The use of wireless medical devices is increasing at an exponential rate, along with all connected products. According to Gartner, the number of connected devices is expected to more than double in the next three years. The environments where medical devices are used are also changing. More devices are being used in the home, and medical facilities are integrating more technology at a rapid pace. As a result, there are more wireless devices interacting with each other. Given the critical functionality of these devices, ensuring their safety, performance, and reliability as they interact with other products is essential.
 
There are many recorded instances of wireless interference leading to medical issues: cell phones causing infusion pumps to stop, electrocautery devices making implants stop working, a pacemaker being controlled from an unauthorized source. Manufacturers must ensure a device can perform when presented with interference, based on guidance from authoritative bodies.
 
While the Federal Communications Commission (FCC) regulates emissions for wireless products, the U.S. Food and Drug Administration (FDA) regulates medical device safety. The FDA’s main concern for any device is whether it is safe enough for medical use. Wireless products must be evaluated for coexistence to illustrate safety. Ultimately it is up to the manufacturer to take on the bulk of this responsibility, but the FDA did help develop a standard for illustrating wireless medical device safety in relation to various interferences.
 
ANSI C63.27 focuses on wireless coexistence, laying out several considerations for testing, including wireless protocols, test setups, and risk-based testing tiers. Wireless protocols include:
 

• Wi-Fi—Best for large amounts of data and frequency hopping
• Bluetooth—Best for small personal devices used in a small area and not intended to span large distances
• Zigbee—For simple apps using smaller amounts of data
• DECT EUT operating in the UPCS band—A form of wireless data found at a frequency of 1900-1930 MHz.

 
The standard identifies two test setups: RF conducted (along a wire, with a direct cable connection to signal inputs) and RF radiated (wireless, with data transferred over the air). It also establishes four risk-based test tiers:
 

• Tier 1—Major risks, such as death or serious injury, are associated with coexistence failure. This is the most difficult tier to find success with because the stakes are so high and potentially require backups. This tier requires testing with three competing devices.
• Tier 2—Illustrates moderate risks that could include delayed or disrupted service. It requires two devices for testing.
• Tier 3—Minor risk that would not significantly impact health; tested with one competing device.
• Tier 4—Negligible risks, an inconvenience or discomfort. No testing is required for this tier.

 
To determine which tier a product falls under, manufacturers should consider several factors while developing a test plan.
 
The manufacturer must define intended environment, intended use and performance, and test methods for each device. Intended environment, the most important item to define, means either a professional healthcare setting or a home environment. Professional healthcare settings can vary based on the limitations, interferences, and standards that need to be considered. A doctor’s office or clinic, for example, is a very different setting than an operating room or an intensive care unit. Home healthcare settings include residential settings and, largely in the EU, nursing homes. They are less regulated, presenting a greater chance of interference from competing devices.
 
Once the intended environment is established, how a device will be used and its optimal functionality must be taken into account. Will the device be used for critical care or something non-critical, like data transfer? Will it have one function or multiple? Consider the functionality that uses the wireless capabilities of the equipment and would result in unacceptable consequences if degraded or disrupted. Ultimately, this total functionality defines coexistence for the device.
 
To determine functionality, establish the functional wireless performance (FWP) of a given device, defining the key performance indicators (KPIs) appropriate in the intended environment. Define optimum performance, as well as acceptable failure. For instance, if designing a wireless nurse call system, what level of failure are you willing to tolerate? Must it never fail or is there a minimum of missed calls that is acceptable? Considerations such as these will inform your test plan and ultimately, results.
 
Next, define the wireless protocols and radio frequency (RF) bands the device will use. Consider the needs of your test and set up end-to-end verification. Start by establishing baseline FWP and signals, such as ambient noise and extraneous signals. These baselines will depend largely on the parameters established in the test plan. Next, test the FWP to the acceptance criteria and KPIs set up in the plan. Begin by testing for the intended environment without any signals. Introduce interference to see how the device, signals, and interference all interact.
 
Testing may take days or weeks, depending on several considerations, including the plan’s robustness, the device itself, intended environment, and spectrums. If the test is not successful and essential performance is not achieved, the device will need to be redesigned with a review of the information and fail safes in place to improve performance to meet KPIs.
 
There are other things to keep in mind when it comes to wireless coexistence. It’s important to plan for the worst case scenario and conduct risk management, required under AAMI TIR69. This standard says wireless technology must be assessed in relationship to various hazardous situations, including factors external to the manufacturer. During the assessment, identify potential issues and consequences, as well as ways to mitigate risks and manage hazards. Consider networks, external systems, infrastructure limitations, electromagnetic interference, access points, and power backups. Finally, consider cybersecurity, backup mechanisms, and redundancy when it comes to wireless coexistence.
 
In our increasingly connected world, wireless medical devices offer convenience and ease that consumers and medical professionals demand. However, the results of interference with those devices can be complicated, even dangerous. It is up to manufacturers to mitigate these risks to prove their devices are safe. Using ANSI C63.27 and AAMI TIR 69 to develop a test plan and risk management practices, and conduct thorough testing can help ensure a device’s performance, making it safer and securing a brand’s reputation.