safe use of cellular

FOCUS: Mobile Computing

38 Journal of Healthcare Information Management Vol. 19, No. 4

Introduction

Inpatient healthcare requires multiple, simultaneousprocesses and teamwork involving physicians, nurses, unitsecretaries, and ancillary staff. Frequent communication isnecessary to ensure safe and efficient delivery of healthcare.The inefficiencies of traditional communications methodswere highlighted by a recent study comparing wirelessvoice communications to overhead paging, estimating a

potential savings of more than 3,400 hours per year on two32-patient hospital wards.1 Furthermore, it is estimated thatfrom 44,000 to 98,000 fatal medical errors occur annually inU.S. hospitals2 and that many could have been avoidedthrough better communication. Efficient and improvedcommunications should contribute to both cost savings andsafety improvements in healthcare delivery.

Other industries and many private individuals have

Safe Use of CellularTelephones in Hospitals:Fundamental Principles

and Case StudiesTed Cohen, MS, CCE; Willard S. Ellis, PhD, MD; Joseph J. Morrissey, PhD;

Craig Bakuzonis, MEng, CCE; Yadin David, PE, EdD, CCE; and W. David Paperman, CE

A B S T R A C T

Many industries and individuals have embraced cellular telephones.They provide mobile,

synchronous communication, which could hypothetically increase the efficiency and safety of

inpatient healthcare. However, reports of early analog cellular telephones interfering with critical life-

support machines had led many hospitals to strictly prohibit cellular telephones.A literature search

revealed that individual hospitals now are allowing cellular telephone use with various policies to

prevent electromagnetic interference with medical devices.The fundamental principles underlying

electromagnetic interference are immunity, frequency, modulation technology, distance, and power.

Electromagnetic interference risk mitigation methods based on these principles have been

successfully implemented. In one case study, a minimum distance between cellular telephones and

medical devices is maintained, with restrictions in critical areas. In another case study, cellular

telephone coverage is augmented to automatically control the power of the cellular telephone.

While no uniform safety standard yet exists, cellular telephones can be safely used in

hospitals when their use is managed carefully.

K E Y W O R D S

Cellular telephones Hospital Medical devices Safety Interference EMI Power Distance


Journal of Healthcare Information Management Vol. 19, No. 4 39

embraced cellular telephones to increase productivity andfacilitate mobile communication. To date, there is littlepublished data describing the benefits of cellular telephoneuse by healthcare providers. Even so, many cliniciansreportedly prefer to be contacted by mobile phone,3 andsome large hospitals already have incorporated wirelesscommunications devices, including cellular phone systems,for their staff as a principle means of in-house and off-campus communication.

Many hypothesize that another benefit from cellulartelephone use is the reduction in ambient noise, such asoverhead pages.4 Cellular phone systems also offer mobilityto both caller and receiver, increasing efficiency by helpingthem make use of time moving between tasks inside thehospital. In addition, patients and visitors have frequentlyindicated that they would like the convenience of usingtheir cellular phones in the hospital.5

Despite these possible benefits, the healthcare industryhas been reluctant to embrace cell phones. Much of thisreluctance stems from anecdotal reports of early analogcellular telephones and handheld radios interfering withcritical life-support machines and later reports that evenmodern, digital cellular telephones can cause malfunctions,including irrecoverable cessation of ventilation under testconditions.6 Hospitals in England, France, Germany, andsome in the United States (see Table 1), have strictlyprohibited cellular telephones, with some employingelectronic mobile phone detectors to enforce the ban.7

However, many hospitals are in the process of changingtheir policies. Specifically, in July 2004, the Medicines andHealthcare Products Regulatory Agency (MHRA) of the UKreleased new guidance specifying that a total ban onmobile phones in hospitals was not necessary, althoughappropriate management procedures were needed.

For this review, researchers attempted to identify appro-

priate management procedures with a review of the litera-ture. A search of the PubMed database using the termscellular telephone identified 443 articles published as ofMarch 2005. Of these, 38 articles were identified as relevantto cell phone use in hospitals. Articles were excluded thataddressed interference with implanted devices and biolog-ical effects of electromagnetic fields because those topicsare not specific to a hospital environment. Although manyarticles exist, they report testing of specific devices; nouniversal guidelines or management procedures have been published.

