US20070068928A1

US20070068928A1 - Temperature sensor assemblies for electric warming blankets

Info

Publication number: US20070068928A1
Application number: US11/537,189
Authority: US
Inventors: Scott Augustine; Scott Entenman; Keith Leland; Gordon Lawrence
Original assignee: Individual
Current assignee: Augustine Temperature Management LLC
Priority date: 2005-09-29
Filing date: 2006-09-29
Publication date: 2007-03-29
Also published as: US20070068931A1; US20070068929A1; US20100204763A1; US20070068923A1; US20070080155A1; US8604391B2; US7714255B2; CA2624454A1; WO2007041389A1; US7786408B2; EP1942847A1; CN101312698A; US20110233185A1; AU2006299636A1

Abstract

An electric warming blanket for warming patients during surgery and other medical procedures includes a flexible heater and a temperature sensor assembly coupled thereto; a first layer of water resistant material coupled to a second layer of water resistant material, about a perimeter of the heater, forms a substantially hermetically sealed space for the heater and the temperature sensor assembly. The blanket may further include a thermal insulation layer disposed between the temperature sensor assembly and the first layer of water resistant material. The temperature sensor assembly may provide input of an average temperature over a portion of a surface area of the heater to a temperature controller, when the heater and sensor assembly are coupled to the controller.

Description

PRIORITY CLAIM

The present application claims priority to co-pending provisional applications Ser. No. 60/825,573, entitled HEATING BLANKET SYSTEM filed on Sep. 13, 2006; Ser. No. 60/722,106, entitled ELECTRIC WARMING BLANKET INCLUDING TEMPERATURE ZONES AUTOMATICALLY OPTIMIZED, filed Sep. 29, 2005; and Ser. No. 60/722,246, entitled HEATING BLANKET, filed Sep. 29, 2005; all of which are incorporated by reference in their entireties herein.

RELATED APPLICATIONS

The present application is related to the following commonly assigned utility patent applications, all of which are filed concurrently herewith and all of which are hereby incorporated by reference in their entireties: A) ELECTRIC WARMING BLANKET HAVING OPTIMIZED TEMPERATURE ZONES, Practitioner docket number 49278.2.5.2; B) NOVEL DESIGNS FOR HEATING BLANKETS AND PADS, Practitioner docket number 49278.2.7.2; C) FLEXIBLE HEATING ELEMENT CONSTRUCTION, Practitioner docket number 49278.2.15; D) BUS BAR ATTACHMENTS FOR FLEXIBLE HEATING ELEMENTS, Practitioner docket number 49278.2.16; and E) BUS BAR INTERFACES FOR FLEXIBLE HEATING ELEMENTS, Practitioner docket number 49278.2.17.

TECHNICAL FIELD

The present invention is related to heating or warming blankets or pads and more particularly to those including electrical heating elements.

