No assignee for this patent application has been made.
Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates generally to medical devices and methods and, more particularly, to a programmable, microprocessor based system and method for controlling the temperature and flow of a thermal exchange fluid that is circulated through a heat exchange catheter inserted into a patient's body for the purpose of cooling or warming at least a portion of the patient's body.
"Under ordinary circumstances, the thermoregulatory mechanisms of a healthy human body serve to maintain the body at a constant temperature of about 37.degree. C. (98.6.degree. F.), a condition sometimes referred to as normothermia. To maintain normothermia, the thermoregulatory mechanisms act so that heat lost from the person's body is replaced by the same amount of heat generated by metabolic activity within the body. For various reasons such as extreme environmental exposure to a cold environment or loss of thermoregulatory ability as a result of disease or anesthesia, a person may develop a body temperature that is below normal, a condition known as hypothermia. A person may develop a condition that is above normothermia, a condition known as hyperthermia, as a result of extreme exposure to a hot environment, or malfunctioning thermoregulatory mechanisms, the latter being a condition sometimes called malignant hyperthermia. The body may also establish a set point temperature (that is, the temperature which the body's thermoregulatory mechanisms function to maintain) that is above normothermia, a condition usually referred to as fever. The present invention addresses all of these situations.
"Accidental hypothermia is generally a dangerous condition that may even be life threatening, and requires treatment. If severe, for example where the body temperature drops below 30.degree. C., hypothermia may have serious consequences such as cardiac arrhythmias, inability of the blood to clot normally, or interference with normal metabolism. If the period of hypothermia is extensive, the patient may even experience impaired immune response and increased incidence of infection.
"Simple methods for treating accidental hypothermia have been known since very early times. Such methods include wrapping the patient in blankets, administering warm fluids by mouth, and immersing the patient in a warm water bath. If the hypothermia is not too severe, these methods may be effective. However, wrapping a patient in a blanket depends on the ability of the patient's own body to generate heat to re-warm the body. Administering warm fluids by mouth relies on the patient's ability to swallow, and is limited in the temperature of the liquid consumed and the amount of fluid that may be administered in a limited period of time. Immersing a patient in warm water is often impractical, particularly if the patient is simultaneously undergoing surgery or some other medical procedure.
"More recently, hypothermia may be treated in a more complex fashion. Heated warming blankets may be applied to a patient or warming lamps that apply heat to the skin of the patient may be used. Heat applied to the patient's skin, however, has to transmit through the skin by conduction or radiation which may be slow and inefficient, and the blood flow to the skin may be shut down by the body's thermoregulatory response, and thus, even if the skin is warmed, such mechanisms may be ineffective in providing heat to the core of the patient's body. When breathing gases are administered to a patient, for example a patient under anesthesia, the breathing gases may be warmed. This provides heat relatively fast to the patient, but the amount of heat that can be administered without injuring the patient's lungs is very limited. An alternative method of warming a hypothermic patient involves infusing a hot liquid into the patient via an IV infusion, but this is limited by the amount of liquid that can be infused and the temperature of the liquid.
"In extreme situations, a very invasive method may be employed to control hypothermia. Shunts may be placed into the patient to direct blood from the patient through an external machine such as a cardiopulmonary by-pass (CPB) machine which includes a heater. In this way, the blood may be removed from the patient, heated externally, and pumped back into the patient. Such extreme measures have obvious advantages as to effectiveness, but also obvious drawbacks as to invasiveness. The pumping of blood through an external circuit that treats the blood is generally quite damaging to the blood, and the procedure is only possible in a hospital setting with highly trained personnel operating the equipment.
"Accidental hyperthermia may also result from various conditions. Where the normal thermoregulatory ability of the body is lost, because of disease or anesthesia, run-away hyperthermia, also known as malignant hyperthermia, may result. The body may also set a higher than normal set point resulting in fever which is a type of hyperthermia. Like hypothermia, accidental hyperthermia is a serious condition that may sometimes be fatal. In particular, hyperthermia has been found to be neurodestructive, both in itself or in conjunction with other health problems such as traumatic brain injury or stroke, where a body temperature in excess of normal has been shown to result in dramatically worse outcomes, even death.
