BACKGROUND: The absorption of irrigation fluid during transurethral resection of the prostate (TURP) is determined primarily by hydrostatic pressure in the bladder and prostatic venous pressure. In comparison to spontaneously breathing patients, patients undergoing mechanical ventilation with positive pressure have a raised central venous pressure and a reduced venous return, both of which can influence intravascular absorption. The purpose of the prospective study was to compare the effects of general (GA) and spinal anaesthetic (SA) techniques on the perioperative absorption of irrigating fluid in patients undergoing TURP. METHODS: Forty patients undergoing TURP were randomised and assigned either to group GA or SA. Irrigating fluid absorption was traced by adding 1.5% (w/v) ethanol to the irrigating fluid. Perioperative blood ethanol concentration (BEC), haemoglobin concentration, haematocrit, serum sodium concentration and central venous pressure (CVP) were measured at 10-min intervals during TURP and at 30-min intervals while patients were recovering. Absorption routes were indexed by the BEC and changes in serum sodium concentrations. Where the BEC was greater than 0.05 mg.mL-1, absorption of irrigating fluid was assumed. For assessing the volume of irrigating fluid absorbed, the maximum BEC, the absorption rate, the area under the BEC curve (AUC), and the volumes calculated according to the Hahn nomogram (Volin) for each patient were taken into consideration. RESULTS: There were 15 cases of irrigating fluid absorption in patients receiving GA (75%), and 11 in those receiving SA (55%). CVP was significantly lower in spontaneously breathing patients with SA as compared to those with GA (P < 0.05). In patients with irrigating fluid absorption the maximum BEC (P < 0.02), as well as the rate of irrigant fluid absorption (P < 0.01), were significantly higher amongst patients receiving SA. In this group, the calculated area under the curve and the absorbed fluid volumes determined with the nomogram were significantly increased (P < 0.05). CONCLUSION: The absorption of irrigation fluid during the TURP is significantly more marked amongst spontaneously breathing patients with regional anaesthesia in comparison to patients undergoing general anaesthesia with positive pressure ventilation. The markedly lower central venous pressure before the start of irrigation should be considered as a possible cause of this effect.
H. Gehring, W. Nahm, J. Baerwald, E. Konecny, and P. Schmucker. Atem-Alkoholmeßgeräte mit elektrochemischem Sensor - Meßgenauigkeit bei Beatmung am Lungenmodell - Breath alcohol analyzers with electrochemical sensory--accuracy of measurements in lung model ventilation. In Biomedizinische Technik. Biomedical Engineering, vol. 41(3) , pp. 54-9, 1996
Absorption of irrigating fluid by blood vessels during endoscopic urological surgery may result in cardiac insufficiency, impairment of electrolyte metabolism and neurological disorders. For detection and quantification of the volume absorbed, ethanol is added to the irrigating fluid. The resulting blood alcohol concentration can be obtained by measuring the alcohol concentration in the expired air. For artificially ventilated patients receiving a general anesthetic, electrochemical sensors that remain uneffected by volatile anaesthetics are used. In the present study, the measuring accuracy of three different alcohol analyzers using electrochemical sensors was tested against an infrared reference sensor during simulated ventilation in a lung model, and the optimal trigger time point for sampling determined. All three devices tested show the same degree of accuracy as the reference. For manual endexpiratory triggering devices with short sampling times are best suitable. Portable devices powered by rechargeable batteries and usable with both spontaneously breathing and ventilated patients are recommended for clinical application.
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.
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.
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.