BACKGROUND

It is well established that surgical patients under anesthesia become poikilothermic. This means that the patients lose their ability to control their body temperature and will take on or lose heat depending on the temperature of the environment. Since modern operating rooms are all air conditioned to a relatively low temperature for surgeon comfort, the majority of patients undergoing general anesthesia will lose heat and become clinically hypothermic if not warmed.
Over the past 15 years, forced-air warming (FAW) has become the “standard of care” for preventing and treating the hypothermia caused by anesthesia and surgery. FAW consists of a large heater/blower attached by a hose to an inflatable air blanket. The warm air is distributed over the patient within the chambers of the blanket and then is exhausted onto the patient through holes in the bottom surface of the blanket.
Although FAW is clinically effective, it suffers from several problems including: a relatively high price; air blowing in the operating room, which can be noisy and can potentially contaminate the surgical field; and bulkiness, which, at times, may obscure the view of the surgeon. Moreover, the low specific heat of air and the rapid loss of heat from air require that the temperature of the air, as it leaves the hose, be dangerously high —in some products as high as 45° C. This poses significant dangers for the patient. Second and third degree burns have occurred both because of contact between the hose and the patient's skin, and by blowing hot air directly from the hose onto the skin without connecting a blanket to the hose. This condition is common enough to have its own name—“hosing.” The manufacturers of forced air warming equipment actively warn their users against hosing and the risks it poses to the patient.
To overcome the aforementioned problems with FAW, several companies have developed electric warming blankets. However, there is still a need for electrically heated blankets or pads that can be used safely and effectively warm patients undergoing surgery or other medical treatments. These blankets need to be flexible in order to effectively drape over the patient (making excellent contact for conductive heat transfer and maximizing the area of the patient's skin receiving conductive as well as radiant heat transfer), and should incorporate means for precise temperature control.
Precise temperature control is important because non-uniform heat distribution can occur within an electric warming blanket. Unfortunately, many temperature sensors used to provide feedback to a temperature controller do not dependably report an accurate average temperature of the blanket because they sense temperature from too small of an area. For example, if the temperature of a measured location is cooler than the average blanket temperature, the temperature sensor will cause the controller to deliver more power to the heater and the resulting average temperature of the heater will be higher than desired.
Further, an electric blanket can overheat if the temperature sensor is thermally grounded to a cool object. This condition can occur if a cool object such as a metal pan is placed on top of the heater in the area of the temperature sensor. The sensor “feels” cool and tells the temperature controller to deliver more power to the heater.
Accordingly, there is a need for a blanket that utilizes a temperature sensor that takes temperature measurements that are representative of the average temperature of the blanket. Further, there is a need for a blanket with a temperature sensor that will not cause the blanket to overheat if a cool object is placed in proximity to it. Various embodiments of the invention described herein solve one or more of the problems discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.
FIG. 1A is a plan view of a flexible heating blanket subassembly for a heating blanket, according to some embodiments of the present invention.
FIGS. 1B-C are end views of two embodiments of the subassembly shown in FIG. 1A.
FIG. 1D is a schematic showing a blanket including the subassembly of FIG. 1A draped over a body.
FIG. 2A is a top plan view of a heating element assembly, according to some embodiments of the present invention, which may be incorporated in the blanket shown in FIG. 3A.
FIG. 2B is a section view through section line A-A of FIG. 2A.
FIG. 2C is an enlarged plan view and corresponding end view schematic of a portion of the assembly shown in FIG. 2A, according to some embodiments of the present invention.
FIG. 2D is an enlarged view of a portion of the assembly shown in FIG. 2A, according to some embodiments of the present invention.
FIG. 3A is a top plan view, including partial cut-away views, of a lower body heating blanket, according to some embodiments of the present invention.
FIG. 3B is a schematic side view of the blanket of FIG. 3A draped over a lower body portion of a patient.
FIG. 3C is a top plan view of a heating element assembly, which may be incorporated in the blanket shown in FIG. 3A.
FIG. 3D is a cross-section view through section line D-D of FIG. 3C.
FIG. 4A is a plan view of flexible heating element, according to some alternate embodiments of the present invention.
FIG. 4B is a top plan view, including a partial cut-away view, of a heating element assembly, according to some embodiments of the present invention, which may be incorporated in the blanket shown in FIG. 4C.
FIG. 4C is a top plan view, including a partial cut-away view, of an upper body heating blanket, according to some embodiments of the present invention.
FIG. 4D is a schematic end view of the blanket of FIG. 4B draped over an upper body portion of a patient.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing exemplary embodiments of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of skill in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that can be utilized. The term ‘blanket’, used to describe embodiments of the present invention, may be considered to encompass heating blankets and pads.
FIG. 1A is a plan view of a flexible heating blanket subassembly 100, according to some embodiments of the present invention; and FIGS. 1B-C are end views of two embodiments of the subassembly shown in FIG. 1A. FIG. 1A illustrates a flexible sheet-like heating element, or heater, 10 of subassembly 100 including a first end 101, a second end 102, a first lateral portion 11 extending between ends 101, 102, and a second lateral portion 12, opposite first lateral portion 11, also extending between ends 101, 102. According to preferred embodiments of the present invention, heater 10 comprises a conductive fabric or a fabric incorporating closely spaced conductive elements such that heater 10 has a substantially uniform watt density output, preferably less than approximately 0.5 watts/sq. inch, and more preferably between approximately 0.2 and approximately 0.4 watts/sq. inch, across a surface area, of one or both sides 13, 14 (FIGS. 1B-C), the surface area including and extending between lateral portions 11, 12 of heater 10. Some examples of conductive fabrics which may be employed by embodiments of the present invention include, without limitation, carbon fiber fabrics, fabrics made from carbonized fibers, woven or non-woven non-conductive substrates coated with a conductive material, for example, polypyrrole, carbonized ink, or metalized ink.
