Abstract:
A thermal retention hood for reducing heat loss from a patient&#39;s head during and following surgery includes an enclosure configured to cover the face and head of the patient, and configured to retain heat within the enclosure. The enclosure is at least partially transparent, to give a practitioner visual access to a patient&#39;s face. The hood further includes a scored line in the enclosure in a position corresponding to the patient&#39;s nose and mouth, a second scored line surrounding a region of the enclosure corresponding to the location of the patient&#39;s face, and a strap configured to secure an open end of the enclosure around the patient&#39;s neck. The hood may also include an absorbent pad within the enclosure, positioned to cover a portion of the back of the patient&#39;s head to absorb excess moisture.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a surgical hood, and more particularly to a patient hood for retaining heat during surgery and recovery and to provide access for visual inspection and treatment. 
   2. Description of the Related Art 
   Recent clinical studies have demonstrated that mild perioperative and postoperative hypothermia is associated with several significant adverse effects on patient health. For example, in cases in which the core body temperature of a patient is moderately depressed, surgical wounds have been shown to heal more slowly, and be more susceptible to infection; duration of hospitalization may be two to three days longer, on average; blood loss during surgery is increased; incidences of serious cardiac complications are significantly more common; postanesthetic recovery is longer; and patient comfort during recovery is significantly reduced. 
   Maintaining a patient&#39;s core temperature during surgery can be a significant problem, inasmuch as the patient&#39;s metabolism is typically depressed due to anesthesia, and surgical theaters are commonly maintained at a relatively cool temperature, for the comfort of the surgical team. Meanwhile, the patient is commonly lightly draped, with portions of the patient&#39;s body exposed to the cool environment. Additionally, in cases where the patient is undergoing major surgery, the patient may lose significant body heat directly from the surgical site. Studies have also shown that the face and upper chest are far more sensitive to temperature loss than other regions of the body. 
   Body heat is lost by a combination of four sources: 
   (a) Conduction heat loss is the passage of heat energy from one mass to a cooler mass in direct contact therewith. In the case of a human body it occurs when a portion of the body is in contact with a surface or medium that is colder than that portion of the body. Heat is conducted from the warmer region to the colder region, thus drawing heat away from the body. In a cool environment, air in contact with the body will draw heat from the body. 
   (b) The second source of thermal energy loss is convection. Convection occurs in a fluid when one portion of the fluid is warmer than another, causing motion in the fluid, as the warmer, less dense, fluid rises, while the colder, denser fluid drops. Convection occurs in conjunction with conduction, when fluid, such as air, is warmed in a localized area by conduction through contact with a warmer mass, and is then carried away from the heat source by convection, which draws cool air into contact with the mass. Convection is also used to describe heat transfer due to motion or circulation of fluid by other sources. Thus, convection heat losses in a body increase when portions of the body are exposed to moving or circulating air that is cooler than the body. 
   (c) A third source of heat loss is evaporative heat loss. Evaporative heat loss occurs when a fluid in contact with a surface evaporates into the surrounding atmosphere. The energy required for the fluid to transition from a liquid state to a gaseous state is significant, and it is generally drawn from the surface in the form of heat. The human body&#39;s normal heat regulatory system exploits this phenomenon by producing sweat. As sweat evaporates from the skin, the skin is cooled, Thus, by conduction the body core temperature is regulated. During the course of a surgical procedure, cleansers, disinfectants, and other fluids are placed in contact with the body, together with the sweat that is normally produced. Heat is thus drawn from the body due to conduction and evaporation. 
   (d) The fourth source of heat loss is radiation. Radiation, mostly in the infrared spectrum, propagates outward from a warm mass and is a function of the absolute temperature of the mass, regardless of the ambient temperature, and, unlike the other three sources, is independent of any transmission medium. Radiation heat loss occurs when the energy radiated from a body exceeds heat either produced by the body or taken in by the body from other sources, such as conduction and convection. 
   Of the four sources of heat loss, conduction and convection contribute the most to the loss of core body temperature during surgery. An extensive examination of the causes and effects of heat loss to patients may be found in an article entitled  Complications and Treatment of Mild Hypothermia  ( Anesthesiology , V95, No. 2, August 2001). 
