This is a continuation of U.S. patent application Ser. No. 09/277,628, filed Mar. 26, 1999 now U.S. Pat. No. 6,168,612. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to inflatable thermal blankets and, more particularly, to an inflatable thermal blanket with a multilayer sheet in which, after use, a layer of the multilayer sheet can be detached, thereby enabling the inflatable thermal blanket to be reused. 
     2. Description of the Related Art 
     It often is necessary to control a person&#39;s body temperature using means external to the person. For example, it is important to keep a person warm during surgery and to warm the person post-operatively to reduce the risk of hypothermia. 60-70% of surgical persons will experience hypothermia during surgery, if not treated. Many studies have been published showing the detrimental effects of hypothermia that occur during surgery. Such effects include a higher incidence of infections, more bleeding, more adverse cardiac events, higher death rates, slower recovery and longer hospitalizations. One means of preventing or treating hypothermia is the inflatable thermal blanket. 
     Inflatable thermal blankets have been in clinical use for the past ten years. Such a blanket may be inflated with cooled or warmed air and deployed over a person in need of thermal management where it bathes the person in a flow of cool or warm air. Persons needing thermal management include accidental hypothermia victims, persons with fever and persons undergoing surgery. Numerous research studies have shown that inflatable thermal blankets provide a highly effective and safe mode of thermal management. 
     In one use, an inflatable thermal blanket is inflated with warm air and placed adjacent a person. Warm air is expelled through a surface of the device that faces the person, creating a warmed environment about the person, thereby reducing and even reversing the transfer of heat from the person to the environment. Inflatable thermal blankets are provided for generalized and specialized uses, for which various inflatable structures have been developed. See, for example, U.S. Pat. Nos. 4,572,188; 5,300,101; 5,300,102; 5,324,320; 5,336,250 and 5,350,417 assigned to Augustine Medical, Inc. and incorporated herein by this reference. With the introduction of the BAIR HUGGER® family of inflatable thermal blankets by Augustine Medical, Inc., clinicians have been enabled to provide safe and effective thermal therapy to persons in a number of clinical settings, including surgery and recovery. 
     An inflatable thermal blanket typically includes a surface through which the inflating medium is expelled. Such a surface may include apertures formed in it by a manufacturing process, or may comprise an air-permeable material, for example. The blanket is deployed with the surface facing the person and the thermally-controlled air which inflates the device is exhausted from the blanket, through the surface, toward the person. The temperature of the thermally controlled air can be precisely controlled in order to warm or cool a person. 
     The majority of inflatable thermal blankets sold today are disposable “single use” products made of polymeric films and non-woven material. Extreme pressure to control costs has forced many health care providers to carefully examine their use of such disposables. In some cases, providers may reuse “single use” blankets which have been in contact with a previous person&#39;s skin and bodily fluids. There is no suitable way to clean and sterilize these “single use” blankets and therefore this practice can transmit infection from one person to another. 
     In response to the trend toward reuse of medical products, some manufacturers are now providing inflatable thermal blankets made of durable materials which can be cleaned and sterilized between uses. These blankets also appeal to the providers who believe that disposables are not friendly to the environment. However, reusable inflatable thermal blankets also have several draw-backs. First, they are expensive. Second, their durability is severely limited by the high temperatures and strong detergents necessary to clean and sterilize them. Finally, the detergents themselves are environmentally unfriendly. 
     From the discussion above, it should be apparent that there is a need for an inflatable thermal blanket that can be safely and economically used multiple times on one or more persons without requiring sterilization between uses. The present invention satisfies this need. 
     SUMMARY OF THE INVENTION 
     Broadly, the present invention concerns an inflatable thermal blanket with a multilayer sheet providing a surface through which air is transferred from the blanket toward a person. Presently, once an inflatable thermal blanket has been used on a person, this surface may be contaminated. Consequently, the blanket must be cleaned and sterilized or discarded. The advantage of a multilayer sheet is that the layers in the plurality of layers that make up the multilayer sheet may be detached from the sheet one or more at a time and discarded. So, following use of the inflatable thermal blanket, the contaminated layer or layers may be removed to render the inflatable thermal blanket ready for use again. 
