Abstract:
Devices, methods and systems for endovascular cooling of human or animal subjects are disclosed. A heat exchange catheter ( 12 ) having a heat exchanger ( 22 ) is attached to a source of a thermal exchange fluid ( 32 ) that circulates through the heat exchanger, thereby cooling the subject&#39;s flowing blood. This invention provides cooling devices, systems and methods for cooling the thermal exchange fluid more rapidly and/or to a lower temperature than was achieved by the prior art.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/572,199 filed on May 18, 2004, the entirety of which is expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to medical devices, systems and methods and more particularly to devices, systems and methods for endovascular cooling of human or animal subjects. 
       BACKGROUND OF THE INVENTION 
       [0003]    This invention relates generally to medical devices for selectively controlling the temperature of a patient&#39;s body, or portion of the patient&#39;s body, by adding or removing heat from the patient&#39;s body fluid. More particularly, this invention relates to apparatus and method for reducing the temperature of a heat exchange fluid before the fluid is circulated through a heat-exchange catheter. 
         [0004]    Heat exchange catheters are frequently used for raising or lowering the body temperature of patients suffering from either hyperthermia or hypothermia due to conditions such as exposure to a very hot or cold environment. Such catheters are also used to induce hypothermia in initially normothermic patients undergoing cardiovascular and/or neurosurgery and to victims of head trauma, spinal trauma, stroke, spinal surgery, aneurysm repair and the like, since hypothermia has a recognized neuroprotectant effect. 
         [0005]    One type of heat exchange system available for medical use comprises a catheter having at least one heat transfer surface and at least one flow lumen which permits flow of a fluid past the heat transfer surface. The flow lumen receives fluid from an extracorporeal thermoelectric heat exchanger coupled to a control module including a pump or other discharge assistant and various controls for controlling the amount and direction of heat exchange occurring through the heat exchanger. Examples of prior art heat exchange catheter systems are disclosed in U.S. Pat. No. 5,486,208 to Ginsburg, U.S. Pat. No. 6,610,083 to Keller et al., U.S. Pat. No. 6,620,188 to Ginsburg, legally incapacitated, et al, and U.S. Pat. No. 6,673,098 to Machold et al. The complete disclosures of each of these patents are incorporated herein by reference. 
         [0006]    Under certain circumstances, the thermoelectric heat exchangers used in the heat exchange catheter systems described above may not be able to cool the heat exchange fluid as quickly as required. Accordingly, there exists a need for cooling devices that can be incorporated into new or pre-existing heat exchange catheter systems, either in lieu of or in addition to a thermoelectric heat exchanger. Ideally, such devices should be free of moving mechanical parts, allowing the devices to be manufactured and maintained simply, quickly, and economically. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a cooling device for use with a heat exchange catheter having at least one heat transfer surface and at least one flow lumen which permits flow of a fluid past the heat transfer surface. The cooling device includes an inlet configured to be connected in fluid communication with a fluid source upstream of the cooling device, a chamber containing a cooling medium, and an outlet configured to be connected in fluid communication with the flow lumen of the intravascular catheter to allow cooled fluid to pass from the chamber to the flow lumen. The cooling medium, which may be, for instance, a frozen liquid or gel, or a combination of ice and liquid, is preferably maintained in a substantially still condition in the chamber. Thus, no additional ducting or discharge assistants are required for circulating the cooling medium through the chamber. 
         [0008]    In one embodiment, the cooling device comprises a substantially cylindrical or plate-shaped vessel having each end sealed with an end cap. The interior of the vessel between the two end caps is filled with a liquid, such as water, or a gel. An inlet tube extending through one of the end caps carries a first quick-disconnect fastener for detachably coupling the inlet tube in fluid communication with the fluid source, and an outlet tube extending through the other end cap carries a second quick-disconnect fastener for detachably coupling the outlet tube in fluid communication with the flow lumen of the heat exchange catheter. A tubular helical coil extends between the inlet tube and the outlet tube, allowing heat exchange fluid such as, for instance, saline solution, to flow past the liquid or gel in the chamber. 