FIG. 1A further illustrates subassembly 100 including two bus bars 15 coupled to heating element 10 for powering element 10; each bar 15 is shown extending alongside opposing lateral portions 11, 12, between first and second ends 101, 102. With reference to FIG. 1B, according to some embodiments, bus bars 15 are coupled to heating element 10 within folds of opposing wrapped perimeter edges 108 of heating element 10 by a stitched coupling 145, for example, formed with conductive thread such as silver-coated polyester or nylon thread (Marktek Inc., Chesterfield, Mo.), extending through edges 108 of heating element 10, bars 15, and again through heating element 10 on opposite side of bars 15. According to alternate embodiments heating element 10 is not folded over bus bars 15 as shown. Alternative threads or yarns employed by embodiments of the present invention may be made of other polymeric or natural fibers coated with other electrically conductive materials; in addition, nickel, gold, platinum and various conductive polymers can be used to make conductive threads. Metal threads such as stainless steel, copper or nickel could also be used for this application. According to an exemplary embodiment, bars 15 are comprised of flattened tubes of braided wires, such as are known to those skilled in the art, for example, a flat braided silver coated copper wire, and may thus accommodate the thread extending therethrough, passing through openings between the braided wires thereof. In addition such bars are flexible to enhance the flexibility of blanket subassembly 100. According to alternate embodiments, bus bars 15 can be a conductive foil or wire, flattened braided wires not formed in tubes, an embroidery of conductive thread, or a printing of conductive ink. Preferably, bus bars 15 are each a flat braided silver-coated copper wire material, since a silver coating has shown superior durability with repeated flexion, as compared to tin-coated wire, for example, and may be less susceptible to oxidative interaction with a polypyrrole coating of heating element 10 according to an embodiment described below. Additionally, an oxidative potential, related to dissimilar metals in contact with one another is reduced if a silver-coated thread is used for stitched coupling 145 of a silver-coated bus bar 15.
According to an exemplary embodiment, a conductive fabric comprising heating element 10 comprises a non-woven polyester having a basis weight of approximately 130 g/m²and being 100% coated with polypyrrole (available from Eeonyx Inc., Pinole, Calif.); the coated fabric has an average resistance, for example, determined with a four point probe measurement, of approximately 15-20 ohms per square inch at about 48 volts, which is suitable to produce the preferred watt density of 0.2 to 0.4 watts/sq. in. for surface areas of heating element 10 having a width, between bus bars 15, in the neighborhood of about 20 inches. Such a width is suitable for a lower body heating blanket, some embodiments of which will be described below. A resistance of such a conductive fabric may be tailored for different widths between bus bars (wider requiring a lower resistance and narrower requiring a higher resistance) by increasing or decreasing a surface area of the fabric that can receive the conductive coating, for example by increasing or decreasing the basis weight of the fabric. Resistance over the surface area of the conductive fabrics is generally uniform in many embodiments of the present invention. However, the resistance over different portions of the surface area of conductive fabrics such as these may vary, for example, due to variation in a thickness of a conductive coating, variation within the conductive coating itself, variation in effective surface area of the substrate which is available to receive the conductive coating, or variation in the density of the substrate itself. Local surface resistance across a heating element, for example heater 10, is directly related to heat generation according to the following relationship:
Q (Joules)=I ²(Amps)×R(Ohms)
Variability in resistance thus translates into variability in heat generation, which is measured as a temperature. According to preferred embodiments of the present invention, which are employed to warm patients undergoing surgery, precise temperature control is desirable. Means for determining heating element temperatures, which average out temperature variability caused by resistance variability across a surface of the heating element, are described below in conjunction with FIGS. 2A-B.
A flexibility of blanket subassembly 100, provided primarily by flexible heating element 10, and optionally enhanced by the incorporation of flexible bus bars, allows blanket subassembly 100 to conform to the contours of a body, for example, all or a portion of a patient undergoing surgery, rather than simply bridging across high spots of the body; such conformance may optimize a conductive heat transfer from element 10 to a surface of the body. However, as illustrated in FIG. 1D, heating element 10 may be draped over a body 16 such that lateral portions 11, 12 do not contact side surfaces of body 16; the mechanism of heat transfer between portions 11, 12 and body 16, as illustrated in FIG. 1D, is primarily radiant with some convection.
The uniform watt-density output across the surface areas of preferred embodiments of heating element 10 translates into generally uniform heating of the surface areas, but not necessarily a uniform temperature. At locations of heating element 10 which are in conductive contact with a body acting as a heat sink, for example, body 16, the heat is efficiently drawn away from heating element 10 and into the body, for example by blood flow, while at those locations where element 10 does not come into conductive contact with the body, for example lateral portions 11, 12 as illustrated in FIG. 1D, an insulating air gap exists between the body and those portions, so that the heat is not drawn off those portions as easily. Therefore, those portions of heating element 10 not in conductive contact with the body will gain in temperature, since heat is not transferred as efficiently from these portions as from those in conductive contact with the body. The ‘non-contacting’ portions will reach a higher equilibrium temperature than that of the ‘contacting’ portions, when the radiant and convective heat loss equal the constant heat production through heating element 10. Although radiant and convective heat transfer are more efficient at higher heater temperatures, the laws of thermodynamics dictate that as