     In an example that embodies, but which does not limit, the invention, an inflatable thermal blanket with a multilayer base sheet comprises an inflatable structure formed by attaching a first sheet to a second sheet. An inflation port is provided in the inflatable structure for admitting a stream of thermally-controlled air (e.g., heated or cooled air) into the inflatable structure. The multilayer sheet is assembled from a plurality bf sheets releasably attached together. The multilayer sheet is attached to the second sheet of the inflatable structure. Finally, a plurality of air passageways through the second sheet and the multilayer sheet allow the thermally-controlled air to flow through the inflatable structure. In a preferred embodiment, one or more layers of the multilayer sheet can be removed at one time without detaching the rest of the plurality of sheets. In this way, contaminated sheets can be removed individually, or multiply, and the inflatable thermal blanket can be reused. 
     Other features and advantages of the present invention should be apparent from the following description of the preferred embodiments, which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The nature, objects, and advantages of the invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings, in which like reference numerals designate like parts throughout, wherein: 
     FIG. 1 is a perspective view showing one embodiment of the present invention of an inflatable thermal blanket with a multilayer sheet disposed on a base sheet; 
     FIG. 2 is an exploded view of FIG. 1 showing the inflatable structure and the multiple layers of the sheet; 
     FIG. 3 is a perspective view similar to FIG. 1 showing another embodiment of the inflatable structure; 
     FIG. 4 is a cross-sectional view of FIG. 1 prior to the attachment of the multiple layers to the inflatable structure; 
     FIG. 5 is a cross-sectional view of FIG. 1 showing the attachment of the multiple layers to the inflatable structure; 
     FIG. 6 is another exploded view of FIG. 1 showing the multiple layers laminated before attachment to the inflatable structure; 
     FIG. 7 is a sectional view  7 — 7  of FIG. 6 showing one embodiment of the multiple layers with a melted hole; 
     FIG. 8 is a sectional view  8 — 8  of FIG. 6 showing another assembly embodiment of the multiple layers with a punched hole; 
     FIG.  9  and FIG. 10 are cross-sectional views of FIG. 3 showing another embodiment of the inflatable structure; and 
     FIG. 11 is a cross-sectional view similar to FIG. 10 showing an alternate structure for the multiple layers. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The figures show an inflatable thermal blanket in an inflated condition for clarity and ease of understanding. It is to be understood however, that the invention applies to inflatable thermal blankets in an uninflated condition as well. 
     The invention concerns a unitary, integral structure with a plurality of layers that may be detached one-by-one from the unitary integral structure. The structure is referred to as a “multilayer sheet”. As the following discussion will reveal, each layer of the multilayer is best embodied as a sheet. However, in order to avoid confusing each sheet of a layer with the multilayer sheet, the individual sheets of the multilayer sheet will be referred to in the description and claims as “layers”, with the understanding that “layer” may mean “sheet”. 
     FIG. 1 is an instructive illustration of the present invention, in the form of an inflatable thermal blanket  100 . The inflatable thermal blanket  100  includes an inflatable structure  102  and a multilayer sheet  104 . The multilayer sheet  104  is made from a plurality of sheets or layers  106  assembled together in such a manner as to make each layer detachable from a neighboring layer. The inflatable thermal blanket  100  also includes an inflation port  108  located in the inflatable structure  102 , which may be connected to a tube (not shown) leading to an external heater/blower unit (not shown). Together, the tube and blower unit provide pressurized thermally-controlled air (for either heating or cooling) to inflate the thermal blanket  100 . 
