"Silent" malfunction of a critical-care device caused by electromagnetic interference

Although there have been many previous reports of serious medical device malfunctions caused by electromagnetic interference (EMI), it is not widely recognized that many such malfunctions were "silent," having occurred without triggering a device alarm. The authors describe one such malfunction, and its implications. An 8-year-old radiant heater, which appeared to be operating normally in a neonatal intensive care unit, was observed, by mere chance, to intermittently register an increased, or decreased, neonatal skin temperature of about 1 degree C, depending on personnel movements and on its location in the room. The possibility that EMI had been the cause of this malfunction was investigated. The malfunction stopped in an adjacent windowless room, but again occurred when a 146-MHz walkie-talkie (100 mW) was used within a 1-2-m radius. More complete (0.1-1,000 MHz, 4.5-10 V/m maximum) test-chamber assessment of EMI susceptibility showed that the heater malfunctioned at electric field strengths above 0.3-1 V/m over four roughly 50-MHz bands between about 10 and 600 MHz. A previous electromagnetic environment survey had documented fairly high fields (0.01-0.3 V/m, 30-1,000 MHz) in the original malfunction area. Combined results suggested that the malfunction had been due to EMI from nearby fixed-source FM transmission antennas, which could be seen from the room's windows. The device had probably been malfunctioning for months, even though it had been regularly checked during preventive maintenance. Other identical, but newer, units functioned normally, or malfunctioned negligibly. Although operation of the older device deviated only "slightly" from normal, the consequences of this malfunction could have been serious.(ABSTRACT TRUNCATED AT 250 WORDS)