H. Gehring, W. Nahm, K. F. Klotz, A. Knipper, K. Zimmermann, J. Baerwald, and P. Schmucker. Messung der Atem-Alkoholkonzentration mit einem neuen elektronischen Sensor. Modelluntersuchung zur Querempfindlichkeit gegenüber volatile Anästhetika und klinische Anwendung - Measurement of expired alcohol concentrations with a new electrochemical sensor. A model investigation to determine interference with volatile anesthetics and clinical application. In Der Anaesthesist, vol. 45(2) , pp. 154-62, 1996
UNLABELLED: Absorption of irrigating fluid in transurethral prostatic resection (TURP) and percutaneous nephrolitholapaxy (PNL) into veins or delayed absorption due to fluid extravasation may result in a TURP syndrome. The measurement of end-tidal breath alcohol concentration (et AC) as a monitor of absorption of irrigating fluid labelled with 2% ethanol is limited by the disturbance of infrared sensors by volatile anaesthetics and nitrous oxide (N2O) (Fig. 2). An electrochemical sensor is acceptable for this method. The aim of the present study was the evaluation of breath alcohol measurements using an electrochemical sensor device (Alcomed 3010, Envitec). The stability of the sensor in the presence of volatile anaesthetics was examined using a lung model. In a clinical investigation, the device was then applied to spontaneously breathing or mechanically ventilated patients inhaling volatile anaesthetics during endoscopic urological surgery. METHOD: A two-chamber lung model filled with water for performing noninvasive measurements at the mouth of a patient has already been introduced by Brunner et al. (Fig. 1). With the addition of different amounts of ethanol to the temperature-controlled water, a constant ethanol concentration is achievable in the air above the water that is dependent on adjustments of the ventilator. Increasing concentrations of volatile anaesthetics (isoflurane, enflurane, halothane, and sevoflurane) were added to the fresh gas flow (2 l O2/3 l N2O) and etACs were measured using the manually triggered self-absorbent electrochemical sensor. First, regression equations were established between breath alcohol concentrations and increased volatile anaesthetic concentrations. Regression equations were then established between end-tidal anaesthetic gas concentrations and vaporizer adjustments in order to rule out an influence of ethanol on the anaesthetic gas monitor Ultima V (Datex). In the clinical investigation, 53 intubated and ventilated patients (33 undergoing PNL, 20 undergoing TURP) and 48 patients breathing spontaneously (32 with inhalation anaesthesia, 16 with spinal anaesthesia) were investigated. The etAC was measured with the Alcomed 3010 and compared with gas-chromatographically registered blood alcohol concentrations (BAC). The study had previously been approved by the Ethical Committee of the Medical University of Luebeck. Patients with liver disease and a history of toxic abuse were excluded. Only one value per patient (maximum BAC) was included in the statistics in order to avoid a cluster effect. RESULTS: The lung model experiments demonstrated that the measurement of etAC with an electrochemical sensor is free of interference by volatile anaesthetics (Table 1). The slope of the regression between the measured alcohol concentration and increased concentrations of anaesthetics did not differ significantly from baseline values. The measurement of end-tidal anaesthetic concentrations was not significantly different from vaporizer adjustments in the presence of increased alcohol concentrations (Table 2). During the clinical investigation, a regression between etAC and BAC was determined for both groups. For the group of patients breathing spontaneously, the correlation coefficient was 0.961 and the regression equation revealed etAC = 0.5677*BAC-0.1303 (Fig. 5). However, in the group of ventilated patients a biphasic course was shown that was dependent on BAC (Fig. 6). At BAC < 0.4%, a similar correlation (r = 0.856) to the spontaneously breathing group could be seen (regression equation: etAC = 0.617*BAC-0.020). Above 0.4% BAC there was no acceptable correlation (r = 0.444, regression equation: etAC = 0.202*BAC+0.104). CONCLUSIONS: The tested electrochemical sensor does not interfere with volatile anaesthetics and N2O as demonstrated by a lung model. There is a good correlation between etAC and BAC measurements in patients breathing spontaneously with special regard to the slope of the regression (s = 0.57).
