To provide a method and device for fixing a sensor of the body cavity and for protecting the sensor when inserting the sensor into the body cavity.

The device including the sensor which contains a mechanically vibratable membrane and a protective layer which is formed of a polyxylylene polymer material and is deposited by evaporation on the mechanically vibratable membrane is provided. A bypass 11 is connected between the aortas at a point 13 and point 15 lower than a blockade part 9. The sensor 1 is arranged in at least either of a proximal port 17 or proximal part of the bypass 19. The sensor 1 may otherwise be arranged in a distal port 21, a distal part before a distal port 23 or a distal part behind a distal port 25. The sensor 1 is fixed to a proper point by using two holes 3 for mounting to a suture part 9. The sensor 1 may otherwise be fixed to a proper point by using surgical adhesives or surgical staples.