breath ratio.²⁷ Legal statutes that include in their offense definition breath alcohol results expressed in units of g/210 L of exhaled air eliminate the need to convert breath alcohol to blood alcohol, largely mitigating arguments based on the breath-to-blood ratio.

Three general analytical detection principles have been extensively validated and are currently used in breath alcohol testing instruments. These are, infrared spectroscopy, electrochemical oxidation/fuel cell, and chemical oxidation/photometry.²⁴ Additionally, combination of multiple technologies is sometimes used, as in infrared/fuel cell dual detectors. Breath testing instruments may be generally divided into four broad categories: passive alcohol sensors (PASs), screening devices (preliminary breath testers, {PBTs}), breath alcohol ignition interlock devices (BAIIDs), and evidential breath testers (EBTs).²⁴

A PAS device may be concealed in a device such as a modified police flashlight and is used to detect alcohol on or in the immediate vicinity of a subject through passive means (ie, with no requirement for subject cooperation). BAIIDs are used to prevent drinking and driving by requiring the driver to blow into a sensor in order to start the ignition of the vehicle. The devices are typically installed on a court order designed to modify drinking and driving behavior in habitual DUI offenders, with the cost of installation typically borne by the offender. A number of mechanisms are employed to prevent substitution of breath samples, including preset patterns of exhalation or humming while blowing into the sampling tube. Additionally, random rolling retests may be required, failure of which may result in the vehicle’s lights flashing or horn blowing. Neither PAS nor BAIID results are useful for quantitative measurement of breath or blood alcohol for prosecution of a per se DUI case.

The PBT and EBT devices are the most common breath alcohol testing devices encountered in cases of DUI arrest. In this setting, PBT results are used in conjunction with observation and field sobriety tests to establish probable cause for DUI arrest. Although a measured BrAC is often provided as a digital readout on a PBT, these results are not admissible as evidence for proceedings other than probable cause hearings in most jurisdictions. Use of PBT devices is also common in nonlegal settings such as hospital emergency departments, alcohol detoxification units, homeless shelters, and workplaces. As with DUI prosecution, these results are generally used for screening for alcohol presence and not for establishing impairment.

In contrast to PBT results, measurements from an EBT device are admissible in court and administrative proceedings and can be used as the basis for establishment of per se DUI cases without the necessity of blood collection and analysis. Although mobile EBT devices are available, most often the EBT is maintained in a fixed location such as a police station. For the results to be considered valid and admissible, the operator of the EBT must be trained and certified, and the operation must be performed using an accepted testing protocol.

Required procedures for the use of EBT devices exist for the both the subject as well as the instrument. The subject must have a period of alcohol deprivation of at least 15 minutes in which trained personnel observe him or her for a minimum of 15 minutes to ensure not only that no additional ethanol is consumed, but also that no regurgitation, emesis, or eructation occurs, which could result in residual ethanol in the mouth prior to breath alcohol analysis. With respect to the instrument, both blank and control analyses must be performed prior to analysis of the subject sample. A blank analysis, typically done with room air, purges the instrument of contamination from previous samples and demonstrates a lack of environmental contamination. A control analysis is performed on a gaseous ethanol sample of known concentration, usually an ethanol gas canister or wet bath simulator, and demonstrates proper instrument calibration and maintenance. Certification of instrument maintenance of calibration must be documented, demonstrating compliance with applicable rules, regulations, laws, and standards for routine maintenance, troubleshooting, and corrective actions. These documents are then retained for a relevant time period after inspections are complete. Additional documentation for individual cases should include written verification that all steps in the accepted protocol were followed. This documentation may also include automated printouts from the analyzer used, and well as copies of manual checklists.²⁴

Beyond the required procedures, additional recommendations include the use of g/210 L as the reporting units, rather than reporting breath alcohol concentration as a converted blood alcohol concentration of %w/v, g/100 mL, or g/dL. Serial collection and analysis of at least two separate sequential breath samples taken 2 to 10 minutes apart should be done in order to demonstrate the absence of residual mouth alcohol, instrument artifacts, frequency interference, and spurious results. Agreement of the serial results must be within prescribed limits (usually, 0.02 g/210 L) to be considered acceptable.²⁴