H. Gehring, W. Nahm, K. F. Klotz, O. Zais, R. Schreiber, and P. Schüren. Plasmavolumenbestimmung mit dem Farbstoff ICG bei Änderung des intravasalen Volumens - Plasma volume determination with ICG dye in changes of intravascular volume. In Infusionstherapie und Transfusionsmedizin, vol. 23, pp. 86-91, 1996
Ziel: Die Messung des aktuellen intravasalen Volumens mit Hilfe der Indikator-Verdünnungsmethode ist sowohl von klini-schem als auch von wissenschaftlichem Interesse. Bei der Ver-wendung des rasch eliminierten Farbstoffes Indocyanin-Grün (ICG) sind wiederholte Messungen und damit Verlaufskontrollen möglich. In der vorliegenden Studie sollten folgende Fragen geprüft werden: 1. Stimmen die von uns mit der ICG-Methode bei gesunden Probanden bestimmten Werte mit den in der Literatur angegebenen Kontrollwerten überein, und ist somit die Grundlage für die Durchführung weiterer klinischer Studien gegeben, und 2. Stimmen die Differenzen der vor und nach Eigenblutentnahme bzw. Retransfusion bestimmten Werte für das Plasmavolumen mit den tatsächlich entnommenen bzw. retransfundierten Volumina überein? Design: Prospektive Studie (an je 20 gesunden weiblichen bzw. männlichen Probanden). Rahmen: Forschungslabor einer anästhesiologischen Universitätsklinik. Teilnehmer: Je 20 gesunde weibliche bzw. männliche Probanden. Interventionen: Plasmavolumenbestimmung mit ICG vor und nach Entnahme von 10% des ge-schätzten Blutvolumens und nach Retransfusion. Ergebnisse: In der Gruppe der Frauen betrug das Plasmavolumen pro Körperoberfläche (PV/KO) 1639 ± 198 und bei den Männern 1687 ± 224 ml/m2 (Mittelwert ± SD). Durch die Eigenblutspende wurde den Frauen 188 ± 23 und den Männern 149 ± 26 ml/m2 PV entzogen. Die PV-Messung mit ICG ergab für diesen Ent-zug einen Wert von 198 ± 174 bzw. 171 ± 158 ml/m2 und für die Retransfusion 190 ± 169 bzw. 142 ± 154 ml/m2. Schluβfolgerungen: Die Kontrollwerte liegen in dem in der Literatur be-schriebenen Normbereich. Die gemessenen Differenzen der Plasmavolumina vor und nach Eigenblutspende bzw. nach Retransfusion stimmen mit den tatsächlich entnommenen Plasmavolumina im Mittel gut überein. Bei der klinischen Beurteilung im Einzelfall ist die methodisch bedingte hohe Standardabweichung zu berücksichtigen.
BACKGROUND: The most common complication during percutaneous nephrolithotripsy (PNL) is the destruction of organ structures with extravasation of the irrigation fluid into the retroperitoneal space. Consequently, there is an increased risk of a urosepsis and a complicated therapeutic course. In this study we aimed to show that extravascular absorption could be differentiated from intravascular absorption due to their unique absorption characteristics, and that these characteristics enable a prediction of possible post-operative complications. METHODS: In a prospective study of 31 patients with PNL, ethanol was added to the irrigating fluid and blood ethanol concentration (BEC) was measured by gas chromatography during the endoscopic procedure and in the recovery room. Following the guidelines of Hahn, patients were divided into two groups: group EVA, in whom extravasation had occurred with subsequent absorption; group IVA, those with intravascular absorption. Patients' post-operative progress along with diagnoses of renal perforations or bleeding, or signs of infection or sepsis, were comprehensively listed. RESULTS: EVA was diagnosed in 19 cases, and IVA in 12 cases. Maximum BEC levels were achieved after 20 min (median) in the IVA group, and 75 min in the EVA group (P < 0.05). Apart from their significantly higher demand for opioids (P < 0.05), EVA patients had been hospitalised for a substantially and significantly longer period of time (P < 0.01). Although without statistical significance, there was a higher rate of peri-operatively confirmed complications and prolonged intensive therapeutic treatment in the extravasation group. CONCLUSION: Retroperitoneal extravasation can be identified by using ethanol monitoring during and after PNL. Afflicted patients require considerably longer hospitalisation, probably because of the additional injury to surrounding organ structures.
OBJECTIVE: To develop and test a method for standardized calibration of pulse oximeters. METHODS: A novel pulse oximeter calibration technique capable of simulating the behavior of real patients is discussed. It is based on an artificial finger with a variable spectral-resolved light attenuator in conjunction with an extensive clinical database of time-resolved optical transmission spectra of patients fingers in the wavelength range 600-1000 nm. The arterial oxygen saturation of the patients at the time of recording was derived by analyzing a corresponding blood sample with a CO-oximeter. These spectra are used to compute the modulation of the light attenuator which is attached to the artificial finger. This calibration method was tested by arbitrarily playing back recorded spectra to pulse oximeters and comparing their display to the value they displayed when the spectra were recorded. RESULTS: We were able to demonstrate that the calibrator could generate physiological signals which are accepted by a pulse oximeter. We also present some experience of playing back recorded patient spectra. The mean difference between the original reading of the pulse oximeters and the display when attached to the calibrator is 1.2 saturation points (displayed oxygen saturation SpO2) with a standard deviation of 1.9 saturation points. CONCLUSIONS: The tests have shown the capabilities of a spectral light modulator for use as a possible calibration standard for pulse oximeters. If some improvements of the current prototype can be achieved we conclude from the experience with the device that this novel concept for the calibration of pulse oximeters is feasible and that it could become an important tool for assessing the performance of pulse oximeters.
