WO2001062194A1 - Portable i.v. fluid warming system - Google Patents

Abstract

A portable disposable intravenous fluid warming system (20). Power FET's (104, 106, 108, 110) provide heater drive current from an unregulated DC input source. A first sensor (72) is coupled to a microprocessor (120) which samples the temperature, about 5,000/second so as to allow determination of when the desired temperature is reached and to control the FET's (104, 106, 108, 110) as necessary to hold the temperature at the correct point without exceeding the temperature. Interfacing is provided to an optional external digital readout unit for monitoring. The addition of an in-line thermocircuit breaker will provide an independent over-temperature shutdown failsafe.

Description

PORTABLE I.V. FLUID WARMING SYSTEM

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention generally relates to an apparatus to warm fluids meant to be infused into the body, including blood products, to a desired temperature, approximately the normal body temperature. This apparatus is small, portable, and disposable and is easily used by the care giver without special training.

2. DESCRIPTION OF RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR 1.97 AND 1.98

Fluid introduced intravenously should be warmed to a temperature approximating normal body temperature to prevent the lowering of core body temperature. Intravenous fluids are normally stored at ambient temperature with some products stored at refrigerated temperatures. Normal core body temperature is 37° C (98.6° F), ambient temperature is 23.9 °C (75 °F) and refrigerated temperatures are from 0°C to 4.4°C (32°F to 40°F). In emergency situations, such intravenous fluids may necessarily be introduced at refrigerated temperatures directly into the body through intravenous (LV.) tubes. Introduction of such liquids at these refrigerated temperatures, however, presents a substantial risk for injurious chill hypothermia and/or shock to the body.

A variety of devices have been developed to address the issue of the warming of intravenous fluids. Current systems are generally of two types. Bulk warmers require a sufficient period of time to warm the product to a desired temperature and will only warm up a set number of fluid units at a time. Moreover, in order for the bulk warmer to be constantly ready for emergency use, it must be maintained at a proper and set temperature. This requires a system which is bulky, heavy, and/or fixed. Prewarming and holding such fluids, as set forth above, is not practical for certain blood products and pharmaceuticals that are degraded if held at an elevated temperature. Moreover, the bulk warmers allow the fluid to cool in the line set as it is administered. A bulk warmer system also experiences drawbacks associated with emergency use since it requires prior anticipation of the need for warmed fluid units as well as the number of fluid units which will ultimately be needed. Furthermore, and assuming the aforereferenced conditions are met, fluid units that are warmed and ready for use must move through several feet of tubing in addition to the drip chamber thereby offering substantial time and opportunity for such liquids to cool before entering the body.

The second type are in-line fluid warmers. Previous in-line fluid warmers somewhat address the disadvantages described above except that such in-line systems attempt to warm the fluid in the existing plastic line, which is an inefficient means of heat transfer. Moreover, in-line warming systems are generally limited in volume, e.g., 30-40 millimeters per minute, and require a 120- volt AC power source. Additionally, the accuracy of such a system is only plus or minus 5 degrees. They are also bulky and require significant time to set up.

One such system is known as the Animec Infusion Warmer. It is electrically powered and is a dry warmer that supplies external heat to plastic tubes by an aluminum heating plate. Temperature sensors contact the tubing and regulate the temperature. The plastic tube to be heated can be placed in an S-shaped channel in the heating plate in the warmer. Different size tubes can be used. This unit has several disadvantages. First, the length of tubing being heated is comparatively short. Second, the tubing is contacted by the aluminum plate over only a portion of its surface area. Third, total heating of the heating plate is based only on the output temperature of the fluid. Fourth, different models must be used for different sized tubing. Fifth, it is not portable but requires a 110- volt AC power source. Sixth, it is possible that excessive warming of the fluid can occur. Seventh, it is not a disposable warming unit. SUMMARY OF THE INVENTION