     FIG. 2 is an exploded view of FIG. 1 showing the inflatable structure  102  and the multilayer sheet  104 . The inflatable structure  102  of the thermal blanket  100  includes a first sheet  110  and a second sheet  112  (see also FIGS.  4  and  5 ). The sheet  110  is preferably made of a polymeric film material. The second sheet  112  may be made of a polymeric film, a fibrous or non-woven material or a combination of these materials. The first sheet  110  and second sheet  112  are joined at one or more locations to form the inflatable structure  102 . For example, the sheets may be joined along a substantially continuous seam near the peripheries of the sheets, but other configurations are possible. The location of such a seam with reference to the first sheet  110  is indicated by reference numeral  114 . The first sheet  110  and second sheet  112  may also be joined together at one or more locations  118  within the peripheral seam at  114 . These additional locations  118  help to direct the air flow and prevent the inflatable structure  102  from blowing up like a beach ball. FIG. 3 illustrates another inflatable structure  103 . The inflatable structure  103  is similar to inflatable structure  102  but the locations  118  are a plurality of stake points, forming a quilt-like structure. These embodiments are but two examples of some of the shapes and structures that the inflatable thermal blanket can be formed into. Many other, but nevertheless equivalent variations are possible. 
     Referring again to FIG. 2, the inflatable thermal blanket  100  includes one or more additional layers  106  that are joined together to form the multilayer sheet  104 . The additional layers  106  include a layer  122 , which is adjacent to the second sheet  112  (i.e., the layer closest to the inflatable structure). Preferably, the additional layers  106  are made of a non-woven material that is hydrophobic and therefore fluid repelling or a non-woven material that has been “waterproofed” by laminating it to a polymeric film layer. Alternately, the additional layers  106  may be made of a polymeric film, fibrous materials, woven or non-woven materials or a combination of these materials. 
     For the inflatable thermal blanket  100  to heat or cool a person, it must be attached to a unit that provides a stream of warmed or cooled air. The inflation port  108  allows the temperature controlled stream of air to enter the inflatable structure  102 , the usual connection being an air hose. At least one surface of the thermal blanket  100 , the air is released through a plurality of air passageways, which allow the air to flow from the thermal blanket  100  toward a person (not shown). 
     FIG. 4 shows a cross-sectional view of the inflatable structure  102  when inflated, with the multilayer sheet  104  unattached. The inflatable structure  102  is assembled with the first sheet  110  and the second sheet  112  joined together along a substantially continuous seam at  114 . As is evident, when the structure  102  is inflated it manifests parallel flattened tubes. Also shown is the multilayer sheet  104  assembled with the plurality of layers  106 , one of which may be designated as a “closest” layer  122 . It is contemplated by the inventors that the closest layer  122  of the multilayer sheet  104  could also serve as the second sheet  112  by directly attaching the first sheet  110  to the closest layer  122 . 
     FIG. 5 is a cross-sectional view of the thermal blanket  100  showing the inflatable structure  102  assembled with the multilayer sheet  104 . As discussed above, pressurized air flows out of the thermal blanket  100  through the second sheet  112 . In the second sheet  112 , a plurality of air passageways  124  are formed to allow air to flow from the inflatable structure  102 . In addition to these air passageways there are also air passageways  124  through the multilayer sheet  104 . Preferably these air passageways  124  are created through all of the layers  106  by forming the air passageways  124  through all of the layers  106  of the sheet  104  at once. Alternately, the air passageways  124  may be inherent if the layers  106  are made of a non-woven or woven material (i.e., a porous material). Finally, air passageways  124  may be formed in the individual layers  106  before stacking. 
     FIG. 6 is an exploded view similar to FIG. 2 showing the layers  106  assembled into the multilayer sheet  104 . In one embodiment, the layers  106  are joined together at  134 . However, the layers are separated at a corner  136  to allow the separation of an individual layer  106  when required (described in more detail below). 