   Methods and devices for mitigating the loss of heat during and immediately following surgery include the use of thermal blankets of various designs, which are placed around the patient during or following surgery. Also known is the use of heated surfaces on which a patient is placed during surgery. In U.S. Pat. No. 5,877,279, issued to Elting et al. on Mar. 30, 1999, a surgical garment is disclosed in which a patient is draped with a lightweight garment having several components that covers most of the body. The garment includes a hood that is configured to cover the top and the back of the patient&#39;s head, while leaving the patient&#39;s face exposed. However, this solution is incomplete, inasmuch as a significant percentage of heat loss occurs at the patient&#39;s face. This has been recognized, and occasional informal attempts have been made to address this issue. For example, in some cases practitioners have improvised by placing a plastic trash bag over a patient&#39;s head and face during surgery to prevent this heat loss. 
   There are, however, several drawbacks with using plastic bags. The bag obscures the patient&#39;s face, which should be visible to the anesthesiologist for the purpose of monitoring the patient&#39;s condition. The bag tends to be generally unwieldy and difficult to situate and typically the patient will have an endotrachial tube in the nose or throat, requiring an opening in the bag to permit passage of the tube. It is at least uncomfortable, and possibly dangerous for a patient to wear such a bag while conscious, such as during procedures requiring only local anesthesia or during recovery. 
   These and other disadvantages, including the difficulty of appropriately configuring such a bag, and the danger to the patient imposed by the obscuring of the patient&#39;s face, make the use of a plastic bag less than ideal. 
   BRIEF SUMMARY OF THE INVENTION 
   The disclosed embodiments of the invention provide a thermal retention hood for reducing all forms of heat loss from a patient&#39;s head during and following surgery. The hood includes a translucent or transparent plastic enclosure configured to cover the face and head of the patient in order to retain heat within the enclosure and limit heat loss due to the various sources described in the background section, above. The hood further includes a scored line in the enclosure in a position corresponding to the patient&#39;s nose and mouth, a second scored line surrounding a region of the enclosure corresponding to the location of the patient&#39;s face, and a strap configured to secure an open end of the enclosure around the patient&#39;s neck. The hood may also include an absorbent pad within the enclosure, with the pad positioned to cover a portion of the back of the patient&#39;s head to absorb excess moisture and retain heat. 
   According to another embodiment of the invention, a method of retaining body heat during surgery is provided, the method including the steps of trapping a layer of still air against the head and face of the patient by covering the patient&#39;s head and face with a plastic hood, inserting a tube into patient&#39;s nose or mouth via an opening provided in the hood, and tensioning a strap attached to the hood under the patient&#39;s chin to close the hood. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       FIG. 1  shows a front view of a thermal retention hood in place on a patient&#39;s head according to one embodiment of the invention; 
       FIG. 2  shows a profile view of the embodiment of  FIG. 1 ; 
       FIG. 3A  shows a front view of a section of the hood according to another embodiment of the invention; and 
       FIG. 3B  shows a front view of a section of the hood according to an alternate embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A thermal retention patient hood is disclosed and described with reference to  FIGS. 1-3B . 
   In  FIG. 1  a patient  102  is shown from the front wearing a thermal retention hood  100  according to the principles of the invention. The hood  100  is formed from a suitable transparent plastic material such as polyethylene having a thickness of around 2 mils and is configured to be drawn over, and conform to, the shape of a normal sized adult human head, via an opening  103  at a bottom portion  105  of the hood  100 . Although not shown, it will be understood that the thermal retention hood  100  may incorporate the use of gussets, tucks, darts, or other known methods of tailoring the hood to conform to the shape of a human head, and such methods will not be discussed in detail here. 
   The thermal retention hood includes a perforated line  108 . A portion of the line  108  may be separated by gently pulling on either side of the line to create a hole  109  to provide access to the patient&#39;s mouth or nose.  FIG. 1  shows an endotrachial tube  112  passing through the hole  109  and into the patient&#39;s mouth. Preferably the line  108  is vertical, but in some embodiments it may be desirable to use a horizontal line. 
