Extravasation, the unintended migration of intravenous fluids from the vein and into surrounding tissue, is a risk factor associated with CT scans and MRIs that rely on contrast media (chemical substances) injected into the bloodstream to enable visualization of pathologies. Early extravasation detection and the ability to reduce complications associated with extravasations are highly requested product features in power injectors, complex devices used to inject the contrast media into the bloodstream.

In response, a technology for early detection of extravasations has emerged from the development labs at Columbus-based Battelle. The technology exploits a physical property called permittivity, a property that describes how a material (organic or inorganic) stores and/or dissipates energy in the presence of an electric field.

Since all radio waves have an electric field component, they can be used effectively to detect changes in permittivity. In collaboration with MEDRAD, Inc (medrad.com), Warrendale, PA, Battelle began developing the technology specifically to detect extravasations during a powered CT injection. This is achieved by transmitting low-power radio waves through the skin and into the tissue around the catheter site. An additional pair of sensors receives the signal from the tissue at a second location.

At the onset of an extravasation, changes in subcutaneous electrical permittivity occur. These changes impact the propagation of the radio waves being transmitted and received, which allows the system to be highly sensitive to the extravasation event.

Human centric design
With a detailed understanding of the technical abilities of this emerging technology, it was critical for the technology development team to fully understand the context of use for the new sensor. For several months, a multi-disciplinary team from Battelle conducted extensive contextual research activities across the country.

The team visited small, medium and large imaging facilities, each varying in its capabilities of staff, amount of patient throughput per day and typical patient profile. Among all the variables analyzed, it became clear that a common practice of CT technologists across all areas was the use of medical tape to secure tubes, wires and any other items they felt were necessary.

While this was common practice in the field to improve patient safety, it was a critical piece of insight for the technology development team, and was subsequently flagged during a Failure Modes and Effects Analysis (FMEA) as one of the highest risks to sensor performance.

In order to assure optimum performance of the sensor, it needed to be placed consistently and accurately over the target site without the flexible sensor housing being distorted by external methods of attachment (i.e. tape). It was also discovered that end users were unwilling to add any additional steps to their current workflow. Further inquiry by the team uncovered that in order to increase user acceptance of the new sensor technology, it needed to be applied in three steps or less and not interfere with the current workflow for pre-procedure set up.

An additional risk identified was the conflicting requirements for attaching the sensor to the patient. The sensor technology requires a strong, secure attachment to the patient with an aggressive adhesive that maintains close proximity between the sensor and the skin, across its entirety. In stark contrast, a characteristic of this particular patient population is tender, vulnerable skin that was prone to damage when medical tapes and adhesives were applied. To mitigate the high risk of damage to the patient while enabling the sensor to perform optimally, the team was challenged with developing a single, disposable method of adhesion which had to have both high and low adhesion properties.

Material Solution
To mitigate the risks discovered during the contextual research, the solution needed to incorporate both an aggressive, sensor-facing adhesive and a lighter, less aggressive skin-facing adhesive while allowing the user to apply it in as few steps as possible. The solution is a single carrier layer with dual adhesive properties on both top and bottom for the patient and sensor surfaces.

To assure the end users placed the sensor appropriately over the target area, sensor- and catheter-specific markings are printed on the carrier layer to assure proper placement of the sensor pads and distance from the catheter. The design of the disposable also integrates into the current workflow by requiring the user to go through two steps to apply: 1) remove bottom layer and attach to patient, 2) remove top layer and attach sensor.

While the sensor disposable facilitates proper placement, the development team needed to assure the user would not continue using tape to secure other items in the sensor area. Using excessive tape to secure catheters, tubes and cables within close proximity to the sensor, as well as on the sensor itself, could introduce enough tissue compression under the skin to alter sensor performance. Rather than requiring users to stop using tape, this risk was mitigated by developing a set of custom shaped adhesive strips. These adhesive strips were not only a seamless replacement for tape, they allowed the users to effectively secure items within the sensor field without interfering with performance. For example, the adhesive strip for securing the catheter is notched to provide maximum adhesion over the catheter tip while minimizing interference with the sensor pads.

Based on the workflow observed during the contextual research, each adhesive strip was designed for a specific task in the workflow. The strips allow the user to:
- Secure the catheter hub
- Secure the sensor cables
- Secure two tube sets
- Secure the cotton ball once the catheter is removed

Human centric pays
To assure the new technology performed to its full potential, a human centric, interdisciplinary approach was used to understand how users would interact with the sensor and what potential risks could be identified.

The approach provided insights into potential risks, allowing the technology development team to make changes early in the development and mitigate risk before the sensor was fully developed. Making necessary changes this early in the development process has much less impact on cost and schedule, as the requirements are still in process and not under design control.

This ultimately enabled a cutting-edge medical device to live up to its full potential in a cost-effective and timely manner.