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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, however, are extrapolated from the legal to the medical setting. Throughout this chapter, the terms ethanol and alcohol are used interchangeably in order to retain the forensic, legislative, and medical contexts in which the terms are used. Similarly, words such as drunk and punishable are also occasionally used in this chapter in order to preserve the specific language used in the early studies and legal writings.
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Numerous well-designed laboratory studies assessing alcohol-induced impairment are published. However, application of study results to actual cases of possible impaired driving 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 at least the 1850s, the first arrest for drunk driving in an automobile was that of a London taxicab driver in 1897.22 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.” In 1910, New York was the first US state to enact such a law.22
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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 work by Widmark67 in Sweden, and by Heise27 in the United States, 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).
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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 is 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.
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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” does not exist. A typical medical definition focuses on altered mental status, ataxia, or the ability to care for oneself, whereas the focus of a legal definition is on the ability to safely operate a motor vehicle or successfully perform field sobriety tests, or whether the patron of a bar or restaurant should be served additional alcohol. A lay public definition may include parts of both.
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Although alcohol intoxication is an important factor in a nearly infinite number of settings, 2 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 additional alcohol. Discussion of alcohol use in the workplace and alcohol-abstinence monitoring are beyond the scope of this chapter.
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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 1939.28 The approach taken by the Indiana legislature resulted in a 3-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 deemed guilty of driving while impaired by alcohol, even without any other evidence of intoxication or impairment.
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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.28 This reduction in the per se legal BAC for an alcohol-impaired driving 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 legislators were then forced to define more clearly and objectively.
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Different states use different acronyms to apply to alcohol-impaired driving, including DUI (driving under the influence), DUIL (driving under the influence of liquor), DWI (driving while intoxicated), OUI (operating under the influence), OWI (operating while intoxicated), and OMVI (operating a motor vehicle while intoxicated). Regardless of the acronym used, the definitions are effectively the same. Depending on the state, the same terms may also be used in drug-impaired driving, whereas in other states, a separate charge, such as DUID (driving under the influence of drugs) may be applied to nonalcohol drug-related driving impairment.
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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.69 The 2014 NHTSA data suggest a slight decrease in alcohol-related fatalities, with 31% of fatal motor vehicle crashes involving a driver with a BAC of 80 mg/dL or greater, corresponding to one alcohol-impaired-driving fatality occurring every 53 minutes.43 However, it must be noted that NHTSA considers any fatal crash in which a driver has a BAC of 80 mg/dL or greater to be an alcohol-impaired driving crash; and, fatalities in these crashes are considered to be due to alcohol-impaired driving.43 Critics of the NHTSA data claim this method for counting likely overestimates the number of actual fatalities involved in alcohol-related crashes as the mere fact that a driver had consumed alcohol and had a BAC of greater than or equal to 80 mg/dL does not prove crash causality. Nonetheless, there is little argument that alcohol use increases crash risk. Epidemiologic 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 4-fold at a BrAC of 80 mg/dL, 7-fold at a BrAC of 100 mg/dL, and 25-fold at a BrAC of 150 mg/dL.5,28 In 1994, a successful campaign, vigorously supported by the AMA and Mothers Against Drunk Driving (MADD), encouraged all states in the US to lower the BAC used to define per se intoxicated driving to 80 mg/dL.22 Although all states technically have the right to set drunk-driving statutes at their discretion, political advocates for more strict alcohol-impaired driving statutes were 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.22 Consequently, as of July 2004, all US 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 US 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. Some US states also have legal standards defining an “aggravated DUI.” Definitions of “aggravated DUI” are variable by state, but some of the actions that may lead to this charge include, committing a DUI while under court order to use an approved ignition interlock device, committing a DUI while the offender’s driver’s license or driving privileges are suspended, canceled, or revoked because of a prior DUI violation, or committing multiple DUIs in a specified time period (eg, 10 years). States such as Montana have an additional standard that charges an individual with aggravated DUI if the driver’s BAC is found to be 160 mg/dL, or more.
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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.
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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 concentrations have all formed bases for legal challenges to per se laws.22 However, despite such challenges, the courts consistently uphold these laws.
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ANALYTICAL CONSIDERATIONS
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Accurate measurement of ethanol concentration in various biological matrices can be done using a number of analytical techniques. Historically, Widmark employed wet chemical oxidation, using potassium dichromate and excess sulfuric acid, followed by iodometric titration of the remaining amount of oxidizing agent.67 Although this method is effective, it is laborious and lacks specificity if other volatiles (eg, methanol, acetone, ether) are present, as these substances are also oxidized, causing a falsely elevated ethanol result. Such wet chemical methods are now obsolete and no longer used in forensic and clinical laboratories.
