Abstract:
Certain embodiments pertain to a heater for warming a patient&#39;s extremity in order to cause vasodilation for facilitating venous catheterization.

Description:
PRIORITY CLAIM  
       [0001]     The present application claims priority to provisional application Ser. No. 60/722,241 entitled: DISPOSABLE SLEEVE AND ELECTRIC HEATER FOR ASSISTING IN INTRAVENOUS CATHERIZATION, filed on Sep. 29, 2005 and to provisional application Ser. No. 60/722,256 entitled: HEATING CUFF, also filed on Sep. 29, 2005, each being hereby incorporated by reference in its entirety.  
       RELATED APPLICATION  
       [0002]     The present application is related to the following commonly assigned utility patent application, filed concurrently herewith, and which is hereby incorporated by reference in its entirety: DISPOSABLE SLEEVE FOR ASSISTING IN VENOUS CATHETERIZATION, Practitioner Docket No. 49278.2.8.2. 
     
    
     BACKGROUND  
       [0003]     Catheterization of human veins with needles and catheters is a common medical procedure. Clinicians frequently need to access patients&#39; veins in order to draw blood for laboratory testing or for placement of intravenous (IV) catheters, for the administration of medicines, fluids or blood.  
         [0004]     Catheterization is typically accomplished by placing a rubber tourniquet around an extremity, for example a forearm, proximal to the planned point of catheterization. The tourniquet causes compression of the superficial veins without compressing the associated arteries. Therefore, the blood is pumped through the arteries past the tourniquet into the distal extremity. Since the veins are compressed, the blood is prevented from returning to the heart. The veins typically dilate due to the increased intravascular pressure and are thus more visible and easier to access with the needle or catheter. Once the dilated vein is identified, the skin is cleaned and usually numbed with a local anesthetic. The needle or catheter is then inserted into the dilated vein.  
         [0005]     Catheterization can be difficult to accomplish in infants and children, obese patients, patients with darker skin, IV drug abusers and patients receiving chemotherapy for cancer. Additionally, any patient can be difficult to cannulate if he or she is cold, frightened, apprehensive or dehydrated. This commonly occurs in patients that are injured or are about to undergo surgery. In these situations, veins are actively constricted by the sympathetic nervous system and, therefore, will not dilate in response to an increase in intravenous pressure. Even the application of a tourniquet may not cause the veins to visibly dilate.  
         [0006]     It has been known that application of heat to the skin of a forearm helps to reduce vasoconstriction and dilate veins. Traditionally, heat has been applied by soaking towels in warm water and then wrapping the towel around a forearm. However, the use of wet towels has several significant drawbacks. The wet towels quickly cool. The wet skin experiences an evaporative heat loss that may actually cool the skin. The water is messy and may cause the skin to macerate. Therefore, the use of we towels has many significant deficiencies in effectiveness and convenience.  
         [0007]     Electric heating pads have also been used for heating the skin of the forearm to aid IV catheterization. Electric heating pads do not have the cooling and messy problems associated with wet towels. However, electric heating pads may not be hot enough to achieve rapid vasodilation. If they are hot enough, the high temperature may inadvertently be applied for too long, risking thermal injury. Electric heating pads are difficult to wrap snuggly around the forearm and, therefore, typically do not maintain good contact with the skin for optimal conductive heat transfer.  
         [0008]     Forced air patient blankets such as the Bair Hugger® blanket (distributed by Arizant Inc., Eden Prairie, Minn.), have also been used to warm the arms of patients for starting IVs. Such blankets are wrapped around a patient and then inflated with warm, forced air. However, the warm air cools inside of the blanket and does not remain warm enough to cause rapid vasodilation. Clinicians have attempted to avoid this cooling of forced air by blowing warm air directly onto a patient without using a blanket (a process known as “hosing”). However, hosing is not recommended because the direct contact of warm air with skin increases the risk of thermal burns. Moreover, the forced air is supplied by noisy blowers that are relatively energy-inefficient and complicated.  
         [0009]     A loose fitting mitt made of carbon fiber conductive fabric has also been used. Lenhardt et al. published a study (in British Medical Journal 325:409, August 2002) that evaluated the effectiveness of such a loose fitting mitt. The mitt was heated to 52° C. and applied to patients for 15 minutes prior to starting an IV. The success rate for catheterization was 94% compared to 72% for an unheated control group. Warming the hand and forearm with a loose fitting mitt appeared to be useful for improving the success rate of catheterization. However, the required 15 minutes of warming time may be too long to be practical in clinical settings. In addition, an increase in temperature could subject the patients to a risk for thermal burn injuries. Additionally, the loose fitting mitt does not optimize conductive heat transfer to the skin because it does not conform to the skin to maximize skin-heater contact.  