The present invention addresses the above and other disadvantages of prior art systems for warming intravenous fluids. The preferred embodiment of the invention preferably comprises a single stainless steel tube unit containing a plurality of parallel straight sections in the same plane. The tube unit is wrapped in a flexible material which supports resistance heater elements. The inlet cap contains the power supply connector, data input/output jacks, fluid inlet connector, and LED's for indicators such as power and temperature. These various connections are connected to corresponding components on a printed circuit card. The printed circuit card or "daughter board" is also connected to the flexible resistance heaters and a thermistor which is located in the outlet tube. The outlet cap holds the fluid outlet connector. The fluid line connectors are standard size to fit standard LV. line connections. The power source is a portable battery, vehicle/aircraft power supply, or standard 120 AC power. The power source will connect into a jack on the inlet end cap or manifold as shown, or any other convenient location in the housing.

In the preferred embodiment, the heating elements are divided into four groups that are connected in electrical parallel. However, more groups or even fewer groups could be used if desired, and would preferably be equal to the number of straight sections in the stainless steel tube unit. Each of the groups has a plurality of heating elements connected in electrical series and each heating element is in direct heat transfer relationship with a corresponding one of the appropriate straight tubing sections.

A first temperature sensor such as a thermistor senses the temperature in the outlet tube. Another sensor or thermistor monitors the temperature just before the fluid leaves the last tube. The first sensor is coupled to a central microprocessor which takes readings from the first sensor approximately 5,000 times per second so as to maintain the fluid temperature above a preselected minimum temperature such as, for example, 38 °C plus or minus 1°C.

The other thermistor is in a separate fail safe circuit which blows a fuse in the power input line if the thermistor senses a preset safe temperature such as, for example, 41 °C has been exceeded. Appropriate light-emitting diodes indicate when the power is ON and when power is connected to the various groups of heating elements.

Thus, the present invention presents a number of advantages over the prior art. One such advantage is the ability to quickly warm an unlimited amount of fluid within a specific temperature range. Another advantage presented by the invention is the reduction in heat loss after the fluid is warmed by heating the fluid close to the point of entry into the patient's body.

Still another advantage of the present invention is ready adaptation and application to conventional LV. line-set assemblies. In such a fashion, economy of energy is observed while assembly and interconnection may be accomplished in a short amount of time.

Also, another advantage of the present invention lies in its low cost construction thereby enabling a disposable use. In such a fashion, a sterile environment is ensured for each use. Yet another advantage is the adaptability of the present invention to emergency field conditions without loss of time in treatment or in transport.

A further advantage of the invention is that the entire unit is in one piece, without a separate, reusable, control unit.

Still other advantages of the present invention will become obvious after review of the detailed description of the drawings.

Thus, the invention relates to a portable intravenous fluid warming system comprising a housing having an I. V. fluid input port and an LV. fluid output port, a stainless steel tube unit having a plurality of straight sections all located in the housing carrying the LV. fluid to be warmed from the fluid input port to the fluid output port, each one of the tube sections having an outer periphery, one or more flexible heating elements providing heat to the plurality of straight tube sections for heating the LV. fluid therein, the flexible heating elements being in contact with, and surrounding at least the majority of the peripheral surface of a corresponding straight tube section. BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will be more fully disclosed when taken in conjunction with the following Detailed Description of the Preferred Embodiment(s) in which like numerals represent like elements and in which: FIG. 1 A illustrates the elements of a conventional I. V. system;

FIG. IB illustrates the various elements of one preferred embodiment of the present invention;

FIG. 2 is a perspective view of one embodiment of the portable, disposable fluid warming unit incorporating the teachings of the present invention; FIGS. 2 A and 2B are perspective views of the fluid inlet end cap and fluid outlet cap respectively of the embodiment of FIG. 2;

FIG. 3 illustrates a computer with a connector suitable for connecting to the embodiment of FIG. 2;

FIG. 4 is a top view of the embodiment of the stainless steel tube unit and also showing a phantom view of the outside casing of the fluid inlet and outlet caps without the central body casing;

FIG. 4 A shows an insert in the outlet portion of the stainless steel tube unit supporting a pair of temperature sensors such as thermistors;

