The present paper examined the question as to the extent to which the taking of gas samples for the purpose of measuring the breath alcohol concentration (BAC) in the expired air of patients on artificial respiration is influenced by temperature and humidity. For this purpose a lung model standardized at different alcohol concentrations was used, in which the temperature (T: 25, 30 and 35 degrees C) and the relative humidity (RH: 50, 75 and 95%) were varied.
UNLABELLED: When looking for the possible cause of distortions in values measured for the determination of breath ethanol concentration (BEC) in artificially respirated patients, consideration must be given to the humidity and temperature of the gas examined. In the present study, the effects of humidified and warmed and of dry and cold air on the accuracy of a newly developed BEC measuring device, as compared to a reference model and to a conventional system, were examined in a lung model. METHODS: A temperature-regulated pediatric incubator was used containing a 10 I gas reservoir and a breath humidifier with temperature regulated water bath. This setup provided constant temperature and humidity in the gas examined during measurement period. In the 'expiration' the air was directed from the breath humidifier through a measuring unit via a 'mouthpiece' into the reference system (Alcotest 7110, Dräger Inc., Lübeck) and then out. The measuring unit consisted of sensors for the temperature and relative humidity, and of a connector for the three sample extraction systems (PES). PES I was the conventional system with a 100-cm gas-sample pipe (Alcomed 3010), PES II the newly developed system (AlcoMed 3011, both from Envitec, Wismar) with a 10-cm gas-sample pipe, and PES III with a 20-cm heated gas-sample pipe. During 'inspiration' 2 l of air was fed into the system to rinse the measuring unit and to fill the reservoir. 61 measurements were performed with dry and cold air, and 71 with humidified and warmed air, in the course of which the ethanol concentration was increased from 0 to 1.5/1000. Data were evaluated using regression analysis and the Bland & Altman method. RESULTS AND CONCLUSIONS: The constancy of the values set for temperature, relative humidity and absolute humidity in the lung model was given for all measurements. In the dry and cold air, the results from all three test systems coincided almost perfectly with the reference values. The measured BEC in the humidified and warmed air using sample-extraction systems II and III corresponded to a high degree with the reference, while in the case of PES I, only a moderate linear correlation was achieved. The temperature and humidity of the expired gas during artificial respiration influence the gas samples extracted for the purposes of BEC measurement. Newly developed sample-extraction systems II and III coincide with the reference system, even under respiration-simulated gas conditions.
One way of determining pulmonary CO2 elimination during anaesthesia is the breath-by-breath method. With this technique, CO2 analysis is carried out using either the mainstream method (MSM), that is, directly in the expired air flow, or in samples of expired air. A disadvantage of MSM is the lack of sensor signal correction for changes in the composition of the gas mixture and barometric pressure. Sidestream Systems (SSM) measure respiratory gas flow and gas con- centration with adequate accuracy, and also correct the measured values for gas composition and ambient parameters. Disadvantages of breath-by-breath analysis are the SSM-system-rela- ted delay and distortion of the CO2 curves. In the present study, a computer-assisted comparati- ve analysis of CO, elimination measurement by the sidestream and mainstream methods was carried out using ctiff erent mixtures of gases in a lung model. Under the selected conditions simulated in the lung model, evaluation of CO2 elimination using SSM and MSM is possible with an error of between 0 and 10 % versus reference Systems.Measu- ring accuracy of the MSM System in particular is found to depend directly on the composition of the gas mixture. Using the method described here, the measuring error of an SSM System in terms of delay and response time can be compensated with adequate accuracy.
Der Effekt von Temperatur und Luftfeuchtigkeit auf die Gasprobenentnahme zur Messung der Atem-Alkoholkonzentration (AAK) wurde zwischen 0 und 1,5‰ in einem Lungenmodell bei Messungen sowohl in trockener und kühler als auch in feuchter und angewärmter Luft untersucht. Methodik: Neben dem herkömmlichen Probenentnahmesystem (PES) mit einem 100 cm langen Schlauch (Alcomed 3010®, PES I) wurde ein weiterentwickeltes Gerät mit verbessertem Gasprobentransport (AlcoMed 3011®, beide Fa. Envitec, Wismar) und 10 cm kurzem (PES II) sowie 20 cm kurzem und auf 36°C beheiztem Gasprobenschlauch (PES III) gegenüber einem Referenzsystem mit Infrarot-Sensor (Alcotest 7110®, Fa. Dräger, Lübeck) eingesetzt. Ergebnisse: In der trockenen und kühlen Luft entsprachen die Meßergebnisse aller 3 Testsysteme fast idealerweise den Referenzwerten. Bei den Messungen in feuchter und angewärmter Luft bestand diese Übereinstimmung für das PES II und III, während das PES I keinen linearen Zusammenhang mit den Referenzwerten zeigte. Schlußfolgerung: Die Temperatur und die Luftfeuchtigkeit hat einen erheblichen Einfluß auf die AAK-Messung bei beatmeten Patienten und ist bei der Probenentnahme zu berücksichtigen.
Conference Contributions (1)
H. Gehring, W. Nahm, D. Hufker, A. Schmitz, W. Mertins, and E. Konecny. Messung der Atem-Alkoholkonzentration während der Beatmung. Modelluntersuchungen zum Einfluß der Temperatur und Luftfeuchtigkeit auf die Reproduzierbarkeit der Messung verschiedener Probenentnahmesystem - Measuring breath alcohol concentration during artificial ventilation. Model studies of the effect of temperature and humidity on the reproducibility of measurements of various sampling systems].. In Biomedizinische Technik. Biomedical Engineering, vol. 42 Suppl, pp. 356-7, 1997