Abstract:
An inflatable cover is constructed with a base sheet to which is attached an overlaying material sheet in order to form an inflatable structure. There is an opening to admit warmed air into the inflatable structure. A plurality of apertures open through the base sheet, into the inflatable structure for the purpose of exhausting warmed air therefrom, through the base sheet. The plurality of apertures vary in density toward an edge of the base sheet for the purpose of establishing various temperature profiles with respect to the inflatable cover. In a particular embodiment, the density of the apertures increases toward the edges of the base sheet, from the center of the inflatable cover.

Description:
This is a continuation of U.S. patent application Ser. No. 08/846,089, filed May 16, 1997, entitled THERMAL BLANKET which is a continuation of Ser. No. 08/658,315, filed Jun. 5, 1996, abandoned, which is a continuation of Ser. No. 08/386,324, filed Feb. 10, 1995, abandoned, which is a continuation of Ser. No. 08/225,141 Apr. 4, 1994 abondoned, which is a continuction of Ser. No. 07,703,592, filed May 20, 1991, now U.S. Pat. No. 5,324,320. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to thermal blankets used in a medical setting to deliver a bath of a thermally-controlled medium to a patient. 
     The thermal blanket prior art is best expressed in our prior U.S. Pat. No. 4,572,188 entitled “AIRFLOW COVER FOR CONTROLLING BODY TEMPERATURE.” In our prior patent, a self-erecting, inflatable airflow cover is inflated by the introduction into the cover of a thermally-controlled inflating medium, such as warmed air. When inflated, the cover self-erects about a patient, thereby creating an ambient environment about the patient, the thermal characteristics of which are determined by the temperature of the inflating medium. Holes on the underside of our prior art airflow cover exhaust the thermally-controlled, inflating medium from inside the cover to the interior of the erected structure. Our airflow cover is intended for the treatment of hypothermia, as might occur post-operatively. 
     Evaluation of our airflow cover by skilled practitioners has resulted in general approbation: the opinion is that the airflow cover efficiently and effectively accomplishes its purpose of giving a thermally-controlled bath. We have realized, however, that, while our prior art airflow cover achieves its objective, certain improvements to it are necessary in order to realize additional clinical objectives and to enjoy further advantages in its use. 
     SUMMARY OF THE INVENTION 
     We have improved the clinical usefulness of our self-erecting airflow cover by observing that controlling the contour of its inflatable portion at its head end to define a generally concave non-inflatable portion will permit a care giver to more easily observe a patient&#39;s head, face, neck and chest. Further, we have observed that limited venting of the thermally controlled inflating medium from the edges of the cover results in more efficient, more uniform heating within the cover. We have also observed that it is good clinical practice to keep the area of the care site in the vicinity of the patient&#39;s head and face as clean as possible. 
     These three observations have resulted in an improved thermal blanket in which a self-erecting inflatable covering has a head end, a foot end, two edges, and an undersurface. An inflating inlet adjacent said foot end admits a thermally-controlled inflating medium into the covering. An aperture array on the undersurface of the covering exhausts the thermally-controlled inflating medium from the covering into the structure created when the covering self-erects upon inflation. The improvements to this basic structural complement include an uninflatable section at the head end of the covering, exhaust port openings at the edges of the covering, an absorbent bib attached to the covering at the head end adjacent the uninflatable section, and structural features that make the covering simple and economical to produce. 
     With these improvements, the thermal blanket, when inflated and erected over a patient, delivers the thermally-controlled inflating medium into the interior of the structure covering the patient, thereby thermally bathing the patient. The first improvement permits full viewing of the head and face of the patient from almost any aspect around the thermal blanket. The exhaust port openings increase the rate of circulation of the inflating medium within the blanket, thereby increasing the temperature within the structure and making the temperature distribution more uniform. The absorbent bib soaks up and retains liquids which might otherwise spread over the care site in the area of a patient&#39;s head. Such liquids can include the patient&#39;s own perspiration, blood, vomit, saliva, or liquids which are administered to the patient. The absorbent bib also acts to some extent to seal the head end of the inflated structure. 
     From another aspect, the invention is a thermal blanket for covering and bathing a person in a thermally-controlled medium. The thermal blanket includes a flexible base sheet having a head end, a foot end, two edges, and a plurality of apertures opening between the first and second surface of the base sheet. An overlying material sheet is attached to the first surface of the base sheet by a plurality of discontinuous seams which form the material sheet into a plurality of substantially parallel, inflatable chambers. A continuous seam is provided between the material sheet and the base sheet at the head end to form a non-inflatable viewing recess at the head end. Exhaust port openings are provided through the material sheet to vent the medium from the chambers away from the base sheet. An absorbent bib is attached to the head end in the vicinity of the viewing recess. 
     Therefore the invention accomplishes the important objective of providing a self-erecting, inflatable thermal blanket that permits a relatively unobstructed view of a patient&#39;s head and face when in use. 
     Another objective is the efficient and uniform heating of the interior of the structure created when the blanket is inflated with a heat inflating medium. 
     A signal advantage of the invention is the provision of such a blanket with a means for maintaining the cleanliness of the care site in the vicinity of the patient&#39;s head and face. 
     The advantageous simplified structure of the thermal blanket make its production straightforward and economical. 
    