"As with hypothermia, when the condition is not too severe, simple methods for treating the condition exist, such as cold water baths and cooling blankets, or antipyretic drugs such as aspirin or acetominophen, and for the more extreme cases, more effective but complex and invasive means such as cooled breathing gases, cold infusions, and blood cooled during CPB also exist. These, however, are subject to the limitations and complications as described above in connection with hypothermia.
"Although both hypothermia and hyperthermia may be harmful and require treatment in some case, in other cases hyperthermia, and especially hypothermia, may be therapeutic or otherwise advantageous, and therefore may be intentionally induced. For example, periods of cardiac arrest or cardiac insufficiency in heart surgery result in insufficient blood to the brain and spinal cord, and thus can produce brain damage or other nerve damage. Hypothermia is recognized in the medical community as an accepted neuroprotectant and therefore a patient is often kept in a state of induced hypothermia while undergoing treatment for the underlying cause of the condition. Hypothermia also has similar advantageous protective ability for treating or minimizing the adverse effects of certain neurological diseases or disorders such as head trauma, spinal trauma and hemorrhagic or ischemic stroke. Therefore it is sometimes desirable to induce whole-body or regional hypothermia for the purpose of facilitating or minimizing adverse effects of certain surgical or interventional procedures such as open heart surgery, aneurysm repair surgeries, endovascular aneurysm repair procedures, spinal surgeries, or other surgeries where blood flow to the brain, spinal cord or vital organs may be interrupted or compromised. Hypothermia has even been found to be advantageous to protect cardiac muscle tissue after a myocardial infarct (MI).
"Current methods of attempting to induce hypothermia generally involve constant surface cooling, by cooling blanket or by alcohol or ice water rubs. However, such cooling methods are extremely cumbersome, and generally ineffective to cool the body's core. The body's response to cold alcohol or ice water applied to the surface is to shut down the circulation of blood through the capillary beds, and to the surface of the body generally, and thus to prevent the cold surface from cooling the core. If the surface cooling works at all, it does so very slowly. There is also an inability to precisely control the temperature of the patient by this method.
"If the patient is in a surgical setting, the patient may be anesthetized and cooled by CPB as described above. Generally, however, this is only available in the most extreme situations involving a full surgical team and full surgical suite, and importantly, is only available for a short period of time because of the damage to the blood caused by pumping. Generally surgeons do not wish to pump the blood for periods longer than four hours, and in the case of stroke or traumatic brain damage, it may be desirable to induce hypothermia for longer than a full day. Because of the direct control of the temperature of a large amount of blood, this method allows fairly precise control of the patient's temperature. However, it is this very external manipulation of large amounts of the patient's blood that makes long term use of this procedure very undesirable.
"Means for effectively adding heat to the core of the body that do not involve pumping the blood with an external, mechanical pump have been suggested. For example, a method of treating hypothermia or hyperthermia by means of a heat exchange catheter placed in the bloodstream of a patient was described in U.S. Pat. No. 5,486,208 to
"A number of catheter systems for cooling tissue adjacent the catheter or regulating the temperature of the catheter using the temperature of fluid circulating within the catheter are shown in the published art. Some such catheters rely on a reservoir or similar tank for a supply of heat exchange fluid. For such systems that involve a catheter placed in the bloodstream, however, difficulties arise in sterilizing the fluid source between uses and rapidly changing the temperature of a large volume of fluid having a significant thermal mass.
"Various approaches have been used to add or remove heat the heat exchange fluid that is circulated through the catheter. For example, the heat exchange fluid may be circulated through a bath containing a second heat exchange fluid, such as a glycol based heat exchange fluid, water, or the like. Another approach uses a refrigeration system to either directly or indirectly cool the circulating heat exchange fluid. Yet another approach employs a thermoelectric system for heating and cooling the circulating heat exchange fluid.