         [0010]     The prior art heaters have several drawbacks. Some of the heaters have rigid structures or loose fitting structures, which are undesirable because they do not conform to a patient&#39;s extremity. For example, a patient with a smaller arm may not have very much skin in contact with a loose fitting or rigid heater. This prevents optimal heat conductive heat transfer between the heater and the skin. Some of the heaters are also unnecessarily complicated and include a variety of support structures, chambers, forced air devices, suction devices and the like. Complicated heaters are difficult to apply to a patient during a clinical setting and delay the overall dilation time. Complicated heaters may also intimidate a patient.  
         [0011]     Prior art heaters either do not heat at temperatures or lengths of time appropriate for rapid venous dilation, which is beneficial in a clinical setting. For instance, some prior art heaters heat at too low of temperatures or for insufficient lengths of time. The heaters also do not include a timing device to limit the duration of exposure to heat, thereby increasing the risk of thermal injury to a patient&#39;s skin. In addition, some of the heaters are provided in direct contact with a patient&#39;s extremity and must be cleaned between patients to avoid cross-contamination. A patient&#39;s bodily fluids may contaminate the heater and must be cleaned before the heater is used on the next patient. The cleaning of medical equipment is both expensive and inefficient.  
         [0012]     There is a need for an improved heater that is simple to apply, is easy to clean, achieves rapid dilation, optimizes heat transfer, and/or reduces the risk of thermal injury. Certain embodiments of the invention described below solve one or more of the limitations of the prior art described above.  
       SUMMARY  
       [0013]     Certain embodiments pertain to a heater for warming a patient&#39;s extremity in order to cause vasodilation for enhancing venous catheterization. Such a heater can also be used for improving venous blood flow during chemotherapy. Additionally, such a heater can be used for causing vasodilation and optimizing blood flow in patients with Reynaud&#39;s disease, post vascular surgery, skin grafting, appendage reattachment surgery, post-hemodialysis, blood donation, wound treatment, or other situations. Certain embodiments optimize the conductive heat transfer, allowing the temperature of a heating device to be minimized, thereby reducing the risks of thermal burns, and allowing the heating time to be reduced, thereby improving the practicality and effectiveness of the device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a top view of a heater according to an embodiment;  
         [0015]      FIG. 2  is a section view of a heater according to an embodiment;  
         [0016]      FIG. 3  is a side perspective view of a heater formed as a heating cuff and arranged on an extremity according to an embodiment;  
         [0017]      FIG. 4  is a cross-section view of a heating cuff having its sides connected together according to an embodiment;  
         [0018]      FIG. 5  is a cross-section view of a heating cuff having a flap for connecting its sides together according to an embodiment;  
         [0019]      FIG. 6  is a perspective view of a heating cuff according to an embodiment;  
         [0020]      FIG. 7  is a side perspective view of a heating cuff in an unfastened position and arranged on a forearm according to an embodiment; and  
         [0021]      FIG. 8  is a side perspective view of the heating cuff in a fastened position and arranged on a forearm according to an embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0022]     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.  
         [0023]      FIGS. 1-2  illustrate a heater  100  according to one embodiment. The heater  100  includes a heating element  10  enclosed between a first layer  13 A and a second layer  13 B. The layers  13 A,  13 B are sealed together about a generally rectangular perimeter  11  to hold the heating element  10  therebetween. While the illustrated perimeter  11  is shown as a rectangle, the perimeter can have any suitable size and shape to accommodate the length of an extremity, for example a patient&#39;s forearm and hand. The layers  13 A,  13 B can be sealed together using any mechanism known in the art. In some cases, the heating element  10  is embedded in, or attached to, one of the layers  13 A,  13 B. The layers  13 A,  13 B are comprised of any material. In some cases, the layers  13 A,  13 B are made of a water-resistant or water-proof material. An antimicrobial substance can be provided on the layers  13 A,  13 B to prevent the spread of germs between patients. Examples of anti-microbial substances include but are not limited to metals such as silver or copper and other antimicrobial chemical agents.  
         [0024]     The heating element  10  may comprise any heating mechanism known in the art. In most cases, the heating element  10  includes a flexible material, for example a flexible wire. In the illustrated embodiment, the heating element  10  is a single wire (e.g., an electrically resistive wire) routed throughout the area of the heater. Of course, the element  10  can alternately be a matrix of wires. Likewise, other resistive heating elements can be employed, examples of which include, but are not limited to carbon fiber and carbonized fiber fabrics and other conductive fabrics such as those coated with conductive materials such as polypyrrole or conductive inks. In some cases, fabric incorporates a matrix of wires or closely spaced conductive heating elements.  