The Science of Interference

The ability of electromagnetic emissions from cell phonesto interfere with medical devices is based on properties ofpropagation of electromagnetic energy: the output power ofthe cell phone (source), the frequency and modulationtechnology, the separation distance between the source andmedical device, and the immunity of the medical device.

Irnich and Tobish tested more than 220 electronicdevices in a hospital environment and were able to demon-strate greater than 98 percent safety when cellulartelephones were kept more than one meter away.8

However, using different cell phones and medical devices,various hospitals have recommended safe distances varyingfrom arms length to three feet, one meter, two meters, toeven five meters.6,7,8,9,10 One practical version of distancingcell phones from critical medical devices is to allow them inspecific locations, such as non-patient care areas of thehospital, but exclude them from more sensitive areas, suchas intensive care units and emergency departments.7

More recent policies among several hospitals have takenadvantage of the dynamic power control feature in moderndigital cell phones designed initially to conserve theirbatteries by transmitting at low power in areas of goodcellular coverage. Switching to low power decreases theelectromagnetic field generated by a cell phone and itspotential to interfere with medical devices.

Thus, some hospitals have chosen to embrace andcontrol the technology.11 These hospitals have arranged forinstallation of either microcells (small-scale base stationsites) or repeater antennas (in-building antennas linked toan external antenna to augment interior coverage) toincrease signal coverage, thereby causing staff telephones to

Other industries and many privateindividuals have embraced cellular telephones

to increase productivity and facilitate

mobile communication.



transmit at lower power levels. Some hospitals have chosena single service provider to outfit their building, althoughonly cell phones operating on that network can be assuredof appropriate dynamic power control. However, thisconcept can be extended to any modern digital cellulartelephone technology. For example, Beth Israel in Bostonhas chosen a vendor-neutral solution by installing a micro-cell, and when you walk into the building, your cell phoneswitches to B[eth] I[srael] as your service provider.11

Recognizing the current flux in hospital policies, this article further reviews and explores the fundamentals ofmedical device interference from cellular telephones andincludes two case studies demonstrating successful mitigation methods.

Interference

As shown in Table 2, and described in several otherstudies,12,13,14,15,16 cell-phone-induced electromagnetic interfer-ence, or EMI, events can be repeatedly generated under test

conditions in susceptible medical devices. To test worst-casescenarios and create repeatable test methodologies, many ofthese reported laboratory tests were performed with themobile phones transmitting at maximum handset power.

Problems encountered are shown in Table 2 and rangefrom small changes in ventilator parameters at close range(test samples number 1,4,5,7) to total shutdown of aninfusion pump at close range (test sample number 12) tochronic interference on a defibrillator monitors ECG display(test sample number 9C). Figure 1 shows more detail on thedefibrillator monitor test sample. Additional testing wasdone on some very sensitive equipment used in theoperating roomthe Cadwell model Cascade 16 neuromon-itoring device17 showed interference at low power levelsfrom most cell phones. These EEG devices are intended toamplify very low signal levels, and because of that, theirhigh-gain amplifiers are prone to interference, even fromrelatively low-power interference sources.

Recognizing that interference occurs with specific



medical devices and cellular telephones is the first step inrisk mitigation. The criticality of the EMI event must beobjectively determined by the hospital. Interference is afunction of several differing and interacting factors thatinclude medical device immunity, frequency, modulationtechnology, distance, and power.

