Refrigeration – Using electrical or magnetic effect – Thermoelectric; e.g. – peltier effect
Reexamination Certificate
2002-10-24
2004-06-29
Doerrler, William C. (Department: 3744)
Refrigeration
Using electrical or magnetic effect
Thermoelectric; e.g., peltier effect
C062S003300, C607S106000
Reexamination Certificate
active
06755026
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for heating and/or cooling sterilized fluids. In particular, the present invention relates to a method and device for heating and cooling physiological fluids such as blood, that may be administered to a patient during medical procedures.
2. Description of the Background Art
The invention relates to a device for heating sterilized fluids, such as blood or other fluids that are to be administered to a patient. It is frequently necessary during the course of medical treatment to heat or cool physiological fluids. For example, haemodialysis removes waste products from the blood by passing it out of the body, through a filtering system (dialyser) and returning it, cleaned, to the body. While in the filtering system, the blood flows through tubes made of a membrane that allows the waste products (which are much smaller than blood cells) to pass out through it. It is common practice to heat the dialysis fluid before it enters the blood dialyzer to aid in filtering.
In the collection of whole blood from donors, it is sometimes desirable to cool the collected blood prior to further processing. Plasmapheresis, or plasma exchange, is a procedure in which blood is separated into cells and plasma. The plasma is removed and replaced with fresh frozen plasma and/or a plasma substitute. Similarly, in plasmapheresis, when blood is taken from a donor and separated, it is desirable to have heating apparatus or cooling apparatus available prior to further handling of the separated fractions.
If a component fraction were to be returned to the patient, it would be advantageous to warm this fraction to approximately body temperature prior to such return. On the other hand, apparatus for cooling may be needed if the separated plasma fraction is to be subjected to further processing.
Alternatively, heating may be used in connection with the transfusion of blood that has been refrigerated and needs to be warmed before the patient is transfused.
In other circumstances, it may be necessary or desirable to effect heating or cooling on a continuous basis. In blood dialysis, for example, it is customary to heat the dialysate prior to passing it through the dialyzer. In plasmapheresis procedures, it may be desirable to cool either the separated cellular fraction or the separated plasma fraction on a continuous basis.
Medical research has demonstrated that rapid cooling of a patient's body temperature following a cerebral stroke or other serious trauma significantly improves the prognosis. Several devices employing alternate technologies are currently being clinically evaluated. Companies such as “Innercool” and “Alicius” have been promoting catheter based cooling driven by the use of refrigeration.
In Cardiopulmonary Bypass (CPB) surgery, the body temperature of the patient is dropped below normal temperature during surgery and then returned to normal temperature towards the end of the procedure. This is accomplished by regulating the temperature of the extra-corporeal blood by means of a heat exchanger integrated with an oxygenator.
However, the task of heating or cooling of the blood in the CPB circuit is difficult for a variety of reasons. Perfusionists use typically complex heat exchangers, with large surface area, to circulate water opposite the blood in order to regulate the temperature of blood. It is critical to maintain the temperature differential between the water and blood within 10 degrees.
During CPB surgery, cardioplegia is administered at very low temperatures. This is accomplished by using water-based heat exchangers. The inadequacies of current devices has necessitated the use of ice to assist in the cooling process. This has minimized the ability for temperature regulation, but it is still a common practice.
Typical CPB heat exchanger configurations are inconvenient to use and present many problems to practitioners. It is often difficult to adhere to the surgeon's temperature protocol. An undetected water to blood leak can lead to hemolysis which can be catastrophic to the patient's well being. Further, the risk of complications due to exposure to foreign surfaces is well documented. Companies such as Cardioventions have been striving to capitalize on the advantages of reduced blood contact surface area.
U.S. Pat. No. 4,309,592 to Le Boeuf and U.S. Pat. No. 4,476,685 to Aid describe apparatus for heating or cooling physiological fluids utilizing thermoelectric/resistive heating elements arranged in a spaced apart relationship. A flexible container is disposed within a space formed between the two heating elements. Heat sinks or fins are also provided in order to effectuate heat transfer.
U.S. Pat. No. 5,899,077 to Wright et al. describes an apparatus for the heating and cooling of high purity and/or corrosive fluids. Plastic tubing containing the fluid is interposed and press-fitted between a pair of heat exchanger plates that further sandwich a thermoelectric module. A thermally conductive grease is further provided to enhance contact between the plastic tubing and a base plate of one of the heat exchanger plates.
Similarly, U.S. Pat. No. 3,293,868 to Gonzalez describes a cooling apparatus having a base with a collector plate mounted therein. A flexible tube carrying a fluid is routed and coiled between guide fins toward the center of the collector plate. A thermocouple engaged with a transfer block is included with a heat-dissipating assembly.
The devices and methods of the background art suffer from the following disadvantages. For the medical procedures and devices described hereinabove, water has been the preferred energy transfer medium to effect the desired temperature change. However, the use of water presents patient safety issues that are well documented. In some cases, electrical resistance has been used as an alternative. While this eliminates water, desired performance has been difficult to achieve and cooling is not possible or is otherwise inefficient.
If performance standards can be met, safety and convenience for medical procedures requiring temperature regulation would be improved by the elimination of water. This is especially true for the CPB circuit. A unique energy transfer system is required that meets the special energy transfer needs of medical procedures, i.e. the CPB circuit, and does not rely on water. The method and apparatus for temperature regulation in medical, especially cardiopulmonary, applications is embodied in the method and apparatus described hereinafter.
SUMMARY OF THE INVENTION
The present invention overcomes the shortcomings associated with conventional devices and methods, and achieves other advantages not realized by the background art.
It is an aspect of the present invention to provide a method and apparatus that eliminates the risk of blood hemolysis associated with water to blood leaks, including those that are often non-detectable. In addition to the safety risks to patients, procedures utilizing ice and water-based systems and methods require additional floor space, manpower and costs.
It is an aspect of the present invention to minimize the amount of foreign surface area required of a heat exchange device to thereby reduce the probability of systemic inflammatory response in patients.
It is an aspect of the present invention to minimize pumping volumes in order to reduce hemodilution of patients.
It is a further aspect of the present invention to improve heat exchange efficiency and to facilitate precise temperature control of heating and cooling protocols. A method, system and apparatus offering more efficient heat transfer and precise temperature control will lead to the reduction of the length of medical procedures, will free up valuable personnel resources such as surgeons and perfusionists, and will permit less-invasive medical procedures.
The present invention is a recognition, in part, that the ability provide safer methodologies that are intended to reduce the probability of post operative liabilities and
Birch & Stewart Kolasch & Birch, LLP
Tech Medical Devices Inc.
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