long as there is a uniform watt-density of heat production, even at the higher temperature, the radiant and convective heat transfer from a blanket of this construction will result in a lower heat flux to the skin than the heat flux caused by the conductive heat transfer at the ‘contacting’ portions at the lower temperature. Even though the temperature is higher, the watt-density is uniform and, since the radiant and convective heat transfer are less efficient than conductive heat transfer, the ‘non-contacting’ portions must have a lower heat flux. Therefore, by controlling the ‘contacting’ portions to a safe temperature, for example, via a temperature sensor 121 coupled to heating element 10 in a location where element 10 will be in conductive contact with the body, as illustrated in FIG. 1D, the ‘non-contacting’ portions, for example, lateral portions 11, 12, will also be operating at a safe temperature because of the less efficient radiant and convective heat transfer. According to preferred embodiments, heating element 10 comprises a conductive fabric having a relatively small thermal mass so that when a portion of the heater that is operating at the higher temperature is touched, suddenly converting a ‘non-contacting’ portion into a ‘contacting’ portion, that portion will cool almost instantly to the lower operating temperature.
According to embodiments of the present invention, zones of heating element 10 may be differentiated according to whether or not portions of element 10 are in conductive contact with a body, for example, a patient undergoing surgery. In the case of conductive heating, gentle external pressure may be applied to a heating blanket including heating element 10, which pressure forces heating element 10 into better conductive contact with the patient to improve heat transfer. However, if excessive pressure is applied the blood flow to that skin may be reduced at the same time that the heat transfer is improved and this combination of heat and pressure to the skin can be dangerous. It is well known that patients with poor perfusion should not have prolonged contact with conductive heat in excess of approximately 42° C. 42° C. has been shown in several studies to be the highest skin temperature, which cannot cause thermal damage to normally perfused skin, even with prolonged exposure. (Stoll & Greene, Relationship between pain and tissue damage due to thermal radiation. J. Applied Physiology 14(3):373-382. 1959 and Moritz and Henriques, Studies of thermal injury: The relative importance of time and surface temperature in the causation of cutaneous burns. Am. J. Pathology 23:695-720, 1947) Thus, according to certain embodiments of the present invention, the portion of heating element 10 that is in conductive contact with the patient is controlled to approximately 43° C. in order to achieve a temperature of about 41-42° C. on a surface a heating blanket cover that surrounds element 10, for example, a cover or shell 20, 40 which will be described below in conjunction with FIGS. 3A and 4C. With further reference to FIG. 1D, flaps 125 are shown extending laterally from either side of heating element 10 in order to enclose the sides of body 16 thereby preventing heat loss; according to preferred embodiments of the present invention, flaps 125 are not heated and thus provide no thermal injury risk to body if they were to be tucked beneath sides of body 16.
Referring now to the end view of FIG. 1C, an alternate embodiment to that shown in FIG. 1B is presented. FIG. 1C illustrates subassembly 100 wherein insulating members 18, for example, fiberglass material strips having an optional PTFE coating and a thickness of approximately 0.003 inch, extend between bus bars 15 and heating element 10 at each stitched coupling 145, so that electrical contact points between bars 15 and heating element 10 are solely defined by the conductive thread of stitched couplings 145.
FIG. 2A is a top plan view of a heating element assembly 250, according to some embodiments of the present invention, which may be incorporated by blanket 200, which is shown in FIG. 3A and further described below. FIG. 2B is a section view through section line A-A of FIG. 2A. FIGS. 2A-B illustrate a temperature sensor assembly 421 assembled on side 14 of heater 10, and heater 10 overlaid on both sides 13, 14 with an electrically insulating layer 210, preferably formed of a flexible non-woven high loft fibrous material, for example, 1.5 OSY (ounces per square yard) nylon, which is preferably laminated to sides 13, 14 with a hotmelt laminating adhesive. In some embodiments, the adhesive is applied over the entire interfaces between layer 210 and heater 10. Other examples of suitable materials for layer 210 include, without limitation, polymeric foam, a woven fabric, such as cotton or fiberglass, and a relatively thin plastic film. According to preferred embodiments, overlaid layers 210, without compromising the flexibility of heating assembly 250, prevent electrical shorting of one portion of heater 10 with another portion of heater 10 if heater 10 is folded over onto itself. Heating element assembly 250 may be enclosed within a relatively durable and waterproof shell, for example shell 20 shown with dashed lines in FIG. 2B, and will be powered by a relatively low voltage (approximately 48V). Layers 210 may even be porous in nature to further maintain the desired flexibility of assembly 250.
FIG. 2C is an enlarged plan view and a corresponding end view schematic showing some details of the corner of assembly 250 that is circled in FIG. 2A, according to some embodiments. FIG. 2C is representative of each corner of assembly 250. FIG. 2C illustrates insulating layer 210 disposed over side 14 of heater 10 and extending beneath bus bar 15, optional electrical insulating member 18, and layer 210 disposed over side 13 of heater 10 and terminated adjacent bus bar 15 within lateral portion 12 so that threads of conductive stitching 145 securing bus bars 15 to heater 10 electrically contact heating element 10 along side 13 of heating element 10. FIG. 2C further illustrates two rows of conductive stitching 145 coupling bus bar 15 to heating element 10, and bus bar 15 and insulating member 18 extending past end 102.
FIG. 2A further illustrates junctions 50 coupling leads 205 to each bus bar 15, and another lead 221 coupled to and extending from temperature sensor assembly 421; each of leads 205, 221 extend over insulating layer 210 and into an electrical connector housing 225 containing a connector 23, which will be described in greater detail below, in conjunction with FIGS. 3A-C. FIG. 2D is an enlarged view of junction 50, which is circled in FIG. 2A, according to some embodiments of the present invention. FIG. 2D illustrates junction 50 including a conductive insert 55 which has been secured to bus bar 15, for example, by inserting insert 55 through a side wall of bus bar 15 and into an inner diameter thereof. FIG. 2D further illustrates lead 205 coupled to insert 55, for example, via soldering, and an insulating tube and strain relief 54, for example, a polymer shrink tube, surrounding the coupling between lead 205 and insert 55.
