Researchers Warn RFID May Disrupt Medical Equipment

The researchers ran each device through three EMI tests: one involving the passive tag and reader, another involving the active tag and interrogator, and a third with the active tag but no reader). Each device test incorporated three procedures: the medical device was checked for normal operation; the device was tested when the RFID equipment was activated and the interrogator and tag were positioned at a distance of 200 cm (6.6 feet) from the medical device; and the device was tested once more with the RFID equipment turned on, and the distance between RFID equipment and medical device was increased by 50 cm (20 inches) if the device exhibited no effects of EMI, or decreased by that same amount if such effects were observed.

Once a detection of EMI appeared or vanished during a stepwise increment or decrement of 50 cm, the precise EMI distance was determined by moving the RFID equipment at a rate of approximately 1 cm (0.4 inch) every 3 seconds. Whenever an EMI incident was detected, the distance between the reader/tag and the device was measured in centimeters, with the type of incident categorized according to its severity.

For the purpose of the tests, the term incident was defined as "every unintended change in function of a medical device," and was characterized as being hazardous, significant or light. Hazardous was defined as having "direct physical influence on a patient by unintended change in equipment function" (for instance, the total stopping of a syringe pump, or incorrect pacing by an external pacemaker). Significant was defined as having an "influence on monitoring with significant level of attention needed, causing substantial distraction from patient care" (for example, an incorrect alarm or inaccurate monitoring of blood pressure). Light denoted "without significant level of patient influence or change in equipment function" (such as a disturbed display).

During the tests—of which there were 123 altogether (three per medical device)—a total of 34 EMI incidents occurred. Of those, 22 were hazardous, two were significant and 10 were light. The passive system produced more incidents than the active system (26 versus eight). Some of the "hazardous" incidents recorded included the shutdown and restart of mechanical ventilators tested, as well as the shutdown of syringe pumps.

For the 34 EMI incidents, a total of eight were initiated at a distance of more than 50 cm. The median distance at which hazardous EMI-related incidents occurred was 25 cm (10 inches), and the median distance for all incidents was 30 cm (12 inches). Only three tests resulted in incidents in which the reader/tag and the medical device were as far apart as 600 cm (19.7 feet)—the maximum distance at which EMI was observed. One medical device (a ventilator) exhibited an EMI incident beginning at a distance of 400 cm (13.1 feet), causing it to exhibit behavior classified as hazardous—in this case, triggering ventilation erroneously and at a higher frequency.

The published study compares the EMI caused by RFID to that of EMI from mobile phones, which have been studied and been known to disrupt medical devices, though newer generations of phones are much less problematic since they can operate at much lower power levels. The study's findings do not surprise John Collins, the director of engineering and compliance with the American Society for Healthcare Engineering (ASHE), a professional membership group within the American Hospital Association (AHA). The AHA is a national organization that represents and serves all types of hospitals, health-care networks, and their patients and communities.