         [0009]    The cooling device according to this embodiment is configured for convenient storage in a cold environment such as a freezer, which maintains the cooling medium (i.e. the liquid or gel) in the vessel at a very cold temperature. The vessel may be stored at a temperature at or below the freezing point of the cooling medium so that the cooling medium is in a solid state when initially removed from storage. When needed, the device is simply removed from the freezer and detachably coupled between the fluid source and the inlet lumen of the heat exchange catheter. The fluid from the fluid source then circulates through the helical coil past the cooling medium, and enters the heat exchange catheter at a reduced temperature. If at some point the temperature of the cooling medium becomes too high to effectively cool the heat exchange fluid, the cooling device may quickly be removed from the system and replaced with a fresh cooling device from the freezer. 
         [0010]    In an alternate embodiment, the cooling device is a direct contact heat exchanger in the form of a vessel, for instance an insulated pressure vessel, filled with a cooling medium such as an ice and saline bath. The vessel includes an inlet configured to be coupled to a fluid source and an outlet configured to be coupled to the inlet lumen of a heat exchange catheter, with the outlet positioned relative to the inlet so that flow from the inlet to the outlet is assisted by gravity. Advantageously, the inlet opens into an upper portion of the chamber and the outlet is in the form of an outlet tube having an entrance end opening into a lower portion of the chamber and an exit end proximate the upper end of the chamber. Both the inlet and the outlet tube may extend through a removable cap that is mounted in sealing engagement with the side wall of the vessel. The removable cap allows a user to easily add more ice or the like if the cooling medium becomes too warm. 
         [0011]    A method of cooling a heat transfer fluid for use in a heat exchange catheter according to the present invention comprises the steps of providing a cooling medium in a vessel having an inlet and an outlet and defining an interior chamber, detachably coupling the inlet of the vessel in fluid communication with a fluid source containing the heat transfer fluid and the outlet of the vessel to the flow lumen of the heat exchange catheter, passing the heat transfer fluid through the interior chamber to allow heat exchange between the cooling medium and the heat transfer fluid, and passing the heat transfer fluid from the interior chamber to the flow lumen of the heat exchange catheter. The method optionally also includes steps of storing the vessel in a freezer when not in use and replacing the vessel with a similar, freshly frozen vessel when the temperature of the cooling medium in the vessel exceeds a predetermined level. Alternatively, the method may include a step of adding ice or the like to the vessel when the cooling medium becomes too warm. 
         [0012]    The cooling device of the present invention may be easily incorporated to a pre-existing heat-exchange catheter system, either in lieu of or in addition to the thermoelectrically controlled cooler that it is conventionally provided with such systems. The heat exchange catheter system may also include a pump for assisting the flow of the heat transfer fluid from the fluid source to the inflow lumen of the heat exchange catheter. 
         [0013]    Additional aspects and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view showing a prior art heat exchange catheter system; 
           [0015]      FIG. 2  is a perspective view, partially broken away, of a cooling device according to one embodiment of the present invention; 
           [0016]      FIG. 3  is a longitudinal sectional view through the cooling device of  FIG. 2 ; and 
           [0017]      FIG. 4  is longitudinal sectional view through a cooling device according to an alternate embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0018]      FIG. 1  illustrates a prior art heat exchange catheter system  10  including a heat exchange catheter  12 , a heat exchange cassette  14 , and a control module  16  which houses a fluid source  16 , for instance an IV bag of saline, and various controls such as a thermoelectric cooler (not shown) for adding or withdrawing heat from the heat exchange cassette  14 . The system may also include a pump (not shown), which may either be part of or external to the heat exchange cassette  14 , for circulating heat exchange fluid through the system. 
         [0019]    The heat exchange catheter  12  is formed with an inlet flow line  18 , an outlet flow line  20 , and a heat exchange element  22  which may be, for instance, a heat exchange balloon. The inlet and outlet flow lines  18 ,  20  define inflow and outflow lumens (not shown), respectively, that are coupled to corresponding openings in the heat exchange cassette  14 . The catheter  12  may, for instance, be any of the types disclosed in U.S. Pat. No. 5,486,208 to Ginsburg, U.S. Pat. No. 6,610,083 to Keller et al. and U.S. Pat. No. 6,620,188 to Ginsburg, legally incapacitated, et al., the entire contents of which are expressly incorporated herein by reference. 