Returning now to FIG. 2B, temperature sensor assembly 421 will be described in greater detail. FIG. 2B illustrates assembly 421 including a substrate 211, for example, of polyimide (Kapton), on which a temperature sensor 21, for example, a surface mount chip thermistor (such as a Panasonic ERT-J1VG103FA: 10 K, 1% chip thermistor), is mounted; a heat spreader 212, for example, a copper or aluminum foil, is mounted to an opposite side of substrate 211, for example, being bonded with a pressure sensitive adhesive; substrate 211 is relatively thin, for example about 0.0005 inch thick, so that heat transfer between heat spreader 212 and sensor is not significantly impeded. Temperature sensor assembly 421 may be bonded to layer 210 with an adhesive layer 213, for example, hotmelt EVA. Although not shown, it should be noted that sensor assembly 421 may be potted with a flexible electrically insulating material, such as silicon or polyurethane.
According to the illustrated embodiment, heat spreader 212 is sized to contact an enlarged surface area so that a temperature sensed by sensor 21 is more representative of an average temperature over a region of heater 10 surrounding sensor 21, which is positioned such that, when a heating blanket including heater 10 is placed over a body, the regions surrounding sensor 21 will be in conductive contact with the body. As previously described, it is desirable that a temperature of approximately 43° C. be maintained over a surface of heater 10 which is in conductive contact with a body of a patient undergoing surgery. Other types of heat spreaders, in addition to metallic foils, include metallic meshes or screens, or an adhesive/epoxy filled with a thermally conductive material.
Heat spreader 212 is a desirable component of a temperature sensor assembly, according to some embodiments of the present invention, since conductive fabrics employed by heating element 10, such as those previously described, may not exhibit uniform resistance across surface areas thereof. Heat spreader 212, having a surface area that does not exceed approximately four square inches, according to a preferred embodiment, may be effective in averaging out relatively small scale spatial resistance variation, for example, about 3% to 10% variability over less than about one or two inches. Such a limitation on heat spreader 212 surface area may be necessary so that heat spreader 212 does not become too bulky, since the larger the surface area, the greater the thickness of spreader 212 needed in order to maintain effective heat transfer across spreader 212 and to sensor 21. In addition, if spreader 212 is too thick, a thermal mass of spreader 212 will cause spreader 212 to respond too slowly to changes in heat loss or gain by heating element. According to an exemplary embodiment of the present invention, spreader 212 has a surface area of no greater than approximately four square inches and a thickness of no greater than approximately 0.001 inch. Some alternate embodiments of the present invention address a non-uniform resistance across a surface area of element 10 by employing a distributed temperature sensor, for example, a resistance temperature detector (RTD) laid out in flat plane across a surface of heater 10, or by employing an infrared temperature measurement device positioned to receive thermal radiation from a given area of heater 10. An additional alternate embodiment is contemplated in which an array of temperature sensors are positioned over the surface of heater 10, being spaced apart so as to collect temperature readings which may be averaged to account for resistance variance.
According to a preferred embodiment, assembly 421 includes a second, redundant, temperature sensor mounted to substrate 211, close enough to sensor 21 to detect approximately the same temperature; while sensor 21 may be coupled to a microprocessor temperature control, the second sensor, for example, a chip thermistor similar to sensor 21, may be coupled to an analog over-temperature cutout that cuts power to element 10, and/or sends a signal triggering an audible or visible alarm. The design of the second sensor may be the same as the first sensor and need not be described again. Another safety check may be provided by mounting an identification resistor to substrate 211 in order to detect an increase in resistance of element 10, due, for example, to degradation of the material of element 10, or a fractured bus bar; the optional identification resistor monitors a resistance of heating element 10 and compares the measured resistance to an original resistance of element 10.
According to some embodiments of the present invention, for example as illustrated in FIG. 2A, super over-temperature sensors 41 are incorporated to detect overheating of areas of assembly 250 susceptible to rucking, that is areas, for example, lateral portions 11, 12, where assembly 250 is most likely to be folded over on itself, either inadvertently or on purpose to gain access to a portion of a patient disposed beneath a blanket including assembly 250. An area of assembly 250 which is beneath the folded-over portion of assembly 250, and not in close proximity to sensor assembly 421, can become significantly warmer due to the additional thermal insulation provided by the folded-over portion that goes undetected by sensor 21. According to preferred embodiments, sensors 41 are wired in series, as illustrated in FIG. 2A. Super over-temperature sensors 41 may be set to open, or significantly increase resistance in, a circuit, for example, the over-temperature circuit, thereby activating an alarm and/or cutting power to heating element 10, at prescribed temperatures that are significantly above the normal operating range, for example, temperatures between approximately 45° C. and approximately 60° C. Alternately, sensors 41 may be part of the bus bar power circuit, in which case sensors 41 directly shut down power to heating element 10 when in an open condition or add sufficient resistance when in a high resistance condition to substantially reduce heating of element 10.