A driver whose BAC exceeds the established legal standard is considered per se intoxicated and may be convicted without behavioral evidence of intoxication. However, some objective findings of impairment may be important in establishing probable cause to demand chemical testing, initiate a DUI arrest, or prosecute a charge of impairment, without invoking per se limits. In these settings, results of a specific group of behavioral tests may be of value in discriminating and prosecuting an impaired driving charge, although submitting to these behavioral tests is typically voluntary. Additionally, an objective measurement of alcohol effect may be helpful in assessing alcohol-related impairment in nondriving situations, where it is inappropriate to apply per se standards.

Under a contract with the NHTSA, a group of 15 candidate sobriety tests were evaluated in a laboratory study.⁹ From this original group, the investigators developed a series of three specific tests that have subsequently been standardized as a test battery, known as standardized “field sobriety tests” (FSTs), for assessing driver impairment in the United States. The three tests comprising the standardized FSTs are the one-leg stand (OLS), walk-and-turn (WAT), and horizontal gaze nystagmus (HGN). Descriptions of these tests are provided in Table SC6–1.

A 1981 study of 297 drinking volunteers with BACs ranging from 0 to 180 mg/dL who were evaluated by trained police officers showed adequate interrater reliability (correlations, 0.6–0.8) and test-retest correlations (0.40–0.75).⁴⁶ Using all three field sobriety tests, the officers were able to distinguish whether BAC was above or below 100 mg/dL in 81% of participants. Test results were observed to correlate with BAC. However, the specificity and sensitivity of each individual test was not evaluated.

In the few studies evaluating the performance of individual FSTs, correlation between test performance and BAC is generally observed. Although the correlation magnitudes for the WAT and OLS tests are low, the HGN test showed excellent sensitivity and specificity across a range of BACs.³⁸ When the BAC was 0, using the WAT test, approximately 50% of the participants were judged to be impaired, and in the OLS test, 30% of the participants were rated as impaired. When the BAC was >150 mg/dL, sensitivity in the WAT and OLS tests improved to 78% and 88%, respectively. The rate of false positives (specificity; ie, those with a zero BAC who failed the HGN test) was only 3%. As seen with the other FSTs, the sensitivity of the HGN test increased with increasing BAC, being 81% for those with a BAC between 100 and 149 mg/dL and 100% for those with a BAC >150 mg/dL. The presence of horizontal gaze nystagmus, even in alcohol-tolerant drinkers, may give this test an advantage over the WAT and OLS tests in detecting the presence of alcohol.⁸ It is noteworthy that balance and coordination can be affected by factors unrelated to alcohol consumption, such as physical disability, age, and nervousness about potential arrest; however, chronic drinkers with substantial alcohol tolerance may be able to complete balance tests with few errors, even with moderate to high BACs.⁸

The three tests utilized for field sobriety assessment have some advantages, in that they are standardized and are easily understood by test takers; in addition, personnel administering the tests can be trained in a reasonable period of time.³³ However, because the test results are approximately correlated with BAC, their use is limited by the threshold BAC they are supposed to detect. Predictably, various scientific and legal challenges to the use of the FSTs have also been made. For example, the tests were designed and validated at a time when the per se DUI limit in most of the United States was 100 mg/dL; however, that threshold is now 80 mg/dL in every state (and 20–50 mg/dL in many European countries).³³ Due to the variability of psychomotor effects of alcohol as a result of individual tolerance, FST assessments are generally not allowed as a means of estimating BAC in court proceedings. The effects of fear, fatigue, rehearsal of test performance, the arresting officer’s knowledge of estimated BAC prior to administering the standardized FSTs, and various medical conditions have not been fully addressed. It has further been argued that the studies most strongly supporting use of standardized FSTs are those conducted by NHTSA-affiliated investigators and published in non–peer-reviewed government publications. So contentious has the debate been that in 2004 Booker openly leveled the charge that, “the United States Department of Transportation indulged in deliberate fraud in order to mislead the law enforcement and legal communities into believing the test (HGN) was scientifically meritorious and overvaluing its worth in the context of criminal evidence.” A comprehensive review detailing this, and other, legal and scientific issues surrounding standardized FSTs was published by in 2008.³⁹

