US20070068928A1 - Temperature sensor assemblies for electric warming blankets - Google Patents

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 inFIG. 1A.
• FIG. 1D is a schematic showing a blanket including the subassembly ofFIG. 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 inFIG. 3A.
• FIG. 2B is a section view through section line A-A ofFIG. 2A.
• FIG. 2C is an enlarged plan view and corresponding end view schematic of a portion of the assembly shown inFIG. 2A, according to some embodiments of the present invention.
• FIG. 2D is an enlarged view of a portion of the assembly shown inFIG. 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 ofFIG. 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 inFIG. 3A.
• FIG. 3D is a cross-section view through section line D-D ofFIG. 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 inFIG. 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 ofFIG. 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 flexibleheating blanket subassembly100, according to some embodiments of the present invention; and FIGS.1B-C are end views of two embodiments of the subassembly shown inFIG. 1A.FIG. 1A illustrates a flexible sheet-like heating element, or heater,10 ofsubassembly100 including afirst end101, asecond end102, a first lateral portion11 extending betweenends101,102, and a secondlateral portion12, opposite first lateral portion11, also extending betweenends101,102. According to preferred embodiments of the present invention,heater10 comprises a conductive fabric or a fabric incorporating closely spaced conductive elements such thatheater10 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 bothsides13,14 (FIGS.1B-C), the surface area including and extending betweenlateral portions11,12 ofheater10. 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 subassembly100 including twobus bars15 coupled toheating element10 for poweringelement10; eachbar15 is shown extending alongside opposinglateral portions11,12, between first and second ends101,102. With reference toFIG. 1B, according to some embodiments, bus bars15 are coupled toheating element10 within folds of opposing wrapped perimeter edges108 ofheating element10 by a stitchedcoupling145, for example, formed with conductive thread such as silver-coated polyester or nylon thread (Marktek Inc., Chesterfield, Mo.), extending throughedges108 ofheating element10, bars15, and again throughheating element10 on opposite side ofbars15. According to alternateembodiments heating element10 is not folded overbus bars15 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, bars15 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 ofblanket subassembly100. According to alternate embodiments, bus bars15 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 bars15 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 ofheating element10 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 stitchedcoupling145 of a silver-coatedbus bar15.
• According to an exemplary embodiment, a conductive fabric comprisingheating element10 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 ofheating element10 having a width, betweenbus bars15, 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, forexample heater10, is directly related to heat generation according to the following relationship:
  Q(Joules)=I²(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 ofblanket subassembly100, provided primarily byflexible heating element10, and optionally enhanced by the incorporation of flexible bus bars, allowsblanket subassembly100 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 fromelement10 to a surface of the body. However, as illustrated inFIG. 1D,heating element10 may be draped over a body16 such thatlateral portions11,12 do not contact side surfaces of body16; the mechanism of heat transfer betweenportions11,12 and body16, as illustrated inFIG. 1D, is primarily radiant with some convection.
• The uniform watt-density output across the surface areas of preferred embodiments ofheating element10 translates into generally uniform heating of the surface areas, but not necessarily a uniform temperature. At locations ofheating element10 which are in conductive contact with a body acting as a heat sink, for example, body16, the heat is efficiently drawn away fromheating element10 and into the body, for example by blood flow, while at those locations whereelement10 does not come into conductive contact with the body, forexample lateral portions11,12 as illustrated inFIG. 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 ofheating element10 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 throughheating element10. 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 atemperature sensor121 coupled toheating element10 in a location whereelement10 will be in conductive contact with the body, as illustrated inFIG. 1D, the ‘non-contacting’ portions, for example,lateral portions11,12, will also be operating at a safe temperature because of the less efficient radiant and convective heat transfer. According to preferred embodiments,heating element10 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 ofheating element10 may be differentiated according to whether or not portions ofelement10 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 includingheating element10, which pressureforces heating element10 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 ofheating element10 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 surroundselement10, for example, a cover orshell20,40 which will be described below in conjunction withFIGS. 3A and 4C. With further reference toFIG. 1D, flaps125 are shown extending laterally from either side ofheating element10 in order to enclose the sides of body16 thereby preventing heat loss; according to preferred embodiments of the present invention, flaps125 are not heated and thus provide no thermal injury risk to body if they were to be tucked beneath sides of body16.
