Testing Ultrasound to Track, Monitor Patients

As for an RFID system, because a tag's signal can pass through walls, its location must be pinpointed to a specific room or location. An access point on Floor 2 might pick up a tag located on Floor 1, for example. Thus, to improve the granularity of an RFID system, vendors use algorithms that calculate the distance of the tag from the access point, based on such factors as the amount of time elapsed between the issuance of the signal and its receipt. Moreover, three or more access points can be used to locate a tag through triangulation. By interfacing with a map of the monitored areas, these indoor positioning systems can then direct users to a specific floor and room. The tags and access points can also be tuned so the signals are less likely to bleed through walls or floors.

"The floor-bleed issue used to be a bigger problem before RFID companies' technology improved. But now, the more readers that can see a tag, the more granularity you can get [on its location]," says Mike Braatz, PanGo Network's senior vice president of marketing and business development.

Dr. Stair models the fanny pack while holding an ultrasound tag. Attached on one side, oriented vertically, is a Sonitor RFID tag.

"Ultrasound signals can be heard by our detectors at levels similar to how humans hear voices," says Terry Aasen, Sonitor's president and CEO. Just as voices can't easily be heard between walls or through floors, neither can ultrasound signals. Sonitor receivers have a 100-foot read range and can differentiate between strong and weak ultrasound signals. Therefore, in a large, open area, more than one detector can be installed to determine in which part of the room a person or asset is located—the east side versus the west side, for example—and the same approach would be taken with an RFID system. With either RFID or ultrasound technology, notes Hampton, "the more [location] resolution you want, the more sensors [interrogators/access points] you need."

To link a patient's location with his vital signs, the Sonitor tags are placed inside fanny packs containing a device that monitors heart activity through three leads attached to the chest, and blood-oxygen saturation level through a lead attached to the fingertip. The cardiovascular data is entered into a Hewlett Packard PDA, also inside the fanny pack, that runs a customized Linux-based program written by hospital staff, and transmits the data, along with the patient's ID number, to the hospital's Wi-Fi network. ER staff-members carry PDAs as well, but theirs show both the location and the vital signs of each patient being tracked. When any vital signs go above or below a set range, the staff is sent alerts through the PDA.

"So far, we've tried the equipment on healthy volunteers, and we're about ready to transition to real patients," says Stair. This step will be important because in the volunteer-based testing, not surprisingly, none of the volunteer's vital signs dropped below or exceeded the safe range, so the alerting component of the system has not actually been tested yet. This transition to testing patients will require setting up a means of explaining the technology to them, Stair explains, as well as getting their consent to use the system to track their vital signs and location within the ER's waiting area.

Initially, the hospital plans to use the system only to monitor and track patients suffering from chest pains or shortness of breath. But in the long term, Stair says, it hopes to be able to track the locations of all patients, rather than just those whose vital signs need to be monitored, because locating them quickly—whether in the waiting room or cafeteria, or assigned to a makeshift room or bed in a hallway—will save staff time and improve the speed and quality of care. Stair says he does not believe emergency room patients will object to the use of the location-tracking technology. "I think they will want to be able to be found quickly," he says.