FIG. 5 illustrates a cross-sectional view of the tubes and the method of wrapping heating elements to make the heat exchanger of the warming blanket of the embodiment of FIG. 2;

FIG. 6 is an unfolded layout of the electrical heating element of the warming blanket or flexible printed circuit used in the embodiment of FIG. 2; FIG. 6 A shows a small printed circuit board for supporting the system control unit and control switches;

FIG. 7 is a diagrammatic representation of various electronic components along with the warming blanket or printed circuit with the flexible heating elements thereon in relation to the tube sections that are to be heated; and FIG 8 is a wiring diagram of the electrical circuit of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODEMENT(S)

An illustration of a conventional intravenous setup 10 may be seen by reference to FIG. 1A. As illustrated in FIG. 1A, an intravenous solution, e.g., a saline solution, is contained in a bag or bottle 11 which is normally suspended above the patient. Fluid from the bag 11 passes by gravity or positive pressure through a conduit or tube 12 into a drip chamber 13 whereupon the flow rate is monitored. Fluid passes from drip chamber 13 through a second conduit 14 that is coupled to a catheter 15 to be inserted into selected blood vessels of the body.

The aforedescribed intravenous system has been used as a standard method of administering intravenous fluids and blood and blood products. These products are administered at the temperature at which they are stored (ambient temperature or from refrigerant storage). In some cases, they are prewarmed and then administered allowing them to again cool toward ambient temperature while being administered. Other intravenous fluids, such as blood products, must be maintained at a refrigerated temperature of 40 °F (5°C) or less immediately prior to being administered to the patient. Moreover, the flow rate at which such products must be introduced to the body forecloses their use unless or until warmed near body temperature.

The present invention is intended to overcome these disadvantage and is designed to be operated by field emergency medical technicians (paramedics) trained in administering LV. fluids under adverse conditions. The normal patients are the victims of trauma or serious acute illness with a substantial potential of progressing into hypothermia and shock. Fluids may be administered under adverse conditions such as to individuals trapped in vehicles or collapsed buildings as well as in other cluttered and chaotic field conditions. These settings dictate small, easily handled mechanisms that do not add to the confusion and difficulty of the situation.

Since most trauma and acute illnesses happen in environments of considerably less than body temperature, virtually all patients requiring I. V. solution will have the potential of entering shock while being handled in emergency channels. Control of I. V. fluid temperatures would be appropriate. Certainly, all patients requiring the addition of a significant volume of fluid should receive fluids at body temperature. Such a system must warm LV. fluids to a range of 37 °C to 40°C (98.6°F to 104°F) and must infuse the fluid into a patient at the rate of up to 200 ml per minute. There must be no danger of malfunction causing overheating of the fluid being infused. The equipment involved must be lightweight and easy to handle (idiot proof) in confined areas in all weather and environmental conditions. The system must be sterile and any parts coming in contact with a patient must be disposable. The system must be compatible with existing I. V. fluid systems and must be capable of being made ready within one minute with only a minimum of additional steps being required over the standard system. The system must be usable as close as possible to the patient when starting LV. solution to prevent re- cooling of the I. V. fluid. The operating time before a change in the power source is required to be a minimum of 30 minutes under normal expected uses. Further, the warming system must be independent of the I. V. solution bag temperature. The LV. fluid warming system of the present invention provides an outlet temperature in the range of 37°C (98.6°F) to 39°C (102.2°F). A shutdown occurs at any desired preset temperature, such as 41 °C (105°F). The unit will handle a flow rate up to 200 ml per minute from 21 °C (70°F) to 37°C (98.6°F) or at smaller flow rates at lower temperatures. The unit can be used in all types of weather and is a disposable unit. It is compatible with existing LV. fluid systems and takes approximately 30 seconds to set up. Power can be supplied either from a 12-volt battery, a 12-volt DC adapter or an AC adapter. An optional external digital readout may be provided with an external monitor or computer 34 attached to a data connector jack 40a as shown in FIG. 3. The data connector may also be used to connect a temperature adjustment device for use by appropriate medical personnel when needed. The connector may also be used to connect to a computer to monitor whether power is ON or OFF in each of the stages of the heater. For example, the data can be transferred to a computer program such as the well-known EXCEL program. Thus, FIG. IB shows a preferred embodiment of the present invention as it may be incorporated into the aforedescribed conventional intravenous system in order to warm the solution prior to administration to the patient. Fluid from an LV. bag or bottle 16 passes through a conduit 17 to a drip chamber 18 as described above in conjunction with a conventional intravenous system illustrated in FIG. 1A. Fluid then passes through a second conduit 19 into the system 20 of the present invention which comprises a fluid warming element. The warmed fluid then passes through a third conduit 21 that is coupled at its terminal end to a catheter 22 to be inserted into the body. A battery 23 provides power through a conductor 24 to the unit 20. Alternatively, the unit 20 may be connected to a power converter connected to standard AC power or to a vehicle power source directly.

