BACKGROUND OF THE INVENTION

Intravenous or infusion fluid such as blood is commonly used in hospitals and in the field for example in emergency or war zones. The infusion fluid is important for virtually all medical procedures and applications. Such infusion is typically delivered from an IV fluid bag or container into a blood vessel of a patient. It is desirable to warm the blood or IV fluid to a certain range of temperature (e.g. between 36 and 37 degrees Celsius) to avoid temperature drop in the patient which may lead to hypothermia.

There exist various conventional devices and techniques for heating or warming infusion fluids before being administrated to a patient. However, these conventional devices and techniques suffer from a number of drawbacks. The conventional infusion fluid warmers are bulky and heavy which make them unsuited for portable applications where they have to be transported by foot for example by soldiers, rescue workers or ambulance crews to reach inaccessible emergency sites. The heavy and bulky nature of existing infusion fluid warmers also makes it difficult or impossible to secure or attach these to the patient's body in a convenient and safe manner. Another disadvantage of existing fluid warmers is that they are composed of a large number of separate parts which make them expensive to manufacture and tend to reduce reliability due to a multitude of separate engaging parts.

Yet another disadvantage of existing fluid warmers is a lack of a mechanism for capturing and coupling heat energy dissipated in the energy source during fluid warming to the infusion fluid. This leads to inefficient use of energy stored in the energy source, such as rechargeable or non-rechargeable batteries, and therefore a need for larger, heavier and more costly energy sources than strictly required to warm a given volume or amount of infusion fluid. According to one aspect of the present invention, this problem is solved by conducting excess heat energy generated by a portable energy source to the infusion fluid to heat the latter. Thus, ensuring that the energy held in the portable energy source is put to efficient use.

WO 2003/049790 A1 describes a system for heating transfusion fluids comprising a fluid warmer having an inlet channel and an outlet channel. A fluid passage of meandering shape is formed in a separate cartridge arranged between a pair of heat contact plates.

SUMMARY OF THE INVENTION

A first aspect of the invention relates to an infusion fluid warmer which comprises a casing shell having an upper wall structure and a lower, opposing, wall structure. The casing shell enclosing:

a fluid channel or passage extending through the casing shell in-between the upper and lower wall structures,

fluid inlet and outlet ports coupled to opposite ends of the fluid channel or passage to allow a flow of infusion fluid through the casing shell. A housing shell is formed in a thermally conducting and electrically insulating material and a heating element is bonded to the housing shell and thermally coupled thereto. The fluid channel or passage extends through the housing shell or extends around the housing shell such that heat energy is transferred to the infusion fluid by direct physical contact with housing shell material. The casing shell of the infusion fluid warmer may comprise a thermoplastic material or elastomeric compound fabricated by a suitable manufacturing process such as injection moulding. The casing shell may function to protect the housing shell from mechanical shock, impacts and pollutants in the external environment. The casing shell may have a shape with rectangular, elliptical or circular cross-sectional profile, i.e. along a cross-section transversal to the direction of infusion fluid flow at the fluid inlet and outlet ports.

The fluid inlet and outlet ports of the casing shell allow the infusion fluid to flow through the infusion fluid warmer with cold or unheated infusion fluid entering at the inlet port and heated or warmed infusion fluid exiting through the outlet port on its way to the patient.

The housing shell possesses an advantageous multi-purpose role in the present infusion fluid warmer by acting as a physical carrier for the heating element bonded thereto, e.g. thick film and/or thin film resistor(s), and as a heat exchanger or heat plate transmitting heat energy directly to the infusion fluid by the physical contact between the housing shell material and the fluid. This property is capable of providing a compact infusion fluid warmer requiring only a minimum of separate parts to be manufactured and assembled. The housing material preferably comprises ceramic material such as Aluminium Oxide (Al.sub.2O.sub.3), Aluminium Nitrate or Beryllium Oxide which all are well-suited as substrate materials for a large range of heating element materials, in particular thick film and thin file resistors. The ceramic material additionally possesses good thermal conductivity and good electrically insulating properties. The skilled person will appreciate that the material of the housing shell is preferably bio-compatible for example a bio-compatible ceramic material such as Aluminium oxide (Al.sub.2O.sub.3) due to its direct contact with the infusion fluid to be distributed to the patient. Alternatively, materials that are not bio-compatible may be used such as ceramics Aluminium Nitrate or Beryllium Oxide.

