EXPERIENCES IN USING THE ALCOTEST FOR TESTING BREATH AS A GUIDE TO ALCOHOL CONCENTRATION IN THE BLOOD

Transcription

1 EXPERIENCES IN USING THE ALCOTEST FOR TESTING BREATH AS A GUIDE TO ALCOHOL CONCENTRATION IN THE BLOOD by K. GROSSKOPF f o r n e a r l y 10 years, the police patrols on the roads of the German Federal Republic have been using the Alcotest method for ascertaining at once in traffic offences whether the persons involved have taken alcohol. This simple method of alcohol detection in a sample of expired air was, at the outset, considered solely as a preliminary test designed to facilitate the officer s decision whether, in a given instance, the taking of a blood sample was justified or not. Since these tests were introduced in Germany, and later also in Sweden and Austria, almost two million Alcotests have been conducted. This figure alone speaks for the fact that the intended purpose has been fulfilled. The indication of the Alcotest Detector Tube is based on Widmark s reaction principle. The alcohol in the expired air is oxidized by chromosulphuric acid (impregnated on silica gel). For the test, one litre of ordinary expired air, i.e. a mixture of tidal and alveolar air, is blown through the tube into a flexible but nonelastic test bag in about 15 seconds. The test should not be conducted until at least 15 minutes after alcoholic drinks have been taken. Alcotest detector tubes are calibrated at body temperature with aqueous solutions of known vapour pressure. In the calibration process, the ratio of tidal air to alveolar air in the expired air sample is taken into account. This ratio was ascertained by tests using carbon-monoxide (which was previously inhaled up to a CO.Hb level of some 15%) as well as carbon-dioxide, as the guiding component. The respired air samples were collected in the same way as for the Alcotest itself and then analysed. Furthermore, the concentration of the guiding component was determined directly afterwards in an air sample which was re-respired twice. The quotients of the concentration values ascertained showed that the proportion of alveolar air, under the conditions of the test and therefore also in the Alcotest sample, averaged 70%. For the rest, the tests also showed that the COa content of the alveolar air fluctuates so considerably from one person to the next that it cannot be taken as a reference value for breath analysis. We found values ranging from 3-9 to 6-7%-vol.; the most frequent finding was 5-3%-vol.; standard divergence 0-5%-vol.1 The calibration data for the Alcotest detector tube, found by laboratory investigation, were checked repeatedly by comparative blood tests. As regards the latitude of error in breath alcohol tests, the conformity of the blood test findings with the Alcotest results must be regarded as satisfactory.2 3 This fact may be stressed as essential because it forms the basis of a reliable monitoring of detector tube qualities. From the extensive experience now available, the following statements can be made as to the qualities of the Alcotest detector tube. The tube will indicate an absolute quantity of alcohol of as little as 5 mg., the indicating layer becoming visibly discoloured green. Under the conditions of the test, this amount corresponds to a blood alcohol concentration of approx. 0-3 promille. With a smaller blood alcohol concentration, the test will always give a negative result, i.e. the indicating layer of the tube will remain yellow. The length of the green discoloured zone of the indicating layer increases in roughly the same proportion as the blood alcohol concentration. Discoloration extending to the mark printed on the tube corresponds, in the majority of cases, to a blood alcohol concentration between 0-7 and 0-8 promille. Knowledge of the spread of the tube indication is essential to practical use of the 281

