Agencies who can help in setting a Hospital?

Answer 1

Advances in medical technology have made it possible to save patients who as little as five years ago wouldn’t have stood a chance. The innovations that have given patients an even better chance of recovery have been as simple as a new procedure or as complex as a new breed of medical imaging equipment. Among those innovations is one that saves hospitals from frustration while it helps clinicians save lives.

The introduction of wireless local-area network (WLAN) products can add value that network components have never before provided. Health systems using wireless devices report a 47% increase in the accuracy of patient information.1 By helping a hospital maintain accurate, up-to-date patient records, the use of WLAN devices can lower costs.

However, just as a good WLAN system can help increase efficiency, improperly deployed wireless devices can disrupt sensitive medical equipment. Wireless devices can disrupt medical monitoring equipment, and they can interfere with medical devices such as hearing aids or implanted devices such as pacemakers. Another concern centers on whether users are safe from radio-frequency exposure.

These issues, though important, can be mitigated when properly addressed.

Preparing the Installation

When installing any wireless system in a healthcare environment, it is critical to keep several factors in mind. Wireless networking systems emit and receive radio frequencies in the 2.4 GHz band, as do some medical devices. Therefore, if a network is not properly designed, interference will likely occur. A site survey should be conducted before beginning the installation. A test of all non-mission-critical components in the system should also be conducted. Some interference can be avoided simply by locating an access point just a few feet from where it was originally planned.

It is best to have a wireless network designed and installed by a trained, professional installer. Some interference is relatively benign, causing no serious effects or producing only low-grade interference, such as snow on a monitor. However, more-severe interference can cause a medical device to produce erroneous readings or to reset, or it can jam its communications. In a medical environment, where many decisions are a matter of life and death, avoiding such problems is essential.

Preparation Is Key

The first step in preparing to install WLAN devices is to determine whether there is any potential interference with medical equipment. Some medical devices are not properly hardened for immunity from certain RF levels and frequencies common to wireless networking. This is particularly true of older medical devices that were manufactured prior to the adoption of certain certifications and standards. It also depends on the standard being used. It is important to check the standards and certification labels carried by the equipment. Once these limits are known, the network can be designed with the associated limitations in mind.

It is critical to involve the hospital’s biomedical engineering department in the testing of a WLAN. Testing should be done in a controlled environment with other sources of electromagnetic interference. The biomedical engineering department is responsible for testing devices and defining the policies and procedures relating to these devices and their usage. Most such departments have a standard test set that is based on known industry issues and the electromagnetic devices that the hospital already has installed. Knowing the location of other electromagnetic devices is extremely important, because proximity to such devices must be considered during the site survey.

Selection of the operating frequency is also critical. In some cases, an 802.11b/g device operating at 2.4 GHz may operate without any problems. In some installations, however, an 802.11a device operating in the 5 GHz band may help avoid or reduce interference.

The selection of power output is equally important. In most cases, using smaller cell sizes with low-power radios may be more beneficial than using fewer systems operating at higher power.

Medical EMC Standards

Another critical factor is to determine whether the medical equipment deployed has been tested with various wireless devices. It is particularly important to determine the electromagnetic compatibility of any medical devices in the facility that are used to provide direct patient care or peripheral support. Some medical equipment manufacturers may list minimum distances for various wireless devices. It should be noted that a piece of medical equipment that has been tested and certified to IEC 60601-1-2 standards is still subject to interference.

Based on the frequencies of operation, the WLAN devices in most cases should not disrupt operation of any wireless medical monitoring devices unless a medical device is operating in either the 2.4 or the 5 GHz band.

The next issue to address is whether the WLAN device has been tested for use in a medical environment. This means the WLAN device should comply with IEC 60601-1-2 standards. Compliance requires that the device be tested to the emission requirements as called out in CISPR 11.2 There are two levels of compliance for CISPR 11: Class A and Class B emissions. According to the requirements called out in IEC 60601-1-2, if the digital device has been tested to the requirements of CISPR 22, then the product does not need to be tested to CISPR 11.3 The emission levels set forth in CISPR 11 address only the unintentional spurious emissions from the device and do not cover any of the transmitter emission parameters. Compliance with the transmitter parameters would be to the appropriate radio standard.

Meeting International Certifications

Before being placed on the market, WLAN radios must be thoroughly tested and certified for international regulatory standards that are applicable to 802.11a, 802.11b, and 802.11g devices, and these radios must be labeled accordingly. Some installations may require further tests based on emissions and immunity requirements specific to that environment. Table I shows the international regulatory standards that 802.11a, 802.11b, and 802.11g WLAN devices must comply with.

Country WLAN U-NII
Canada RSS-210 RSS-210
European Union EN 301-328 EN 301-893
Japan Std. 66 and Std. 33a Std. 71
United States FCC Part 15.247 FCC Part 15.401
Table II. ANSI and CISPR numbers of bits according to dynamic range.


It should be understood that compliance with these standards does not guarantee there will be no interference, although interference to other systems operating in other bands will be greatly reduced.