Immunity. EMI is not limited to cellular telephones; itcan theoretically occur between any two devices that eitherintentionally or unintentionally emit electromagnetic energy.Medical equipment manufacturers generally comply with a10 volts per meter immunity level against interference fromradio frequency emissions in the design of new life-criticalmedical devices.18 However, not all new medical devicescomply with the IEC immunity standard, and there aremany older medical devices in use that do not meet thisstandard. Even on relatively new devices, some manufac-turers continue to recommend cell phone/medical deviceseparations of as much as 10 meters presumably becausetheir devices do not meet the IEC immunity standard.19 Acareful inventory of medical devices and their immunitycharacteristics is very useful in designing a risk mitigationpolicy. However, even a hospital with new equipment,uniformly meeting the IEC immunity standard, still wouldbe vulnerable to interference because cellular telephonesmay exceed 10 volts per meter when operating in closeproximity.16

Frequency and modulation technology. Cell phonesutilize transmission frequencies that are licensed by the FCC

and other government organiza-tions outside the US and arededicated to cell phone use.Over time, and in differentcountries throughout the world,various cell phone modulationtechnologies and frequencieshave been used. Older, so-calledfirst-generation analog (1G) andearly digital technologies, such ascertain types of TDMA, are beingphased out and replaced bysecond-generation (2G) GSM andCDMA technologies.15 Newerglobal CDMA standards (3G)have been defined, and this newtechnology is under develop-ment. No one has yet developeda way to empirically determinethe interference impact of aspecific frequency or modulationtechnology on a given medicaldevice. However, even limitedtesting (see Table 2) demon-strates that cellular telephoneswith different frequency or

modulation technologies produce different patterns of inter-ference. Also, some handsets are multi-mode and can havediffering potential interference characteristics, depending onthe network available at a particular location. Morrissey15

discusses more detailed information on power control,frequency, and modulation technology. Because interfer-ence risk as a result of frequency and modulation is difficultto predict, hospitals should choose staff cell phones withone specific technology or perform worst-case scenariotesting with multiple technologies.

Distance. A fundamental principle of electromagneticfields is that they decrease exponentially as distance fromtheir source increases. Figure 2 shows the average electro-magnetic field strength generated by cell phones as afunction of distance. At close distancesless than onemeterfield strengths can exceed the current IEC medicaldevice immunity standard for life-critical equipment of 10volts per meter.18 At distances greater than one meter, fieldstrengths rapidly decrease and become increasingly unlikely

Recognizing that interference occurs withspecific medical devices and cellular telephones

is the first step in risk mitigation.



to cause any interference issues. Therefore, separation is one key to safe use of cell phones in healthcare environments.

However, although the fundamental principles apply toany cell phone technology, actual field strengths at anyparticular distance vary depending on the specific environ-ment, cell phone modulation technology, and maximumhandset power. The first case study describes the testingrequired and implementation of a safe cellular telephonepolicy based on specific devices and separation distances(see Figure 2).

Power. Modern digital, cellular telephones have asecond characteristic that can be exploited to create a safecellular telephone policy. To optimize battery life andprevent interference with other cellular telephones,individual handsets attempt to operate at the lowest powerthat provides reasonable signal quality. Cell phone systemsautomatically adjust for low signal strength by increasingpower up to the power maximum of the particular cellphone handset. Cell phone systems make this power adjust-ment automatically without respect to the reason for thepoor signal quality, for reasons that can include buildinginterference, distance, and other factors. Building construc-tion, including the density and thickness of steel andconcrete, the number of walls separating the handset fromthe controlling base station, shielding and reflecting objects,multipath considerations, and location of external basestation sites with respect to the building all can greatlyaffect the transmission characteristics of the cell phone

signal. Hospitals are typically builtwith large amounts of steel andconcrete, and are often comprisedof interconnecting buildings builtat different times with differingconstruction and materials. Figure3 shows typical average cellphone power levels of 0.1 wattsfor facility A, which has fair topoor coverage, but typical powerlevels are 10 times lower (0.01watts and less) at facility B, whichhas good coverage.

Following electrical engineeringconvention, powerthe Y axis inFigure 3has been plotted on alogarithmic scale. The values listedare average power output from aGSM handset operating on a US1900 MHz network and may bedifferent for GSM handsetsoperating on other frequencybands (850 MHz in the US, 900 or1800 MHz in Europe) or forhandsets operating on other

technologies, such as CDMA. Because the digital GSMsignal is repeatedly pulsed over a series of timeframes, the peak power values will be higher than the listedaverage power values (for GSM, by a factor of eight times,since there are eight available time slots in a repeating time frame).