• Referring now to the end view ofFIG. 1C, an alternate embodiment to that shown inFIG. 1B is presented.FIG. 1C illustrates subassembly100 wherein insulatingmembers18, for example, fiberglass material strips having an optional PTFE coating and a thickness of approximately 0.003 inch, extend betweenbus bars15 andheating element10 at each stitchedcoupling145, so that electrical contact points betweenbars15 andheating element10 are solely defined by the conductive thread of stitchedcouplings145.
• FIG. 2A is a top plan view of aheating element assembly250, according to some embodiments of the present invention, which may be incorporated byblanket200, which is shown inFIG. 3A and further described below.FIG. 2B is a section view through section line A-A ofFIG. 2A. FIGS.2A-B illustrate atemperature sensor assembly421 assembled onside14 ofheater10, andheater10 overlaid on bothsides13,14 with an electrically insulatinglayer210, 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 tosides13,14 with a hotmelt laminating adhesive. In some embodiments, the adhesive is applied over the entire interfaces betweenlayer210 andheater10. Other examples of suitable materials forlayer210 include, without limitation, polymeric foam, a woven fabric, such as cotton or fiberglass, and a relatively thin plastic film. According to preferred embodiments, overlaidlayers210, without compromising the flexibility ofheating assembly250, prevent electrical shorting of one portion ofheater10 with another portion ofheater10 ifheater10 is folded over onto itself.Heating element assembly250 may be enclosed within a relatively durable and waterproof shell, forexample shell20 shown with dashed lines inFIG. 2B, and will be powered by a relatively low voltage (approximately 48V).Layers210 may even be porous in nature to further maintain the desired flexibility ofassembly250.
• FIG. 2C is an enlarged plan view and a corresponding end view schematic showing some details of the corner ofassembly250 that is circled inFIG. 2A, according to some embodiments.FIG. 2C is representative of each corner ofassembly250.FIG. 2C illustrates insulatinglayer210 disposed overside14 ofheater10 and extending beneathbus bar15, optional electrical insulatingmember18, andlayer210 disposed overside13 ofheater10 and terminatedadjacent bus bar15 withinlateral portion12 so that threads ofconductive stitching145 securingbus bars15 toheater10 electricallycontact heating element10 alongside13 ofheating element10.FIG. 2C further illustrates two rows ofconductive stitching145coupling bus bar15 toheating element10, andbus bar15 and insulatingmember18 extendingpast end102.
• FIG. 2A further illustratesjunctions50 coupling leads205 to eachbus bar15, and another lead221 coupled to and extending fromtemperature sensor assembly421; each of leads205,221 extend overinsulating layer210 and into anelectrical connector housing225 containing aconnector23, which will be described in greater detail below, in conjunction with FIGS.3A-C.FIG. 2D is an enlarged view ofjunction50, which is circled inFIG. 2A, according to some embodiments of the present invention.FIG. 2D illustratesjunction50 including a conductive insert55 which has been secured tobus bar15, for example, by inserting insert55 through a side wall ofbus bar15 and into an inner diameter thereof.FIG. 2D further illustrates lead205 coupled to insert55, for example, via soldering, and an insulating tube andstrain relief54, for example, a polymer shrink tube, surrounding the coupling betweenlead205 and insert55.
• Returning now toFIG. 2B,temperature sensor assembly421 will be described in greater detail.FIG. 2B illustrates assembly421 including a substrate211, for example, of polyimide (Kapton), on which atemperature sensor21, for example, a surface mount chip thermistor (such as a Panasonic ERT-J1VG103FA: 10 K, 1% chip thermistor), is mounted; aheat spreader212, for example, a copper or aluminum foil, is mounted to an opposite side of substrate211, for example, being bonded with a pressure sensitive adhesive; substrate211 is relatively thin, for example about 0.0005 inch thick, so that heat transfer betweenheat spreader212 and sensor is not significantly impeded.Temperature sensor assembly421 may be bonded to layer210 with an adhesive layer213, for example, hotmelt EVA. Although not shown, it should be noted thatsensor assembly421 may be potted with a flexible electrically insulating material, such as silicon or polyurethane.
• According to the illustrated embodiment,heat spreader212 is sized to contact an enlarged surface area so that a temperature sensed bysensor21 is more representative of an average temperature over a region ofheater10 surroundingsensor21, which is positioned such that, when a heatingblanket including heater10 is placed over a body, theregions surrounding sensor21 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 ofheater10 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 spreader212 is a desirable component of a temperature sensor assembly, according to some embodiments of the present invention, since conductive fabrics employed byheating element10, such as those previously described, may not exhibit uniform resistance across surface areas thereof.Heat spreader212, 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 onheat spreader212 surface area may be necessary so thatheat spreader212 does not become too bulky, since