   A second perforated line  106  defines a face panel  107  that is sized and shaped to cover the patient&#39;s face. By tearing along this line, the face panel  107  may be removed from the hood, thereby uncovering a portion of the patient&#39;s face while maintaining coverage over the majority of the face and head. In this way, the areas of the patient&#39;s face to which access is needed will be uncovered during recovery or during the performance of surgical procedures that require only local anesthesia. This gives the patient some freedom while maintaining coverage and heat retention over most of the patient&#39;s head. 
   Ideally, perforations are used to provide separability of the material of the hood  100 . However, other weakening structures, such as scores or creases may be employed to permit controlled separation of the material. As used herein, the word score is used inclusively for such structures. 
   A strap  104  is attached to one side of the hood  100 , and is configured to be drawn under the patient&#39;s chin and attached to the opposite side of the hood  100 , thereby securely attaching the hood  100  to the patient&#39;s head.  FIG. 2  shows a patch of adhesive  110  that may be provided on the strap  104 . Alternatively, the strap  104  may be affixed under the patient&#39;s chin using hook and loop fasteners (Velcro™) or surgical tape, which is commonly available. 
     FIG. 2 , which is a profile view of the embodiment of  FIG. 1 , shows a panel of absorbent material  114  affixed to or comprising the back of the hood  100 . In one embodiment, the panel  114  is formed from material configured to absorb moisture and hold moisture in a central layer and remain relatively dry on a top layer, thus preventing fluid from passing through to the back side. In this application, the top layer is the side in contact with the back of the patient&#39;s head  102 , while the backside is on the outside of the hood  100 . One such material is commonly known in the industry as chux. The absorbent panel  114  functions to absorb moisture resulting from sweat and condensation within the hood  100 , allowing the patient  102  to remain relatively dry. 
   According to one embodiment of the invention, the back section  118  of the hood  100  includes a heat reflective surface, such as Mylar™ to reduce radiant heat loss. 
   The front and back sections  120 ,  118  of the hood  100  can be formed from different kinds of material or fabric. It is desirable, however, that the front section  120 , or at least the portion of the hood defined by the face panel  107  in the embodiment of  FIGS. 1 and 2 , be transparent or translucent to permit proper monitoring by a practitioner. 
     FIG. 2  also shows a welded line  116  passing from one side of the hood  100  to the other, marking the location where front and back sections  120 ,  118  of the hood  100  are welded together. As has been previously explained, the actual shape of the sections and configuration of weld lines are selected to permit the hood  100  to conform to the shape of a human head  102 . 
     FIG. 3A  shows a front section  120   a  of the thermal retention hood  100  according to one embodiment of the invention in which the strap  104   a  is shown as being defined from the rest of the front section  120   a  by a cut line  122 , encompassing most of the width of the front section  120   a  of the hood  100 . A region  130  on one side of the front section  120   a  remains uncut by the line  122  and defines a portion of the hood  100  where the strap  104   a  remains attached to the hood  100 . A small tab  124  on the opposite end  127  of the strap  104  is provided to hold the strap  104   a  in position during the manufacturing process and during storage. A pressure sensitive adhesive patch  110  is provided on the inside of the strap  104   a  of the hood  100  and covered by a liner (not shown). In use, when the hood is to be attached to a patient the tab  124  is easily broken, permitting the end  127  of the strap  104   a  to be pulled away from the rest of the hood. The practitioner peels the liner from the pressure sensitive patch and draws the strap  104   a  more tightly under the chin of the patient. The pressure sensitive adhesive patch  110  is then pressed to a portion of the hood  100  on the opposite side of the patient&#39;s neck. 
   A notch  126  is provided in the front section  120   a  of the hood  100  such that, when the front section  120   a  is joined with the back section  118  of the hood  100  along weld line  116 , the extreme end  127  of the strap  104   a  is not welded to a corresponding portion of the back section  118  of the hood  100 . Thus, the end  127  of the strap is free to be tightened. 
   The perforated lines  106   a ,  108  are shown intersecting the cut line  122 . A small portion of the perforated line  108  may be separated to provide passage for an airway tube. Upon separation of the perforated line  106   a  and removal of the face panel  107 , the face panel  107   a  can be removed from the airway tube by separating the remainder of the perforated line  108 . 
