Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2001-02-23
2002-07-09
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S573100, C340S644000
Reexamination Certificate
active
06417777
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to monitoring systems and, more particularly, concerns pressure-sensitive devices and systems used to monitor patients in hospital or other care giving environments.
BACKGROUND OF THE INVENTION
It is well documented that the elderly and post-surgical patients are at a heightened risk of falling. There are many reasons for this but, broadly speaking, these individuals are often afflicted by gait and balance disorders, weakness, dizziness, confusion, visual impairment, and postural hypotension (i.e., a sudden drop in blood pressure that causes dizziness and fainting), all of which are recognized as potential contributors to a fall. Additionally, cognitive and functional impairment, and sedating and psychoactive medications are also well recognized risk factors.
A fall places the patient at risk of various injuries including sprains, fractures, and broken bones—injuries which in some cases can be severe enough to eventually lead to a fatality. Of course, those most susceptible to falls are often those in the poorest general health and least likely to recover quickly from their injuries. In addition to the obvious physiological consequences of fall-related injuries, there are also a variety of adverse economic and legal consequences that include the actual cost of treating the victim and, in some cases, caretaker liability issues.
In the past, it has been commonplace to treat patients that are prone to falling by limiting their mobility through the use of restraints, the underlying theory being that if the patient is not free to move about, he or she will not be as likely to fall. However, research has shown that restraint-based patient treatment strategies are often more harmful than beneficial and should generally be avoided—the emphasis today being on the promotion of mobility rather than immobility. Among the more successful mobility-based strategies for fall prevention include interventions to improve patient strength and functional status, reduction of environmental hazards, and staff identification and monitoring of high-risk hospital patients and nursing home residents.
Of course, monitoring high-risk patients, as effective as that care strategy might appear to be in theory, suffers from the obvious practical disadvantage of requiring additional staff if the monitoring is to be in the form of direct observation. Thus, the trend in patient monitoring has been toward the use of electrical devices to signal changes in a patient's circumstance to a caregiver who might be located either nearby or remotely at a central monitoring facility, such as a nurse's station. The obvious advantage of an electronic monitoring arrangement is that it frees the caregiver to pursue other tasks away from the patient. Additionally, when the monitoring is done at a central facility a single nurse can monitor multiple patients which can result in decreased staffing requirements.
Generally speaking, electronic monitors work by first sensing an initial status of a patient, and then generating a signal when that status changes, e.g., he or she has sat up in bed, left the bed, risen from a chair, etc., any of which situations could pose a potential cause for concern in the case of an at-risk patient. Electronic bed and chair monitors typically use a pressure sensitive switch in combination with a separate monitor/microprocessor. In a common arrangement, a patient's weight resting on a pressure sensitive mat (i.e., a “sensing” mat) completes an electrical circuit, thereby signaling the presence of the patient to the microprocessor. When the weight is removed from the pressure sensitive switch, the electrical circuit is interrupted, which fact is sensed by the microprocessor. The software logic that drives the monitor is typically programmed to respond to the now-opened circuit by triggering some sort of alarm—either electronically (e.g., to the nursing station via a conventional nurse call system) or audibly (via a built-in siren).
General information relating to mats for use in patient monitoring may be found in patent application Ser. No. 09/285,956 filed Apr. 2, 1999, now U.S. Pat. No. 6,307,476, the disclosure of which is specifically incorporated herein by reference. Additionally, U.S. Pat. Nos. 4,179,692, 4,295,133, 4,700,180, 5,600,108, 5,633,627, 5,640,145, and 5,654,694 (concerning electronic monitors generally) contain further information generally pertinent to this same subject matter, as do U.S. Pat. Nos. 4,484,043, 4,565,910, 5,554,835, and 5,623,760 (switch patents), the disclosures of all of which are all incorporated herein by reference.
By way of general background, in a typical arrangement, a pressure-sensing mat is a sealed “sandwich” composed of three layers: two outer layers and an inner (central) layer positioned therebetween. The outer layers are usually made of some sort of plastic and are impermeable to fluids and electrically non-conductive on their outer faces, where “outer” is determined with respect to the middle layer. The inner surface of each of the outer layers—which inner surfaces are oriented to face each other from opposite sides of the central layer—is made to be electrically conductive, usually by printing a conductive (e.g., carbon-based) ink on that surface. The compressible middle “central spacer” is made of a non-conductive material and serves to keep the two conductive faces apart when a patient is not present on the sensor. The central spacer is discontinuous, which makes it possible for the two conductive inner surfaces to be forced into contact through the discontinuities when weight is applied to the switch. By attaching a separate electrical lead to each of the conductive inner faces, it can readily be determined (e.g., via a simple continuity check) whether a weight is present on the sensor (e.g., whether a patient is seated thereon). Removal of the weight causes the central spacer to expand and press apart the two conducting faces, thereby breaking the electrical connection between them. Thus, a device that monitors the resistance across the two electrical leads may determine when a patient has risen to his or her feet.
One disadvantage of the current generation of pressure sensitive mats is that they cannot be completely (e.g., hermetically) sealed against the external environment. The reason for this should be clear: if the interior of the mat were completely sealed, air pressure inside of the mat would tend to oppose the urging of the mat faces into contact, thereby making it difficult or impossible to complete the circuit (e.g., think of compressing an “air pillow”). Thus, it is customary to intentionally leave gaps in the seal between the two halves of the mat which allow for movement of air into and out of the switch.
Another disadvantage of the prior art is that partial sealing of the perimeter of the mat can cause it to resist expansion after weight is removed therefrom. That is, when a patient places weight on a conventional mat, air is slowly expelled from the mat interior, typically through a small opening in the perimeter of the mat. However, when the patient rises the opening in the mat can collapse or narrow in response to air pressure on the now-deflated mat body, thereby retarding the process of reinflating it. As a consequence, the mat may continue to signal that the patient is still present on the mat for a time after he or she has risen.
Of course, the fact that the interior of the mat must kept open to the atmosphere results in a mat that is highly susceptible to invasion by bodily fluids or cleaning solutions, as the in-rushing air tends to carry fluids along with it into the interior of the mat. Further, it is well known that some common disinfecting cleaners can loosen the adhesives that hold the layers of the mat together, thereby ruining the sensor. Thus, cleaning soiled mats that have air passages placed therein becomes problematic. In summary, what is needed is a pressure sensitive mat that is more resistant to invasion by fluids than is presently availabl
Fitzgerald Sanford G.
Smith Toby E.
Bed-Check Corporation
Fellers Snider Blankenship Bailey & Tippens, P.C.
Wu Daniel J.
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