Evolution of blood ethanol concentrations at traffic controls. Validation of a formula to calculate the imprecision of a retrospective extrapolation

Transcription

1 UNIDAD DE TOXICOLOGIA CLINICA HOSPITAL CLINICO UNIVERSITARIO DE ZARAGOZA Evolution of blood ethanol concentrations at traffic controls. Validation of a formula to calculate the imprecision of a retrospective extrapolation Ana Ferrer Dufol, Sebastián Menao Guillén, Francisco Ruiz Ruiz, María Santamaría Gonzalez

2 Rational of Traffic Controls of BAC To try to avoid the behavior of driving under effect due to its well established risk The effect of ethanol on the driving skills is reasonably correlated with the blood alcohol concentration Introduction

3 Legal limits Fine limit: Legal implications GP 0,25 mg/l (breath) 0,50 g/l (blood) YD, PD 0,15 mg/l (breath) 0,30 g/l (blood) Criminal offence (Prison sentence) : 0,60 mg/l (breath) 1,20 g/l (blood) Legal right to obtain a blood analysis if the breath result is over the legal limit GP = General Population YD = Young Drivers PD = Proffesional Drivers

4 Introduction Traffic Controls of BAC Random controls Driving offences Traffic accidents BAC estimation Extrapolation from Breath [etoh] Ethylometer combining infrared spectrophotometer and electrochemical technology Blood analysis GC/FID after head space extraction

5 Scenarios The breath result is accepted The breath result is challenged and a blood analysis is requested No breath analysis is performed and a blood analysis is requested Time?

6 Widmark Graph C 0 C t C 0 = C t + (t x β) 0,9 = 0,5 + (2 x 0,2)

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8 VARIABLES RANGES Absorption speed <===> plasmatic peak Fasting: 0,5 2 h No fasting: 1 6 h Distribution volume men: 0,50 0,90 L/kg women: 0,46 0,86 L/kg Ethyloxidation coeficient men: 0,11 0,22 g/l/h (mean = 0,15) women: 0,11 0,22 g/l/h (mean = 0,18) alcoholics: 0,16 0,43 g/l/h (mean = 0,27)

9 UNIT OF CLINICAL TOXICOLOGY ethanol blood analysis coming from traffic events 9597 ethanol blood analysis coming from clinic events

10 Ratio [EtOH] serum/blood: mean 1,27/1 ± 0,5

11 OBJETIVE Time? BAC?

12 Material and Methods 952 samples received at our laboratory coming from traffic controls Data: Breath alcohol concentration and time between breath and blood samples

13 Material and Methods The breath ethanol concentration was obtained by means of the standard evidential ethylometer BAC was measured by GC/FID after head space extraction Conversion factors for breath data: 2000 and 2100

14 Results CF 2000 CF 2100 Mean [EtOH] calculated from breath Mean [EtOH] blood Mean time between samples (±0.51) g/l (±0.51) g/l (±0.58) g/l 71.8 (17-388) min Factor 2000 Factor ,4 66,7 Breath > Blood 22,8 Breath = Blood 2,2 Breath > Blood 75 Breath > Blood Breath = Blood Breath >Blood 1,9

15 1,2 1 0,8 0,6 0,4 Co-Ct 0,2 0-0,2 G ,4-0,6-0,8-1 Time(min)

16 1 0,8 0,6 y = 0,0012x 0,4 0,2 (Co - Ct)/ Co 0-0, ,4-0,6 Time between samples(min) -0,8

17 Frequency Median= -0,01 Typical deviation = 0,183 N = 963 f r e q u e n c y Distribution

18 BAC (C 0 ) BAC t (g/l) 0 0,66 0,66 0,66 Time (min) mean BAC 0 0,00 0,70 0,74 0,77 BAC 0 max (95% conf) 0,00 1,14 1,26 1,35 BAC 0 min (95% conf) 0,00 0,50 0,52 0,54 BAC 0 max (99% conf) 0,00 1,40 1,59 1,74 BAC 0 min (99% conf) 0,00 0,46 0,48 0,50

19 BAC (C 0 ) BAC t (g/l) 0 0,74 0,74 Time (min) mean BAC 0 0,00 0,76 0,97 0,00 BAC 0 max (95% conf) 0,00 1,22 1,88 0,00 BAC 0 min (95% conf) 0,00 0,55 0,66 0,00 BAC 0 max (99% conf) 0,00 1,48 2,60 0,00 BAC 0 min (99% conf) 0,00 0,51 0,60 0,00

20 t = 20 ci 95% 1.22 g/l 0.76 g/l 0.74 g/l 0.55 g/l

21 t = 20 ci 99% 1.48 g/l 0.76 g/l 0.74 g/l 0.51 g/l

22 t = 200 ci 95% 1.88 g/l 0.97 g/l 0.66 g/l 0.74 g/l

23 t = 200 ci 99% 2.60 g/l 0.97 g/l 0.60 g/l 0.74 g/l

24 Formula Validation Overestimated values 95% conf 99% conf 33 (3,5 %) 15 (1,6%) Right values 900 (94,5%) 930 (97,7%) Underestimated values 19 (2%) 7 (0,7%)

25 Conclusion Ethanol kinetics in real situations produces a high degree of variability in the evolution of BAC We have developed a formula to predict, with a confidence interval of 99%, the range of values of a BAC at a given, previous, time from the current BAC The range of this estimation is very wide, in a concentration and time-dependent function Current legislation should be modified to establish a time limit for the accepted confirmation test