         [0025]     In some embodiments, the heater  100  is used with a forearm and hand, and the heat element  10  is configured so that it has a watt-density greater in the area in contact with the forearm compared to the area in contact with the hand. The forearm has a greater mass than the hand and therefore acts as a greater heat-sink. Increasing the watt-density to the forearm optimizes the heat transfer to both areas.  
         [0026]     A cord  12  extends from heating element  10  to a unit  15  that includes a temperature control and power source. The temperature control can include one or more temperature settings and a timer for the temperature settings. At least one of the temperature settings is set high enough to achieve rapid venous dilation and the timer is set to prevent that high setting from being applied so long as to cause thermal injury. In some cases, the high temperature setting is at least 52° C. and the timer has a time period of less than 15 minutes for the high setting.  
         [0027]     The relatively high temperature causes more rapid and effective vasodilation without risks of thermal injury. The susceptibility of skin to thermal injury is determined by the combination of temperature and time. High temperatures are tolerated for short periods of time. The skin temperature does not come close to equilibrating with the temperature of the heater during the short heating period. For example, when the heater is applied to a forearm, the thermal mass of the tissue in the forearm and hand act as a heat sink and the blood flow rapidly removes the excess heat. Additionally, there is a high degree of thermal resistance between the heater and the skin as compared to the thermal resistance between the skin surface and the deeper layers of tissue which is blood flow regulated.  
         [0028]     In one embodiment, the temperature control includes a first temperature setting. The unit  15  is also provided with a timer that is configured to maintain the first temperature setting for a given time period. A switch is also provided on the unit  14  that is coupled to the temperature control and is configured to switch from the first temperature setting to an off setting or to an optional second temperature setting when the time period expires. The optional second temperature setting is lower than the first temperature setting. The first temperature setting can be between about 52° C. and about 70° C., for example about 60° C. The optional second temperature setting can be between about 40° C. and about 50° C., for example about 45° C. The time period can be less than about 15 minutes to avoid thermal damage to the forearm. In some cases, the time period is in a range extending from about 7 minutes to about 10 minutes. In other cases, the time period is less than 15 minutes. Once the time period expires, the first temperature setting switches to an off setting or to the second temperature setting. The second temperature setting, if used, can maintain the state of vasodilation achieved by the first temperature setting for a period of time that a clinician may need to, for example, set up an IV. In some embodiments, a signal is provided (e.g., a light or sound) on the unit  15  to alert a clinician when the time period for the first temperature setting is complete.  
         [0029]     The unit  15  and described temperature control system can be used with any appropriate heater known in the art, not just the illustrated heater. In some embodiments, a clinician places a heater having the described temperature control system over an extremity and heats a heating element of that heater to a first temperature for a given time period. Once the given time period expires, the clinician turns the element off or heats the element to a second temperature, the second temperature being lower than the first temperature. The first temperature setting can be between about 52° C. and about 70° C., for example about 60° C. The optional second temperature setting can be between about 40° C. and about 50° C., for example about 45° C. The time period can be less than about 15 minutes or less than about 10 minutes to avoid thermal damage to the forearm.  
         [0030]     With reference to  FIG. 2 , a compressible material  14  can be disposed between the heating element  10  and one of the layers  13 A,  13 B. In some embodiments, the compressible material  14  is positioned between the element  10  and the layer which is not in contact with the patient extremity. For example, in  FIG. 2 , layer  13 A serves as an outer layer and layer  13 B serves as an inner layer in contact with the patient extremity. Examples of suitable compressible materials include but are not limited to foam rubber, foam plastic and a high loft non-woven polymeric material.  
         [0031]     When the heater  100  is secured around the extremity, the compressible material  14  presses against the heating element  10  and presses it into closer contact with the skin. This close contact with the skin optimizes conductive heat transfer from the element  10  to the skin and optimizes the efficiency of the heat transfer for any given temperature. The efficient heat transfer allows the heater to be operated at lower temperatures and still be clinically effective. The close contact also maximizes the uniformity of the temperature across the heater. This is important because areas of the heater that do not contact the skin can undesirably become excessively hot. The compressible material  14  also helps to make the fit more comfortable for the patient.  
         [0032]     Alternately, or additionally, the heater  100  can include a heat permeable standoff material (not shown), to diffuse heat from heating element  10  towards the layer  13 B in contact with the extremity. For example, a metal foil can be provided.  
         [0033]      FIG. 3  illustrates a heater  100  that has been rolled into a cuff  200 , which encloses an extremity  19  in a generally tubular cavity. The cuff can be held in place around the extremity  19  using any known mechanism. For example,  FIG. 4  illustrates an embodiment wherein the side edges  21  of the heater  100  are connected together to form a cuff  200 . In some cases, the edges  21  are sewn together to form cuff prior to fitting the cuff onto the extremity. Alternatively, side edges  21  are connected together using reversible fasteners, for example hook-and-loop, snap-fit, button, buckle, ties and adhesive fasteners after having rolled heater  100  about the extremity.  
