Medical Devices and Electromagnetic Interference

Tuesday, November 29, 2011

shawn merdinger

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Recently I came across an interesting paper: “Electromagnetic Interference From Radio Frequency Identification Inducing Potentially Hazardous Incidents in Critical Care Medical Equipment” [1] that covered research conducted on medical devices’ susceptibility to EMI (electromagnetic interference) from RFID (radio frequency identifier).

RFID tags are common in medical environments to wirelessly track assets in inventory, as well as real-time location.  

The research used active and passive RFID tags placed in proximity to medical devices ranging from infusion pumps to ventilators to external pacemakers – in all, 41 devices in 17 categories from 22 manufacturers.

RFID readers were used to read RFID tags and out of 123 tests, 34 incidents of EMI occurred, of which 22 were determined hazardous (e.g. turned the medical equipment off, caused inaccurate reading, etc.).  

The testing methodology used was IEEE’s American National Standard Recommended Practice for On-site Ad Hoc Test Method for Estimating Radiated Electromagnetic Immunity of Medical Devices to Specific Radio-frequency Transmitters (Standard C63.18).

While fairly technical, this article highlights the ever-increasing risks of potential EMI we face in medical environments resulting from increasing numbers and complexity of technology and wireless devices.

 We literally are surrounded by the “Internet of Things” and Cisco Systems estimates that in 2008 the number of “things” connected to the Internet exceeded the number of people on Earth, and that by 2020 the number will exceed 50 billion. [2]

Enamored by technology, we tend to place tremendous faith in electronic gadgets that are almost “magical” and “just seem to work” – perhaps we are lulled into a sense of technical complacency by the general reliability of technology around us?  Do we even have insight into the potential EMI problems?  

Unintended Consequences

Technology today is amazing, and is constantly influencing the ways in which we work and live.  In medical environments, the influx of technology over the past several years has permeated hospitals.  

We see, for example, the dependence upon medical information technology growing, from migration to EMR (electronic medical records), to RFID tracking of equipment and people, and recently the emergence of thousands of medical apps for devices like the iPad.

Despite all of the apparent benefits, however, it’s also important to consider that not all of the costs of technology are readily accounted for, or even lend themselves to analysis – in a Rumsfeldian sense, the so-called “unknown unknowns – the ones we don’t know we don’t know.” [3]    

The unknown unknowns can likely cause high costs, in both monetary and health terms, via failing to recognize and address risks arising via wireless interconnectedness and the potential for unintended consequences like EMI.

Wireless devices of all types (RFID, Bluetooth, Zigbee, 802.11a/b/g/n) are constantly creating signals across a fairly narrow frequency band, and one result is a challenge in recognizing and mitigating the EMI problem.  

Wireless interference is invisible to the human eye, and requires specialized equipment and training to accurately understand, in particular its effects on specialized medical equipment.  

As more and more wireless devices enter the medical environment, we have to question what kinds of interference testing is expected of vendors, implementers and practitioners, as well as understand in detail what current wireless technology is already in place, and is planned, in the environment that the medical device is used.

Even with excellent technical due diligence, it’s difficult to control what kinds of wireless devices may appear in a medical setting that are outside the control of medical IT.   For example, in the case of consumer wireless electronic devices, they can literally “walk in through the door” in a visitor’s pocket and subsequently create an EMI impact on a medical device.  

Just this year, documented in the FDA MAUDE database, an instance of wireless interference from a consumer Bluetooth device impacting a medical device (implantable pulse generator) resulted in “overstimulation” and loss of telemetry. [4] 

FDA MAUDE

The challenges of EMI interference extend to the home as well.  Increased efforts of creating the “medical home” must take into account the multitude of wireless devices and potential impact to medical devices placed in patients’ homes.  The expected impact from wireless sharing the same frequency range of 2.4 Ghz – 5Ghz is unknown, and the devices can include microwaves, TVs, home wireless routers, garage door openers, baby monitors, etc.  

In the case of newly deployed smartmeters, recent reports indicate over 200 customers of Central Maine Power Company noticed after the smartmeter installation, several wireless devices in their homes started acting erratically, or stopped working altogether. [5]

In closing, the influx of more wireless devices in shared frequency spectrums raises valid concerns for EMI.  To adequately measure the impact and mitigate risk will require significant effort from the entire supply chain and lifecycle of medical devices, from vendors to implementers to medical providers.  

Still, many other difficult questions remain – issues of liability, scope of testing and how to train hospital staff to recognize EMI – after all, a medical professional is not a wireless technical expert, so what are the expectations for medical staff?

The “Internet of things” is upon us, and these questions and issues will surface in the coming years!

End notes: 

[1]  van der Togt R, van Lieshout EJ, Hensbroek R, Beinat E, Binnekade JM, Bakker PJM. Electromagnetic Interference From Radio Frequency Identification Inducing Potentially Hazardous Incidents in Critical Care Medical Equipment. JAMA. 2008;299(24):2884–2890.  Online: http://jama.ama-assn.org/content/299/24/2884.full  [accessed 15 November, 2011]. 

[2]  Evans, Dave.  Cisco Blog.  Online: http://blogs.cisco.com/news/the-internet-of-things-infographic/  [accessed 15 November, 2011]. 

[3]  WikiQuote.  Online: http://en.wikiquote.org/wiki/Donald_Rumsfeld [accessed 15 November, 2011]. 

[4]  FDA MAUDE record.  Online:  http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=2093189  [accessed 15 November, 2011]. 

[5]  Vamosi, R.  Smart Meters Interfering With Home Electronics.  Security Week.  23 November, 2011.  Online: http://www.securityweek.com/smart-meters-interfering-home-electronics  [accessed 15 November, 2011].

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