Finally, while the figure accurately illustrates dynamicpower control over a short time period, even in thepresence of good network coverage, handsets may transmitseveral short bursts at full power immediately followingpower-on and registration or when receiving signal andexchanging information with a priority network site. Also,because of very high traffic volume, a handset might bereallocated to a more distant network site. However, thesescenarios would be uncommon in a fixed location, such asa hospital room, and any transmission bursts would be veryshort, such as fractions of a second; the vast majority of thetime, handsets localized to a confined hospital area wouldremain under the constant control of a single network basestation with dynamic power control.

Recognizing that digital cellular telephone power outputvaries automatically, it is possible to design an environment

Many hospitals are choosing to implement acontrolled mobile phone system for use by

hospital staff.



in which handsets operating on that network transmit at managed power levels. The second case study describes the testing, design and implementation of a safecellular telephone system based on creating adequatecellular coverage.

Risk Mitigation Methods

Most hospitals have policies on mobile phone use,however these policies can run the gamut from total ban tocontrolled use of only certain tested and labeled cellphones to no controls at all. There are currently no regula-

tions or requirements in the US that mandate mobile phonecontrols in hospitals. Although testing at maximum powershows potential for cell phone-caused interference tosusceptible medical devices, cell phones are increasinglycommon in hospitals, and reports of adverse interference-related events from the government and other patientsafety-related databases suggest that the overall risk topatients remains very small.14 It is unknown if such events are not occurring or if underreporting of such events is substantial.

Many hospitals are choosing to implement a controlledmobile phone system for use by hospital staff. Such acontrolled system can take many forms, including adding

additional infrastructure,such as microcells orrepeaters, using onlycertain tested and labeledphones, designated areasfor cell phone bans (ICUs,operating rooms, and EEG laboratories), desig-nated areas for public cell phone use, and anyand all combinations ofthese and other manage-ment strategies.

The appendix to thisarticle documents two casestudies of controlledimplementation of cellphones. In both cases,considerable testing wascompleted by hospital

clinical engineering staff using simplified versions of theANSI/IEEE ad hoc testing recommendations.20 Also in both cases, administrative controls were developed toregulate policies, separation requirements, signs, andcontinued testing.

Texas Childrens Hospital recently conducted a cellphone testing program in two of its inpatient areas. Thefacility previously had a total ban on cell phones. Based onthe study, the facility implemented administrative controls toallow cell phone use (from several different carriers but notall) with a three-foot separation recommendationthroughout the institution. However, the ban will continuein critical care areas until further testing is completed.

Shands Hospital at the University of Florida used addedinfrastructure in key areas to provide coverage at reducedtransmission power (targeted 60 milliwatts maximum) in allpatient care areas. In its case, the infrastructure was fundedby the cell phone carrier, with the hospital guaranteeing anincrease in the number of subscribers to that carrier. Also,public use of that specific carriers cell phones is allowedwithin the hospital.

Conclusions and Future Directions

Safe cell phone use in hospitals requires managementcontrols. Patient safety should not be compromised for staffand visitor convenience. However, cell phones offer signifi-cant communication improvements for staff, which may, initself, improve patient safety. Various safe methods can beused to manage cell phones, with the primary tradeoffbeing cost (for example, adding in-building cellular infra-structure) vs. coverage. Options include adding widespreadinfrastructure, adding limited infrastructure in areas where itis believed to be most essential to tightly manage cellphone emissions, mandating specific tested cell phone

As communications technology evolves,medical devices become less EMI-prone and

more is learned about medical device

interference, additional less complex options

will become available.



models only, banning cell phones in certain critical areas,mandating separation between cell phones, patients, andtheir medical devices, and many other controls.