The kinetic profile of ethanol in the blood has been extensively studied. In general, it is known that when blood ethanol concentration is greater than 20 mg/dL, it follows a zero-order elimination profile and then converts to first-order elimination when the concentration drops below this ­threshold.²⁵ In the zero-order portion of the curve, typical elimination rates range from 10 to 20 mg/dL/h in social drinkers. In one study of adult patients in an urban hospital emergency department, nonchronic users of alcohol (n = 9) demonstrated a mean elimination rate of 18.7 mg/dL/h (range, 16.1–21.4), while chronic users (n = 15; defined as more than two drinks per day, history of delirium tremens, or prior detoxification) had a mean elimination rate of 20.3 mg/dL/h (range, 16.1–24.6).⁵ The difference in elimination rates between the populations was statistically significant. Other studies have reported elimination rates of 30 to 50 mg/dL/h in chronic alcoholics due, at least in part, to enzyme induction.^5,6 Pharmacokinetic calculations in healthy nonalcoholic persons often employ a range of elimination rates of 10 to 20 mg/dL/h in order to best bracket individual differences.⁶

The estimation of the number of drinks ingested in order to achieve a given BAC has been extensively studied and is predicated on knowing several case-specific pieces of information. First, the specific definition of a “drink” in terms of alcohol content must be stated. According to the US Department of Agriculture, a standard drink consists of 12 ounces of beer (5% v/v), 5 ounces of wine (12% v/v), or 1.5 ounces of 80 proof spirits (40% v/v); each of these drinks contains approximately 14 g of ethanol.^6,50 The time period over which the ingestion occurred, the time of the last drink, and time of blood alcohol specimen collection must be known. It is helpful to know whether the subject was fasting or had a full stomach at the time of drinking because the presence of food in the stomach alters ethanol absorption.^29,52 Finally, the gender, age, height, and weight of the individual should be known and considered.

Using this information, estimation of the number of drinks is possible. The original work in which the prediction of ethanol concentrations from known doses was performed by Widmark in 1932 using 20 volunteer healthy moderate drinkers (10 of each gender). This research was translated from the original German into English by Baselt in 1981.^6,25 The basis of Widmark’s work was that the BAC in the body was directly proportional to the administered amount of alcohol (“dose”); the body weight of the subject; and a unitless scaling factor that Widmark referred to as “ρ” rho, which corrected the subject’s body weight for water content. Of note, in present-day pharmacokinetics, Widmark’s ρ represents the volume of distribution of ethanol. Due to the differences in body water content between sexes, ρ was determined to be approximately 0.6 in women and 0.7 in men. The original Widmark equation is therefore written as

where A represents the total amount of ethanol equilibrated in all fluids and tissues at the time of sampling (ie, total dose ingested), C is blood ethanol concentration in g/kg, ρ is the previously described Widmark ρ factor, and p is subject body weight in kilograms. Although the calculation has served well as an estimating tool for more than 70 years, it does have some limitations, principally in the ρ factor. As a result, refinement of Widmark’s original ρ was undertaken by others.^6,53 In his work, Watson derived a method for the estimation of total body water (TBW), which takes into account not only gender but also individual age, weight, and height. Watson’s method for estimation of TBW (abbreviated ΣV_d) for men aged 17 to 86 years yields the following equation:

For women aged 17 to 84 years, the TBW equation is:

In all persons, the height is measured in inches and the weight is measured in pounds. Note that the equation for men includes a mathematical term derived from age, and the equation for women does not.⁵³ The significance of this calculation is its ability to be tailored to a specific person, rather than the broad extrapolation of the relatively few subjects in the original study. Inclusion of such individual information improves the accuracy of such calculations.⁴²

The need for a more standardized approach to calculations involving alcohol in forensic medicine has been known for some time. This challenge was largely undertaken in a 2006.⁶ In this paper, the author summarizes 20 of the most common calculations with respect to alcohol. As an example, the following equation is derived to calculate the estimated dose of ethanol necessary to achieve a specific blood alcohol concentration:

where g EtOH is the ingested dose of ethanol in grams; BAC_target is the observed blood alcohol concentration in mg/dL; β_1–n is a range of alcohol elimination rates (typically, 10–20 mg/dL/h); t_s is the time from the start of drinking to the last drink; t_p is the range of times from the last drink to the peak PAC (typically, 30–90 minutes); ΣV_d is the Watson TBW, which is the volume of distribution based on age, weight, height and gender; and Bl_H2O is the approximate percentage of water in whole blood (80.65%).⁶ Noting the inherent variability in terms such as β_1–n and absent specific kinetic data from the individual in question, it can be seen that results of such equations should be presented as a range, rather than a discrete calculated value.

Some legal arguments have held that ethanol is odorless. This is, however, incorrect because ethanol has a characteristic pleasant smell, with an odor threshold of approximately 50 ppm.¹³ The presence or absence of breath alcohol odor is often used by police officers in the decision to proceed further with sobriety testing. In one study, 20 experienced police officers assessed alcohol odor on 14 subjects with BACs ranging from 0 to 130 mg/dL after drinking beer, wine, bourbon, or vodka.³⁵ Assessments were initiated 30 minutes after cessation of drinking. The strength of breath alcohol odor was determined to be an unreliable indicator of BAC. Correct detection of the presence of alcohol was 85% for BACs at or above 80 mg/dL but declined with decreasing BAC or the presence of food. The authors also noted that there were only small differences in odor intensity as a function of beverage type, meaning fusel oils and other constituents of alcoholic drinks are not the primary determinant of detectable odor after absorption of the beverage.

Liquor liability or “dram shop” laws hold the server of alcoholic beverages liable for damages or injuries caused by an individual who was provided alcohol when such service should have been refused. For example, if a minor or an individual who was already intoxicated is served alcohol and crashes his or her car, the person and/or establishment who served the alcohol may be liable for damages or injuries sustained in the crash.

Interestingly, US dram shop laws were first enacted in the mid 1800s, although they were rarely used. The initial intent of these laws was to provide financial support to the families of persons who had become “habitual drunkards” through their patronage of a drinking establishment.⁴¹ Repeal of Prohibition in the United States in 1933 shifted laws governing alcohol sales from federal to state control, resulting in state-to-state variability in alcohol availability, criminal and administrative laws, and liquor liability. There was also a move from public focus on habitual drunkenness to the damage caused by drunk drivers, as well as a paradigm shift in the standard for irresponsible service away from serving a “drunkard” to serving an individual who was “visibly intoxicated.”⁴¹ The purpose of liquor liability laws has also changed over time. In the 19th century, laws were enacted to punish tavern owners who contributed to the downfall of patrons. In contrast, current application of the laws is typically as a means to compensate innocent victims injured by an intoxicated patron. This action on behalf of the innocent victim is why liquor liability law is sometimes referred to as “third party” liability.