     FIGS. 7 and 8 show alternate methods of forming the air passageways  124  in the multilayer sheet  104 . In the preferred embodiment, the air passageways  124  may be formed by melting and/or by punching in such a manner as to join the layers  106  together at the perimeter of each hole. If a passageway is created by melting for example, as shown in FIG. 7, the melted material joins each layer  106  to the next at the passageway, forming the multilayer sheet  104 . If the passageway  124  is created by punching, as shown in FIG. 8, the design of the punch and die can be optimized so as to entangle fibers from the adjacent layers  106  of material, resulting in a mechanical “bond”  128  between the layers  106  forming the multilayer sheet  104 . Further, a combination of punching and melting may be utilized. The advantage of this design is that the bonds joining the layers  106  at the perimeters of the passageways  124  assure that the corresponding passageways  124  in each layer  106  are oriented with one another. Precisely aligning the passageways  124  in the layers  106  reduces the total resistance to air flow by providing a direct air flow path  126  through all of the layers  106 . This direct air flow path  126  is advantageous because it provides more air flow through the inflatable thermal blanket. Alternately, if the layers  106  are “breathable” (i.e., formed of porous material) and do not require holes punched in them for air flow, the layers  106  may be joined (adhesively or thermally, for example) together at multiple locations  130  across their surfaces or at their peripheries or at combinations of these locations (see FIG.  11 ). 
     Referring again to FIGS. 4 and 5, when attaching the multilayer sheet  104  to the inflatable structure  102 , the “closest” layer  122  is placed proximate the second sheet  112  and attached at multiple locations  138 . For example, the closest layer  122  may be adhesively attached at  138  to the second sheet  112 . Alternately, the closest layer  122  may be thermally bonded at  138  to the second sheet  112 . In another embodiment, the closest layer  122  is removeably attached to the second sheet  112  at  138  with a hook-and-eye material. Preferably the closest layer  122  is attached to the second sheet  112  at multiple locations  138  across its surface. 
     Finally, since the inflatable thermal blanket with a multilayer sheet is reusable in multiple successive deployments, each layer  106  must be detachable from an adjacent layer  106 . In the preferred embodiment, the bottom-most layer  106  (i.e., the layer  106  furthest from layer  122 ) can be separated (i.e., detached) from the adjacent layer by tearing the relatively weak thermal and/or entangled fiber bond  128  at the periphery of each passageway  124 . This allows the bottom-most layer of the thermal blanket  100 , which was in contact with a person in a first deployment and therefore may have been contaminated, to be discarded after use. The remaining thermal blanket  100  is fully functional and clean for the next deployment. The closest layer  122  may also be detachable from the second sheet  112 . In that way, once all the layers  106  of the multilayer sheet  104  have been used, layer  122  is detached from the second sheet  112  and another multilayer base sheet  104  can be attached and the inflatable thermal blanket can be used in the same manner as previously described. 
     Optionally, for user convenience and cleanliness, a comer of the multilayer sheet  104  can have the individual layers  106  accessible for the clinician or user to remove, one layer at a time. Optionally, a pull-tab  140  may be attached to each layer  106  for additional ease of use (see FIG.  2 ). The pull-tab  140  aids the clinician in removing only the bottom-most layer, leaving the remaining blanket  100  intact. 
     FIGS. 9 and 10 illustrate a possible alternate embodiment of the inflatable structure  103  of FIGS. 3,  4  and  5  with the multilayer sheet  104 . As may be appreciated with inspection of these figures, the first and second sheets are joined in such a way as to form parallel fully rounded tubes when the structure  103  is inflated. 
     FIG. 11 shows an alternate embodiment inflatable structure  103  along with an alternate embodiment of the multilayer sheet  105 . In this embodiment, the plurality of layers  106  are constructed from a porous or “breathable” material which allows the air to flow from the inflatable structure through the layers of “breathable” material and onto the person. In this construction, the multilayer sheet  105  is constructed from a plurality of layers  106  attached together at a plurality of locations  130 . The multilayer sheet  105  may be attached to inflatable structure  103  by adhesive, heat bond or hook-and-eye material as described previously. The layers  106  may also be joined together around the periphery  132 . 
