A device for fixing a segment of tubing in the form of a loop, for an apparatus by which a fluid is fed to or out from a patient via tubing, in particular for monitoring vascular access in extra-corporeal blood treatment, and a tubing and an arrangement for monitoring, each having the device for fixing the segment, are also described. The fixing of the segment includes a guiding piece and a securing piece. The guiding piece fixes intersecting portions of the segment which forms an eye, thereby forming a loop which contracts under a tractive stress. The securing piece fixes a portion of the segment forming the eye such that when the loop tightens, that portion of the segment does not slip through the guiding piece. Alternatively, intersecting portions of the segment are fixed in a loop only by a guiding piece formed as an annular body.