Beginning in the late 1970s and early 1980s, political activists began to take note of dram shop laws as an effective means for prevention of drunk driving. Outreach began to bring attention to irresponsible commercial and social service of alcohol. Various drunk-driving prevention strategies emerged, including “server intervention” (ie, the practice of bar or restaurant workers intervening to prevent an intoxicated patron from driving). Interestingly, although the goal of keeping intoxicated patrons from “getting behind the wheel” is certainly praiseworthy, these programs put notably less emphasis on preventing intoxication in the first place. The 1983 Presidential Commission on Drunk Driving recommended dram shop liability and server intervention as drunk-driving prevention strategies, and federal grant funds for state drunk-driving initiatives also listed such programs as qualifying criteria.¹⁶

Alcoholic Beverage Control agencies in the various states are responsible for reviewing and approving liquor licenses of commercial establishments, collecting taxes, and enforcing criminal and administrative laws prohibiting service to minors and intoxicated persons. Largely as a tool to improve public perception of the industry, the alcoholic beverage producers have largely been responsible for development of training programs for servers in the retail community. Numerous programs offering Responsible Beverage Service (RBS) training for servers are administered at the state or regional level, or even sponsored by the server’s employer themselves. Calls for greater organization and standardization of RBS programs in the United States have been answered, at least in part, by the Responsibility Hospitality Council, whose work has focused on developing minimum training standards for legitimate RBS training.⁴¹ Although such standards are often welcomed by regulators, some restaurant associations and owners have expressed concern over cost and compliance standards associated with RBS mandates. Nonetheless, the legal climate seems to dictate that alcoholic beverages be served in a “responsible” manner and that liability for “overservice” falls on the serving establishment. It is also noteworthy that cases putting liability onto individuals serving alcohol socially in their home have been successfully argued.

Neither the characteristic odor of ethanol nor various markers of alcohol exposure (eg, ethyl glucuronide, ethyl sulfate, carbohydrate deficient transferrin, and so on) are useful in estimating BAC or degree of intoxication. The ability of an individual to estimate his or her own BAC accurately is poor.^30,40 A lack of accuracy in estimating BAC is also observed in trained medical providers and police officers.^3,12 A large confounding factor in these observations is tolerance. Greater tolerance, as occurs in heavy drinkers and alcoholics, imparts greater difficulty in detecting the clinical effects associated with alcohol intoxication.

Tolerance involves a central adaptation to the intoxicating effects of alcohol. As such, persons with significant tolerance to the effects of ethanol may not manifest signs of intoxication despite having a high BAC. Multiple case reports and case series in the medical literature describe alcoholic individuals with very high BACs but muted or absent clinical effects.^{14,22,26,32,45} As a result of tolerance in the alcoholic population, it may not be possible to detect clinical intoxication even though an individual has a high BAC. This circumstance does not, however, suggest that even in the clinically sober alcoholic that driving abilities are unaffected and the individual is necessarily capable of safely operating a motor vehicle.³ Furthermore, tolerance has no bearing on the potential prosecution of a DUI case on a per se BAC basis.

The circumstance is slightly more straight forward in the social drinker. The intensity of the effects of alcohol on the central nervous system (CNS) is generally proportional to the concentration of alcohol in the blood. Dubowski has tabulated the stages and effects of acute alcohol intoxication, and these tables are used in educational programs and some legal proceedings. In general, the greater the BAC, the greater the clinical effect observed.

However, while useful as a pedagogic tool for explaining the continuum of alcohol intoxication, the table must be used with care as the effects are defined only over a population, thereby making assignment of a specific effect or degree of effect in an individual impossible. The inherent individual variability in the table is apparent in the fact that the BAC ranges for the various stages of alcoholic influence overlap. Furthermore, the population and methods used to compile the table are not described, and the table itself has not been subjected to peer review.

The CNS effects of alcohol intoxication are typically more pronounced on the ascending portion of the blood alcohol kinetic curve than on the descending side due to acute tolerance.¹⁹ In other words, the clinical effect of intoxication is greater during the absorptive arm of the kinetic curve than on the elimination arm, even though the same blood alcohol concentration is measured in both kinetic phases. This principle is known as acute tolerance, or the Mellanby effect.

