• July 2008 FEATURE ARTICLES •
Asset Tracking and Locating: Case History
How Do I Find Thee?
Let Me Count the Ways.
There’s more than one way to locate people and objects in hospitals. The best choice depends on the need.
By Adrian Jennings
Real-time location systems (RTLS) have become
common in today’s hospitals, surgical centers and nursing homes,
resulting in cost savings and improved efficiency. From finding
key assets in the ED, to optimizing patient flow, to automated
billing, RTLS can deliver real benefits across an organization.
However, the plethora of technologies, and
their sometimes significant price tags, can be challenging for
hospital decision makers, especially when budgets are spread
thin. Which technology should you choose? What is the best
balance between performance and cost? Which will grow with you
as your systems expand and diverge?
How Does It Function?
Typical real-time location systems include:
Ultra-wideband (UWB), Wi-Fi, Zigbee and UHF (generally 433 MHz
and 915 MHz), and they all work in essentially the same manner —
tags attached to objects emit signals to a network of receivers,
usually located on walls or in ceilings. Each receiver
calculates the distance of the tag from the receiver’s location,
and by combining the distances from several receivers, the
system determines the location of each tag, similar to the way a
GPS device "listens" to several satellites when calculating a
position.
There are two classes of RTLS technologies:
those that use signal strength to determine the distance to a
tag (the louder the signal, the closer the tag), and those that
use time-of-arrival (the sooner the signal arrives, the closer
the tag).
Time-of-arrival systems are more accurate
than signal-strength systems. Consider the cell phone: The
signal strength increases or decreases depending on the distance
from the phone to the cell tower. It also decreases when moving
from outdoors to indoors, or when rotating the phone, and even
when the wind blows in the wrong direction (or so it seems). The
point being, many more things than distance affect signal
strength. Thus, systems that calculate distance based solely on
signal strength are less accurate than systems that measure
time-of-arrival. Why is timing more accurate? Signals travel at
the speed of light no matter what, so the only thing that
affects the time-of-arrival is distance.
The only time-of-arrival systems currently in
use in healthcare environments are UWB, so most RTLS use signal
strength, including Wi-Fi, Zigbee and UHF. Ultrasound is
sometimes used; however, it doesn’t penetrate walls, so for a
receiver to "hear" a tag, it must be in the same room.
How Do We Use It?
What does all this mean in practice for a
healthcare organization? How accurate is accurate enough? That
depends on your needs. Reasons for deploying a location system
and the technologies required include:
Is a person or object in the building? This is not really a location problem, even though "inside the
building" is a location. The technologies used here tend to be
passive RFID tags, such as those in ID badges that cause doors
to open based on proximity.
In which part of the building is a person or
object? Determining approximate locations, such as
whether a patient is in the ED or the OR, or, where the
wheelchairs are located, requires an accuracy of only 10 to 20
feet, which signal-strength systems can achieve. However,
determining the exact locations of persons and objects so they
can be quickly retrieved requires accuracy of better than 10
feet, which some signal-strength systems can deliver, but often
not reliably. This is the edge where time-of-arrival systems
become necessary.
What is happening to a person or object? How people and things are interacting, is the most highly valued
location information. For example, which bed does patient P
occupy, or with whom is doctor D consulting? Which of two
patients in room A is using the vital-signs monitor? How long
has patient E been waiting in the ED? This level of information
requires location accuracy better than three feet, and
preferably as good as one foot, with high reliability.
Currently, UWB time-of-arrival systems are the only type able to
provide this information.
Hospital organizations can have the most
precise, highest-value location information available by
installing UWB RTLS solutions throughout their facilities, and
some have, even though the initial investment can be higher than
signal-strength systems. However, some hospitals that need a
lower cost of entry into the world of RTLS may be required to
compromise on accuracy (and therefore value).
The reason accuracy may be compromised is
because specific tags are generally only "heard" by specific
receivers. These "single-mode" systems require that the same
type of RTLS be installed throughout the buildings, so that the
tags can be tracked throughout the entire organization. However,
various locations within a hospital might have different RTLS
needs. For example, interaction-level accuracy might be critical
in the ED or OR, where process efficiency has a positive impact
both on quality of care and top-line revenue. While deploying
disparate locations systems throughout the hospital, and placing
multiple tags on everything and everyone, might get around this
dilemma, it’s not desirable, adds cost and is a nightmare to
manage. Whether patients or staff will even tolerate wearing
multiple tags, and whether equipment can accommodate multiple
tags, is highly questionable.
What are my options?
Dual-mode systems integrate UWB with a
signal-strength system. Both receiver types hear all of the tags
and can receive location information from anywhere in the
organization. UWB provides the accuracy of an interaction-grade
RTLS where it’s needed, and the signal-strength system provides
lower cost zone- and room-level accuracy. The choice of which to
use is a matter of preference. Some users want to leverage their
Wi-Fi network for location, and some want to install an overlay
technology and keep Wi-Fi for data and voice.
An installation might include UWB for
interaction-level accuracy only in the ED and a signal-strength
system elsewhere, followed later by a surgical suite upgrade
that includes UWB readers, with no need to replace any legacy
systems. This flexibility makes dual-mode systems a low-risk
option when trying to make an initial RTLS purchase. Perhaps
more importantly, dual-mode systems offer RTLS at competitive
price points, putting organizations on the first rung of the
"high accuracy, high value" RTLS ladder, which can be scaled as
needs require and budgets allow.
Nesconset Center Employs UWB RTLS: A mini case history
As the number of people needing skilled
living assistance increases, facilities employ technology to
improve care management for their residents.
Long Island-based Nesconset Center for
Nursing and Rehabilitation in New York, recently implemented
an Ultra-wideband (UWB) real-time location system (RTLS) to
improve the accuracy of locating Alzheimer’s and Dementia
patients, caregivers and various assets throughout the
facility. The RTLS, from Time Domain Corp., Huntsville,
Ala., includes tags, readers and antennas, and software from
Sysgen Data Ltd., Melville, N.Y.
According to Robert Heppenheimer,
Nesconset’s executive director and owner, "The ability of
our staff to locate their patients and assets associated
with the patients allows for better care management and
faster response times for patient needs and requirements.
For the first time, we can head off problems before they
happen, which in turn, helps lower the risk of elopements."
Nesconset reduces the risk of elopements
using the integrated messaging system. Patients wear UWB
tags, called "Smart Buddies." The tags have "rules" that are
programmed into the system’s software, associating them to
the patients who are wearing them. When a Smart Buddy
violates a rule assigned to it, the system alerts the proper
staff members via a Windows Mobile 6 device that immediately
communicates the violations to a certified nurse assistant
(CNA). The CNA responds to the issue based on the urgency of
the alert, which can be broadcast to staff via e-mail, text
messages, cell phones, alarms and flashing lights.
The UWB system also automatically gathers
information on the precise interactions between Nesconset
staff and patients. This frees staff from manual data
logging, improves data accuracy and optimizes compliance
reporting. Precise tracking of equipment also improves
utilization and automated billing.
Staff involvement in the program enables
valuable information to be collected for future use in
determining the best possible methodologies for treating
patients afflicted with Alzheimer’s disease and Dementia.
Adrian Jennings is CTO at Time Domain Corp.,
Huntsville, Ala. Contact him at
adrian.jennings@timedomain.com.