FIG. 3A is a top plan view, including partial cut-away views, of a lower body heating blanket 200, according to some embodiments of the present invention, which may be used to keep a patient warm during surgery. FIG. 3A illustrates blanket 200 including heating element assembly 250 covered by flexible shell 20; shell 20 protects and isolates assembly 250 from an external environment of blanket 200 and may further protect a patient disposed beneath blanket 200 from electrical shock hazards. According to preferred embodiments of the present invention, shell 20 is waterproof to prevent fluids, for example, bodily fluids, IV fluids, or cleaning fluids, from contacting assembly 250, and may further include an anti-microbial element, for example, being a SILVERion™ antimicrobial fabric available from Domestic Fabrics Corporation. According to the illustrated embodiment, blanket 200 further includes a layer of thermal insulation 201 extending over a top side (corresponding to side 14 of heating element 10) of assembly 250; layer 201 may or may not be bonded to a surface of assembly 250. Layer 201 may serve to prevent heat loss away from a body disposed on the opposite side of blanket 200, particularly if a heat sink comes into contact with the top side of blanket 200. FIG. 3C illustrates insulation 201 extending over an entire surface of side 14 of heating element 10 and over sensor assembly 421. According to the illustrated embodiment, layer 201 is secured to heating element assembly 250 to form an assembly 250′, as will be described in greater detail below. According to an exemplary embodiment of the present invention, insulating layer 201 comprises a polymer foam, for example, a 1 pound density 30 ILD urethane foam, which has a thickness between approximately ⅛^thinch and approximately ¾^thinch. According to alternate embodiments layer 201 comprises any, or a combination of the following: high loft fibrous polymeric non-woven material, non-woven cellulose material, and air, for example, held within a polymeric film bubble.
FIG. 3A further illustrates shell 20 forming flaps 25 extending laterally from either side of assembly 250 and a foot drape 26 extending longitudinally from assembly 250. According to exemplary embodiments of the present invention, a length of assembly 250 is either approximately 28 inches or approximately 48 inches, the shorter length providing adequate coverage for smaller patients or a smaller portion of an average adult patient. FIG. 3B is a schematic side view of blanket 200 draped over a lower body portion of a patient. With reference to FIG. 3B it may be appreciated that flaps 25, extending down on either side of the patient, and foot drape 26, being folded under and secured by reversible fasteners 29 (FIG. 3A) to form a pocket about the feet of the patient, together effectively enclose the lower body portion of the patient to prevent heat loss. With reference to FIG. 2A, in conjunction with FIG. 3B, it may be appreciated that temperature sensor assembly 421 is located on assembly 250 so that, when blanket 200 including assembly 250 is draped over the lower body of the patient, the area of heating element 10 surrounding sensor assembly 421 will be in conductive contact with one of the legs of the patient in order to maintain a safe temperature distribution across element 10.
According to some embodiments of the present invention, shell 20 includes top and bottom sheets extending over either side of assembly 250; the two sheets of shell 20 are coupled together along a seal zone 22 (shown with cross-hatching in the cut-away portion of FIG. 3A) that extends about a perimeter edge 2000 of blanket 200, and within perimeter edge 2000 to form zones, or pockets, where a gap exists between the two sheets.
FIG. 3A further illustrates flaps 25 including zones where there are gaps between the sheets to enclose weighting members, which are shown as relatively flat plastic slabs 255. Alternately flaps 25 can be weighted by attaching weighting members to exterior surfaces thereof.
FIG. 3C is a top plan view, including partial cut-away views, of heating element assembly 250′, which may be incorporated in blanket 200; and FIG. 3D is a cross-section view through section line D-D of FIG. 3C. FIGS. 3C-D illustrates heating element assembly 250′ including heating element 10 overlaid with electrical insulation 210 on both sides 13, 14 and thermal insulation layer 201 extending over the top side 14 thereof (dashed lines show leads and sensor assembly beneath layer 201). According to the illustrated embodiment, layer 201 is inserted beneath a portion of each insulating member 18, each which has been folded over the respective bus bar 15, for example as illustrated by arrow B in FIG. 1C, and then held in place by a respective row of non-conductive stitching 345 that extends through member 18, layer 201 and heating element 10. Although layer 210 is shown extending beneath layer 201 on side 14 of heating element, according to alternate embodiments, layer 201 independently performs as a thermal and electrical insulation so that layer 210 is not required on side 14 of heating element 10.
Returning now to FIG. 2A, to be referenced in conjunction with FIGS. 3A-C, connector housing 225 and connector 23 will be described in greater detail. According to certain embodiments, housing 225 is an injection molded thermoplastic, for example, PVC, and may be coupled to assembly 250 by being stitched into place, over insulating layer 210. FIG. 2A shows housing 225 including a flange 253 through which such stitching can extend. With reference to FIGS. 3A-B, it can be seen that connector 23 protrudes from shell 20 of blanket 200 so that an extension cable 330 may couple bus bars 15 to a power source 234, and temperature sensor assembly 421 to a temperature controller 232, both shown incorporated into a console 333. In certain embodiments, power source 234 supplies a pulse-width-modulated voltage to bus bars 15. The controller 232 may function to interrupt such power supply (e.g., in an over-temperature condition) or to modify the duty cycle to control the heating element temperature. According to the illustrated embodiment, a surface 252 of flange 253 of housing 225 protrudes through a hole formed in thermal insulating layer 201 (FIG. 3C) so that a seal 202 (FIG. 3A) may be formed, for example, by adhesive bonding and/or heat sealing, between an inner surface of shell 20 and surface 252.
FIGS. 3C-D further illustrate a pair of securing strips 217, each extending laterally from and alongside respective lateral portions 11, 12 of heating element 10 and each coupled to side 13 of heating element 10 by the respective row of stitching 345. Another pair of securing strips 271 is shown in FIG. 3C, each strip 271 extending longitudinally from and alongside respective ends 101, 102 of heating element 10 and being coupled thereto by a respective row of non-conductive stitching 354. Strips 217 preferably extend over conductive stitching 145 on side 13 of heating element 10, as shown, to provide a layer of insulation that can prevent shorting between portions of side 13 of heating element 10 if element 10 were to fold over on itself along rows of conductive stitching 145 that couple bus bars 15 to heating element 10; however, strips 217 may alternately extend over insulating member 18 on the opposite side of heating element 10. According to the illustrated embodiment, securing strips 217 and 271 are made of a polymer material, for example polyurethane, so that they may be heat sealed between the sheets of shell 20 in corresponding areas of heat seal zone 22 in order to secure heating element assembly 250′ within the corresponding gap between the two sheets of shell 20 (FIG. 3A).