W. Nahm, and H. Gehring. Non-invasive in vivo measurement of blood spectrum by time-resolved near-infrared spectroscopy. In Sensors and Actuators B: Chemical, vol. 29(1) , pp. 174-179, 1995
Investigation of rapid near-infrared (NIR) spectroscopy in combination with the fibre optics for biomedical sensing is presented. Modern diode-array technology enables sensitive measurement of changes in tissue absorbance caused by blood pulsation. In order to describe the dynamics of this system a multi-layer model based on pulse wave theory is used. The evaluation of the pulsatile part of tissue absorbance at different wavelengths allows the construction of both pulsatile and static tissue spectra. The absorption monitoring of an injected bolus of indocyanine green is presented of non-invasive measurement of an arterial blood spectrum.
Considering the fundamental difficulties to define the term 'depth of anaesthesia', a more feasible concept for assessment of 'adequacy of anaesthesia' will be explained. The basic requirements for a monitoring index are definite response, gradual scaling and independence from the anaesthetic technique used. Additionally the index should be predictive for appearance of clinical signs of an inadequate anaesthesia. Different signal-processing methods will be discussed to extract the relevant information from both the spontaneous and the evoked brain electrical activity. In this context well established methods like spectral analysis are investigated in combination with new and more sophisticated methods like bispectral analysis or wavelet decomposition. Since no single-parameter index has been defined for monitoring depth of anaesthesia, a set of EEG parameters may be more useful to take into account intra- and interindividual variability. In parallel to the description of the monitor concept, the investigation of neural nets and fuzzy techniques, in addition to or in substitution of conventional statistical methods, will be introduced. Examples are given for data quality assessment, parameter extraction and re-classification.
Conference Contributions (10)
H. Gehring, and W. Nahm. Ein neues elektrochemisches Meßgerät für Atemalkohol zur Erkennung eingeschwemmter Flüssigkeit bei beatmeten und spontanatmenden Patienten. In Biomedizinische Technik / Biomedical Engineering, vol. s1, pp. 286-287, 1994
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
C. Du, W. Nahm, H. Gehring, and E. Konecny. Quantification of NIRS data of a blood phantom by spectral multicomponent analysis. In Proceedings of the SPIE, vol. 2626, pp. 130-140, 1995
In order to quantify the chromophore components from in vivo blood NIRS, a blood- equivalent phantom has been developed which consists of properly diluted intralipid and ICG dye. The reflection and transmission near infrared spectroscopy (NIRS) of the phantoms with different scattering backgrounds and ICG concentrations are measured and analyzed by the spectral multicomponent analysis (MCA) method to extract ICG concentration. The experimental results show that the MCA method can be used to quantify absolute ICG concentrations in scattering media if the average path lengths are known. Moreover, it was found by the experiments that both the water absorption peak at 970 nm and the ICG absorption peak at 800 nm show similar behavior during the change of the scattering background. Thus the ratio of the MCA-estimated concentration factor of ICG to water is independent of the blood-phantom scattering.
C. Hornberger, W. Nahm, P. Knoop, H. Gehring, P. Wouters, and E. Konecny. Nicht-invasive Erfassung von Blutspektren durch zeitaufgelöste in vivo Spektroskopie - Noninvasive detection of blood spectra by time resolved in vivo spectroscopy. In Biomedizinische Technik. Biomedical Engineering, vol. 42 s2, pp. 217-8, 1997
W. Nahm, H. Gehring, and C. W. Du. Nichtinvasive Messung der Konzentration von Indocyanin-Grün im arteriellen Blut durch spektrale Photoplethysmonographie. In Biomedizinische Technik / Biomedical Engineering, vol. 39(s1) , pp. 66-67, 1994
W. Nahm, H. Gehring, E. Konecny, and P. Schmucker. Messung der Atemalkoholkonzentration zur Beurteilung des Einschwemmsyndroms bei urologischen Eingriffen unter Vollnarkose.. In Biomedizinische Technik / Biomedical Engineering, vol. 38(s1) , pp. 423-424, 1993