It will be understood from the system in FIG. IB that the warmer 20 may be provided very close to, or even placed on, the body of the patient. Thus, the tube 21 is short and allows for little heat loss prior to the fluid entering the patient's body. FIG. 2 is a diagrammatic representation of the warming unit 20. It has plastic end caps or manifolds 26 and 28, shown in detail in FIG. 2A and FIG. 2B, that pass the incoming fluid through a port 30 in end piece 26 back and forth through a warming tube unit 34 as shown in FIG. 4 and then to an outlet port 32 in end piece 28 as shown in FIG. 2B. The end caps 26 and 28 have their connections to the I. V. lines recessed for protection. The central portion of the warming tube unit 50 as shown in FIG. 4 includes straight tube sections 50 which are connected together by end pieces 44, 46, 48, 66, 68 and 70 to form a continuous serpentine channel from the entrance 30 to the exit 32. In a preferred embodiment, the continuous serpentine channel make of straight tube sections 50 and end pieces 44, 46, 48, 66, 68 and 70 is formed from a single piece of tubing. However, it could be several pieces connected together to form a sealed continuous channel. As will be shown and discussed in detail hereafter, the straight tube sections 50 are wrapped by a special warming blanket or flexible printed circuit containing the heating elements that can be wrapped or formed around the tubes. The entire unit is encased in a protective covering such as a plastic extrusion such as is illustrated in FIG. 2. Light-emitting diodes 36, 37, and 38 indicate selected operating functions of the device. According to one embodiment, LED 36 may indicated that power is being supplied to the heating blanket and LED 38 may indicate the status of the power source. There is also an input power jack 42 and a data port connection 40. It will also be appreciated that the warmer of the present invention could be used for continuous arteriovenous blood warming. For such usage, a computer 43 having a plug 40a suitable for mating with the receiving plug 40 on end cap 26 is shown in FIG. 3. Thus, when plugs 40 and 40a are connected, computer 43 can produce continuous monitoring and recording of the operation of the warming unit 20. For those warmers identified for such continuous or long term use, heparin may be used to coat those portions of the device which will contact the blood to prevent the possibility of blood clotting. In addition, more complex warming units may include the capability of setting, adjusting or changing outlet fluid temperature by sending control signals from computer 43 to microprocessor 120 on board 100 as shown in FIG. 6A.