In a dram shop case, the ultimate question often becomes this—what is the typical BAC at which it is more likely than not that the average nontolerant individual will exhibit signs of intoxication (eg, the odor of alcohol on the breath, clumsiness, difficulty walking or maintaining balance, slurred speech, inappropriate behavior) that are apparent to a bystander or third party? A 1986 report by the Council on Scientific Affairs of the AMA examined a review of seven studies spanning 50 years that included more than 6500 participants for identification of BACs at which individuals appeared “drunk” (ie, clinically intoxicated).¹ BACs were stratified by increments of 50 mg/dL, beginning at 0.0 to 50 mg/dL and extending to 401 mg/dL. In the lowest BAC group (0.0–50 mg/dL), observer perceptions of subject drunkenness ranged from 0% to 10%, with an average of 4%. The percentage of individuals determined by observers to be drunk increased steadily from a mean of 32% (range, 14%–68%) at a BAC of 51 to 100 mg/dL to a mean of 62% (range, 47%–93%) at a BAC of 101 to 150 mg/dL. In this latter range, four of the seven studies indicated a perception of drunkenness by less than or equal to 50% of observers. However, in the next BAC increment of 151 to 200 mg/dL, observers judged a mean of 89% (range, 83%–97%) of the drinkers to be drunk. In each of the subsequent higher increments, the mean percentage of persons classified as drunk ranged from 95% to 100% with no individual study value less than 90%. Therefore, it can be reasonably concluded that, in a nontolerant individual, a BAC of 151 to 200 mg/dL will more likely than not result in observable signs of drunkenness.

The validity of a police officer detecting intoxication in drivers involved in motor vehicle crashes also increases with increasing BAC. A 1996 report examined a total of 1336 subjects over age 15 who were admitted or died at a level 1 trauma center in Seattle during a 5 year period from 1986 to 1993 and in whom both a recorded BAC and a police assessment of sobriety were conducted.²¹ The blood alcohol measurement was conducted in the hospital, and it is not expressly stated if the analytical matrix used was whole blood, serum, or plasma. Four categories of sobriety assessment were used by police: (a) had not been drinking, (b) had been drinking–not impaired, (c) had been drinking–sobriety unknown, and (d) had been drinking–impaired. Officers used a battery of specific criteria to judge whether a driver was intoxicated, including odor on the breath, slurred speech, chemosis, poor coordination of motor function, and the ability to simultaneously perform multiple tasks. The greatest number of drivers were in the two extreme categories: had not been drinking (n = 746) and had been drinking–impaired (n = 568). A direct correlation between measured BAC and police officer assessment of sobriety was observed. The mean BAC associated with the “had been drinking–impaired” group was 190 mg/dL with a 95% confidence interval (CI) of 180 to 200 mg/dL. Those in the “had been drinking–sobriety unknown” group had a mean BAC of 130 mg/dL (95% CI, 110–150). Among all drivers, police field assessment of sobriety had a positive predictive value of 85% with sensitivity and specificity of 91% and 90%, respectively, demonstrating recognition of drunk driving by police with a high degree of accuracy, especially in the group with the highest BAC.

Another study designed to determine the ability of police officers, who have more training than the average lay person, to make assessments about alcohol intoxication in drinking target subjects without the aid of special testing normally available to them (eg, standardized field sobriety tests or the ability to smell the odor of alcohol on the subject’s breath).⁷ This study involved 39 police officers who viewed a series of videotaped interviews with six volunteer moderate drinkers having targeted BACs in three concentration ranges: low (80–90 mg/dL), medium (110–130 mg/dL), and high (150–160 mg/dL). Based on their observations of the taped interviews, the officers answered three questions:

1. Has the person been drinking?

2. Was it OK to serve that person one additional drink?

3. Was the person able to drive a car?

Each of the three questions could be answered “yes,” “no,” or “not sure.” A fourth question assessed the officers’ confidence in their answers as “not sure,” “little uncertain,” or “positive.” Question 2 was to be answered from the perspective of a social host or bartender, not a police officer. None of the police officers had any formal training in the management or service of alcohol to intoxicated people, such as that offered by commercial seller/server training programs such as Techniques in Alcohol Management or Training for Intervention Procedures. With respect to their answers, the police officers were fairly certain that the subjects had been drinking only in the target groups with the highest BAC (150–160 mg/dL). Officers also answered in the affirmative to question 2 (ie, that it was OK to serve the target subject another drink) the majority of the time in the low- and medium-BAC target groups but not in the high BAC target group. The percentage of officers answering affirmatively to this question was 55%, 75%, and 41% for the low, medium, and high target groups, respectively.

