1. Field of the Invention
This invention relates generally to methods and apparatus for exchanging heat with the body of a patient.
2. Description of Related Art
Many advantages of hypothermia are well known. By way of example, it has been found particularly desirable to lower the temperature of body tissue in order to reduce the metabolism of the body. In stroke, trauma and several other pathological conditions, hypothermia also reduces the permeability of the blood/brain barrier. It inhibits release of damaging neurotransmitters and also inhibits calcium-mediated effects. It is also known that hypothermia inhibits brain edema and lowers intracranial pressure.
Hypothermic treatment has been typically addressed systemically, meaning that the overall temperature of the entire body has been lowered to achieve the advantages noted above. This has been particularly desirable in surgical applications where the reduced metabolism has made it possible to more easily accommodate lengthy operative procedures. An example of this systemic approach includes catheters for transferring heat to or from blood flowing within a patient""s vessel, as disclosed by Ginsburg in U.S. Pat. No. 5,486,208. A closed loop heat exchange catheter is also disclosed by Saab in U.S. Pat. No. 5,624,392. A cooling device for whole-body hyperthermia that utilizes the circulatory system of the body is known to be more efficient since the entire volume of the body is constantly perfused with the cold fluid at a capillary level.
Likewise, various other means of cooling the body have been tried with cooling blankets, ice water bladder lavages, ice baths, esophageal catheters and their associated methods. All of these devices require a considerable time to cool the body since the primary heat transfer occurs through the skin or the skull. A more efficient body cooling device that can quickly cool and accurately control the body temperature is required.
The present invention provides a heat exchange system wherein a self-contained primary cooling circuit having a first fluid circulating therein is coupled to a self-contained secondary cooling circuit in a heat exchange relationship. The two circuits are in fluid-flow isolation from each other and are provided with associated pumping mechanisms to effect fluid circulation therein. The primary circuit is in fluid communication with an indwelling heat exchange catheter adapted for insertion into the body of the patient in order to effect heat exchange with a target site in the body. The secondary circuit is cooled or warmed by a temperature control system.
In one aspect of the present invention, the temperature of the system is controlled in accordance with patient temperature determinations. This can be performed automatically, in a closed feedback loop wherein temperature readings from a probe are input to a temperature controller having inputs to at least one of the pumping mechanisms in addition to the heater or cooler of the temperature control system. The temperature controller operates in accordance with temperature control algorithms taking into account the various system and patient parameters to thereby achieve and maintain desired temperature conditions in the patient""s body.