EMI/RFI Management is one of the areas of the CCE examination under the topic of "Technology Management." For a complete list of CCE Examination topics, see the new 2008 Candidate Handbook for Certification in Clinical Engineering, available at www.accefoundation.org/certification.asp.

Electromagnetic interference (EMI)—also called radio frequency interference (RFI)—causes an unwanted effect on the performance of medical equipment by creating an undesirable response or failure. It can cause medical equipment malfunction and harm patients who are dependent on medical equipment, such as with ventilators, for example. The effects of EMI include data corruption, changes in device adjustments, inappropriate activation or failure of alarms, and distortions in the images produced by imaging systems.

Electromagnetic compatibility means that a device is compatible with its electromagnetic (EM) environment and does not emit levels of EM energy that cause EMI in other devices in the vicinity. It is basically the opposite of EMI.

Finding the Friction

EMI depends on a number of factors, including distance between a radio frequency (RF) transmitting device (cellular telephones, walkie-talkies, two-way pagers) and susceptible medical equipment such as apnea monitors and ventilators; and the power and frequency of the RF transmitting device and the susceptibility of the medical equipment. To some degree, these factors are controllable. As the distance decreases, the likelihood of EMI increases. Higher power and lower frequency of an RF transmitter will more likely cause interference. Also, physical barriers such as walls and ceilings may possibly cause EM signals to reflect, increase, or weaken.

Typical cellular phones operate at about 900 MHz with an output power of up to 3 W. To reduce the risk of interference, the cellular telephones should be at least 1 meter away from medical equipment. Typical two-way radios and walkie-talkies operate at about 400 to 500 MHz with output powers of up to 5 W. Since two-way radios and walkie-talkies operate at lower frequencies and at higher output powers, the likelihood of interference is greater than with cellular phones. Therefore, walkie-talkies and two-way radios must be kept farther away from medical equipment.

It should be noted that medical equipment could be affected by EMI from sources besides cellular telephones. This includes electrostatic discharge and disturbances due to nearby power lines, and even other medical equipment like electrosurgical units.

Standards and Rules

The commonly referenced standard for EMI performance is IEC 60601-1-2:2001, published by the International Electrotechnical Commission (IEC). The AAMI/ANSI/IEC 60601-1-2:2001 is the US version of IEC 60601-1-2:2001 with identical requirements. The medical equipment that complies with this standard is less susceptible to

EMI. It, however, does not guarantee EMI immunity under all conditions. According to IEC 60601-1-2, general-purpose medical devices should be immune to electric fields up to 3 V/m and critical life-support devices up to 10 V/m. Another standard, ANSI C63.18-1997, describes a method of testing medical equipment for immunity against devices such as cellular phones and walkie-talkies.

Arif Subhan, MS, CCE, is a senior clinical engineer, Masterplan, Chatsworth, Calif, and chair, education committee, ACCE. For more information, contact .

Suggested References for Further Study

1. ANSI C63.18-1997. American national standard recommended practice for an on-site, ad hoc test method for estimating radiated electromagnetic immunity of medical devices to specific radio-frequency transmitters. http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&isnumber=14032&arnumber=643516&punumber=5190. Accessed April 28, 2008.
2. Cohen T, Ellis WS, Morrissey JJ, Bakuzonis C, David Y, Paperman WD. Safe use of cellular telephones in hospitals: fundamental principles and case studies. J Healthc Inf Manage. 2005;19(4):38-48.
3. FDA. Electromagnetic interference (EMI)/ electromagnetic compatibility (EMC). http://www.accessdata.fda.gov/scripts/cdrh/ cfdocs/cfTopic/topicindex/topindx.cfm?alpha=e. Accessed April 11, 2008.
4. IEC 60601-1-2:2001. Medical electrical equipment, part 1: general requirements for safety. 2. Collateral standard: electromagnetic compatibility — requirements and tests. http://en.wikipedia.org/wiki/List_of_IEC_standards. Accessed April 28, 2008.
5. [No authors listed.] Cell phones and electromagnetic interference revisited. Health Devices. 2006;35(12):449-456.
6. Paperman WD, David Y, Hibbetts J. Electromagnetic Interference in the Hospital (Chapter 63). In: Dyro JD, Ed. Clinical Engineering Handbook. Elsevier Academic Press; 2004.