Method and device for navigating active surgical instruments

A medical system for localizing and for determining an operating state of a surgical instrument in a work region, the surgical instrument having an active operating state and an inactive state, the surgical instrument when in the active operating state configured to emit or influence a first electromagnetic field, comprising:

• a sensor arrangement comprising a first sensor and an instrument sensor, the first sensor configured to be arranged at a known location in the work region and the instrument sensor arranged at the surgical instrument, the first sensor configured to detect the first electromagnetic field emanating from, or influenced by, the surgical instrument when in the active operating state and configured to generate an output signal indicating the detection by the first sensor of the first electromagnetic field emanating from, or influenced by, the surgical instrument in the active operating state,
• a location detection unit configured to establish a location and the operating state of the surgical instrument in the active operating state on the basis of the output signal generated by the first sensor and the known location of the first sensor, and to generate location data, wherein the location data corresponds to the location of the surgical instrument:
• a field generator for generating a second alternating electromagnetic field,
• wherein the instrument sensor arranged at the surgical instrument detects said second alternating electromagnetic field generated by the field generator and causes the generation of an induced current dependent on a position of the instrument sensor, and
• a navigation unit configured to evaluate the induced current so as to determine a position of the surgical instrument relative to a patient when the surgical instrument is in the inactive state and therefore when the surgical instrument is not emitting or influencing said first electromagnetic field.