"Each of the systems mentioned above have their own advantages and disadvantages. For example, in some circumstances, such as in an emergent cardiac arrest, it has been found beneficial to rapidly reduce the patient's temperature. Such a rapid temperature reduction requires a large amount of cooling power, which results in the need for a refrigeration unit that produces a higher than acceptable noise level. Once a patient's temperature has been reduced to the desired level, however, less cooling power is required to maintain the patient at the desired temperature. In such situations, a thermoelectric cooler is preferable, because of the fine control over the temperature of the circulating fluid that can be maintained using such a system.
"For the foregoing reasons, there is a need for a rapid and effective means to add or remove heat from the heat exchange fluid circulating through a catheter used to control the body temperature of a patient in an effective and efficient manner, while avoiding the inadequacies of the prior art methods. Such a system would provide large amounts of cooling power to rapidly reduce the patient's temperature to a desired level, yet would also provide accurate control of the heat removed from the patient to maintain the patient at the desired level without undesirable over- or under-shoot of the patient's temperature. The present invention satisfies these and other needs."
In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventor's summary information for this patent application: "In it most general aspect, the present invention provides a system for providing large amounts of cooling power to remove heat from a heat exchange fluid that is circulating between an external heat exchanger and an intravascular heat exchange catheter inserted into the vasculature of a patient. In this general aspect, the system includes a first stage that capable of providing high cooling power using a refrigeration system utilizing a compressible fluid or gas. The second state of the system provides for more fine control of the rate of heat removal, or cooling provided to the heat exchange fluid. In one aspect, both stages may be used in concert to provide maximal cooling. In another aspect, the first stage may be de-activated when a sensed temperature related to the temperature of a patient indicates that the temperature of the patient is equal to or lower than a threshold temperature close to a target temperature has been achieved, with the second stage providing cooling until the target temperature is reached. In yet another aspect, the second stage may is also capable of providing heat to the heat exchange fluid when necessary to maintain a sensed temperature at the target temperature or to warm a patient.
"In another general aspect, the present invention provides a controller that controls the operation of the stages of the heater/cooler device to provide accurate control of the rate of heating or cooling of a patient, or to maintain the temperature of a patient at a target temperature.
"In another aspect, the present invention includes a system for managing the temperature of a person using an intravascular heat exchanger inserted into the lumen of a body vessel of a patient, comprising: an intravascular heat exchanger having a fluid input port and a fluid output port; an external heat exchanger having an input and an output port, the input and output ports, the intravascular heat exchanger and the external heat exchanger forming a fluid circuit; a pump disposed within the fluid circuit for pumping heat exchange fluid through the fluid circuit; a heater/cooler configured to engage the external heat exchanger in a thermal transfer relationship, the heater/cooler including a primary cooling portion and a reversible secondary portion capable of heating or cooling, the primary cooling portion including a refrigeration circuit including a compressor, a condenser, an expansion valve, and a cold block in thermal communication with the reversible secondary portion; and a controller having a processor configured by software commands to receive temperature indications related to the temperature of a patient and to control operation of the heater/cooler in accordance with a target temperature.
"In still another aspect, the fluid input and the fluid output of the intravascular heat exchanger each have releasable couplings, and wherein the input and output ports of the external heat exchanger have releasable couplings, the releasable coupling of the input port configured to engage the releasable coupling disposed on the fluid output of the intravascular heat exchanger and the releasable coupling of the output port configured to engage the releasable coupling of the fluid input of the intravascular heat exchanger.
"In yet another aspect, the reversible secondary portion is a T/E cooler.
"In still another aspect, the controller activates the primary cooling portion to remove heat from the heat exchange fluid when the difference between the sensed patient temperature and the target temperature exceeds a selected value. In an alternative aspect, the controller activates the primary cooling portion and the reversible secondary portion to remove heat from the heat exchange fluid when the difference between the sensed patient temperature and the target temperature exceeds a selected value. In yet another alternative aspect, the controller activates the reversible secondary portion to remove heat from the heat exchange fluid when the difference between the sensed patient temperature and the target temperature is less than a selected value. In still another alternative aspect, the controller activates the reversible secondary portion to add heat to the heat exchange fluid when the sensed patent temperature is less than the target temperature.
