an epidermal dressing includes an appliance for linking an electromagnetic spectrum sensor with a cannula administering an intravascular infusate . the appliance includes a body and a fitting coupled to the body . the body is configured to space a connector of the cannula from the epidermis . the fitting includes a first arrangement that is configured to retain the electromagnetic spectrum sensor for sensing the infusate in perivascular tissue , and a second arrangement that is configured to release the electromagnetic spectrum sensor from the first arrangement .