2 282 ANALYTICAL METHODS (3) method. Faulty readings can arise, particularly near the critical limit ( promille) both as a result of chance variations in tube qualities - of technical origin and due to the test having been incorrectly conducted. In order to be able to judge both sources of error separately, the obvious solution is to consider the chance divergencies of the tube readings in isolation under the defined conditions of a model test. We therefore evaluated the test findings statistically on our calibration apparatus, i.e. we determined the likelihood of a given blood alcohol concentration being correctly assessed by the Alcotest. In line with the purpose of the test, we defined the correct indication by two requirements. 1. In the case of blood alcohol concentration values below 0-7 promille, the length of the discoloured zone ought not to reach the ring marking. The result is taken as negative. 2. In the case of blood alcohol concentration values of 0-7 promille and more, the discoloured zone should reach this mark or pass beyond it. The result is then taken as positive. In the light of the purpose of the Alcotest, the Yes-No decision can be regarded as fully adequate information. Nor should one ask more of the detector tube reading. T a b l e I L ik e lih o o d o f the O utcom e o f A lc o te st R eadings fo r Various B lo o d A lc o h o l C oncentration T est B a g Inflation T im e: 15 Seconds Blood alcohol Concentration promille Observations Readings* M ark not Reached Mark Reached or Passed Probabilities of the Indication Negative Positive In the region o f the m ark itself, a marked spreaddiminishing effect is observed. For sensory-physiological reasons, the naked eye cannot clearly detect a fallingshort o f the mark by 0-5 mm., a fact already known from earlier publications.*»6 The following conclusions can be drawn from the figures in Table I. They are valid subject to the tests having been conducted in the prescribed manner. 1. Blood alcohol concentration values above 0-9 promille always lead to positive Alcotest findings. 2. The Alcotest reading will be positive, i.e. its outcome will be correct in 98% of all cases for a blood alcohol concentration value of 0-8 promille or in 95% of all cases for a blood alcohol concentration value of 0-7 promille. 3. With blood alcohol concentration values of 0-6 promille, positive (i.e. wrong ) readings can be expected in two-thirds of all cases, although the critical, i.e. the legally important blood alcohol concentration limit is not attained. 4. With a blood alcohol concentration value of 0-5 promille, the Alcotest reading will be negative, i.e. correct in 95% of all cases. 5. Blood alcohol concentration values below 0-5 promille always produce negative Alcotest findings. It is interesting to compare these findings with those drawn from practical experience. Through statistical application of the results of Alcotest indications and comparative blood tests, it was found that the proportion of incorrect results given by the tube is something like 5% either way, i.e. in favour of or against the subject of the test.2 3 Naturally, this includes those errors caused by incorrect conduct of the test. We can, therefore, by comparison with our model findings, draw the conclusion that some of the erroneous results which occasionally occur in practical conduct of tests, can be attributed to the method being incorrectly applied. This is particularly true in those cases where a legally important blood alcohol concentration value was not detected by the Alcotest. On the other hand, it must initially be a source of surprise that in the practical application of the method, the number of incorrect readings in the region of the blood alcohol concentration values between 0-5 and 0-7 promille is still apparently inconsiderable. This can probably be explained by the conjecture that such subjects are tested relatively seldom because they do not give those around them the impression of having taken alcohol, and therefore remain unobtrusive. So, it happens more rarely than expected that the Alcotest finding falsely accuses the suspect. For the rest, comparative blood tests have fully confirmed our findings regarding the reliability of the Alcotest reading for blood alcohol concentration values below 0-5 promille (Alcotest always negative) and above 0-9 promille (Alcotest always positive).

3 GROSSKOPF 283 In any discussion of the incorrect readings in the region of the critical limit, it must also be taken into account that only njm, K- 6- A Konzentration der Alkohol-Losung ~l 3fi 7. Fig. 1. Intensity o f the Alcotest indication by mouth alcohol. Immediately before the Alcotest was conducted, 2 ml. o f aqueous alcohol solution of a definite concentration was placed on the subject s tongue with a pipette those incorrect indications are of legal significance which favour the person tested in other words, those which do not reveal a blood alcohol concentration value which is actually above the critical limit. In the other cases, the person concerned is cleared by the subsequent blood test which is compulsory. should be fully inflated at one go in 15 seconds, and certainly not for more than 20 seconds. The reason for the first condition can readily be seen. Immediately after alcoholic beverages have been drunk, a relatively highly concentrated alcohol solution is present in a limited quantity of saliva, and this must lead to a false Alcotest reading. The quantity of the saliva involved can, on the basis of our experimental data, be estimated at some 20 ml. The curve in Fig. 1 shows the effect of the primarily dissolved saliva alcohol. 2 ml. each of diluted aqueous alcohol solutions (0-1 to 5% weight) were administered by pipette to the tips of the test subjects tongues; they were instructed to distribute the solution over the mucous membranes in the oral cavity. Tests were conducted immediately afterwards. For the rest, this curve is identical with the calibration curve of the tube itself which, after all, only confirms that the tube is incapable of differentiating between alcohol which has been expired from the lungs and that which has been primarily dissolved in the saliva. Fig. 2 shows convincingly that the distorting influence of the saliva alcohol Fig. 2. D rop in the Alcotest reading (as a function of the time) directly after taking an alcoholic drink (a) or orange juice (b). Re Test a: 30 ml. of a 33%-vol. alcohol-water mixture taken at the time Zero. Re Test b: 210 ml. freshly squeezed orange juice taken at the time Zero. The effects of incorrectly conducting the test, as far as the tube readings are concerned, can at least be estimated from laboratory experiments. We have already mentioned the essential conditions to be watched during the test. The test itself should not be conducted sooner than 15 minutes after the taking of alcoholic or strongly aromatic drinks; the test bag disappears after some 10 minutes (curve a). Two test subjects had, at the time Zero, each drunk 30 ml. of a 33%-vol. alcoholwater mixture. The Alcotests were conducted after half a minute and one minute respectively. Curve b in the same illustration shows conclusively that falsification of the Alcotest reading by orange juice, as was often asserted, is as good as out of the

