WO1990010364A1

WO1990010364A1 - Iv fluid warmer

Info

Publication number: WO1990010364A1
Application number: PCT/US1990/000816
Authority: WO
Inventors: Thomas P. Frank; Wendell Thompson
Original assignee: Medex, Inc.
Priority date: 1989-02-21
Filing date: 1990-02-13
Publication date: 1990-09-07

Abstract

An intravenous fluid warmer consisting of an inner dielectric tube (26) of high heat conductivity and high dielectric material. Coextruded over the inner tube is a conductive polymer tube (25). A regulated power supply (35) is attached to the conductive tube to pass current through it, thereby heating it as well as the inner tube through which an IV solution passes.

Description

IV Fluid Warmer

This invention relates to fluid warmers and particularly to fluid warmers for blood or other IV liquids that are administered to patients. BACKGROUND OF THE INVENTION There is considerable prior art relating to

IV fluid warmers. In general, they appear to provide a housing, a tortuous fluid path through the housing, a heater in heat exchange relation to the fluid path and a system for regulating the heat applied to the fluid.

The IV fluid warmers are, in general, rather complicated internally. They deal with a problem of delivering a fluid to the patient from the fluid warmer at a low flow rate as, for example, 1 to 20 ml/min. All appear to require a tube that connects the warmer to the patient. When the rate of flow is quite low, significant amounts of heat imparted to the fluid in the fluid warmer are lost in the transit through the tube between the warmer and the patient. The fluid warmers that provide a tortuous path in a housing for the fluid create a problem of dead volume which is the volume of the fluid that sits in the warmer.

There is a need for disposability, particu¬ larly in the warming of blood. The more complex the fluid warmer is internally in the housing, the more expensive the fluid warmer is likely to be, thereby making its disposability a matter of considerable expense.

BRIEF DESCRIPTION OF THE INVENTION An objective of the present invention has been to provide a fluid warmer that does not have the complexity of prior fluid warmers. As such, the fluid warmer can be made inexpensively and disposable.

Another objective of the present invention has been to provide an IV fluid warmer wherein there is substantially no loss of heat arising out of passing of the heated fluid through a tube between the warmer and the patient.

Another objective of the invention has been to eliminate or minimize dead volume.

The objectives of the present invention are attained by providing a fluid warmer utilizing a tube of conductive polymer. Electric terminals are applied to the conductive polymer so as to pass current, as uniformly as possible, through the polymer, thereby causing its temperature to be raised. Fluid is passed through the tube and the temperature of the fluid is raised by the heating of the conductive tube. It is, of course, important to isolate the patient from the electrical system. The invention therefore contemplates the coextrusion of the con¬ ductive polymer over a tube which has a high thermal conductivity and which is a high dielectric material having as low as possible electrical conductivity. The dielectric inner tube insulates the patient from the electrical system connected to the outer conduc¬ tive polymer tube. In one form of the invention, leads are applied to axially-spaced positions on the conductive polymer tube with current passing axially along the length of the tube. Alternatively, it is contemplated that the tubing would be placed in a housing having diametrically-opposed, axially-extending contacts that make electrical connection with the conductive polymer when the housing is closed upon the tube. In this embodiment, the tube is heated by current passing circumferentially through the conductive polymer between the axially-extending contacts. In this embodiment of the invention, the housing that clamps upon the tube to provide the electrical connection also provides an insulative function to minimize heat loss. A control system is provided in which the temperature of the fluid exiting the warmer is contin¬ uously monitored and the power applied to the warmer is varied to maintain a uniform temperature exiting the tube and to accommodate variations in the flow rate and incoming temperature of the fluid being warmed.

As can be readily perceived, there are several advantages to be derived from the invention. Since the IV warmer is the tubing leading to the patient itself, the unwarmed or exposed tubing between the patient and the warmer can be reduced to substan¬ tially zero, hence eliminating the heat loss in the transit between the warmer and the patient.

The warmer can be manufactured very inexpen¬ sively and, hence, is ideally suited to be disposable.

Dead volume is substantially eliminated. BRIEF DESCRIPTION OF THE DRAWINGS The several objectives and features of the present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a diagrammatic perspective view of one embodiment of the invention;

Fig. 2 is a cross-sectional view taken along lines 2-2 of Fig. 1; and

Fig. 3 is a diagrammatic perspective view of an alternative embodiment of the invention. DETAILED DESCRIPTION OF THE DRAWINGS

Referring to Fig. 1, a patient is shown diagrammatically at 10. A warmer 12 has an inlet end 13 and an outlet end 14. The outlet end 14 is connected directly to a cannula 15 inserted into the body for delivering fluid to the body.

