In the field of Engineering Design and Industrial Design Engineering the fundamental question of analyzing, assessing and designing usability for humanmachine-interaction continuously raises in every thinkable domain. Especially in information-intensive human-machine-systems it is essential not to overload the user and therefore prevent him from operating errors. The present article shows an innovative way for a systematical improvement of an information-intensive humanmachine-system in the high reliability organization of human medicine – the anesthesia workstation. The iFlow-analysis is a methodical approach by which this information-intensive human-machine-system can be abstracted and visualized by the information flows between human and machine. This allows an event-related assessment of physical and mental workload. Subsequently, design interventions can be deducted which lead to a better performance for the anesthetist and a lower load.