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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. Additionally, acetone, which caused 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 occur with ADH isolated from humans and other animals; this interference is reduced by using yeast-derived ADH, which shows greater selectivity for ethanol.31,64 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. 7). Comparative study of ethanol determination by REA and gas chromatography shows excellent agreement in precision and accuracy between the 2 techniques.12 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.3,44
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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°F to 140°F (50°C–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.56 This problem is solved by the addition of sodium azide or sodium dithionite to block the oxidation or simply reducing the equilibrium temperature to 104°F to 122°F (40°C–50°C).56 Once chromatographic separation is achieved, various detection methods, including flame ionization (FID), electron capture (EC), and electrochemical sensing are used (Chap. 7). Dual detection (eg, FID and EC) can also be useful in circumstances where a larger number of volatiles may need to be screened.57
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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 1.1 to 1.35.45 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.69 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.11
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Breath testing is commonly performed to assess BAC because of its relative simplicity and less invasive collection compared to 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.40 In the United States, a blood-to-breath alcohol ratio of 2100:1 is commonly used in the calibration of breath alcohol testing devices, although some experimental evidence suggests that the ratio is actually closer to 2300:1.17 As such, a systematic underestimation of BAC is expected when breath alcohol results are converted to whole blood alcohol results. Several studies document this underestimation with data from suspected impaired drivers and evidential breath alcohol testing instruments.20,25 In 1983, Britain adopted a legal limit in breath of 35 mcg/100 mL, which corresponds to a blood alcohol of 80 mg/dL, using a 2300:1 blood-to-breath ratio.28 Legal statutes that include in their offense definition breath alcohol results expressed in units of grams/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.
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BREATH-TESTING DEVICES
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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.26 Additionally, combination of multiple technologies is sometimes used, as in infrared/fuel cell dual detectors. Breath-testing instruments are generally divided into 4 broad categories: passive alcohol sensors (PASs), screening devices (preliminary breath testers, {PBTs}), breath alcohol ignition interlock devices (BAIIDs), and evidential breath testers (EBTs).26
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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). Breath alcohol ignition interlock devices 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 are required, failure of which 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.
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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, in most jurisdictions these results are not admissible as evidence for proceedings other than probable cause hearings. 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.
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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.
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Required procedures for the use of EBT devices exist for the subject as well as the instrument. The subject must have a period of alcohol deprivation of at least 15 to 20 minutes during which trained personnel observe him or her 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 also includes automated printouts from the analyzer used, and well as copies of manual checklists.26
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Beyond the required procedures, additional recommendations include the use of grams/210 L as the reporting units, rather than reporting breath alcohol concentration as a converted blood alcohol concentration of %weight/volume, grams/100 mL, or grams/deciliter. Serial collection and analysis of at least 2 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.26
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STANDARDIZED FIELD SOBRIETY TESTS
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A driver whose BAC exceeds the established legal standard is considered per se intoxicated and often convicted without behavioral evidence of intoxication. However, some objective findings of impairment assists 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 are of value in discriminating and prosecuting or refuting an impaired driving charge, although submitting to these behavioral tests is typically voluntary. Additionally, an objective measurement of alcohol effect is helpful in assessing alcohol-related impairment in nondriving situations, where it is inappropriate to directly apply per se standards.
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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 3 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 3 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 SC11–1.
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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).59 Using all 3 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 generally correlate with BAC. However, the specificity and sensitivity of each individual test was not evaluated. Field sobriety tests are typically associated with physical, rather than mental, ability other than understanding the instructions for each test. Some aspects of variability in cognitive performance correlate moderately and positively with facets of FSTs, especially those tests evaluating reaction time.16
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In the few studies evaluating the performance of individual FSTs, general correlation between test performance and BAC is 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.46 In the control arm (ie, no alcohol ingested and no detectable ethanol in the blood), approximately 50% of the participants were judged to be impaired using the WAT test, whereas in the OLS test, 30% of the participants were rated as impaired. When the BAC was greater than 150 mg/dL, performance on the WAT and OLS tests improved to 78% and 88%, respectively. The rate of false positives (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 greater than 150 mg/dL. The presence of horizontal gaze nystagmus, even in alcohol-tolerant drinkers, gives this test an advantage over the WAT and OLS tests in detecting the presence of alcohol.10 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 are reportedly able to complete balance tests with few errors, even with moderate to high BACs.9
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The 3 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 matter of hours.39 However, because the test results are only approximately correlated with BAC, their use is limited by the threshold BAC they are able 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).39 Because of 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 reported in non–peer-reviewed government publications. So contentious has the debate been that some have charged 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 in 2008.50 The author concluded that SFTs are not useful in predicting BAC, and that further research is needed to determine whether improvements can be made to the current battery of tests included in FST assessments. Despite arguments of FSTs having limitations, these assessments are still commonly used in arrest and prosecution of alcohol-impaired driving cases.
