Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
2001-02-06
2003-08-26
Dvorak, Linda C. M. (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
C607S104000, C607S096000, C606S020000, C606S021000, C606S024000
Reexamination Certificate
active
06610083
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to medical devices and a method of using them for selectively affecting the temperature of a patient's body, or portion of the patient's body, by adding or removing heat from the patient's body fluid through the use of a heat exchange catheter with a heat exchange region in contact with the body fluid, the heat exchange region being shaped for maximum heat exchange with minimum insertion profile and minimum obstruction to the flow of the body fluid. More particularly, this invention relates to a heat exchange catheter with a heat exchange region which is an advantageously shaped balloon, wherein the balloon is placed in flowing body fluid and heat exchange fluid circulates within the balloon to add or remove heat from the body fluid in order to treat or induce whole body or regional hypothermia or hyperthermia. This invention also relates to a method of controlling the amount of heat removed or added by the heat exchange region to affect the temperature of all or part of the patient's body in response to a signal representing the temperature of all or part of a patient's body.
BACKGROUND OF THE INVENTION
Under ordinary circumstances, thermoregulatory mechanisms exist in the healthy human body to maintain the body at a constant temperature of about 37° C. (98.6° F.), a condition sometimes referred to as normothermia. Normothermia is generally a desirable condition, and to maintain normothermia, the thermoregulatory mechanisms act so that heat lost to the environment is replaced by the same amount of heat generated by metabolic activity in the body.
For various reasons, a person may develop a body temperature that is below normothermia, a condition known as hypothermia, or a temperature that is above normothermia, a condition known as hyperthermia. These conditions are generally harmful and are usually treated to reverse the condition and return the patient to normothermia. In certain other situations, however, they may be desirable and may even be intentionally induced.
Accidental hypothermia may result when heat loss to the environment exceeds the body's ability to produce heat internally or when a person's thermoregulatory ability has been lessened due to injury, illness or anesthesia. For example, a person exposed to a cold environment such as a hiker wandering in a very cold climate for too long, or a sailor overboard in cold water, may become dangerously hypothermic. Likewise, anesthesia generally disables a patient's thermoregulatory ability, and it is often the case that, during long surgery with significant exposure of the patient's internal body cavities, a patient becomes significantly hypothermic. Such hypothermia is generally harmful, and must be quickly reversed to restore the victim to health.
Simple methods for treating 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, and the need to reverse the hypothermia is not too urgent, 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 both 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 by the application of a warming blanket that applies heat to the skin of the patient. Applying heat to the patient's skin, however, may be ineffective in providing heat to the core of the patient's body. Heat applied to the skin has to transmit through the skin by conduction or radiation which may be slow and inefficient, especially if the patient has a significant layer of fat between the warming blanket and the body's core.
Paradoxically, if the patient is suffering significant core hypothermia, the application of warmth to the patient's skin, whether by immersion in hot water or application of a warm blanket, may actually exacerbate the core hypothermia and may even induce shock. The body's thermoregulatory responses to cold that work to conserve heat in the body's core include vasoconstriction and arterio-venous shunting (AV shunts). Vasoconstriction occurs when the capillaries and other blood vessels in the skin and extremities constrict so that most of the blood pumped by the heart circulates within the core rather than through the skin and extremities. Similarly, in AV shunting, naturally occurring blood shunts exist between some arteries providing blood to capillary beds in the skin and extremities and veins returning blood from those capillary beds and extremities. When the body is cooled, the vessels in the capillary beds constrict, and the shunts may be opened, causing blood to by-pass those capillary beds altogether. Thus when the body is cold, the tissues in the extremities, and particularly at the surface, have little blood flowing to them and may become quite cold relative to the body's core temperature.
When heat is applied to the skin of such a patient, the temperature sensors in the skin may cause the vasoconstriction to reverse and the AV shunts to close. When this happens, blood from the core floods into the very cold tissue on the body surface and extremities, and as a result the blood loses heat to those tissues, often far more than the amount of heat being added by the surface warming. As a result, the victim's core temperature may plummet and the patient may even go into shock.
Partly in response to the inadequacies of surface application of heat, methods have been developed for adding heat to a patient's body by internal means. A patient being administered breathing gases, for example a patient under anesthesia, may have the breathing gases warmed. For some situations, particularly mild hypothermia requiring the addition of small amounts of heat, this method may be effective, but it is limited in the amount of heat that can be administered without injuring the lungs. Similarly, a patient receiving IV fluids may have the fluids warmed, or a bolus of warm fluid may be administered intravenously. Again, this may be effective in the case of mild hypothermia, but the amount of heat that may be added to a patient's body is limited because the temperature of the IV fluid is limited to a temperature that will not be destructive to the blood, generally thought to be about 41° C.-49° C., and the amount of fluid that is acceptable to administer to the patient.
A more invasive method may be used to add heat to a patient's blood, particularly in the case of heart surgery. A cannula is attached to a vein, usually the inferior vena cava (IVC) of a patient, the vein clamped off and virtually all the patient's blood shunted through the cannula to an external pump. The blood is then pumped back into the patient's body, generally to the arterial side of the patient's circulation. Blood removed from a patient may be heated or cooled externally before it is reintroduced into the patient's body. An example of such a by-pass arrangement is the Cardio-Pulmonary By-pass system (CPB) often used in open heart surgery.
This by-pass method, once it is initiated, is both fast and effective in adding or removing heat from a patient's blood and in exercising control over the patient's body temperature in general, but has the disadvantage of involving a very invasive medical procedure which requires the use of complex equipment, a team of highly skilled operators, is generally only available in a surgical setting, and because of these complexities, requires a long time to initiate. In fact, it generally cannot begin
Keller Wade A.
Machold Timothy R.
Buyan Robert D.
Dvorak Linda C. M.
Radiant Medical Inc.
Stout, Uxa Buyan & Mullins, LLP
Vrettakos Peter
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