Although no laws in the US exist to control cell phonesin hospitals, the management options outlined above areconsistent with the recommendations of ECRI14 and theInternational Standards Organization (ISO) TC215 technicalreport No. 21730 on electromagnetic compatibility withmedical devices.21

Results of interference testing is just one of severalfactors to consider when deciding on a specific cellular orother wireless communication technology. Other importantfactors include the local wireless environment, localtelecommunications conditions, cost issues, clinical cultureand structure, and timing, because the technology isevolving rapidly. Potential mitigation techniques should bebased on the issues found during testing and local condi-tions. Often, both management and engineering controls areused together to provide a reasonable safety margin. Forexample, at Texas Childrens Hospital, managementcontrols, in the form of policies and education, are used torestrict cell phone use to only certain types of phones andonly in certain hospital areas. Alternatively, at ShandsHospital, an engineering solution in the form of installationof an internal antenna infrastructure facilitating handsetpower management is used to provide a safe cellular phone solution.

Some hospitals have successfully implemented safe cellphone systems, which are subjectively improving staffcommunication and increasing convenience for patients andvisitors. Communication technology should not be chosensolely on EMI considerations, because some RF signals cancause EMI under unmanaged conditions, and all modernwireless communication technologies can be managed tooperate compatibly if appropriate management andengineering controls are implemented.

As communications technology evolves, medical devicesbecome less EMI-prone and more is learned about medicaldevice interference, additional less complex options willbecome available. Decisions must be made that are safe forthe local conditions and planned technology, with theknowledge that changes are inevitable and regular follow-up will be required. Subsequent studies on the potentialpositive effects of communication improvement, as well aspublic sentiment5 will likely increase demand for cell phoneimplementation in hospitals.

Existing and new technology can be expected for bothhealthcare communications and medical device data trans-port. Providers are deploying 802.11b/g (2.45 GHz) and802.11a (5 GHz) systems to carry basic point-of-care

medical device information, and these networks may carryreal-time patient data in the near future. Voice communica-tion on unlicensed bands using Voice over IP (VoIP) proto-cols on 802.11a/b/g networks offer low-power in-buildingalternatives that might be combined with traditional cellulartelephones in the near future. Other low power technolo-gies (e.g., 802.15.1 / Bluetooth, 802.15.4 / Zigbee) as wellas broadband and ultra wideband technologies (e.g.,802.15.3a, 802.16) might have potential healthcare applica-tions in the future. The merging of these technologies withcell phone handsets capable of transmission on manydifferent licensed and unlicensed networks will add morecapability but also increase the complexity of medicaldevice EMI as well as RF spectrum management. Althoughthe field continues to evolve and no uniform standard yetexists, risk mitigation and cell phone use in hospitals willcontinue to expand.

Acknowledgments

The authors wish to acknowledge James Hibbets andBiju Joseph of the Biomedical Engineering Department atTexas Childrens Hospital for their contributions. Theauthors note that Motorola provides equipment to manycellular phone carriers. Each hospital mentioned in thisarticle uses a different cellular telephone carrier and equip-ment from different manufacturers.

About the Authors

Ted Cohen completed his MS in biomedical engineering. He is a certified clinical engineer and iscurrently the manager of clinical engineering for UC Davis Health System.

Willard S. Ellis completed a PhD in bioengineering atUC-Berkeley and MD at UC-San Francisco. He is currently ahospitalist and assistant clinical professor at UC-Davis.

Joseph J. Morrissey is a staff scientist and engineer atMotorola Labs.

Craig Bakuzonis received a BS and MEng in biomedicalengineering from Rensselaer Polytechnic Institute. He iscurrently director of clinical engineering at Shands Hospital.

Yadin David is director of biomedical engineering atTCH, appointed in Pediatrics, Baylor College of Medicine,received Special Citation from the FDA Commissioner, andis president of the Healthcare Technology Foundation.

William D. Paperman studied digital control and communications systems, served in the U.S.A.F. ArmamentSystems Personnel Research Laboratories, and worked asclinical engineer at TCH. He now consults on communica-tions systems.

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Case Study No. 1: Texas Childrens Hospital

Recognizing that the probability of interference decreasesin proportion to the distance between devices, TexasChildrens Hospital wanted to determine if a safe operatingdistance between existing medical and personal telecommu-nication devices could be identified. A test protocol was

designed to measure electromagnetic field strengths beforeintroducing a cellular telephone into the hospital environ-ment and then to observe any effects on the operation ofselected medical devices once cell phones were introduced.

