Electric resistance heating devices – Heating devices – Continuous flow type fluid heater
Reexamination Certificate
1999-05-14
2001-05-08
Jeffery, John A. (Department: 3742)
Electric resistance heating devices
Heating devices
Continuous flow type fluid heater
C219S501000, C219S482000, C604S114000
Reexamination Certificate
active
06229957
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to warming devices required for safely warming physiological fluids, inclusive of blood and non-blood related products, prior to their infusion to a patient. The invention specifically relates to a warming device which utilizes both alternating current (AC) and direct current (DC) sources of energy, in concert, to provide for the safe and effective warming at high rates of infusion.
BACKGROUND OF THE INVENTION
The successful resuscitation of patients suffering from hypovolemic shock requires infusion of fluids at a very rapid rate. Hypovolemic shock, which may have been brought on secondary to intraoperative or possibly traumatic hemorrhage, must be treated aggressively by rapid administration of fluids, for example, crystalloids, blood products, colloids and the like. Reductions in physiological markers such as blood pressure, cardiac output and coronary blood flow may often lead to a reduction in tissue perfusion, organ damage, loss of kidney function and acidosis which, if left untreated, can result in physiologic changes which are often irreversible and sometimes fatal. As various products are infused in order to restore normal fluid volumes, it is most important to maintain normothermic conditions so as to avoid the occurrence of transfusion induced hypothermia. Prior artisans have incorporated various types of extracorporeal heat exchangers in an effort to maintain the infusate temperature at required levels, e.g. above about 37° C. at flow rates of about 500 ml/minute, but such devices have proven inadequate to provide the 1000 ml/minute or more which is so often required. It should be understood that correction of this inadequacy is not so simple as resizing of the heater capacity as a function of flow rate and expected temperature change of the fluid. On the contrary, the problem stems from inadequate amperage capacity in existing facilities, making it virtually impossible to achieve the required heating capacity by utilization of facility provided power alone. Additionally, prior art devices have concentrated on the temperature of the infusate at the outlet of the heat exchanger, giving little regard to the heat lost in the connecting tubing which fluidly couples the heat exchanger to the patient. Thus, the infusate temperature, at the point of entry to the patient, is often below nominal design parameters.
While it is known to provide a fluid warming device which is alternatively powered by AC or DC current—in order to facilitate transport of a patient, e.g. from the ER to the operating room—no prior art device teaches or discloses the use of a battery source (DC power) as an amperage supplement to be used simultaneously with an AC power source, thereby enabling the heating of physiological fluids at a rate which surpasses that possible with AC alone.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 4,019,020 discloses an apparatus for maintaining a fluid supply such as human blood at optimum temperatures by utilizing an electrically heated inner mandrel maintained at a thermostatically controlled temperature. The temperature of the mandrel is controlled via thermostats being electrically coupled in series with electrical heaters.
U.S. Pat. No. 4,523,078 discloses a portable electrically heated warming container for heating a plurality of infusion containers within a case. The device includes a provision for detachably connecting the electric heater plug to a rescue vehicle power supply. A further electrical connector permits energization of the heating element from a nonvehicular power supply when removed from the rescue vehicle.
U.S. Pat. No. 4,678,460 discloses a self-contained portable apparatus for the rapid warming and infusion of massive amounts of parenteral fluid into a patient. The associated fluid warming system is a dual heat system, having a primary heating element for maintaining the apparatus in a stand-by condition when the apparatus is not in use, and a secondary heating element for raising the temperature of the fluid to the desired temperature while the apparatus is in use. By operating the secondary heating element only during the time the primary heating element is inoperative and vice-versa, the electrical load on the hospital electrical system can be more easily maintained within the maximum limit without loss in performance of the fluid warming system.
U.S. Pat. No. 5,125,069 discloses a blood warmer for changing the temperature of an infusible fluid from a first temperature to a second predetermined temperature. The assembly includes a thermoelectric heat pump with a slot for releasably receiving a cartridge so that the heat pump engages the wall of the cartridge. An electrical circuit is responsive to a temperature sensor for controlling operation of the heat pump so that the liquid exiting the cartridge is at a predetermined temperature. The device uses an AC rectified power supply to provide suitable DC power for the heat pumps and control circuitry. A battery may be provided and selectively connected by a switch when the warmer is to be used in a portable application, or when the AC power is not available.
U.S. Pat. No. 5,250,032 discloses a heater for warming blood flowing through an intravenous tube prior to its entry into a patient. The heater is housed in an elongated channel which is secured to the arm of the patient. The housing contains a heating element controlled by a control circuit and powered by batteries.
SUMMARY OF THE INVENTION
The present invention provides both a process and apparatus for rapidly warming and delivering relatively high volumes of a physiological fluid. Unique to this invention is the ability to warm and infuse physiological fluids at a rate of about 1000 ml/min, at a controlled temperature range to the patient, e.g. of about 38° C. +/− at least about 0.5° C., preferably +/− about 0.1° C., without causing damage to the fluid components, e.g. lysing or rupture of cells; and without upsetting the normothermic equilibrium of the patient. Physiological fluids used for infusion into the body are often stored under refrigerated conditions to maintain their freshness, e.g. at temperatures of about 4° C. Such fluids may be selected from blood products such as whole blood, packed cells, plasma or the like, along with non-blood products such as colloids and crystalloids, and various mixtures thereof. Prior to infusion, these fluids must be warmed to a temperature which renders them safe for infusion into a living patient without upsetting the normothermic equilibrium and inducing hypothermia. Additionally, when transporting such fluids to the patient, certain flow conditions can cause damage to the fluids at a cellular level, e.g. the inclusion of areas of high pressure drop can induce unwanted turbulence and produce a shearing effect which may be damaging to the blood cells. The instant invention fluidly couples one or more vessels, such as flexible plastic bags, containing one or more of the desired physiological fluids, to an in-line pumping means which may be operated either manually or motor driven or the pump may be selectively disengaged to allow the use of other means for moving the fluid through the system. The pump, e.g. a line pump along with its associated valves and tubing, is designed to provide laminar flow for transport of the physiological fluid to a heat exchanger. The heat exchanger, which in the preferred embodiment is a spirally wound heat exchange element, is of sufficient capacity to raise the temperature of the physiological fluid to the required level at a flow rate which is designed to prevent cell damage. In order to protect the patient, it is known to simultaneously filter the fluid and remove excessive air bubbles. This invention uniquely positions the filter/air separator within the warming bath to avoid temperature losses while carrying out these processes. In order to maintain the desired physiological fluid outlet temperature, at the maximum required flow rates, the instant invention provides heaters which utilize both a
Jeffery John A.
McHale & Slavin
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