A source of fluid 20 is connected by a tube

21 to the inlet end 13 of the warmer 12. A flow control 22 regulates the flow of fluid from the source

20. There is a detachable connection 24 (Luer lock) between the tube 21 and the warmer 12.

As shown in Fig. 2, the warmer itself is formed of an outer tube 25 of a conductive polymer. That tube 25 is preferably coextruded over a di¬ electric tube 26. The dielectric tube 26 should be as electrically insulative as possible while at the same time being as thermally conductive as possible. A conductive band 31 is mounted as close to the outlet end 14 of the warmer as possible. A conductive band 32 is mounted at the inlet end of the warmer. The bands are connected to a control unit 35 by leads 36. The control unit 35 includes a regulated power supply that applies a voltage to the conductive polymer outer tube via leads 36 and bands 31, 32. The control 35 preferably includes a probe 37 at the discharge end of the warmer, the probe monitoring the temperature of the fluid passing through the warmer. The- probe is connected to the control and provides a signal which determines the power applied between the terminals 31, 32 so as to maintain the temperature at the outlet end of the warmer at a level substantially the same as that of the temperature of the body to which the fluid is being supplied.

The length of the tube can be selected to fit the requirements of the patient. If the fluid is to be administered very slowly, a short length of tube can be used to provide shorter residence in the warmer. On the other hand, if the fluid is introduced relatively rapidly, the longer tube can be used to provide longer residence in the warmer. It can be seen that one of the advantages of the invention over those having a tortuous path within a housing is that the length of path through which the fluid passes can be selected to match the patient requirements.

It can also be seen that the outlet end of the warmer tube can be brought up to and almost in contact with the patient so that there is no measur¬ able heat lost in tubing that is needed for connecting a warmer to the patient.

In an alternative form of the invention, a tube 40 has the cross section shown in Fig. 2 consist¬ ing of an inner dielectric tube and an outer con¬ ductive polymer tube. The tube has connectors 41, 42 diagrammatically shown at each end. The connector 41 at the inlet end is for connection to a source 20 of fluid. The connector 42 at the outlet end is for connection to the cannula 15.

Power to the tube is obtained by placing the tube in a cylindrical housing or cradle 45. The cradle 45 has terminals 46 that extend axially the full length of the cradle and are spaced so as to engage, in a snug electrically-conductive relation, diametrically-opposed lines on the tube 40 when the tube is placed in the cradle. An insulative cap 47 may be optionally provided to mate with the cradle 45 and to enclose the tube so as to thermally insulate it.

A control module 48 is connected via leads 49 to the terminals 46. Preferably, some type of temperature measuring probe is employed and connected to the control module to measure the temperature of the fluid at the outlet end of the tube 40, thereby providing a signal used to maintain the temperature of the fluid at approximately the temperature of the patient or about 37°C.

In the operation of either of the forms of the invention, the source 20 of fluid such as blood or nourishment is connected to the inlet end 13 of the warmer. The outlet end 14 of the warmer 12 is con- nected to a cannula 15 and inserted into a blood vessel of the patient. Fluid is urged into the patient's arm by gravity or by a pressure infusor surrounding a bag of the fluid. The flow controller 22 determines the rate of administration of the fluid into the patient 10.

A power supply in the control module applies a voltage axially along the conductive polymer 25 of the warmer 12 (Fig. 1) or circumferentially (Fig. 2) around the warmer 12. The temperature of the con¬ ductive polymer 25 is raised and is controlled in relation to the incoming temperature and flow rate of the IV solution so as to maintain the temperature of the fluid of the outlet at about 37°C. The fluid passes through the dielectric tube 26 and is main¬ tained by the electric material insulated from the electrical system by which heat is introduced into the system. From the above disclosure of the general principles of the present invention and the preceding detailed description of a preferred embodiment, those skilled in the art will readily comprehend the various modifications to which the present invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof:

What is claimed is:

Claims

1. A fluid warmer comprising, an elongated tube of conductive material, means for applying a voltage across said tube to cause current to flow throughout said tube to raise its temperature, and means for passing fluid through said tube to warm it.

2. A fluid warmer as in claim 1 in which said tube is a conductive polymer coextruded over a di¬ electric.

3. A fluid warmer as in claim 1 in which said voltage-applying means comprises, axially-spaced conductive connectors sur¬ rounding said tube at at least two positions on said tube, a source of voltage, and leads connecting said source of voltage across said connectors.

4. A fluid warmer as in claim 1 which said voltage-applying means comprises, an elongated dielectric holder of arcuate cross section, a pair of elongated contacts mounted in said holder in spaced diametrically-opposed relation, said tube being positioned in said holder in good electrical contact with said contacts engaging diametrically-opposed lines on said tube, and a source of voltage connected to said contacts.

5. A warmer as in claim 1 further comprising, control means regulating the voltage to said warmer to maintain the temperature of the liquid at the outlet of the warmer at about 37°C.