    
     These and other important objectives and advantages will become evident when the detailed description of the invention is read with reference to the below-summarized drawings, in which: 
     FIG. 1 is a side elevation view of the thermal blanket in use, with associated thermal apparatus indicated schematically; 
     FIG. 2 is an enlarged top plan view of the thermal blanket opened flat; 
     FIG. 3 is an enlarged sectional view taken along  3 — 3  of FIG. 2; 
     FIG. 4 is a further enlarged sectional view taken along line  4 — 4  of FIG. 3; and 
     FIG. 5 is a partial underside view of the thermal blanket. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     When used herein, the term “thermal blanket” is intended to be interchangeable with, but not necessarily limited by, the term “airflow cover” used in our U.S. Pat. No. 4,572,188, which is incorporated herein in its entirety by reference. In this description, the term “thermal blanket” is meant to invoke a self-erecting, inflatable structure for delivering a thermally-controlled inflating medium to the interior of the structure created when the thermal blanket is inflated. The purpose of the thermal blanket is to efficiently administer a uniformly thermally-controlled bath of the inflating medium to a patient within the erected structure. 
     Our invention is illustrated as we intend for it to be used in FIG.  1 . In FIG. 1, a self-erecting, inflatable thermal blanket  10  has a head end  12 , a foot end  14  and two lateral edges, one indicated by  15 . An inflation inlet cuff  16  is connected to a heater/blower assembly  18  which provides a stream of heated air through a connecting hose  20 . When the heater/blower  18  is operated, the stream of heated air flows through the inflating hose  20  into the thermal blanket  10  through the inflation cuff  16 . When the blanket is inflated, it erects itself into a Quonset hut-like structure with a quilted upper surface  21 . As described below, a pattern of apertures on the undersurface of the blanket (not shown in FIG. 1) delivers the inflating heated air into the interior space enclosed by the erected thermal blanket. 
     The contour of the inflatable portion of the thermal blanket  10  is varied at the head end  12  of the blanket to provide a non-inflated blanket recess  22  in the quilted upper surface  21 , which remains smooth and flat when the blanket is inflated and erected. Circulation of the heated air is accelerated through the thermal blanket by exhaust port openings in the upper surface, adjacent the lateral edges of the blanket. Two exhaust port openings are indicated by reference numeral  23 . Further, a bib  24  made of an absorbent material is attached to the head end  12  of the thermal blanket in the vicinity of the non-inflated recess  22 . In fact, as shown in FIG. 1, the bib  24  includes a semi-circular tab  25  that extends into the recess  22 . 
     As illustrated in FIG. 1, the thermal blanket of the invention is inflated, erects itself into a bathing structure, and bathes a patient  26  with the thermally-controlled air used to inflate the structure. While the patient is being thermally bathed, the uninflated recess  22  permits observation of the patient&#39;s head, face, neck, and chest from almost any location with respect to the thermal blanket  10 . Thus, if the patient is placed on a gurney or a bed, the head of which is against a wall, a care giver such as a nurse, intern, resident, or doctor, can keep the patient&#39;s face under observation from the foot end  14  of the thermal blanket  10 . Respiration can be detected by the rise and fall of the bib and uninflated area, which rest directly on the patient&#39;s chest. Moreover, the bib  24  will provide an absorbent sink for stray, unconfined liquids in the area of the patient&#39;s head or at the head end  12  of the thermal blanket  10 . 
     FIG. 2 is a plan view of the thermal blanket  10  opened flat to show details of its structure. FIG. 2 illustrates the upper surface of the thermal blanket, that is the side that is visible in FIG.  1 . As seen, the upper surface consists of a parallel array of elongated tubes of which  30  and  32  are the lateralmost tubes,  34  is the center tube, and the tubes  38  are arrayed between one of the lateralmost tubes and the center tube. Each tube is separated from an adjacent tube by a discontinuous seam, one of which is indicated by  40 . The seam  40  separates the tube  32  and its nearest adjacent neighbor  38 . The discontinuous seam  40  is interrupted by passageways  42  communicating between the tubes. An interrupted seam separates every tube from one adjacent neighboring tube. The seams permit the thermal blanket, when inflated, to assume a tubular structure on the upper surface, while the ports  42  permit full circulation of the inflating medium throughout the array of tubes. The foot-end seam  45  is continuous. The tubes are inflated through the center tube  34  which transitions to a port  36 , through which the inflation cuff  16  is inserted. The edge seams  43  are discontinuous only at the exhaust port opening locations  23 . A seal can be made between the inflation port  36  and the inflation cuff  16  by any conventional means, for example, an O-ring, or even tape. When the inflating medium is introduced into the center tube  34 , it flows laterally from the center tube into all of the other tubes through the ports  42 . Near the head end  12 , a continuous seam  40  defines the