         [0034]      FIG. 5  illustrates an embodiment wherein one side edge includes a flap  23  containing a fastener  25 A that connects to a corresponding fastener  25 B located on an external part of layer  13 A. In some cases, fasteners  25 A,  25 B are hook-and-loop fasteners. If a compressible material  14  is provided in between the first layer  13 A and the heating element  10 , the act of connecting and tightening the fasteners  25 A,  25 B compresses the compressible material  14 , which in turn presses the heating element  10  in closer contact with the skin.  
         [0035]     In some embodiments, a distal end  29  of the cuff  200  is closed, for example by sewing one or more edges of the distal end together. This creates a cuff that is closed on three sides. The proximal end is left open so that the extremity can be inserted into the cuff.  
         [0036]      FIGS. 6-8  illustrate a heater formed as a generally tubular cavity or cuff  300  according to one embodiment. Although not shown in these Figures, it should be understood that cuff  300  includes a heating element disposed therein. Again, the heating element can be any heating mechanism element known in the art. In some cases, the heating element is configured according to the embodiments described in conjunction with  FIGS. 1-5 , although this is not required. The heater design shown in  FIGS. 6-8  is advantageous because it is simple and easy to apply to a patient forearm. The heater is also flexible and conforms to any size and shape of forearm. The heater is also designed to completely surround the forearm and hand, in order to optimize the heat transfer and provide for a rapid venous dilation.  
         [0037]      FIGS. 6-8  illustrate a heater formed as a cuff  300  including an inner surface  32  and an outer surface  33 . A heating element is disposed inside of the cuff  300  in between the outer surface  32  and inner surface  33 . According to some embodiments, an additional material, for example a compressible material  14  as described in conjunction with  FIGS. 1-5 , is also enclosed between the outer surface  33  and the heating element. Likewise, in some embodiments, the inner and outer surfaces  32 ,  33  can be configured as the layers  13 A,  13 B described in conjunction with  FIGS. 1-5 , although this is not required.  
         [0038]     The cuff  300  forms a generally tubular cavity  38 . A proximal edge  34  of the cuff forms a proximal end opening of cavity  38 . Likewise, a first side edge  36  and a second side edge  37  form a closable side opening of the cavity  38 . A distal edge  35  is closable and seals the distal end of the cavity  38  to trap a patient&#39;s hand within the cavity. A patient inserts his or her hand into the cavity  38  through the proximal end and side openings. Although  FIGS. 6-8  illustrate a closed distal edge  35  extending distally from side opening formed by first and second sides  36 ,  37 , and around a distal end of cavity  38 , the extent of closed distal edge  35  can vary being either more extensive or less extensive. Closed distal edge  35  can be a bonded or sewn junction or can be a zipper junction. In certain cases, the distal edge  35  is permanently closed.  
         [0039]     The second side edge  37  includes a side flap  31  extending laterally therefrom. In some cases, the flap  31  can simply be an extension of the shell  300 . The flap  31  wraps over the side edge  36  and is secured to the outer surface  33 . The flap  31  and outer surface  33  can be connected together using reversible fasteners, for example hook-and-loop, snap-fit, button, buckle, ties and adhesive fasteners. In the illustrated  FIGS. 6-8 , the flap  31  is provided with a fastener  41  that connects to a corresponding fastener  42  located on the outer surface  33 . In some cases, fasteners  41  and  42  are hook-and-loop fasteners. After the patient&#39;s hand is inserted into the cavity  38 , the flap  31  is wrapped over side edge  36  and fastener  42 A is secured to fastener  42 B. After use, the fasteners are released and flap  31  is pulled off the outer surface  33  to expose the internal cavity and provide easy access for cleaning.  
         [0040]     Once the cuff  300  is closed, as shown in  FIG. 8 , the cuff provides insulation to allow for rapid venous dilation. The entire arm and hand is insulated and prevented from exposure to surrounding cool air. The closed distal edge  35  can further prevent cuff  300  from being unwrapped into a rectangular or square shape and inadvertently used as a heating pad for other parts of the body. This is an important safety feature because a high temperature, for example a temperature of at least 52° C., is provided to the heating element in order to achieve rapid venous dilation. This temperature is much higher than the temperatures used in existing heating pads. Heating pads are also commonly left on the body for prolonged periods of time (often more than 15 minutes). It is not recommended to leave a heating pad with temperatures higher than 52° C. on a body part for a prolonged period of time. Thus, the closed distal edge  35  not only insulates the forearm but also helps to prevent using the cuff  300  as a heating pad.