   It will be observed that all the cuts and perforations of the front section  120   a  of the hood may be made in a single manufacturing step. 
     FIG. 3B  shows the front section  120   b  of the hood  100  according to an alternative embodiment. In the embodiment of  FIG. 3B , the strap  104   b  is a separate piece of material. When the front section  120   b  is affixed to the back section  118  of the hood  100  at the weld line  116 , the edge  132  of the strap  104   b  is welded to the hood in the position indicated by phantom lines in FIG.  3 B. This is done at the same weld line  116  in the same manufacturing step that welds the front section  120   b  to the back section  118 . 
   The perforated line  108  over the patient&#39;s mouth and nose is provided as described in previous embodiments. The perforated line  106   b  is in the form of an oval that corresponds to the position of the patient&#39;s face while wearing the hood  100 . As previously described, this oval section  107   b  may be completely removed for the convenience of the surgeon or the patient. The adhesive patch  110   b  on the inside of the strap  104   b  is ideally formed of a relatively low tack adhesive. During manufacture, the adhesive patch  110   b  is applied to the strap  104   b  and employed to hold the strap flat against the front surface of the front section  120   b . In use, the practitioner lifts the end  127  of the front strap  104   b  having the adhesive patch  110   b , releasing the end  127  from the surface of the hood  100 , and draws the strap further around the side of the patient&#39;s head or neck, while gathering the loose material of the hood  100  under the strap  104   b  beneath the patient&#39;s chin. The practitioner then presses the pressure sensitive adhesive patch  110  to a portion of the hood  100  on the opposite side of the patient&#39;s neck, as previously described with reference to other embodiments. The embodiment of  FIG. 3B  requires an additional manufacturing step to produce the strap, but provides a more complete coverage of the patient&#39;s face, inasmuch as the hood is sealed around the patient&#39;s neck by the strap  104   b.    
   According to another embodiment of the invention, the hood  100  is provided with an elastic closure (not shown) around the bottom portion  105  of the hood. The elastic closure is attached around at least a portion of the circumference of the hood opening  103 , sufficient to draw the opening close around the patient&#39;s neck, without tension enough to endanger the patient&#39;s airway or circulation. Naturally, in this embodiment, the strap  104  is not necessary to provide a secure attachment. 
   A key factor to effective heat retention is the trapping of an insulative layer of still air between the insulator and the skin, which the thermal retention patient hood does very effectively. Studies have shown that virtually any passive insulator reduces heat loss from skin surfaces by a significant amount, and that plastic is substantially as effective an insulator as other materials such as cotton, polypropylene fabric, or metalized plastic. Plastic, however, is superior to other materials in several respects. First, thermal retention hoods made from plastic of a type commonly used for the manufacture of bags, such as polyethylene in a range of around 1 to 4 mils thickness, is significantly less expensive than other materials. Additionally, thermal retention hoods made from lightweight plastic are very compact, and large numbers may be stored in a small space, as compared to the space required to store more expensive and bulkier fabric products. Thus, boxes of disposable thermal retention hoods may be purchased and stocked by surgical facilities at very low cost. 
   Polyethylene has been indicated for use in the manufacture of the hood  100 . However, it will be recognized that any suitable material may be used to produce the hood, including other common formulations and thicknesses of plastics, fabrics, such as cotton, gor-tex™, polypropylene, and polyester, and non-woven material, such as Tyvek™. 
   While the thermal retention patient hood  100  has been described with reference to an adult sized hood, it will be recognized that the hood  100  may be configured to conform to heads of various sizes. For example, a hood  100  may be made to conform to the head of a very small infant, child, or of an adolescent or small adult. Accordingly, variations in the size or shape of a hood are considered to fall within the scope of the invention. 
   A temperature-sensing device may be affixed to an inner surface of the thermal retention hood  100  such that, when the hood is correctly positioned on a patient&#39;s head, the thermal retention device will be in contact with the patient&#39;s skin, usually the forehead, thereby providing the practitioner with a constant temperature reading. 
   All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. 
   From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.