Question of the Month with Comment
MedSun: Newsletter #17, September 2007

Findings of a study by J.L. Tri, M.S.E.E.; R.P. Severson, CBET; L.K. Hyberger, M.A., CCRC; and D.L. Hayes, M.D., published in Mayo Clinic Proceedings [82(3):282–285], showed that no problems were found during 300 tests of two different telephone technologies from different carriers. From February through June 2006, the cell or mobile phones were switched on near 192 medical devices in 75 patient rooms. The incidence of clinically important interferences was 0 percent.

In light of these findings, has your facility changed the cell phone policy? Would you be willing to share these changes?

The Mayo Clinic study is a good one for very specific conditions. It does not, however, address the cause–effect relationship between unintentional radio frequency (RF) sources such as cellular phones and handheld music devices, and medical instruments operating within short distances. Several factors influence electromagnetic interference (EMI), including the power setting of the cellular phone (which varies and is not under user control), the transmission platform, the physical layout of the patient room and building, the distance separating the RF source and the medical instrument, and, very importantly, the medical instrument’s wiring harness and its enclosure design. For example, dialysis machines with long wiring harnesses have demonstrated higher sensitivity to EMI than have small electronic thermometers. In addition, the mode of failure is important: a change in the operation of the instrument, which is not readily detectable by the user, is more critical than a change that generates an alarm or an obvious malfunction and then self-corrects.

The effects of EMI on medical instrument performance have been documented In multi-institution studies.* One of the studies—conducted in the clinical environment of a hospital acute care area after obtaining documented consent from patients—showed that under certain conditions related to power, platform, distance, and medical instrument, EMI problems can be replicated and mitigated by appropriate education, policy, and procedures.

Without a study that includes all the different transmission platforms and combinations of medical instruments used in the clinical environment, the complete relaxation of a cell phone ban is unsafe. Many years ago, in the absence of good clinical studies, we banned cell phone use in our hospital. However, after performing a study involving real-world clinical conditions, we realized that all the interference effects occurred within a 3-foot radius of the medical device or the “sphere of risk.” As a result, 5 years ago, we modified our policy to prohibit the use of cellular phones within the "sphere of risk" in specific locations where the density of medical instruments is higher and where EMI problems were previously observed, namely the dialysis unit, catheterization lab, and intensive care unit. This policy is still in place.

We have relaxed our cell phone policy over the last couple of years. In critical care areas, cell phones can only be used in the waiting areas. As for other areas in the facility, we maintain a 3-foot policy, meaning that one must be at least 3 feet away from a medical device when using a cell phone. We also require that users of two-way radios keep a distance of 15 feet from medical equipment.

From FDA: FDA does not have specific recommendations on the use of cell phones in hospitals. Based on circumstances, each hospital must assess its own risk and manage its electromagnetic environment. "FDA/CDRH Recommendations for EMC/EMI in Healthcare Facilities."

*See “Safe Use of Cellular Telephones in Hospitals: Fundamental Principles and Case Studies,” by T. Cohen, M.S. CCE; W.S. Ellis, Ph.D., M.D.; J.J. Morrissey, Ph.D.; C. Bakuzonis, M.Eng., CCE; Y. David, PE, Ed.D., CCE; W.D. Paperman, CE, in the Journal of Healthcare Information Management 19(4): 38–48,

Additional Information:

FDA/CDRH Recommendations for EMC/EMI in Healthcare Facilities

Additional information on this topic is available at

Safe Use of Cellular Telephones in Hospitals: Fundamental Principles and Case Studies

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