To possess adequate electrically insulating properties, the housing shell preferably comprises a material with specific electrical resistance larger than 1.times.10.sup.9 ohm*m, to meet official requirements. To possess adequate thermally conducting properties, the housing shell is preferably made of a material with specific thermal conductivity larger than 0.5 W/(mK), more preferably larger than 1.0 W/(mK) even more preferably larger than 10.0 W/(mK).

The housing shell may be fabricated as a single unitary element for example by moulding or machining a solid object. The fluid channel may have a largely straight rectangular form extending through a central portion of the element. In alternative embodiments, the housing shell comprises a plurality of separate structures that are bonded together after individual fabrication for example by gluing, soldering, press-fitting, welding etc. In one such embodiment, the housing shell comprises an upper wall structure and a lower wall structure formed in separate upper and lower housing shells, the upper and lower housing shells being bonded to each other. In this embodiment, the fluid channel may extend in-between the upper and lower housing shells for example formed by mating grooves or trenches formed in facing surfaces of the upper and lower wall structures of the housing shell to form a fluid passage extending through the housing shell. The fluid channel may have a variety of different shapes but preferably a shape that maximizes a contact area between the infusion fluid and the housing shell (functioning as a heat exchanger) to increase the fluid heating capacity of the fluid warmer (for example expressed in litres per minute). In one embodiment, the fluid channel has a meandering shape in a cross-sectional plane extending perpendicularly to the flow of infusion fluid at the inlet and outlet ports. This plane may be orthogonally to a longitudinal axis of the housing shell if the latter has a flat plate like structure. In an alternative embodiment, the fluid channel comprises a substantially straight channel extending along the longitudinal axis of the plate shaped housing shell. In the latter embodiment, the fluid channel preferably extends through a substantial portion of a width of the housing shell to maximise the contact area between the infusion fluid and the housing shell. The fluid channel may be formed as a substantially rectangular straight tunnel with a height between 0.1 mm and 5 cm such as between 0.5 mm and 2 cm. If the housing shell has the flat plate shaped structure, its height may be less than 4.0 cm, preferably less than 1.0 cm.

In yet another embodiment of the infusion fluid warmer, the fluid channel extends around the housing shell such that the fluid channel comprises a first channel segment arranged between the upper wall structure of the housing shell and the upper wall structure of the casing. The fluid channel further comprises a second channel segment arranged between the lower wall structure of the housing shell and the lower wall structure of the casing. In this embodiment, the upper and the lower wall structure of the housing shell are both in physical contact with the infusion fluid to provide a large contact area between the housing shell and infusion fluid so as to ensure efficient transfer of heat energy. The skilled person will appreciate that the fluid channel in the alternative may comprise only a single channel segment extending around the housing shell.

The heating element is preferably bonded to a surface of the upper and/or a surface of the lower wall structure facing away from the fluid channel to isolate electrical drive voltages or currents supplied to the heating element from the infusion fluid and prevent corrosion attacks on electrical terminals or components of the heating element. In one such embodiment, the heating element comprises a thin film resistor or a thick film resistor bonded directly on the surface(s) of the upper and/or lower wall structures facing away from the fluid channel for example by screen-printing or other suitable bonding mechanism. Hence, in these embodiments, the electrically insulating property of the upper and lower wall structure(s) is used to electrically insulate the infusion fluid from the DC or AC voltage/current applied to heating element or elements to heat these. The thick film resistor or thin film resistor may naturally comprise a plurality of resistor elements or individual resistors coupled in series or parallel to provide any desired resistance value depending on the requirement of the application. The thick film or thin resistor may cover a considerable portion of the total area of the surface of the upper wall structure facing away from the fluid channel and/or a considerable portion of the total area of the outer surface of the lower wall structure facing away from the fluid channel. The total resistance of the thick film or thin film resistor may vary widely e.g. from 0.001 ohm to 10 Kohm. The thermally conducting property of the upper wall structure and the lower wall structure ensure that heat energy dissipated in the thick film resistor is efficiently conducted to the fluid channel. The surface of the upper and lower wall structures facing away from the fluid channel may comprise a pair of electrical coupling terminals for receipt of electrical power to the thick film or thin film resistor.

According to a preferred embodiment of the invention, the heating element comprises a portable energy source such as rechargeable, non-rechargeable batteries, a super capacitor etc. enclosed between the upper and lower wall structures of the housing shell. This embodiment provides a fully portable infusion fluid warmer which can be used in the field for example in emergency or war zones allowing infusion of fluids such as blood without cooling the patient. The simplicity of the present infusion fluid warmer combined with the small size and low weight is a significant advantage for medical personnel transporting the warmer.