On-Site Testing

To prevent interference, the best approach is to perform real-world on-site testing with the wireless devices. It is recommended that this evaluation be done in accordance with either the radio manufacturers guidelines or the in-situ test procedure recommended in ANSI C63.18.4

For in-situ testing of WLAN with medical devices, it is recommended that the transmitters be designed similarly to their configuration for qualifying the radio for compliance. This setup provides the worst-case scenario for evaluating the WLAN in the intended environment. The transmitter should be configured for maximum power as well as maximum duty cycle (100% preferred), using the worst-case modulation. This information can be derived from the radio compliance report.

The medical device used for testing purposes should be set on a wooden table in an open area. The use of a calibrated site is not required for this testing. The device should be configured to operate as intended. The medical device should be verified to ensure that it is working correctly before performing the tests. Testing distance between the equipment under test (EUT) and the Wi-Fi device can be derived from the ANSI C63.18 standard. For initial tests, however, it is recommended that the antenna be placed on the EUT itself to see whether any anomalies occur at the points at which the measurements will be made. Upon completion of that test, testing can be started as referenced in ANSI C63.18.4 Some manufacturers, including Cisco, have developed alternative procedures for Wi-Fi devices. These procedures are based on ANSI C63.18.

The pass-fail test criteria can be derived from ANSI C63.18 but it is up to the information technology (IT) and biomedical engineering staff to determine what is acceptable for a particular medical facility. Those not familiar with this type of testing should consult the radio manufacturer’s compliance group or consider using a third-party consultant.

Handling Specific Medical Concerns

One concern that comes up often is the possibility that a WLAN device will interfere with hearing aids or pacemakers. The possibility is remote, and tests indicating interference have been done with cordless and cellular phones held up to the ear, not near wireless access points, which are generally far from a person’s hearing aid. The use of 2.4- and 5-GHz VoIP phones has raised new concerns. The VoIP industry is addressing the compatibility of these phones with hearing aids.

Another concern is whether implanted pacemakers operating in the same frequencies as microwave ovens can be disrupted. However, most pacemakers subject to interference were older models, and the interference came from systems operating in bands of 900 MHz and below. Changes and improvements in pacemaker design have helped eliminate most of these problems. These changes were made based on the results of studies performed with Wi-Fi devices and pacemakers.1

Do low-power wireless devices such as WLAN client cards, access points, or radio-frequency identification tags pose a health threat? Available evidence suggests that there is no clear correlation between low-power wireless use and health issues.

There are, however, several concerns that need to be addressed when deploying Wi-Fi in a medical environment:

• Will it interfere with the medical equipment on-site, including life-support systems?
• Does it work without wireless medical telemetry systems, or is it disruptive to them?
• Will the ISM equipment interfere with the medical equipment?
• Is the Wi-Fi equipment safe to use from a health perspective?

Compliance with RF Exposure Requirements

WLAN products must be evaluated to ensure that they conform to the RF emission safety limits adopted by agencies worldwide. These evaluations are in accordance with the various regulations and guidelines adopted or recommended by the U.S. Federal Communications Commission and other agencies worldwide.5 The RF emission levels from a typical radio local-area network (RLAN) are well within the safety emission level thresholds set by the World Health Organization. The RF emission limits adopted by national agencies are based on guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP).6

Compliance for these devices is typically based on the compliance with the maximum permissible exposure (MPE) levels for mobile or fixed devices or per specific absorption rate (SAR) tests for portable devices. For example, Cisco access points and bridges are classified as either mobile or fixed, depending on antenna gain and installation requirements. Cisco client cards and VoIP phones are classified as portable devices and, therefore, may be subject to SAR testing. Depending on the type of product, compliance is based on modeling or technical analysis or on RF measurement testing. The analysis and testing should be performed in accordance with the applicable national and international standards.

Conclusion

The rollout of WLAN in a hospital need not be a nerve-racking experience if properly done. The WLAN industry has developed best-practice guides for the operation of these systems as well as for addressing RF interference in the medical facilities.

Addressing WLAN in the hospital environment can be done if a plan is developed to address concerns regarding interference and safety. By addressing these issues in the initial stages of system planning and by following recommended best practices, a WLAN system should not be disruptive and, in fact, should be beneficial to the medical staff in the performance of their duties.

References

1. “Wireless LAN Benefits Study,” Conducted by NOP World Technology on Behalf of Cisco Systems (San Jose: Cisco Systems, 2003).
2. CISPR 11, Consolidated, Edition 4.1, “Industrial, Scientific, and Medical (ISM) Radio-Frequency Equipment—Electromagnetic Disturbance Characteristics—Limits and Methods of Measurement” (Geneva: International Electrotechnical Commission, 1998).
3. CISPR 22, Amendment 1, Edition 4.0, “Information Technology Equipment—Radio Disturbance Characteristics—Limits and Methods of Measurement” (Geneva: International Electrotechnical Commission, 1997).
4. ANSI C63.18, “Recommended Practice for an On-Site Test Method for Estimating Radiated Electromagnetic Immunity of Medical Devices to Specific Radio-Frequency Transmitters” (Washington, DC: American National Standards Institute, 1997).
5. “Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz),” International Commission on Non-Ionizing Radiation Protection (ICNIRP) (Oberschleissheim, Germany: International Commission on Non-Ionizing Radiation Protection, 1998).
6. Office of Engineering and Technology Bulletin 65C Revision 01-01, “Evaluating Compliance with FCC Guidelines for Human Exposure to Radio-frequency Electromagnetic Fields” (Washington, DC: Federal Communications Commission, 2001).