Tests were conducted in the real clinical environment ofthe hospital after obtaining informed consent from patients

Appendix



and their families and securing nursing staff to assist duringthe studys observation phase. The test protocol wasreviewed and approved by the Baylor College of MedicineInstitutional Review Board. Tests were conducted during atwo-month period. There were a total of 14 valid testsperformed in 13 different rooms of two different designs. Atotal of 43 medical devices were present during the tests.Some medical devices, such as physiological monitoringdevices and infusion pumps, were present in all tests.

The testing consisted of two series of investigationsmeasuring the background levels of relevant electromag-netic radiation and exposing medical devices to the electro-magnetic fields generated by various cellular telephones.The cellular telephones used in the tests were selected asbeing representative of the various types in popular serviceduring the time period in which the tests took place.Operation of the cellular telephones was under the controlof technicians from the biomedical engineering department,who performed the tests.

Multi-mode cellular telephones were placed in locationsmost likely to be occupied during staff and family visits.One location was on the patient bed, positioned so itwould be within convenient reach of the patient. Anotherlocation was in the breast pocket of the technician,simulating a clinician treating the patient carrying an activecell phone. Finally, three additional sites within a patientsroom were selected based on probable locations oftransient non-occupants, such as visitors and medical staff.

Testing was performed in two patient rooms, each ofdifferent design. Tests were conducted sequentially withcellular telephones operated in each of the followingmodes: AMPS-800; CDMA-800; CDMA-1900; IDEN-800;GSM-900; GSM-1800; and GSM-1900

Prior to conducting the tests, in addition to obtainingpatient consent from the parents of the subject patient,approval was required from the local nurse manager. As anadditional precaution, the onsite investigatorsbiomedicalengineering personnel having direct familiarity with themedical devices22also were instructed to immediatelyadvise the nurse manager of any change in the operation ofany medical devices observed during testing.

All clinical devices in service in the test areas wererecorded, including the manufacturer, model, serial number, last date of inspection or maintenance, and mode of operation.

Immediately before the cellular telephone interferencetesting, a spectrum analysis footprint1 of the patient roomswas performed. The spectrum observed was from frequen-cies of 800 MHz to 950 MHz and from 1.9 GHz. to 2.4 GHzin steps of 20 MHz. The emphasis in this observation wasplaced on signal activity levels (density) within the cellulartelephone frequency spectra.

The cellular telephones were programmed by the vendorto operate at full transmission power. Measurements of the

electrical (E) and magnetic (H) field strengths present at theprecise locations at which the cellular telephones were tobe activated were taken both passively, before the cellulartelephone was activated, and while the cellular telephoneswere active. The measurements were taken at distances of12 inches and 1 meter from the cellular phone locations.

To allow cellular telephone emission to interact23,24 withall possible processor cycle states and to observe thepossible effects25,26 on medical devices during multipleclocking cycles (computer-driven clinical devices, bit, orbyte corruption), the test period for each cellular telephoneand mode lasted approximately five minutes. The cellulartelephone was turned on and off at random intervals nofewer than three times during each test period.

During the tests, operation of the medical devicespresent in the test environments were closely monitored,and changes in their operation, including the type ofchangeloss or interruption of program, recoverablefailure, or catastrophic failurewere recorded.

Analysis of the spectrum records obtained in phase oneof each study indicated an average level of electromagneticactivity within the portions of the spectrum of interest. Thelevels of electromagnetic radiation were consistent withthose encountered in a dense urban environment with nocellular telephone sites in the immediate vicinity of the testsite. Further analysis of the records indicated that the riskfactor from aggregated electromagnetic fields in thespectrum of interest during testing was not of sufficientintensity to present additive risk to clinical devices exposedunder the test program.