     In one manufacturing embodiment, the layers  106  may be bonded together to form the multilayer sheet  104 . In the preferred embodiment, the multilayer sheet  104  is assembled before joining the closest layer  122  to the second sheet layer  112 . The preferred material for the layers  106  is a non-woven polyester or polypropylene which has been laminated with a layer of polypropylene or polyethylene film. Unwinding multiple rolls of this material simultaneously, two or more sheets of this material are layered onto one another in a web-type process. The layers  106  are joined together and the passageways  124  are punched through the layers before the individual multilayer sheets are cut from the web. Preferably the passageways  124  are melted and/or punched through all of the layers at once, simultaneously creating passageways  124  and the bonds between the layers  106  at the edge of the holes (as described previously). The passageways  124  may be melted by piercing the layers with a many small hot spikes. Alternately the passageways  124  may be created by melting the material with a laser, jets of hot air or other suitable means. 
     The layers  106  may be joined using a male plain or serrated punch, cutting onto an anvil material or into a female die. The punches serve two purposes. First they create the passageways  124  through the plural layers  106 . Second, the serrations serve to entangle the fibers of the materials  128  of the layers  106 , at the periphery of the passageways  124  (see FIG.  8 ). This creates a mechanical “bond” between the layers and serves to align the passageways  124  in the layers  106 . The shape and size of the punches and the serrations may be varied to achieve various levels of bonding. Finally, the punches, anvil or die may be heated to partially or completely melt the material at the periphery of the hole. In this case, the level of heat may be adjusted to control the strength of the bonding between the layers. 
     Preferably, the layers  106  are bonded together into the multilayer sheet  104  and the air passageways  124  are created before the closest layer  122  is bonded to the second sheet  112  of the previously assembled inflatable structure  102 . The closest layer  122  and the second sheet  112  are adhesively bonded together at multiple locations  138  across their surfaces. The adhesive bond may or may not be detachable between the closest layer  122  and the second sheet  112 . Alternately this bond  138  may be created by thermally melting the materials of the adjacent layers. Finally, both the inflatable structure  102  and the multilayer sheet  104  are cut from the web simultaneously forming the thermal blanket  100 . 
     For cost and environmental reasons, the thin material of the bottom layer minimizes the amount of material being discarded thereby making a practical, safe, effective, economical and environmentally friendly multiple use forced air thermal blanket. 
     The description and illustrations thus far have placed a single multilayer sheet on the bottom surface of an inflatable thermal blanket. This is not intended to, and should not, so limit the practice of the invention. As those skilled in the art will appreciate, air may be expelled through surfaces other than the bottom surface of an inflatable thermal blanket. For example, in certain tubular structures, air is expelled through a side surface, or through a side portion of a generally cylindrical surface. In other, pad-like, structures, air may be expelled through a top surface. Moreover, air may be expelled through more than one surface. A multilayer sheet, or a plurality of multilayer sheets according to this invention, may be attached to one or more such surfaces of an inflatable thermal blanket. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.
An inflatable thermal blanket with a multilayer sheet and a method of use are disclosed for delivering thermally-controlled air to a person. The apparatus includes an inflatable structure formed from joining a first sheet and a second sheet. An inlet is provided into the inflatable structure for receiving thermally-controlled air. A multilayer sheet, made from a plurality of sheets releasably attached together, is attached to the second sheet. Means are provided for exhausting the thermally-controlled air from the inflatable thermal blanket. In the method of use, the inflatable thermal blanket is deployed in a first use and a source of thermally-controlled air is attached to the inflation port admitting thermally-controlled air into the inflatable structure and exhausting thermally-controlled air. Additionally, the inflatable thermal blanket may be reused by detaching the lowest layer of the multilayer sheet, exposing another layer of the multilayer sheet and deploying the inflatable thermal blanket in a second or later use. These steps may be repeated until the last layer of the multilayer sheet is used, when the thermal blanket may be discarded. In an alternate embodiment, when the multilayer sheet is exhausted it is detached and another multilayer base sheet is attached to the inflatable structure and the thermal blanket is used again.