FIG. 4A is a plan view of flexible heating element 30, according to some alternate embodiments of the present invention. Heating element 30 is similar in nature to previously described embodiments of heating element 10, being comprised of a conductive fabric, or a fabric incorporating closely spaced conductive elements, for a substantially uniform watt density output, preferably less than approximately 0.5 watts/sq. inch. While a shape of the surface area of heating element 10 is suited for a lower body blanket, such as blanket 200, that would cover a lower abdomen and legs of a patient (FIG. 3B) undergoing upper body surgery, the shape of a surface area of heating element 30 is suited for an upper body heating blanket, for example, blanket 300 shown in FIG. 4C, that would cover outstretched arms and a chest area of a patient undergoing lower body surgery (FIG. 4D). With reference to FIG. 4B, which shows heating element 30 incorporated into a heating element assembly 450, it can be seen that bus bars 15 are coupled to element 30 alongside respective lateral edges 311, 312 (FIG. 4A).
FIG. 4B is a top plan view, including partial cut-away views, of heating element assembly 450, according to some embodiments of the present invention, which may be incorporated in blanket 300 shown in FIG. 4C. FIG. 4B illustrates assembly 450 having a configuration similar to that of assembly 250′, which is illustrated in FIGS. 3C-D. According to the embodiment illustrated in FIG. 4B, temperature sensor assembly 421 is coupled to heating element 30 at a location where element 30, when incorporated in an upper body heating blanket, for example, blanket 300, would come into conductive contact with the chest of a patient, for example as illustrated in FIG. 4D, in order to maintain a safe temperature distribution across element 30; bus bar junctions 50 and connector housing 225 are located in proximity to sensor assembly 421 in order to keep a length of leads 205 and 221 to a minimum. With reference back to FIGS. 3C-D, in conjunction with FIG. 4B, an electrical insulating layer 310 of assembly 450 corresponds to insulating layers 210 of assembly 250′, a thermal insulating layer 301 of assembly 450 corresponds to layer 201 of assembly 250′, and securing strips 317 and 371 of assembly 450 generally correspond to strips 217 and 271, respectively, of assembly 250′.
FIG. 4C is a top plan view, including partial cut-away views, of upper body heating blanket 300, according to some embodiments of the present invention. FIG. 4C illustrates blanket 300 including heating element assembly 450 covered by a flexible shell 40; shell 40 protects and isolates assembly 450 from an external environment of blanket 300 and may further protect a patient disposed beneath blanket 300 from electrical shock hazards. According to the illustrated embodiment, shell 40, like shell 20, includes top and bottom sheets; the sheets extend over either side of assembly 450 and are coupled together along a seal zone 32 that extends around a perimeter edge 4000 and within edge 4000 to form various zones, or pockets, where gaps exist between the two sheets. The sheets of shell 40 may be heat sealed together along zone 32, as previously described for the sheets of shell 20. With reference to FIG. 4B, securing strips 317 may be heat sealed between the sheets of shell 40 in corresponding areas of seal zone 32, on either side of a central narrowed portion 39 of blanket 300, in order to secure heating element assembly 450 within the corresponding gap between the two sheets of shell 40. According to an alternate embodiment, for example, as shown with dashed lines in FIG. 4A, lateral edges 311, 312 of heating element 30 extend out to form securing edges 27 that each include slots or holes 207 extending therethrough so that inner surfaces of sheets of shell 40 can contact one another to be sealed together and thereby hold edges 27. It should be noted that either of blankets 200, 300, according to alternate embodiments of the present invention, may include more than one heating element 10, 30 and more than one assembly 250/250′, 450.
With reference to FIG. 4C, it may be appreciated that blanket 300 is symmetrical about a central axis 30 and about another central axis, which is orthogonal to axis 30. FIG. 4C illustrates shell 40 forming flaps 35A, 35B and 350, each of which having a mirrored counterpart across central axis 30 and across the central axis orthogonal to axis 30. According to the illustrated embodiment, each of flaps 35A, B include weighting members 305, which are similar to members 255 of blanket 200, and which may stiffen flaps 35A,B (dashed lines indicate outlines of members 305 held between the sheets of cover 40 by surrounding areas of seal zone 32).
FIG. 4C further illustrates straps 38, each extending between respective flaps 35A-B. With reference to FIG. 4D, which is a schematic end view of blanket 300 draped over an upper body portion of a patient, it may be appreciated that flaps 35A-B and 350 extend downward to enclose the outstretched arms of the patient in order to prevent heat loss and that straps 38 secure blanket 300 about the patient.
With further reference to FIG. 4D, it may also be appreciated that, when blanket 300 is positioned over the patient, each strap 38 is positioned in proximity to an elbow of the patient so that either end portion of blanket 300, corresponding to each pair of flaps 35A, may be temporarily folded back, as illustrated, per arrow C, in order for a clinician to access the patient's arm, for example, to insert or adjust an IV. According to some embodiments of the present invention, super over-temperature sensors, for example, sensors 41, previously described, are included in blanket 300 being located according to the anticipated folds, for example at general locations 410 illustrated in FIGS. 4B-C, in order to detect over-heating, which may occur if blanket 300 is folded over on itself, as illustrated in FIG. 4D, for too long a time, and, particularly, if flaps 35A of folded-back portion of blanket are allowed to extend downward as illustrated with the dashed line in FIG. 4D. FIG. 4D further illustrates connector cord 330 plugged into connector 23 to couple heating element 30 and temperature sensor assembly 421 of blanket 300 to control console 333.
In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims. Although embodiments of the invention are described in the context of a hospital operating room, it is contemplated that some embodiments of the invention may be used in other environments. Those embodiments of the present invention, which are not intended for use in an operating environment and need not meet stringent FDA requirements for repeated used in an operating environment, need not including particular features described herein, for example, related to precise temperature control. Thus, some of the features of preferred embodiments described herein are not necessarily included in preferred embodiments of the invention which are intended for alternative uses.