FIG. 4 illustrates in a schematic way the serpentine fashion of the warming unit 34. Thus, the fluid flow path from the input port 30 to the output port 32 is a circuitous serpentine path through the straight parallel spaced tube sections 50 which lie in a horizontal plane. A temperature sensor 72 having connecting wire 73, such as a thermistor and illustrated as located in plastic insert 74, is shown as connected in the last straight tube section 64 in FIGs. 4, 4 A, 7 and 8 for the outgoing fluid. The temperature sensor 72 is shown here merely to indicate its relative placement in the housing. It could, of course, be physically placed in the housing at any location most convenient for the connections so long as it can maintain the proper temperature in the outgoing portion of the warming tube unit 34. A second thermistor 76 having connecting wire 77 is also located in the outgoing tube section 64 just before output coupling 32 and acts as a fail safe safety device to ensure that the output temperature of the fluid stream does not exceed a safe preset temperature such as, for example, 41 °C. This thermistor 76 is part of a separate circuit which blows a fuse to disconnect the input power if the preset temperature is exceeded. In the preferred embodiment, both thermistors 72 and 76 are mounted in a plastic insert 74 which is located in line 64 in the outlet tube as shown in FIGs. 4, 4 A and 7. While seven tube sections are shown in FIGs. 2 and 3, it will be understood that more or less tube sections may be used as desired for a particular warming device. FIG. 2 A is a view of the inlet end cap 26 with the power connector 42, incoming fluid line 30, data connection port 40 and power LED 36, which indicates that the heating elements are functioning. LED 38 indicates the status of power source, and a third LED 37 could be used to indicate fluid temperature status by varying its flashing rate depending upon the temperature. According to one embodiment these elements are molded into the end cap or manifold 26 by injection molding. The electrical connections extend through the end cap so they can be surface mounted to their proper connections on the warming blanket or printed circuit card 100 as shown in FIG. 6A.

FIG. 2B is a perspective view of the outlet end cap 28 showing outgoing fluid line connector 32.

FIG. 5 is a diagrammatic representation of a cross-sectional view of the warming unit at a point where the tubes are covered by the warming blanket or heating element (flexible printed circuit). Each of the straight tube sections 52, 54, 56, 58, 60, 62, and 64 is shown. Note that the bottom half of each of the straight tube sections, except for the last tube section 64, is partially surrounded by a corresponding heating element 88, 90, 92, 94, 96, and 98, respectively. These heating elements are further illustrated in a flat condition in FIG. 6. Referring again to FIG. 5, with respect to the end tube 64, the flexible heating element 82 begins under the tube 64 at 84 and extends substantially around the remaining peripheral surface of tube section 64 as shown at 86 and is in heat transfer relationship therewith. The remaining portions of the printed circuit have corresponding heating elements 88a, 90a, 92a, 94a, 96a, and 98a that surround the top half of the peripheral surface of the six remaining tube sections. Also as shown in FIG. 6A the printed electronic circuit board, shown collectively by reference number 100 which is electrically coupled to power jack 42. Thus, it will be appreciated that the printed circuit substrate or warming blanket shown in FIG. 6 is flexible and forms a special warming blanket that is molded around the tubes as shown more clearly in FIG. 5. The flexible substrate may be, for example only, Mylar or some other suitable flexible material. Although not shown, for some uses an additional insulating layer of material may be placed over the special warming blanket to hold the heat in the unit

In one preferred embodiment, the warming tube unit 34, as shown in FIG. 4 is a serpentine shaped stainless steel 3/16 OD single piece of tubing formed of a medical grade stainless steel, (e.g., 316L or 304L grade) about 50 inches long and with a wall thickness of about 0.035 inches. As mentioned above, the tubing could be formed of several pieces, and other tubing material with high thermal conductivity and medical grade coating could be used. Heating is accomplished with the resistive heaters 88 and 88a, 90 and 90a, 92 and 92a, 94 and 94a, 96 and 96a, and 98 and 98a, along with wrap-around portion 82 etched on the flexible circuit material such as Mylar in a well-known manner. The flexible material is formed around each tube as shown in FIG. 5. Independent heating element circuits, which form stages or zones, are formed as will be discussed hereafter to provide heating to the desired temperature. The heating elements are grouped into four independent heating zones which, according to one embodiment, operate at the same time. However, it will be understood by one skilled in the art that, in an embodiment where all four heating elements operate at the same time, a single continuous heating element would be acceptable. On the other hand, more or fewer than four heating zones may be formed if desired. A separate fuse (102 in FIG. 8) provides input power to the warming blankets or heating elements, and, as mentioned above, will interrupt the circuit if the preset safety temperature is reached.