"In another aspect, the controller deactivates the primary cooling portion and activates the reversible secondary portion when the difference between the sensed patient temperature and the target temperature is less than a selected value. In an alternative aspect, the controller deactivates the primary cooling portion when the difference between the sensed patient temperature and the target temperature is less than a selected value.
"In a further aspect, the present invention includes a communication module configured to communicate information related to the sensed temperature and the operation of the system to a display remote from the system. In an alternative aspect, the communication module is configured to communicate information related to the sensed temperature and the operation of the system to a data management system. In another aspect, the information communicated to the data management system is associated with an electronic medical record of the patient.
"In still another aspect, the present invention includes a communication module configured to communicate with a device monitoring a health parameter of the patient; and a display controlled by the processor of the controller to display information related to the operation of the system and information received from the monitoring device related to the monitored health parameter of the patient.
"In yet another aspect, the present invention includes a secondary cooling circuit disposed between the refrigeration circuit and the fluid circuit, the secondary cooling circuit comprising a pump for pumping secondary heat exchange fluid through the secondary cooling circuit, a secondary cold block configured to engage the cold block of the refrigeration circuit in a heat exchange configuration, and a third cold block configured to engage the external heat exchanger of the fluid circuit in a heat exchange configuration. In one alternative aspect, the reversible secondary portion of the heater cooler is disposed in the secondary cooling circuit rather than the primary cooling circuit. In another alternative aspect, the third block is a container having an input and an output, the container configured to receive the external heat exchanger such that the external heat exchanger is immersed in the secondary heat exchange fluid flowing through the container.
"Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 is a perspective view of a patient undergoing treatment using a system in accordance with the present invention;
"FIG. 2 is a schematic illustration of a disposable heat exchange cassette attached to a heat exchange catheter and an external fluid source; and positioned for insertion into a suitable opening in a re-usable control unit of the present invention;
"FIGS. 3A-3B together show a flowchart of a control scheme of an embodiment of the heat exchange system of the present invention;
"FIG. 4 is a graph of the sensed temperature of a target tissue or body fluid over time under the influence of the control scheme of FIGS. 3A-3B;
"FIG. 5 is a schematic illustration of an embodiment of the present invention utilizing a two-stage heater/cooler to add or remove heat from a heat exchange fluid flowing through a heat exchange catheter.
"FIG. 6 is a flowchart illustrating an embodiment of a control scheme of the embodiment of FIG. 5.
"FIG. 7A is a perspective view of an exemplary re-usable control unit of the present invention;
"FIG. 7B is a perspective view of an upper portion of the control unit of FIG. 7A,
"FIG. 7C is a plan view of an exemplary control panel for the control unit of FIG. 7A;
"FIG. 8 is a perspective view of another embodiment of a re-usable control unit of the present invention illustrating an exemplary placement of a peristaltic pump and fluid supply;
"FIG. 9A is a perspective view of the heat exchange cassette-receiving subassembly;
"FIG. 9B is an exploded view of the heat exchange cassette-receiving subassembly of FIG. 9A;
"FIG. 9C is an exploded view of a heater/cooler unit of the heat exchange cassette-receiving subassembly of FIG. 9A;
"FIGS. 10A-10C are schematic illustrations of the fluid flow using different embodiments of the disposable heat exchange cassette of present invention;
"FIG. 11 is a schematic illustration of an alternative embodiment of the heater/cooler circuits of FIG. 5;
"FIG. 12 is a schematic illustration of an embodiment of the present invention showing the use of a primary refrigeration loop and a secondary glycol loop to add or remove heat from a fluid circuit including a heat exchange catheter; and
"FIG. 13 is a schematic illustration of an alternative embodiment to the embodiment of FIG. 12."
For more information, see this patent application: Dabrowiak, Jeremy. System and Method for Management of Body Temperature. Filed
Keywords for this news article include: Patents, Legal Issues, Information Technology, Information and Data Management.
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