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ESTIMATING THE AMOUNT OF ALCOHOL INGESTED
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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.30 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), whereas chronic users (n = 15; defined as more than 2 drinks per day, history of delirium tremens, or prior detoxification) had a significantly greater mean elimination rate of 20.3 mg/dL/h (range, 16.1–24.6).6 Other studies report elimination rates of 30 to 50 mg/dL/h in chronic heavy drinkers due, at least in part, to metabolic enzyme induction.6,7 Pharmacokinetic calculations in healthy persons often employ a range of elimination rates of 10 to 20 mg/dL/h in order to best bracket individual differences.7
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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. 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.7,63 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 slows ethanol absorption.34,65 Finally, the gender, age, height, and weight of the individual should be known and considered.7
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Using this information, an 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 healthy volunteer moderate drinkers (10 of each gender).67 This work was translated into English from the original German by Baselt in 1981.68 The basis of Widmark’s work was that the BAC 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 effectively represents the volume of distribution of ethanol. Because of 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
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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 grams/kilogram, 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 80 years, it does have some limitations, principally in the ρ factor. As a result, refinement of Widmark’s original ρ was undertaken by others.7,66 One method for the estimation of total body water (TBW), which takes into account not only gender but also individual age, weight, and height (abbreviated ΣVd) for men aged 17 to 86 years yields the following equation:
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For women aged 17 to 84 years, the TBW equation is:
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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.66 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.54
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The need for a more standardized approach to calculations involving alcohol in forensic medicine has been known for decades. One author summarized 20 of the most commonly used alcohol-related calculations.7 As an example, the following equation is derived to calculate the estimated dose of ethanol necessary to achieve a specific blood alcohol concentration:
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where g EtOH is the ingested dose of ethanol in grams; BACtarget is the observed blood alcohol concentration in mg/dL; β1–n is a range of alcohol elimination rates (typically, 10–20 mg/dL/h); ts is the time from the start of drinking to the last drink; tp is the range of times from the last drink to the peak BAC (typically, 30–90 minutes); ΣVd is the Watson TBW, which is the volume of distribution based on age, weight, height and gender; and BlH2O is the approximate percentage of water in whole blood (80.65%).7 Noting the inherent variability in terms such as β1–n and absent specific kinetic data from the individual in question, it can be seen that results of such equations are most reasonably presented as a range, rather than a single discrete calculated value.
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Some legal arguments have quite incorrectly suggested that ethanol is odorless. Ethanol has a characteristic pleasant smell, with an odor threshold of approximately 50 ppm.14 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.42 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.
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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 an individual who was already intoxicated, or any minor, is served alcohol and crashes his or her vehicle, the person and/or establishment who served the alcohol may be liable for damages or injuries sustained in the crash.
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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.52 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 impaired 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.”52 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. By 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.
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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 impaired driving (or DWI). 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 impaired-driving initiatives also listed such programs as qualifying criteria.1
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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 the 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 sometimes even sponsored by the server’s employer. Calls for greater organization and standardization of RBS programs in the United States have been answered, at least in part, by the Responsible Hospitality Council, whose work has focused on developing minimum standards for legitimate RBS training.52 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 US 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 placing liability on individuals serving alcohol socially in their home have been successfully argued.
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Direct comparison of the efficacy of dram shop liability laws between states is difficult as liability laws and insurance vary widely. Historically, different states and regions emphasized different areas of alcohol service liability, and it was noted that research played only a minor role in determining server training, with the majority of policy formation arising from political influence.52 However, even data collected in the 1980s suggested that dram shop laws did result in a statistically significant decline in mortality rates not only for motor vehicle collisions, but also for other alcohol-related causes.55 A more recent study concluded that dram shop liability and RBS laws were associated with significant reduction in per capita beer consumption and fatal crash ratios in drivers under age 21.53 This begged the question of whether enhanced enforcement of dram shop laws would result in a decrease in excessive alcohol consumption and related consequences. An evaluation of 11 studies concluded that while dram shop laws were effective in reducing alcohol-related harms, the data supporting the efficacy of enhanced enforcement on reduction of alcohol-related harms were mixed and ultimately judged insufficient.47
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Specific study of alcohol service liability on younger and underage drinkers has also been investigated. Reduction of the legal age for alcohol purchasing from 20 to 18 in New Zealand in December of 1999 resulted in a statistically significant increase in traffic injuries attributable to male drivers aged 15 to 19 years.33 Review of annual fatal motor vehicle collision data from the United States showed that the most effective interventions for the prevention of underage alcohol-related fatal crashes were those associated with reducing teen drinking, rather than those restricting teen driving.49 An evaluation of 20 minimum legal drinking age 21 (MLDA-21) laws in order to assess which had an effect on fatal underage drinking and driving traffic crashes.18 Nine of the laws were associated with a decrease in fatal crash ratios: fake identification support for retailers (−11.9%), use alcohol and lose your driver’s license (−7.9%), possession of alcohol (−7.1%), purchase of alcohol (−4.2%), age of the bartender greater than or equal to 21 (−4.1%), responsible beverage service program (−3.8%), zero tolerance 0.02 BAC limits for underage drivers (−2.9%), state dram shop liability (−2.5%), and social host civil liability (−1.7%). Interestingly, 2 laws were associated with a significant increase in fatal underage crash ratios (registration of beer kegs [+9.6%], and prohibition of furnishing alcohol to minors [+7.2%]). The authors concluded that 9 effective MLDA-21 laws were responsible for saving an estimated 1,135 lives annually, though only 5 states have adopted all 9 of these laws.