         [0020]      FIGS. 2 and 3  show one embodiment of a cooling device  24  that may be incorporated into the heat exchange catheter system  10  of the present invention, either in place of or in line with the thermoelectrically controlled heat exchange cassette  14 . The illustrated cooling device  24  comprises a cylindrical vessel  26  having each end sealed with an end cap  28 ,  30 . Although shown here as substantially cylindrical, the vessel  26  may also be structured as a flat plate or other suitable configuration. 
         [0021]    The interior of the vessel  26  between the two end caps  28 ,  30  defines a chamber filled with a cooling medium  32 , which may be a liquid, such as water, or a gel. An inlet tube  34  extending through one of the end caps  28  carries a first quick-disconnect fastener  36  for detachably coupling the inlet tube  34  in fluid communication with a fluid source such as an IV bag of saline, and an outlet tube  38  extending through the other end cap  30  carries a second quick-disconnect fastener  40  for detachably coupling the outlet tube  38  in fluid communication with a flow lumen of a heat exchange catheter. A tubular helical coil  42  extends between the inlet tube  34  and the outlet tube  38 , allowing heat exchange fluid such as, for instance, saline solution, to flow past the cooling medium  32  in the vessel  26 . The helical coil  42  may be made of any suitable thermally conductive material such as metal or plastic in order to allow rapid heat exchange between the heat exchange fluid and the cooling medium  32 , while the vessel  26  may be insulated to prevent heat exchange between the cooling medium  32  and the surrounding air. 
         [0022]    The cooling medium  32  is preferably substantially still. In other words, the cooling medium need not circulate. This makes the cooling device  24  substantially simpler, less expensive, and easier to maintain than, for instance a parallel, counterflow, or cross-flow type heat exchanger which would require additional ducting and/or moving mechanical parts to keep the cooling medium flowing. 
         [0023]    A method of cooling a heat transfer fluid for use in a heat exchange catheter according to the present invention comprises detachably coupling the inlet tube  34  of the device  24  to a fluid source containing the heat transfer fluid and the outlet tube  38  to the flow lumen of the heat exchange catheter, passing the heat transfer fluid through the interior chamber of the vessel  26  to allow heat exchange between the cooling medium  32  and the heat transfer fluid, and passing the heat transfer fluid from the interior chamber  32  to the flow lumen of the heat exchange catheter. The vessel  26  containing the cooling medium  32  is preferably stored in a freezer when not in use, so that the cooling medium  32  is in a solid state. When the cooling medium  32  melts and/or rises above a predetermined temperature, it may quickly be detached from the system and replaced with a new vessel  26  recently removed from the freezer and containing colder, perhaps still frozen cooling medium  32 . 
         [0024]    A cooling device  44  according to an alternate embodiment of the invention is shown in  FIG. 4 . The device  44  comprises a vessel  46 , such as for instance, an insulated pressure vessel, defining a cooling chamber  48  containing a cooling medium  50  such as, for instance, a saline ice bath. An inlet tube  52  at the top of the vessel  46  receives heat exchange fluid from a fluid source and introduces the fluid into the cooling chamber  48 , where the fluid directly contacts the cooling medium  50 . The vessel is preferably configured for vertical orientation, so that the fluid entering through the inlet tube is pulled downward by gravity toward the bottom of the vessel  46 . The fluid at the bottom of the vessel  46  then enters the entrance end  56  of a narrow outlet tube  54  and is drawn upward, for instance by capillary action, to exit end  58  of the tube  54 , from whence it passes into the inlet lumen of the heat exchange catheter. 
         [0025]    The vessel  46  preferably includes a removable cap or closure  60  that allows ice to be added to the chamber  48  when needed. A seal is preferably provided between the cap and the side wall of the vessel  46  to prevent heat loss and/or fluid leakage. 
         [0026]    A method of cooling a heat transfer fluid using the device  44  is substantially the same as the method described above in connection with the first embodiment, except that rather than storing the device, filled with cooling medium, in a freezer prior to use, it may be preferable to store the vessel  46  in an empty state at room temperature, and to simply add the mixture of saline and ice just before use. In addition, instead of replacing the vessel  46  with a new vessel when the cooling medium becomes too warm, a user may simply add more ice to reduce the temperature. 
         [0027]    While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.