forward end of all of the tubes, with the seam assuming a bell-curve shape. On the head end side of the seam  40 , the thermal blanket  10  is uninflatable. The bell-shaped seam  40  thus defines the uninflatable area  22  at the head end of the thermal blanket  10 , which is essentially coplanar with, or substantially parallel to, the underside of the blanket. As shown in FIG. 1, by virtue of its structural integration with the rest of the thermal blanket  10 , the non-inflated recess extends over the upper chest of the patient  26  when the blanket is inflated. However, since the recess  22  is uninflated, it provides a wide-angled viewing gap in the inflated contour of the upper surface  21 . The gap is filled by continuation of the underside of the blanket. It is also noted that the pattern of inflatable tubes can be replaced by other suitable patterns of communicating, inflatable chambers. The tubes are preferred since they impart strength and shape to the erected bathing structure; other inflatable structures are contemplated, however. 
     The absorbent bib has an indent  43  cut into its outside edge, which permits the blanket to be drawn up to the chin of a patient and which provides absorbency laterally up the neck of the patient. The absorbent bib can consist of any absorbent material such as a single- or multi-ply tissue paper which is used to make paper towels. 
     Construction details of the thermal blanket  10  are illustrated in FIGS. 3 and 4. The thermal blanket  10  is assembled from a base sheet consisting of an underside layer  50  formed from flexible material capable of bonding to a layer  52  of heat-sealable plastic. For the layers  50  and  52 , we have used a stratum of absorbent tissue paper prelaminated with a layer of heat-sealable plastic. Material of such construction is commercially available in production rolls and is used to make painters&#39; drop cloths. The upper side of the thermal blanket consists of a sheet of plastic bonded to the plastic layer  52  by an interruptible heat-sealing process to form the interrupted seams, one of which is indicated by  54 , and the inflatable tubes, one indicated by  55 . As can be seen in FIG. 3, the interruption of the seam  54  forms a passageway  56  between adjacent tubes  55  and  57 . 
     The absorbent bib and tab are shown in FIG. 3 as a single material layer  60 / 58 . Alternatively, they may be formed from separate material sheets cut to the outlines illustrated in FIG.  2 . The absorbent material forming the bib and tab can be bonded to the upper plastic layer by heat process or by gluing. 
     The inventors also contemplate deletion of the bib and tab. In this instance, the thermal blanket would still have the viewing recess, which would be defined by the continuous seam at the head end, and which would be filled with the forward portion of the base sheet. 
     Circulation of heated air through the blanket is enhanced by the exhaust port openings  23 , which open through the upper plastic sheet sheet, which is heat sealed to the base of the blanket. The openings  23  vent the heated inflating air out of the outermost tubes  30  and  32 , away from the underside of the blanket. Because air can circulate to, and through, the blanket edges, the inflating air in the outermost tubes is hotter than if the openings were absent. This results in hotter air being delivered through the underside apertures toward the edge of the blanket. We have measured the temperature distribution within the thermal blanket for inflating air which is heated to a medium temperature range and for inflating air which is heated to a high temperature range. The results are provided in Table I for a blanket consisting of 13 tubes. Measurements of the temperature of air exhausted through underside apertures were made on the underside of each tube on one side of the blanket. The tubes are numbered  1 - 6 , with  1  being the tube adjacent to the center tube, and tube  6  being the outermost tube adjacent on lateral edge of the blanket. Test apertures were made in the bottom of tube  6  only for the purposes of this test. As is evident, the distribution of temperature within the erected thermal blanket is more uniform when the exhaust port openings are provided. Further, provision of the exhaust ports also increases the average temperature within the erected structure of the blanket. Clearly, the provision of exhaust port openings at the lateral edges of the blanket delivers results which one would not expect when considering the operation of our thermal blanket with no exhaust port openings. 
     In our preferred embodiment, the exhaust port openings are slits in the edge seams of our blanket. These slits vary in length from 1¾ to 2 inches. Each edge seam is discontinuous approximately at each corner of the blanket so that inflating air is vented away from the underside of the erected blanket. This keeps the relatively “colder” air at the blanket edges from mixing with the relatively “hotter” air exhausted into the structure through the underside apertures. The result is a “flatter” temperature profile of air within the blanket than without the vents, which raises the average temperature within the erected structure and makes the temperature distribution in the structure more uniform. Resultantly, the clinical effect of the blanket is enhanced. Heating is better controlled, and more uniform, with greater comfort to the patient. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE I 
               