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INTOXICATION AND ESTIMATION OF BLOOD ALCOHOL CONCENTRATION
++
Neither the characteristic odor of ethanol nor the measurement of 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 accurately estimate his or her own BAC is poor.35,51 Drivers who underestimate their own BAC are more impulsive and riskier drivers than those who overestimate their BAC.36 A lack of accuracy in estimating BAC is also observed in trained medical providers and police officers.4,13 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.
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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 heavy alcohol consumption who have very high BACs but muted or absent clinical effects.15,24,29,38,48,58 As a result of tolerance in the chronic heavy drinking population, it is often difficult to detect clinical intoxication even though an individual has a high BAC. Critically, this circumstance does not suggest that, even in the clinically sober chronic drinker, driving abilities are unaffected or that the individual is necessarily capable of safely operating a motor vehicle.4 Furthermore, tolerance has no bearing on the potential prosecution of a DUI case on a per se BAC or BrAC basis.
++
The circumstance is slightly more straightforward 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 tabulated the stages and effects of acute alcohol intoxication, and these tables are often used in educational programs and some legal proceedings.
++
However, though 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.21 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.
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In a dram shop case, the ultimate question often becomes, 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 untrained casual observer? A 1986 report by the Council on Scientific Affairs of the AMA reviewed 7 studies spanning 50 years that included more than 6,500 participants for identification of BACs at which individuals appeared “drunk” (ie, clinically intoxicated).2 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, 4 of the 7 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 to a casual observer.
++
Study of the effects of alcohol on driving performance has been the subject of decades of research. Driving simulators are often used in laboratory studies of impaired driving and have the benefit of easy replication and control of experimental conditions. A number of simulation devices have also been developed including “fatal vision goggles,” which provide visual distortion to the wearer in order to simulate the effects of alcohol on visual perception.41 Additionally, simulators and simulation devices allow study of the effects of impairing substances in populations in which actual drinking is legally or ethically unacceptable (eg, underage prelicensed drivers). However, it is known that driving performance evaluated in a simulator is less sensitive to the effects of alcohol than actual on-the-road driving.32 Additionally, despite frequent use, many driving simulator tests lack validation and head-to-head comparison with naturalistic driving.32
++
The validity of a police officer detecting intoxication in drivers involved in motor vehicle crashes also increases with increasing BAC. One 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.23 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 2 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).8 This study involved 39 police officers who viewed a series of videotaped interviews with 6 volunteer moderate drinkers having targeted BACs in 3 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 3 questions:
++
Has the person been drinking?
Was it OK to serve that person one additional drink?
Was the person able to drive a car?
++
Each of the 3 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 like Techniques of Alcohol Management (TAM) or Training for Intervention Procedures (TIPS). 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).19,37,60-62 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.19
++
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.61 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 6-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. Details of responsible beverage service (RBS) training for individual servers were not provided, though the authors did comment that such training is an important tool in preventing illegal alcohol sales, especially in younger servers. The authors concluded that sales of alcohol to obviously intoxicated individuals in some US communities is very high and recommended additional study to identify effective training and tools to mitigate such illegal sales.
++
Impaired driving charges may be prosecuted based on BAC and application of a per se statute, as well as on observations of impairment such as standardized field sobriety tests (FSTs).
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.
Casual observers begin to reliably detect signs of alcohol intoxication in nontolerant persons at a BAC of 150 mg/dL.
Clinically apparent signs of alcohol intoxication are 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.
The use of standardized FSTs is the norm for prosecution of impaired driving cases, though this battery of tests has also received significant legal and scientific criticism.
Of the 3 routinely used FSTs, horizontal gaze nystagmus (HGN) has the best correlation with BAC.
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