As mentioned above, FIG. 6 is a diagrammatic representation of the warming unit with the warming blanket or flexible printed circuit substrate being shown in its unfolded condition. FIG. 5 on the other hand shows the heating elements in relation to the tube sections that carry the intravenous fluid. Heating elements 88, 90, 92, 94, 96, and 98 are in contact with the bottom half of the tubes 52, 54, 56, 58, 60, and 62. In a similar manner, heating elements 88a, 90a, 92a, 94a, 96a, and 98a, respectively, are in contact with the top half of the tubes. The last tube 64 is completely wrapped by one heating element 82.

Four controlling FET's 104, 106, 108, and 110 are schematically shown in FIG. 7 coupled between the microprocessor chip 120 and the four stages of heating elements 112, 114, 116, and 118. They control the current by turning the power ON and OFF to the individual stages and can be programmed to come on individually according to a selected profile. However, in a preferred and simplified embodiment, all of the FET's substantially turn ON and OFF together. Thus, it will be appreciated that a single higher current capacity FET could be used in such a preferred embodiment.

FIG. 8 is the schematic wiring diagram of the heating elements and the circuitry shown in FIGs. 6 and 7. Again, the circuit in FIG. 8 is shown as an example only and may include more or less than the four heating zones shown. As can be seen in FIG. 8, a power supply terminal 122 provides voltage through a fuse

102 that will open or "blow" at a predetermined temperature as determined by thermistor 74 to prevent overheating of the intravenous fluid. The voltage is coupled from terminal 122 through fuse 102 and a breaker 124 to the various stages of heating elements in electrical parallel and is also coupled to microprocessor 120. A battery or other power source is connected to the power jack and coupled between input terminal 122 and ground terminal 125 to provide the necessary power thereto.

In operation, when the unit 20 has the intravenous lines connected into and out of the unit and the fluid is flowing, LED 36 indicates the power is being provided to the warmer unit. LED 37 indicates power is actually being sent to the heating elements through the four controllers or FET switches 104, 106, 108, and

110 which are, in turn, controlled by the microprocessor 120 based upon the temperature received from thermistor 72. In one embodiment, LED 37 may also be used to indicate the fluid temperature status by varying its flashing rate depending on the fluid temperature. Thus, for example only, by counting the number of flashes per minute, the temperature of the fluid can be determined. At the start of use, the microprocessor 120, senses low temperature intravenous fluid and turns ON FET switches 104, 106, 108, and 110. Thus, the power is connected from the power source 122 through the fuse 102 and circuit breaker 104 to the parallel heating stage's circuits. These elements can be seen in relation to the tube sections in FIG. 5. Thus, the input heater stage 112 and 112a is associated with the incoming fluid tube sections 52 and 54. The next heater stage 114 and 114a is associated with tube sections 56 and 58; the second intermediate heater stage 116 and 116a is associated with tubes 60 and 62, while the final heater stage 118 is associated with tube section 64. Again, tube sections may be added or subtracted as needed to meet specific requirements.

In the preferred embodiment, sensor 72 senses the output temperature of the intravenous fluid at a rate of 5,000 times a second as determined by microprocessor 120. If the temperature is above the desired range 37°C (98.6°F) to 39°C (101.3 °F) or a signal is generated that is sensed by microprocessor 120 that generates a signal to open switches or FET's 104, 106, 108 and 110 to remove power to the heating elements. Then, while coupling at a rate of 5,000/second when the temperature falls below the desired range, microprocessor 120 will again close switches or FET's 104, 106, 108 and 110 to turn power back on. This ON and OFF cycling is continuous and maintains the outlet temperature of the Aid at the desired temperature range. As mentioned above, when power is flowing to the heater elements, LED 37 may be used to indicate the temperature status. When the battery power is at an acceptable level, LED 36 will be lit.