the larger the surface area, the greater the thickness ofspreader212 needed in order to maintain effective heat transfer acrossspreader212 and tosensor21. In addition, ifspreader212 is too thick, a thermal mass ofspreader212 will causespreader212 to respond too slowly to changes in heat loss or gain by heating element. According to an exemplary embodiment of the present invention,spreader212 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 ofelement10 by employing a distributed temperature sensor, for example, a resistance temperature detector (RTD) laid out in flat plane across a surface ofheater10, or by employing an infrared temperature measurement device positioned to receive thermal radiation from a given area ofheater10. An additional alternate embodiment is contemplated in which an array of temperature sensors are positioned over the surface ofheater10, being spaced apart so as to collect temperature readings which may be averaged to account for resistance variance.
• According to a preferred embodiment,assembly421 includes a second, redundant, temperature sensor mounted to substrate211, close enough tosensor21 to detect approximately the same temperature; whilesensor21 may be coupled to a microprocessor temperature control, the second sensor, for example, a chip thermistor similar tosensor21, may be coupled to an analog over-temperature cutout that cuts power toelement10, 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 substrate211 in order to detect an increase in resistance ofelement10, due, for example, to degradation of the material ofelement10, or a fractured bus bar; the optional identification resistor monitors a resistance ofheating element10 and compares the measured resistance to an original resistance ofelement10.
• According to some embodiments of the present invention, for example as illustrated inFIG. 2A, superover-temperature sensors41 are incorporated to detect overheating of areas ofassembly250 susceptible to rucking, that is areas, for example,lateral portions11,12, whereassembly250 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 ablanket including assembly250. An area ofassembly250 which is beneath the folded-over portion ofassembly250, and not in close proximity tosensor assembly421, can become significantly warmer due to the additional thermal insulation provided by the folded-over portion that goes undetected bysensor21. According to preferred embodiments,sensors41 are wired in series, as illustrated inFIG. 2A. Superover-temperature sensors41 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 toheating element10, at prescribed temperatures that are significantly above the normal operating range, for example, temperatures between approximately 45° C. and approximately 60° C. Alternately,sensors41 may be part of the bus bar power circuit, in whichcase sensors41 directly shut down power toheating element10 when in an open condition or add sufficient resistance when in a high resistance condition to substantially reduce heating ofelement10.
• FIG. 3A is a top plan view, including partial cut-away views, of a lowerbody heating blanket200, according to some embodiments of the present invention, which may be used to keep a patient warm during surgery.FIG. 3A illustratesblanket200 includingheating element assembly250 covered byflexible shell20;shell20 protects and isolates assembly250 from an external environment ofblanket200 and may further protect a patient disposed beneathblanket200 from electrical shock hazards. According to preferred embodiments of the present invention,shell20 is waterproof to prevent fluids, for example, bodily fluids, IV fluids, or cleaning fluids, from contactingassembly250, 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,blanket200 further includes a layer ofthermal insulation201 extending over a top side (corresponding toside14 of heating element10) ofassembly250;layer201 may or may not be bonded to a surface ofassembly250.Layer201 may serve to prevent heat loss away from a body disposed on the opposite side ofblanket200, particularly if a heat sink comes into contact with the top side ofblanket200.FIG. 3C illustratesinsulation201 extending over an entire surface ofside14 ofheating element10 and oversensor assembly421. According to the illustrated embodiment,layer201 is secured toheating element assembly250 to form anassembly250′, as will be described in greater detail below. According to an exemplary embodiment of the present invention, insulatinglayer201 comprises a polymer foam, for example, a 1pound density 30 ILD urethane foam, which has a thickness between approximately ⅛^thinch and approximately ¾^thinch. According toalternate embodiments layer201 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 illustratesshell20 formingflaps25 extending laterally from either side ofassembly250 and a foot drape26 extending longitudinally fromassembly250. According to exemplary embodiments of the present invention, a length ofassembly250 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 ofblanket200 draped over a lower body portion of a patient. With reference toFIG. 3B it may be appreciated that flaps25, extending down on either side of the patient, and foot drape26, being folded under and secured by reversible fasteners29 (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 toFIG. 2A, in conjunction withFIG. 3B, it may be appreciated thattemperature sensor assembly421 is located onassembly250 so that, whenblanket200 includingassembly250 is draped over the lower body of the patient, the area ofheating element10 surroundingsensor assembly421 will be in conductive contact with one of the legs of the patient in order to maintain a safe temperature distribution acrosselement10.