According to this embodiment, the portable energy source is thermally coupled to the fluid channel preferably by direct physical contact with the housing shell to thermally conduct heat energy dissipated in the portable energy source in connection with its depletion to the fluid channel and infusion fluid flowing there through. In this context “direct physical contact” means in contact without any intervening passage or layer of atmospheric air or other gaseous substances. The materials, shape and dimensions of the housing shell, the fluid channel and the portable energy source are preferably configured such that the thermal resistance between a housing of the portable energy source and the infusion fluid is less than 100.degree. C./W, preferably less than 25.degree. C./W, even more preferably less than 10.degree. C./W.

The skilled person will appreciate that the heat energy dissipated in the portable energy source for example due to its internal impedance may exclusively be utilized to heat the infusion fluid or it may supplement heat energy dissipated in the heating element such as the above-discussed thick film or thin film resistor(s). Ion the latter case, both types of heat sources contribute to the heating of the infusion fluid. In this manner, the infusion fluid is warmed or heated by excess heat generated by the portable energy source instead of being wasted to the surrounding air. Consequently, efficient use is made of the energy stored in the portable energy source.

The housing shell may have a flat plate shaped structure with a height less than 2.0 cm, preferably less than 1.0 cm.

Another aspect of the invention relates to an infusion fluid warmer comprising a casing shell having an upper wall structure and a lower, opposing, wall structure. A fluid channel or passage extends through the casing shell in-between the upper and lower wall structures. Fluid inlet and outlet ports are coupled to opposite ends of the fluid channel or passage to allow a flow of infusion fluid through the casing shell. A heating element is thermally coupled to the fluid channel to transfer heat energy to the infusion fluid and the heating element comprises a portable energy source such as a rechargeable battery, a non-rechargeable battery, a super capacitor etc. This aspect of the invention provides a fully portable infusion fluid warmer for a variety of beneficial field uses for example in emergency or war zones allowing infusion of fluids or blood without cooling the patient. The simplicity of the portable infusion warmer combined with small size and low weight are noticeable advantages for the medical personnel transporting the warmer. The casing shell may comprise a thermoplastic material or elastomeric compound and fabricated by injection moulding. The casing shell may fully enclose or surround the heating element and the portable energy source to protect these from mechanical shocks and impacts and pollutants in the external environment. Because the portable energy source is thermally coupled to the fluid channel, heat energy dissipated therein, for example due to internal impedance of the portable energy source, is conveyed to the infusion fluid to heat of the infusion fluid instead of being wasted to the surrounding air. Consequently, energy stored in the portable energy source is put to efficient use which allows size, weight and energy storage capacity of the portable energy source to be reduced, or alternatively to provide higher energy storage capacity of the portable energy source for a given size, weight or capacity. The thermal coupling between the portable energy source energy source and the fluid channel is preferably provided by direct or indirect physical contact between these. In this context “direct or indirect physical contact” means in contact without any intervening passage or layer of atmospheric air or other gaseous substances such as through an electrically insulating and thermally conducting energy source housing as described below. A thermal resistance between the portable energy source and the infusion fluid is preferably less than 100.degree. C./W, preferably less than 25.degree. C./W, even more preferably less than 10.degree. C./W.

The portable energy source is preferably enclosed in a surrounding electrically insulating and thermally conducting energy source housing which preferably is arranged inside the casing shell. In the latter embodiment, the energy source housing and the casing shell may be coaxially aligned to form a fluid channel surrounding the energy source housing for example on all sides. In the latter embodiment, the fluid channel extends around or encircles the entire perimeter of the energy source housing to maximize the transmission of heat energy from the portable energy source to the infusion fluid. At the same time, efficient liquid cooling of the portable energy source is achieved.

Each of the energy source housing and the casing shell may possess a substantially circular, elliptical or rectangular cross-sectional profile. The fluid channel may accordingly be formed in-between an outer surface of the energy source housing and the upper and lower wall structures of the casing shell. The skilled person will understand that the energy source housing may comprise anyone of the ceramic materials discussed above in connection with the material of the housing shell. The heating element may additionally comprise a thin film resistor or a thick film resistor bonded directly, for example by screen-printing, to a surface of the energy source housing facing away from the fluid channel.

The energy source housing may be formed by a shell or casing of the rechargeable or non-rechargeable battery or formed as a separate housing enclosing existing separate battery shell or shells to form a separate battery compartment.

