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A main basis of this habilitation thesis is the development of a portable, mains-free measurement device for determining breath ethanol concentrations (BrEC) both during spontaneous breathing and in mechanically ventilated patinets undergoing inhalation anaesthesia, for detecting and quantifying irrigation fluid absorbed during endourological surgical interventions. Here a respired gas has to be measured which compared to other usually measured gases 1) is present in substatially smaller concentrations, 2) is subject to significant influences by temperature and humidity in the expired air, and 3) can only be measured discontinuously in the alveolar air due to technical limitations of the sensor. The basis for investigating accuracy of measurement was not just evaluation of the device using different lung models, but also a comparison with the target parameter "absorbed irrigation fluid" using another further-developed reference procedure, i.e. direct measurement of sorbitol and mannitol concentrations in serum. This has the added advantage that even when ethanol monitoring is not available, another laboratory procedure is indeed available for directly evaluating the absorption of irrigation fluid. In the clinical aspects of this thesis, ethanol monitoring helped show that during transurethral resection of the prostate (TURP) in spontaneously breathing patients undergoing regional anaesthesia, irrigation fluid was intravascularly absorbed not more often, but more rapidly and in larger quantities than it was in mechanically ventilated patients undergoing inhalation anaesthesia. A possible reason for this was the significantly reduced central venous pressure observed in the group of patients undergoing regional anaesthesia. The diagnosis of a delayed extravascular absorption of irrigation fluid during percutaneous nephrolithotripsy (PNL), made with the assistance of the ethanol monitoring, was associated with a significantly prolonged period of hospitalization in the clinic and an increase in opioid requirements. This finding can be explained pathophysiologically by an increased trauma to the kidney with injury to bordering organ structures. As a result of close co-operation with several departments of the Medical University of Lubeck, we now have at our disposal an excellent BrEC-measuring device for detecting and quantifying absorbed irrigation fluid during urosurgical procedures. The results of the clinical studies presented here underscore the value of the newly-developed AlcoMed 3011.