Wireless lan brings hospital computers to patient`s bedside
A federal hospital system prescribes wireless local area networks for better patient care.
Angela Champness
Lucent Technologies
Hospitals have long relied on computers to maintain patient records. Now, with recent developments in wireless local area network (lan) technology, computers can also be brought to each patient`s bedside.
Without bedside computers, hospital administrators have had to rely on paper records generated by caregivers to document each patient`s treatment. In-room computers could have improved the situation, but this has not been economically feasible. The cost of hardware alone to put a computer into every room housing a patient would have been prohibitive, as would the cost of labor and materials needed to run cables between each computer and the lan hub or server.
Wireless technology overcomes such problems by providing each caregiver with a small, portable computer to carry from patient to patient while maintaining connectivity with the network. Without cables to restrict movement, these wireless terminals can be used anywhere in the hospital. Of greater importance, though, is that these devices let caregivers record an event--such as dispensing medication--where and when it occurs.
This capability is especially important when the medication is a controlled substance. Using traditional paper records, documenting the trail of these drugs from the pharmacy to the patient can be difficult, especially in large hospitals with hundreds of patients.
Hospitals run by the Veterans Health Administration (vha), for example, may admit more than 1000 patients for treatment at any given time. Complicating the situation is the fact that some vha hospitals are in a high-rise building, while others consist of a number of single-floor buildings spread out over a large campus. Although a vha audit has shown that the pharmacy maintains very tight control over narcotics and other dangerous drugs, accountability is less clear at the ward level. This has spurred the vha to implement a better system of tracking drugs from the pharmacy to the patient.
After carefully analyzing how medication moves in a hospital, the vha decided the best solution to the problem was to implement a wireless lan using portable terminals equipped with bar-code readers. The containers into which the pharmacy dispenses medication carry a bar code that identifies the medication, dosage, and patient for whom it is intended. Patient identification bracelets are also bar-coded.
When a drug is dispensed from the pharmacy, the caregiver simply reads the bar-coded label on the container into his or her terminal, which then transmits the data to the server. The server logs the time and date, the medication dispensed, and the caregiver to whom it was dispensed. When the caregiver administers the medication to the patient, the container`s bar code and the patient`s bar-coded ID are read into the terminal, which again transmits the information to the server. In this way, a complete record is automatically maintained.
The vha alpha-tested a large number of different hardware packages for its wireless lans, and eventually chose the Epson eht-400c pen-based subnotebook computer to be the caregiver`s portable data-entry terminal. The wireless interface was provided by a Lucent Technology pcmcia-packaged Wavelan wireless lan transceiver that plugged into the eht-400c.
The eht-400c is a 486-based computer measuring approximately 9 x 8 x 1 inches. It is equipped with a touch-sensitive color screen. Although the eht-400c does not have a keyboard, data can be entered manually either by writing directly on the screen with a stylus or with a virtual keyboard that can be displayed on the screen.
However, the vha realized that a real keyboard was needed to accommodate the occasional lengthy comments about a patient a caregiver wanted to record. A miniature, spill-proof keyboard about one-third the size a typical PC keyboard was chosen. Connection to the vha`s existing wired lan was provided by Lucent Wavepoint bridges.
Because of the sensitive electronic equipment commonly used in hospitals, the wireless lan system had to use as little transmitter power as possible. A microcellular telecommunications architecture was selected.
Optimizing bridge locations
Each ward--depending on its size--has one or two microcells, each of which is connected to the network server`s existing wired lan through its own Wavepoint bridge. In most wards, the bridge is located above a dropped ceiling, but in a few installations it hangs from the ceiling. Placement of the bridges was critical if reliable communications were to be maintained, because the terminals are usually placed on the carts that carry medications to the patients. As a result, a terminal can be transmitting from any place in the ward where the cart can be maneuvered.
Because cost was a concern, the goal was to use as few microcells as possible while maintaining reliable connectivity. Identifying the optimal locations for each bridge required a thorough site survey.
Electromagnetic incompatibility is also a big concern in hospital environments--the wireless lan equipment could not interfere with hospital equipment, and hospital equipment should not interfere with the wireless lan. But knowing whether the wireless lan equipment would interfere with hospital equipment could not be ascertained until all the equipment was installed and operating.
Preliminary tests, however, were performed in the vicinity of hospital equipment that was thought to be susceptible to interference from the wireless lan equipment, which operates in the 900-megahertz and 2.4-gigahertz bands. This dual-bandwidth approach was taken so that, if hospital equipment did suffer interference from the lan equipment on one band, it might not on the other. If hospital equipment suffered from interference on both bands, the strategy was to keep lan equipment far enough away to eliminate the problem.
In existing installations, interference with hospital equipment has not been a problem, because Wavelan and Wavepoint transceivers output less than 1 watt of power and use spread-spectrum technology.
Interference problems--if there are any--are more likely to involve the wireless lan`s operation in conjunction with high-energy X-ray and other diagnostic tools typically found in a hospital. With this potential problem in mind, the entire site can be examined with a spectrum analyzer to determine the levels of radio-frequency (RF) energy present at the frequencies of interest. If RF energy is present at levels that might interfere with the wireless lan`s operation, field trials with the actual equipment to be used will be necessary. Sometimes, simply repositioning the bridge will permit its operation, even in the presence of high RF energy levels. Changing from one operating band to the other may also eliminate the problem.
