Electromagnetic interference of magnetic field based auto identification technologies in healthcare settings

Increasingly, autoidentification technology is being utilized in healthcare settings to make delivery of care cheaper, more efficient, and safer. However, the risk of electromagnetic interference (EMI) when using these autoidentification systems is not entirely clear. Thus, we sough to evaluate the likelihood of electromagnetic interference (EMI) in high technology healthcare areas with a low frequency, magnetic-field based wireless autoidentification protocol.

Thirty-two devices were tested for EMI with an autoidentification technology whose maximal magnetic field output ranged from 8 to 800mgauss between November 2008 and March 2009. Testing was performed at Mayo Clinic (Rochester, MN) and Holy Cross Hospital (Miami, FL). All tests were started from 4 feet away and devices were approached in 1 foot increments with the signal antenna. EMI was characterized as light, significant, hazardous, or none per established testing standards. Significant to hazardous EMI was considered to potentially cause significant problems with clinical management of patients.

Of 32 devices, light to hazardous EMI was seen in 8 (25%). Hazardous EMI was seen in 2 12-lead ECG machines, significant EMI in fluoroscopy, echocardiograms, and 1 of 5 cardiac monitors, and light EMI in a defibrillator and cardiac monitor. Average magnetic field strengths experienced by the devices were similar at each distance regardless of the presence of EMI. No EMI was recorded with any device at distances greater than 4 feet, with no loss of signal fidelity at distances up to 17 feet.

A low frequency, magnetic field based wireless autoidentification technology induced distance dependent EMI in healthcare settings, making implementation potentially safe at antenna distances greater than 4 feet from clinical equipment. However, implementation requires rigorous in vivo testing to ensure the antenna is located a safe distance away.