• According to some embodiments of the present invention,shell20 includes top and bottom sheets extending over either side ofassembly250; the two sheets ofshell20 are coupled together along a seal zone22 (shown with cross-hatching in the cut-away portion ofFIG. 3A) that extends about aperimeter edge2000 ofblanket200, and withinperimeter edge2000 to form zones, or pockets, where a gap exists between the two sheets.
• FIG. 3A further illustratesflaps25 including zones where there are gaps between the sheets to enclose weighting members, which are shown as relatively flatplastic slabs255. Alternately flaps25 can be weighted by attaching weighting members to exterior surfaces thereof.
• FIG. 3C is a top plan view, including partial cut-away views, ofheating element assembly250′, which may be incorporated inblanket200; andFIG. 3D is a cross-section view through section line D-D ofFIG. 3C. FIGS.3C-D illustratesheating element assembly250′ includingheating element10 overlaid withelectrical insulation210 on bothsides13,14 andthermal insulation layer201 extending over thetop side14 thereof (dashed lines show leads and sensor assembly beneath layer201). According to the illustrated embodiment,layer201 is inserted beneath a portion of each insulatingmember18, each which has been folded over therespective bus bar15, for example as illustrated by arrow B inFIG. 1C, and then held in place by a respective row ofnon-conductive stitching345 that extends throughmember18,layer201 andheating element10. Althoughlayer210 is shown extending beneathlayer201 onside14 of heating element, according to alternate embodiments,layer201 independently performs as a thermal and electrical insulation so thatlayer210 is not required onside14 ofheating element10.
• Returning now toFIG. 2A, to be referenced in conjunction with FIGS.3A-C,connector housing225 andconnector23 will be described in greater detail. According to certain embodiments,housing225 is an injection molded thermoplastic, for example, PVC, and may be coupled toassembly250 by being stitched into place, over insulatinglayer210.FIG. 2A showshousing225 including aflange253 through which such stitching can extend. With reference to FIGS.3A-B, it can be seen thatconnector23 protrudes fromshell20 ofblanket200 so that anextension cable330 may couple bus bars15 to apower source234, andtemperature sensor assembly421 to atemperature controller232, both shown incorporated into aconsole333. In certain embodiments,power source234 supplies a pulse-width-modulated voltage to bus bars15. Thecontroller232 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, asurface252 offlange253 ofhousing225 protrudes through a hole formed in thermal insulating layer201 (FIG. 3C) so that a seal202 (FIG. 3A) may be formed, for example, by adhesive bonding and/or heat sealing, between an inner surface ofshell20 andsurface252.
• FIGS.3C-D further illustrate a pair of securingstrips217, each extending laterally from and alongside respectivelateral portions11,12 ofheating element10 and each coupled toside13 ofheating element10 by the respective row ofstitching345. Another pair of securing strips271 is shown inFIG. 3C, each strip271 extending longitudinally from and alongside respective ends101,102 ofheating element10 and being coupled thereto by a respective row ofnon-conductive stitching354.Strips217 preferably extend overconductive stitching145 onside13 ofheating element10, as shown, to provide a layer of insulation that can prevent shorting between portions ofside13 ofheating element10 ifelement10 were to fold over on itself along rows ofconductive stitching145 that couple bus bars15 toheating element10; however, strips217 may alternately extend over insulatingmember18 on the opposite side ofheating element10. According to the illustrated embodiment, securingstrips217 and271 are made of a polymer material, for example polyurethane, so that they may be heat sealed between the sheets ofshell20 in corresponding areas ofheat seal zone22 in order to secureheating element assembly250′ within the corresponding gap between the two sheets of shell20 (FIG. 3A).
• FIG. 4A is a plan view offlexible heating element30, according to some alternate embodiments of the present invention.Heating element30 is similar in nature to previously described embodiments ofheating element10, 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 ofheating element10 is suited for a lower body blanket, such asblanket200, that would cover a lower abdomen and legs of a patient (FIG. 3B) undergoing upper body surgery, the shape of a surface area ofheating element30 is suited for an upper body heating blanket, for example,blanket300 shown inFIG. 4C, that would cover outstretched arms and a chest area of a patient undergoing lower body surgery (FIG. 4D). With reference toFIG. 4B, which showsheating element30 incorporated into aheating element assembly450, it can be seen that bus bars15 are coupled toelement30 alongside respectivelateral edges311,312 (FIG. 4A).
• FIG. 4B is a top plan view, including partial cut-away views, ofheating element assembly450, according to some embodiments of the present invention, which may be incorporated inblanket300 shown inFIG. 4C.FIG. 4B illustrates assembly450 having a configuration similar to that ofassembly250′, which is illustrated in FIGS.3C-D. According to the embodiment illustrated inFIG. 4B,temperature sensor assembly421 is coupled toheating element30 at a location whereelement30, when incorporated in an upper body heating blanket, for example,blanket300, would come into conductive contact with the chest of a patient, for example as illustrated inFIG. 4D, in order to maintain a safe temperature distribution acrosselement30;bus bar junctions50 andconnector housing225 are located in proximity tosensor assembly421 in order to keep a length ofleads205 and221 to a minimum. With reference back to FIGS.3C-D, in conjunction withFIG. 4B, an electrical insulatinglayer310 ofassembly450 corresponds to insulatinglayers210 ofassembly250′, a thermal insulatinglayer301 ofassembly450 corresponds to layer201 ofassembly250′, and securingstrips317 and371 ofassembly450 generally correspond tostrips217 and271, respectively, ofassembly250′.