The existence of other wireless products within the area served by a wireless lan can be an issue. High-performance cordless telephones, for example, operate in the same 900-MHz band as wireless lan equipment. Some equipment, such as wireless intercoms, wireless speaker systems, and wireless communication links, also operate in the 900-MHz or 2.4-GHz bands. Since these products are not usually powered when not in use, their presence may not be detected by the spectrum analyzer during a site survey. In such a case, a visual search of the site for these kinds of products should also be made.
Once the spectrum analysis is completed, the site must be surveyed for its physical characteristics. Radio waves can pass through some materials better than others. Metal, for example, exhibits very high resistance to the passage of radio waves, whereas wood exhibits low resistance. A ranking of materials typically found in hospital and office environments helps in planning a wireless lan. If a bridge must support operation in more than one room, it must be located so that its transmission path is not obstructed by objects with high resistance to the passage of radio waves. These include cabinets, partitions, fixtures, and the walls themselves.
The first step in the survey is to sketch the floor plan of the area to be covered by the lan, including rooms, hallways, passages, elevator shafts, and other architectural features. The next step is to examine these plans carefully to identify areas and objects that exhibit high resistance to the passage of radio waves. Based on the location of these areas and objects, bridge sites that offer the highest probability of reliable communications within the room or set of rooms can be determined.
Positioning multiple bridges
If the wireless lan must cover a large area, such as in a typical hospital, more than one bridge will be required to provide complete coverage. The area covered by a bridge is more or less spherical. If the facility is a single-story building, only the area covered in the horizontal plane is important. But in a multifloor building, vertical coverage must also be considered.
Because the area covered is circular, complete coverage of rectangular spaces cannot be provided without some overlap of areas covered by adjacent bridges. This means that a mobile terminal may, at times, be communicating with two or more bridges. Ordinarily, this will not cause problems. In the case of the Wavelan equipment used in the vha hospitals, for example, the lan is operated as a microcellular system in which a given mobile terminal is handled by the bridge that has the best communications with it. As the terminal moves from patient to patient and from ward to ward, its communications are handed off from one bridge to another in response to changing signal strength.
If the total cost of the wireless lan is a concern, the goal is to use as few bridges as possible while still providing coverage in the service area. To accomplish this, the circular area covered by each of the bridges must be plotted on the floor plans with an emphasis on minimizing overlap. Data sheets provided by the wireless equipment manufacturer specify the minimum radius of the sphere around the bridge in which reliable communications can be provided. However, the actual size and shape of the area covered by a bridge depend on the materials through which the radio waves must pass. This is especially true in modern buildings that have a steel frame or use cinder blocks for internal walls.
In multistory buildings, a vertical plot must also be created. Depending on the materials used in the flooring, walls, furnishings, fixtures, appliances, and other items on each floor, a set of bridges on one floor may also cover the floors immediately above and below it. For instance, depending on the areas in which service is required, a set of bridges on the second and fifth floors may provide full coverage from the first to the sixth floors. However, some multistory buildings have steel-reinforced, poured-concrete floors, which can inhibit the bridge from providing reliable communications between floors.
Even if the site survey is diligently conducted, it is possible that coverage may not be as good as expected at the edges of the service area. This can result from materials through which the radio waves must pass exhibiting resistance that is higher than expected. Signal degradation due to multipath propagation, which results from part of the transmitted signal being reflected off walls, floors, ceilings, and furnishings, can also be a factor. Some of these reflections arrive at the receiving antenna slightly out of phase with each other and the actual, transmitted signal.
Verify sites
To eliminate the expense of installing bridges by trial and error, the effectiveness of prospective bridge sites should first be verified. Lucent offers a software product called Wavemonitor that simplifies the verification process. It transmits a signal from one transceiver to another which, in turn, transmits it back to the originating transceiver, where its strength is measured.
For an installation involving mobile terminals and a bridge, the bridge itself can be used in place of one of the transceivers. The bridge or substitute transceiver is positioned at the potential bridge site and the other transceiver is moved around the area of coverage. The transmit-receive-measure process is handled by the software, with the results displayed as a bar graph of signal strength on the mobile terminal`s display. Thus, by observing the display on the terminal as it moves around the area of coverage, areas in which coverage is poor or nonexistent can quickly be identified. By relocating the bridge or substitute transceiver and repeating the test, a bridge site that provides effective coverage throughout the area of interest can usually be found.
Once positioned in optimum locations, bridges must be connected into the facility`s existing wired lan, which is usually done with Category 5 cable run between the bridge and the nearest wired hub.
The success of a wireless lan implementation depends largely on the attention to detail paid by the installers. Lucent, for example, sells its products through value-added retailers selected, in part, because of their networking experience. This is because most of the start-up problems encountered with a wireless lan are network-related and not the result of the hardware being used.
A Wavelan transceiver from Lucent Technologies (mounted on the wall, right) connects both laptop and desktop PCs (on the table, left) to the local area network.
A flowchart can help to match a wireless lan environment against the manufacturer`s equipment specifications.
A wireless lan, such as Lucent`s Wavelan system, depends on wireless transceivers connected to a wired lan. The transceivers broadcast and receive in roughly circular service areas that must be overlapped to provide complete coverage of rectangular buildings.
Angela Champness is the director of product and business development for Lucent Technologies` Wavelan wireless lan group. She is responsible for worldwide product management, marketing, and business development.