Phase two of the series of tests involved the activation ofcommonly used cellular telephones operating in commonlyused modes. Of the 43 medical devices present and activeduring this series of tests, the cell phones affected threedevicestwo pulse oximeters and one case of disruption ofaudio in a nurse call system pillow speaker. There was noevidence of a deterioration of performance or a permanentalteration in function because of the interfering electromag-netic radiation. In all cases, the interfering cellulartelephone was a Motorola iDEN and the disruption ofoperation occurred when the cellular telephone was withinless than one meter of the device. Interference ceased anddevices fully recovered when the cellular telephone wasremoved from the testing site.

Based on the data acquired from the testing and analysisphases, the following policies regarding the use of cellulartelephones in the Texas Childrens Hospital clinical environ-ment were proposed and implemented:

The use of cellular telephones is permitted (with theexception of iDEN cellular telephones, primarilyemployed in the Nextel Direct Connect system) in gen-eral patient rooms with the recommendation that cellulartelephone devices not be activated within 1 meter of anymedical device. Cell phones can be used with no



restrictions in all common areas; in hallways, corridors,offices and administrative areas; in the outpatient carecenter; and in the emergency department areas.

The use of cell phones is restricted in all critical careareas (NICU, PICU, Cath Lab, and Dialysis, among others). Testing in those areas of high concentrations ofclinical devices was not yet attempted.

The use of cell phones is restricted in operating roomswithin 1 meter of any medical device.

Case Study No. 2: Shands Hospital at the University of Florida

In 2001, Shands Hospital at the University of Floridabegan to explore a single method to communicate withstaff and physicians as they moved throughout the seven-hospital system. It sought a wireless device that couldenable limited data and unlimited voice traffic in a seamlessprocess. Cellular phone technology appeared to be able tomeet these needs with a data access application added tothe basic phone menu.

The organization did not want to restrict the use of thehandsets under any condition, but it also did not want tocompromise any aspect of patient safety. To meet the goalof safe handset use in any patient care area, the organiza-tion elected to make use of the dynamic power controlfeature in all current cell phones that extends battery life byminimizing required transmission power depending onreceived signal strength. By installing a distributed antennasystem that provides coverage throughout all patient careareas, the transmission power level of cellular phones canbe reduced to levels that do not interfere with surroundingmedical equipment.

The vendor selection process included an evaluation ofthe guarantee of hospital coverage, expanded local areacoverage and engineering experience with safe use ofhandsets in a medical environment. The method used atShands was successfully applied for one cellular phonevendor, and it can be extended to a vendor-neutral system.The financial model required that the installation of thesystem have no capital or lease investment, but it couldguarantee an increase in user volume for the vendor.

A test tool also was needed to test both existing and new medical equipment for electromagnetic compatibility at expected transmission power levels, and a survey tool to confirm the correct signal strength in all patient care areas to ensure that the final environment meets thedesign specification.

In the final design, in-building coverage is provided by amanaged distributed antenna system, or DAS, that providesreal-time monitoring and status of the DAS elementsthehardware links, the amplifiers, and the antennas. The safecoverage area includes all patient care areas wheremonitoring, diagnostic, therapeutic, and treatment activities

are performed. Also included were common patient trans-port zones between these areas.

Initial testing of critical medical equipment, such as life-support and high-risk devices, was performed using amodified ANSI C63.18 Recommended Practice for an On-Site, Ad Hoc Test procedure.27 The purpose of ANSIC63.18 is to provide a guideline test method to assess in arelatively reproducible manner the radiated RF immunity ofspecific medical devices to specific RF transmitters. Basedon this testing methodology, when interference is noted, aminimum safe distance often can be determined.

ANSI C63.18 includes guidelines on the selection ofmedical devices to be tested and the selection of RF transmitters to test and test methodology, including selec-tions of the test area, placement of the medical device,evaluation of medical device performance, and precautionson RF transmitter use. In addition, it includes a specific testprocedure indicating antenna orientation, device location,initial and minimum separation distances as a function oftransmitter power, multiple axis testing, and more.

