[The "trend magnifier"--a methodological tool for patient monitoring]

In different fields of patient monitoring there is an increasing knowledge about the clinical importance of variations of short-term patterns in the courses of vital parameters. They can be used as diagnostic hints and warning signs as well as means for therapy control. This paper first gives a critical survey of methods suitable to meet the resulting requirements in the operation theater and the postoperative intensive care unit. Then it presents a methodological tool which gives improved possibilities for detecting and analyzing meaningful patterns. Minicomputers or microcomputers are used to sample and to display both the primary signals and the courses of vital parameters (courses of extracted features) in three steps: The first step corresponds to the trend registration in conventional monitoring systems. The vital parameters are registered with sampling intervals between 10 and 30 seconds, and are held for the whole staying period of the patient. In the second step the same parameters are registered for a limited time span with sampling intervals in the order of a beat-to-beat registration. In the third step the primary signals are registered for a certain time span (in a ringbuffer). The sampling interval depends on the individual signal. It should be in the order of 10 ms. After having detected an interesting event, it can be located and studied in more detail by using the second- and third-step-display. From each display, a hardcopy on a multi-color plotter may be produced to overcome the display limitations of the CRT and to obtain legal documents.