4 284 ANALYTICAL METHODS (3) question under practical conditions. At the time Zero, each had drunk 210 ml. of freshly extracted orange juice (in l \ minutes). It may be taken as certain that, a quarter of an hour after drinks have been taken, it is only the alcohol expired by the lungs, and in vapour balance with the blood alcohol, which is measured. This source of error, which is caused by premature testing, is therefore easily avoided. However, it is also possible to avoid wrong conclusions from those incorrect tube indications which can be expected if the test subject falls considerably short of, or greatly exceeds, the time prescribed for inflating the test bag. We have investigated the effect of the rate of flow through the tube statistically, on a model. Table II shows the probable outcome of detector tube indications with a blood alcohol concentration of 0-7 promille for various test bag filling times. One ought never to fall short of the shortest inflation time in this test series (10 seconds), although, for physiological reasons, this could only rarely happen due to the tube resistance to be overcome. There is, therefore, little likelihood of the suspect damaging his own case by inflating the bag too quickly. T a b l e II L ik e lih o o d o f the O utcom e o f A lc o te st R eadings fo r B lo o d A lcohol C o n cen tra tio n = 0-7 prom ille as a F unction o f the T est B a g Inflation T im e Inflation Time (secs.) Observations Probabilities of the Indication Negative Positive According to this, no value should be attached to a negative Alcotest result if inflation of the test bag took longer than 20 seconds. It can easily be demonstrated that, even with 2 promille and an inflation time of 60 seconds, the reading can still be negative! We should, therefore, like to assume that this source of error is the most frequent cause of misjudgments. On the other hand, it is obvious that a positive finding under these same circumstances may, without hesitation, be taken as indicative. Finally, no importance ought to be attached to a negative Alcotest result if the test bag was not inflated in at least two attempts. On account of the increased proportion of tidal air in the expired sample, the Alcotest finding should prove to be correspondingly too low, which will show up particularly in the borderline region of 0-7 promille. We have already stated that, according to the results of comparative blood tests, the Alcotest finding agreed with the blood alcohol value in at least 90% of cases. It has been our intention in this investigation to point out that this proportion of error can be still further reduced if the person conducting the test knows the most important sources of error and gives heed to them. We hope we have given some suggestions on the training of those who are to supervise and evaluate the results of the test. It is also important that they should be able to see the physiological connections, at least in their broad outlines. Even now, though, it can be said that this simple test which was conceived as a preliminary test, has already proved itself. Summary The Alcotest method has been used for almost 10 years by the Road Traffic Police in the German Federal Republic and for not quite such a long time by the police forces in Sweden and Austria as a preliminary test to judge immediately following traffic accidents whether the persons involved have taken alcohol; the results have been satisfactory. The present report deals with the reliability of Alcotest readings. Since the calibration data reached in laboratory work has been confirmed by comparative blood tests in numerous, repeated tests, it is possible to ascertain the statistical reliability of an Alcotest reading on the basis of a model test. In this way, it is possible to distinguish between chance variations and results which are inaccurate on account of the test having been improperly conducted. Some of the discrepancies observed in practice between the Alcotest reading and the actual blood alcohol value can be clearly attributed to wrong test procedure. The essential sources of error and their effect on the Alcotest findings are discussed. ' R e f e r e n c e s 1 Grosskopf, K. (1961). Zbl. Asbeitsmed., 11, Sachs, V. (1959). Dtsch. Z. ges. gerichtl. Med., 48, Herbich, J., and Kaiser, G. (1962). Wien. med. Wschr., 112, Sachs, V. (1955). Scientific Information Bulletin o f the Draeger Works, No. 25, p Grosskopf, K. (1954). Chem. Zeitung, 78, 11.

5 Dr. S. Tara (France): As the General Secretary of the National Committee for Defence against Alcoholism, I have been concerned with the Alcotest. I can confirm that if you use the instrument according to Dr. Grosskopf s instructions you will get absolutely valid results. Professor Monot, who is a member of K. GROSSKOPF 285 DISCUSSION the Academy of Medicine in France, has obtained the consent of the Ministry of Justice to use the Alcotest to test motorists involved in accidents. Monsieur Obr6s has also told me this morning that the Alcotest can identify intoxicated workers in factories and thereby reduce accidents.