• FIG. 4C is a top plan view, including partial cut-away views, of upperbody heating blanket300, according to some embodiments of the present invention.FIG. 4C illustratesblanket300 includingheating element assembly450 covered by aflexible shell40;shell40 protects and isolates assembly450 from an external environment ofblanket300 and may further protect a patient disposed beneathblanket300 from electrical shock hazards. According to the illustrated embodiment,shell40, likeshell20, includes top and bottom sheets; the sheets extend over either side ofassembly450 and are coupled together along aseal zone32 that extends around aperimeter edge4000 and withinedge4000 to form various zones, or pockets, where gaps exist between the two sheets. The sheets ofshell40 may be heat sealed together alongzone32, as previously described for the sheets ofshell20. With reference toFIG. 4B, securingstrips317 may be heat sealed between the sheets ofshell40 in corresponding areas ofseal zone32, on either side of a central narrowedportion39 ofblanket300, in order to secureheating element assembly450 within the corresponding gap between the two sheets ofshell40. According to an alternate embodiment, for example, as shown with dashed lines inFIG. 4A,lateral edges311,312 ofheating element30 extend out to form securingedges27 that each include slots orholes207 extending therethrough so that inner surfaces of sheets ofshell40 can contact one another to be sealed together and thereby hold edges27. It should be noted that either ofblankets200,300, according to alternate embodiments of the present invention, may include more than oneheating element10,30 and more than oneassembly250/250′,450.
• With reference toFIG. 4C, it may be appreciated thatblanket300 is symmetrical about acentral axis30 and about another central axis, which is orthogonal toaxis30.FIG. 4C illustratesshell40 formingflaps35A,35B and350, each of which having a mirrored counterpart acrosscentral axis30 and across the central axis orthogonal toaxis30. According to the illustrated embodiment, each offlaps35A, B includeweighting members305, which are similar tomembers255 ofblanket200, and which may stiffenflaps35A,B (dashed lines indicate outlines ofmembers305 held between the sheets ofcover40 by surrounding areas of seal zone32).
• FIG. 4C further illustratesstraps38, each extending betweenrespective flaps35A-B. With reference toFIG. 4D, which is a schematic end view ofblanket300 draped over an upper body portion of a patient, it may be appreciated that flaps35A-B and350 extend downward to enclose the outstretched arms of the patient in order to prevent heat loss and that straps38secure blanket300 about the patient.
• With further reference toFIG. 4D, it may also be appreciated that, whenblanket300 is positioned over the patient, eachstrap38 is positioned in proximity to an elbow of the patient so that either end portion ofblanket300, corresponding to each pair offlaps35A, 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,sensors41, previously described, are included inblanket300 being located according to the anticipated folds, for example atgeneral locations410 illustrated in FIGS.4B-C, in order to detect over-heating, which may occur ifblanket300 is folded over on itself, as illustrated inFIG. 4D, for too long a time, and, particularly, ifflaps35A of folded-back portion of blanket are allowed to extend downward as illustrated with the dashed line inFIG. 4D.FIG. 4D further illustratesconnector cord330 plugged intoconnector23 to coupleheating element30 andtemperature sensor assembly421 ofblanket300 to controlconsole333.
• 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 (26)

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 ofclaim 1, wherein the heater comprises a conductive fabric.

3. The blanket ofclaim 1, wherein the heater comprises carbon.

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

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

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

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

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

11. The blanket ofclaim 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 ofclaim 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 ofclaim 13, wherein the flexible heater comprises a conductive fabric.

15. The blanket ofclaim 13, wherein the heater comprises carbon.

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

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

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

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

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

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

22. The blanket ofclaim 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 ofclaim 23, wherein the temperature sensor comprises a surface mount chip thermistor.

25. The blanket ofclaim 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 ofclaim 23 wherein the heater spreader has a thickness that is no greater than approximately 0.001 inch.

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