Each of the infusion fluid warmers described above in connection with the first and second aspects of the invention may advantageously comprise a temperature sensor for determining a temperature of the infusion fluid in the fluid channel at a suitable location such as at or proximate to the outlet port. A controller circuit may be operatively coupled to the temperature sensor and to the heating element to control instantaneous power dissipation of the heating element. The controller circuit is adapted to adjust power dissipation in the heating element in accordance with a desired or target temperature of the infusion fluid based on temperature data from the temperature sensor. The controller circuit preferably comprises a programmable microprocessor such as a Digital Signal Processor and suitable program code or instructions implementing the control algorithm. The programmable microprocessor may be an off-the-shelf industry standard type of microprocessor, preferably comprising appropriate input and output ports and peripheral devices such as EEPROM or Flash memory. However, the skilled person will understand that the controller circuit alternatively may be implemented by appropriately configured programmable logic such as FPGA devices or hard-wired circuitry comprising combinatorial logic and memory integrated on an Application Specific Integrated Circuit (ASIC). The controller circuit is preferably bonded to the surface of the upper wall structure facing away from the fluid channel or the surface of the lower wall structure facing away from the fluid channel. The controller circuit may be arranged on the same surface of the upper or lower wall structure as the thick film resistor or resistor if sufficient surface area is available. The use of the housing shell as carrier of the control circuit in accordance with the above embodiments of the invention provides a further size reduction of the infusion fluid warmer and reduces the number of separate parts that must be assembled during manufacturing of these infusion fluid warmers. In some embodiments of the invention, the controller circuit comprises one or more semiconductor transistors and/or semiconductors diodes configured for delivering a modulated drive signal to the heating element to dissipate power therein. The semiconductor transistors may comprise one or more power MOS transistors or IGBTs. The controller circuit controls the semiconductor transistors to apply a PWM (Pulse Width Modulated) drive signal across the heating element, e.g. the thick film resistor(s), such that a known quantity of electrical power is dissipated in the heating element. The controller circuit may be adapted to adjust the amount of electrical power dissipated in the heating element by adjusting the duty cycle of the PWM drive signal. Excess heat energy dissipated in the one or more semiconductor transistors and/or semiconductors diodes of the controller circuit during operation of the heating element may also be transmitted to the fluid channel by bonding these semiconductors to the surface of the upper and/or lower wall structure facing away from the fluid channel. The excess heat energy is caused by resistive and capacitive parasitic losses in the one or more semiconductor transistors and/or semiconductors diodes.

The temperature sensor(s) may comprise a semiconductor based sensor(s) placed in the fluid channel for example at or close to the outlet port such that a temperature of the heated or warmed infusion fluid can be accurately measured. Infusion fluid temperature data may be transmitted to the controller circuit in digitally coded format or as an analogue voltage, charge or current signal that is sampled by an analogue to digital converter (A/D-converter) in the controller circuit.

An advantageous embodiment of the temperature sensor comprises a thick film resistor or thin film resistor, preferably a thick or thin film resistor of the heating element. Since the resistance of thick film resistors is strongly temperature dependent these are particularly useful for temperature sensing and the controller circuit may be adapted to measure the instantaneous resistance of the thick film resistor. The controller can subsequently determine the temperature of the resistor from the determined instantaneous resistance by a suitable computing algorithm or look-up table. Furthermore, if the thick film resistor and the upper or lower wall structure of the housing shell has good thermal contact with the fluid channel, the temperature of the thick film resistor is approximately the same as the temperature of the infusion fluid such that the resistor temperature is a good estimate of the infusion fluid temperature, possibly adjusted with a predetermined correction factor.

Another, third aspect of the invention relates to a method of warming infusion fluid during administration to a patient, comprising steps of:

providing an infusion fluid warmer according to any of the above described aspects and embodiments thereof,

fastening the infusion fluid warmer to the patient for example with a bracelet or tape, connecting the outlet port to a Venflon or IV-catheter inserted in the patient's vein, connecting the inlet port to a fluid bag or container comprising a volume of infusion fluid. If necessary, a short extension tube may be inserted between the outlet port and the Venflon or IV-catheter. Likewise, an extension tube may be coupled between the inlet port and the fluid bag or container.

The ability to manufacture the present infusion fluid warmers with very compact dimensions makes it possible to conveniently fasten the infusion fluid warmer directly on a patient's body for example on the leg or arm with a suitable adhesive device or substance such as tape, plaster, bandage, elastic band etc. This simplifies the fluid delivery process and minimizes risk of accidental detachment.