The Shands modified procedure included all sides ofmedical equipment and distances in very close proximityless than 5 centimetersto the device being tested. Thecellular phone company was required to provide ahandheld unit of which the transmission power level couldbe controlled as the distance was varied between the unitand the medical device. In general, the test requiredapproaching the medical device at all sides, one at a time,with the cell phone set to a specific transmission powerlevel. Records were kept of the interaction or interferencecaused, and then a lower transmission power level wasselected and the test was repeated. The purpose of theseinitial tests was to determine the transmission power levelat which interference could not be identified. Medicaldevices tested included anesthesia machines, perfusionsystems, ventilators, patient monitors, defibrillators, andtelemetry systems.

At maximum transmission power levels, researchersfound instances of interference and, in one case, acomplete medical device shutdown, with no notice oralarm. Decreased transmission power levels resulted indecreased levels of interference.

Testing demonstrated that at power levels of -10db (60milliWatts), the devices under test exhibited normal opera-tion at all tested distances. Based on these tests, researchersidentified that the design environment was to provide asignal strength that would enable the handsets to transmit atpower levels of 60 mW (average) or below in all patientcare areas. All other areas were required to have the vendorminimal signal strength for adequate system use.

The final design of the cellular system included locatinga typical cell site on the roof of the building and putting adistributed antenna system on almost every floor of the



hospital. The final design was qualified by the installationcontractor and an independent walkthrough by hospitalpersonnel using the survey tool. The internal marketingplan to our employees, physicians, and contractors was acoordinated effort that emphasized the unique in-buildingcoverage (that) will ensure a quality signal and compati-bility with patient care equipment. For visitors, the facilityposts signs indicating that it allows the use of the vendorscell phone anywhere in the hospital.

Medical equipment that is new to the hospital undergoesan electromagnetic compatibility test with the test tool, atthe 60 mW power level for either every device or 20percent of the devices if there are more than five in a single shipment. To date, no other medical devices havefailed this test.

Quarterly walkthroughs are performed with the surveytool to determine adequate signal strength in the coveredpatient care areas. These quarterly surveys have twiceidentified inadequate signal strength in a section of the

coverage area. The reduction was traced to vendor activityoutside the hospital related to either new or modifiedexisting cell tower sites. Vendors constantly tune theirsystems for optimal performance, coverage, and expandedcapacity; these adjustments made by the vendor affectedShands internal building coverage. A network engineerfrom the vendor was assigned to the hospitals account to handle change management that may affect in-building coverage.

The hospital also experienced system busy callblocking once, at the end of a Florida State-University ofFlorida football game attended by 90,407 fans. TheUniversity of Florida football stadium is less than one mileaway from the hospital, and cellular traffic temporarilysaturated the hospital cell site. The vendor confirmed thisproblem and modified the system to reserve adequatecapacity for hospital call volume.

The Employer of Choice in Southwest Florida

I choseI choseAt Lee Memorial Health System, we are proud of our passion forexcellence, for recently having earned one of the nations 100 MostWired hospitals and health care systems award, Top 100 Hospitals andEmployer of Choice (second year running) awards. With an eye on thefuture, Lee Memorial offers the opportunity to work collaboratively withboth the Information Technology team and the clinical community indeveloping and implementing innovative and cutting edge healthinformation technology solutions.

We are currently seeking Clinical Informatics Project Managers to provide

technological support for several departments within the Health System.

Clinical Informatics - Project Manager, Clinical Ancillary

Clinical Informatics - Project Manager, Post Acute

Clinical Informatics - Project Manager

Lee Memorial offers outstanding benefits and competitive compensation,including relocation assistance and sign-on bonuses.

To learn more about available positions, top-rated benefits, our ongoingexpansion and to apply online, please visit us at www.LeeMemorial.org,or you may apply in person at our new Employment Center located at4380 Cleveland Avenue, Suite B-2, Ft. Myers, FL 33901 (Next toCircuit City). Phone: 1-800-642-5627. Relocation assistance is availablefor select positions.

Drug/Smoke-free workplace. EOE

www.LeeMemorial.org

an award winninghealthcare provider with

astonishing resources.

an award winninghealthcare provider with

astonishing resources.

safe use of cellular

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