Multiple studies have examined the likelihood of on-premise (bars and restaurants) and off-premise (liquor stores, grocery stores, and convenience stores) as well as outdoor events like festivals to sell alcohol to obviously intoxicated persons (typically, paid professional actors pretending to be drunk).^{17,31,47, 48, and 49} The results are fairly uniform in that the majority of the time the alcohol was sold or served to the individual. Additionally, it was noted that male servers/clerks who appeared younger than age 31 were more likely to make such sales and the sales were more likely to occur in off-premise establishments.¹⁷

In a typical study, the authors employed 19 actors who were specifically hired based on their ability to feign intoxication. All actors were male and ranged in age from 31 to 59 years, with a mean of 42 years.⁴⁸ The actors used a standardized script to attempt to purchase either a single vodka drink after asking what beers were available on tap (on-premise) or a six-pack of beer (off-premise). Prior to entering the establishment, the actor received specific instructions to demonstrate multiple signs of intoxication, including disheveled hair and clothing, smelling of alcohol, lack of coordination, stumbling, fumbling with money, slurring words, repeating questions, appearing forgetful, and laughing inappropriately. If the actor was asked if he was driving, he responded “no” and if he was asked if he had been drinking, he responded, “I’ve had a few beers.” Attempts at alcohol purchase were made at 223 on-premise and 132 off-premise establishments.

Of the 355 attempts, actors were able to successfully make the alcohol purchase in 280 instances (79%). On-premise establishments served the actors 76% of the time, whereas off-premise establishments allowed the sale 83% of the time. Actors and a nondrinking observer also watched for clues that the server/clerk indicated an awareness or suspicion that the buyer was obviously intoxicated. Verbal indications, including asking the buyer to leave, suggesting a nonalcoholic drink, offering to call a cab, and so on, as well as nonverbal indications, such as staring or rolling of eyes, were recorded. A similar series of observations were made of security staff, other staff/bartenders/cashiers, and other customers. In 51% of the attempted purchases, there was an indication from the server of the recognition of the intoxication of the buyer. Even within the group that recognized signs of apparent intoxication, the alcohol was sold 61% of the time. When the server made no indication of the apparent intoxication, alcohol sales were completed 97% of the time. In 45% of purchase attempts, another staff member or customer made an indication that they believed the buyer was intoxicated. Still, alcohol purchases were completed in 66% of these cases. When no other staff member or customer indicating an awareness of the buyer’s behavior, the actor was served 89% of the time. The authors concluded that sales of alcohol to obviously intoxicated individuals in some US communities is very high and recommend additional study to identify effective training and tools to mitigate such illegal sales.

• Alcohol use is associated with clinical effects, which adversely affect the ability to safely operate a motor vehicle.

• Impaired driving charges may be prosecuted based on BAC and application of a per se statute, and analytical techniques capable of accurately measuring alcohol concentration in a variety of biological matrices have been available for decades.

• The ability to accurately predict a BAC after drinking is poor, not only for the drinking individual, but also for trained personnel such as police officers and medical professionals.

• Clinically apparent signs of alcohol intoxication may be difficult to detect in individuals with significant tolerance, increasing the probability of driving when BAC exceeds a per se value, or “overservice” in a bar or restaurant. Tolerance also seriously limits the applicability of tables correlating BAC with specific clinical effects in an individual case.

• While the use of standardized FSTs has become the norm in the prosecution of impaired driving cases, this battery of tests has also received significant legal and scientific criticism.

References