Claims

1. An electric warming blanket for warming patients during surgery and other medical procedures, comprising:

a flexible heater having a surface area and a substantially uniform watt density output across the surface area when the heater is electrically powered;

a temperature sensor assembly coupled to the heater and providing input of an average temperature over a portion of the surface area of the heater to a temperature controller when the heater and the sensor assembly are coupled to the controller; and

a first layer of water resistant material coupled to a second layer of water resistant material about a perimeter of the heater to form a substantially hermetically sealed space for the heater and the temperature sensor assembly.

2. The blanket of claim 1, wherein the heater comprises a conductive fabric.

3. The blanket of claim 1, wherein the heater comprises carbon.

4. The blanket of claim 1, wherein the heater comprises a nonconductive layer coated with a conductive material.

5. The blanket of claim 4, wherein the nonconductive layer comprises a woven polyester and the conductive material comprises polypyrrole.

6. The blanket of claim 1, wherein the heater comprises a fabric incorporating closely spaced conductive elements.

7. The blanket of claim 1, wherein the portion is disposed along the surface area so at to be in conductive contact with the patient when the blanket is placed over the patient to warm the patient.

8. The blanket of claim 1, wherein the temperature sensor assembly includes a temperature sensor coupled to a heat spreader, the heat spreader extending over the portion of the surface area.

9. The blanket of claim 8, wherein the portion of the surface area is no greater than approximately four square inches.

10. The blanket of claim of claim 8, wherein the heat spreader comprises a metal foil.

11. The blanket of claim 1, wherein the temperature sensor assembly includes a distributed temperature sensor comprising a resistance temperature detector (RTD) laid out in a flat plane across the portion of the surface area.

12. The blanket of claim 1, wherein the temperature sensor assembly includes an array of temperature sensors spaced apart over the portion of the surface area.

13. An electric warming blanket for warming patients during surgery and other medical procedures, comprising:

a flexible heater including a first side and a second side, at least one of the first and second sides having a surface area and a substantially uniform watt density output across the surface area when the heater is electrically powered;

a temperature sensor assembly coupled to the first side of the heater;

a first layer of water resistant material disposed over the first side of the heater, being un-adhered thereto, and forming a top surface of the blanket when the blanket is placed over the patient;

a second layer of water resistant material disposed over the second side of the heater, being un-adhered thereto, and forming a bottom surface of the blanket, adjacent to the patient, when the blanket is placed over the patient,

the first layer of water resistant material coupled to the second layer of water resistant material about a perimeter of the heater to form a substantially hermetically sealed space for the heater and the temperature sensor; and

a layer of thermal insulation disposed between the temperature sensor assembly and the first layer of water resistant material.

14. The blanket of claim 13, wherein the flexible heater comprises a conductive fabric.

15. The blanket of claim 13, wherein the heater comprises carbon.

16. The blanket of claim 13, wherein the heater comprises a nonconductive layer coated with a conductive material.

17. The blanket of claim 16, wherein the nonconductive layer comprises a woven polyester and the conductive material comprises polypyrrole.

18. The blanket of claim 13, wherein the flexible heater comprises a fabric incorporating closely spaced conductive elements.

19. The blanket of claim 13, wherein the layer of thermal insulation comprises flexible polymeric foam.

20. The blanket of claim 13, wherein the layer of thermal insulation comprises high loft fibrous polymeric non-woven material.

21. The blanket of claim 13, wherein the layer of thermal insulation comprises non-woven cellulose material.

22. The blanket of claim 13, wherein the layer of thermal insulation comprises air.

23. An electric warming blanket for warming patients during surgery and other medical procedures, comprising:

a flexible heater having a surface area and a substantially uniform watt density output across the surface area when the heater is electrically powered; and

a temperature sensor assembly coupled to the heater,

the sensor assembly including a temperature sensor and a heat spreader, and

the heat spreader comprising a metal foil disposed between the temperature sensor and the heater.

24. The blanket of claim 23, wherein the temperature sensor comprises a surface mount chip thermistor.

25. The blanket of claim 23, wherein the heat spreader extends over a portion of the surface area of the heater, the portion being no greater than approximately four square inches.

26. The blanket of claim 23 wherein the heater spreader has a thickness that is no greater than approximately 0.001 inch.