If the temperature of the I. V. fluid exceeds a predetermined maximum temperature as indicated by thermistor 76 in the separate fail safe circuit, fuse 102 opens or blows removing power to the unit. This may be accomplished in any number of ways, including, as an example only, an output signal from microprocessor 120 on line 126 which simply turns on power FET 128. When power FET 128 is turned on the current through fuse 102 increases significantly as the power bus 130 is shorted to ground through current limiting resistor 132. Also, if any of the FET's 104 - 110 do not operate properly, microprocessor 120 may shut down the circuit or preferably turn only the failed FET OFF, such that only three heating circuits operate.

The warmer of this invention will warm fluid to a preset temperature at any input/output rate (1 milliliter/minutes to 200 milliliters per minute) regardless of the incoming temperature or flow rate and maintain that temperature within + 1 °F.

The condition of various components of the system may be connected to data connector 42 that can be coupled to a remote analyzer or computer if desired. Typically, the data may be extracted from the microprocessor and displayed and/or recorded using clean text "ASCII" format. Thus, there has been disclosed a novel portable I. V. fluid warming system that is economical to construct, easy to operate, portable, disposable, and efficient in use.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed.

Claims

WHAT IS CLAIMED IS:

1. A portable intravenous fluid warming system comprising: a housing having an intravenous fluid input port and intravenous fluid output port; a plurality of straight tube sections connected together and located in said housing to carry said intravenous fluid to be warmed between said input port and said output port, each one of said tube sections having an outer periphery; a flexible heating element for heating the intravenous fluid flowing through said straight tube sections, said flexible heating element being wrapped around, in contact with, and surrounding the peripheral surface of said tube sections; a power supply having a voltage and a ground potential; a switch coupled between said heating element and said power supply for coupling a voltage to said heating elements in response to a control signal; a heat sensor for sensing the output temperature of said warmed intravenous fluid and for providing a control signal to said switch to disconnect power from said heating elements when said output temperature of said intravenous fluid exceeds a first preset temperature level.

2. The portable intravenous fluid warming system of claim 1 further including: a first LED for coupling to said power supply voltage to indicate when said power supply voltage is coupled to said warming system; and a second LED coupled to said heating elements to provide an indication when said heating elements are heating.

3. The portable intravenous fluid warming system of claim 1 further comprising an external electrical connection panel on said housing for providing test connections to said sensors and said switches.

4. The portable intravenous fluid warming system of claim 4 further including a second heat sensor for receiving the output temperature of said intravenous fluid, and a power interruption device coupled to said heating elements, said power interruption device disconnecting said heating elements from said power supply voltage in response to said second sensor sensing a second preset temperature level, said second preset temperature level being higher than said first preset temperature level.

5. The portable intravenous fluid warming system of claim 1 further including a power jack in said housing for coupling to an external power source.

6. The portable intravenous fluid warming system of claim 1 further including an insulated covering disposed about said heating elements.

7. The portable intravenous fluid warming system of claim 1 wherein said tube unit is formed of stainless steel.

8. The portable intravenous fluid warming system of claim 4 wherein said tube sections are formed from a single piece of tubing.

9. The portable intravenous fluid warming system of claim 1 wherein said microprocessor provides operational data from said system in ASCII format and further comprising means for displaying said data.

10. The portable intravenous fluid warming system of claim 9 and further comprising means for recording said data.

11. The portable intravenous fluid warming system of claim 1 wherein at least some of said interconnected tube sections are coated with heparin.

12. The portable intravenous fluid warming system of claim 4 wherein said system will maintain a preset temperature to within + 1 °C at an input/output flow rate of between approximately 1 milliliter per minute and approximately 200 milliliters per minute.

13. The portable intravenous fluid warming system of claim 1 wherein said flexible heating element is made up of a plurality of sections connected together.

14. The portable intravenous fluid warming system of claim 1 wherein said flexible heating element is made up of a plurality of sections connected in a number of groups equal to the plurality of straight tube sections.

15. The portable intravenous fluid warming system of claim 14 and further including at least one other switch such that selected one of said groups of heating sections can be turned ON and OFF independent of each other.

16. The portable intravenous fluid warming system of claim 15 wherein said switch and said at least one other switch comprises from a switch for independent controlling four groups of heating sections.