             
             
               
                   
                   
               
               
                   
                 MEDIUM TEMPER- 
                   
                 HIGH TEMPER- 
               
               
                   
                 ATURE RANGE 
                   
                 ATURE RANGE 
               
             
          
           
               
                   
                 WITHOUT 
                 WITH 2″ 
                 WITHOUT 
                 WITH 2″ 
               
               
                   
                 EXHAUST 
                 EXHAUST 
                 EXHAUST 
                 EXHAUST 
               
               
                 TUBE NO. 
                 PORTS 
                 PORTS 
                 PORTS 
                 PORTS 
               
               
                   
               
               
                 center (inlet) 
                 113.3° F. 
                 114.1° F. 
                 121.3° F. 
                 121.3° F. 
               
               
                 tube 
               
               
                 Tube #1 
                 109.9° 
                 112.3° 
                 117.3° 
                 117.7° 
               
               
                 Tube #2 
                 105.3° 
                 109.8° 
                 113.4° 
                 115.0° 
               
               
                 Tube #3 
                 103.2° 
                 107.1° 
                 111.0° 
                 113.3° 
               
               
                 Tube #4 
                  99.9° 
                 104.3° 
                 101.4° 
                 108.6° 
               
               
                 Tube #5 
                  97.2° 
                 100.0° 
                  95.7° 
                 104.4° 
               
               
                 Tube #6 
                  85.2° 
                  95.8° 
                  89.6° 
                  99.4° 
               
               
                 (outermost) 
               
               
                 Average 
                 103.8° 
                 106.7° 
                 108.4° 
                 112.5° 
               
               
                 temp. 
               
               
                 under cover 
               
               
                   
               
             
          
         
       
     
     The thermal blanket of the invention is enabled to bathe a patient in the thermally-controlled inflating medium introduced into the upper side tubes by means of a plurality of apertures  62  shown in FIGS. 4 and 5. The apertures extend through the underside of the blanket, which includes the layers  50  and  52 . The apertures  62  are made in the footprints of the tubes of the blanket upper side according to a pattern which has been determined to deliver a very uniform thermal bath. In this regard, no apertures are provided through the underside into the lateralmost tubes  30  and  32 , or into the center tube  34 . In addition, the apertures  62  are provided through the underside to the apertured tubes in a density which varies inversely with the proximity of the tube to the center tube  34 . Thus, the hole density increases from the tube  38   a  through the tube  38   d . Even with the exhaust port openings, the temperature of the inflating medium exhibits a drop from the center to the lateralmost tubes. The varying density of the apertures  62  tends to reduce this gradient further by forcing hotter air to the edges of the blanket. Thus, the thermal bath delivered to the patient is of a generally uniform temperature. The aperture density variation also equalizes the flow of inflating medium out of the apertures. As will be evident, the inflating pressure will be greatest at the center tube  34  and will tend to diminish toward the lateral edges of the thermal blanket. Therefore, fewer apertures are required for the tubes near the center tube  34  to deliver the same amount of air as the relatively greater number of apertures in the tubes at a greater distance from the center tube  34 . 
     The apertures comprise openings which can be of any appropriate shape. For example, we have produced blankets with elongated apertures, approximately ¼ inch in length. 
     Many modifications and variations of our invention will be evident to those skilled in the art. It is understood that such variations may deviate from specific teachings of this description without departing from the essence of the invention, which is expressed in the following claims.