DE1954019A1 - Thermal facility for clinical fluids - Google Patents

Description

Applicant: Thermolyne Corporation, 2555 Kerper Boulevard, Dubugue , Iowa 52 001, USA

Clinical fluid heating device

The invention relates to a heating device for heating clinical fluids, in particular a blood warmer for heating cooled blood to the transfusion temperature.

Blood is usually stored at a temperature of around 4 ° C. Before using it, it must be brought to body temperature heated to 37 C. It is common to have enough blood for a given surgical use warm to adequately meet transfusion needs, often resulting in significant loss, when the expected need does not arise. The warmed blood cannot be cooled again and is therefore no longer usable.

Blood warmers have already been proposed in which a liquid heating bath is used, in which a helical one Heat transfer device is immersed in which the blood flowing through is heated. With facilities this However, the blood may be heated too much or too little, depending on the flow rate of the blood. It is therefore desirable to design a blood warmer so that blood is brought to a temperature within a narrow temperature range can be heated despite major changes in the flow rate. This suggested blood warmer

0098 Λ 2/1025

enables a controlled temperature of the blood at flow rates of up to 150 cm / min. With this Blood warmer can deliver blood within an acceptable range for transfusion purposes based on blood at 4 ° C or less even if the flow rate increases from the maximum of 150 cm / min during the transfusion Zero is decreased. However, this blood warmer has a problem that it cannot be easily disassembled and assembled and that no satisfactory control of the blood temperature can be made for all purposes.

The invention is therefore intended to create a blood warmer that allows easier switching from one blood supply or from one patient to another. Further is to create a blood warmer for a dry supply of heat which can be easily cleaned, even if any Should damage occur and the blood or other transfusion fluid will leak. Furthermore, the Blood warmers allow for improved temperature control by adjusting the electrical heating elements accordingly the decreasing heat absorption of the liquid to be heated, which flows through the device, suitably designed will.

A heating device according to the invention works with dry heat and enables the heating of blood or other fluids on one safe for transfusion purposes suitable temperature from zero flow rate to a given maximum flow rate, and is characterized by first and second thermally conductive heating plates, a device on which the heating plates can be pivoted hinged and between a closed position in which the heating plates are arranged close to each other and parallel, and an open position in which the heating plates are relatively far apart. The heating device also has a support device for the removable mounting of a thin, flat, channels through

009842/1029 ORIGINAL INSPECTED

drawn bag on one side of the heating plates, which has an inlet and an outlet at opposite ends having. When the heating plates are in the closed position and the bag is filled with liquid, the opposite sides of the bag are in contact with the first and second heating plates, respectively. For the first and second heating plates, first and second heating elements are provided. Each heating element tapers from the inlet end to the outlet end so that the heat transfer increases according to the decreasing heat absorption of the liquid flowing from the inlet of the bag to the outlet thereof. To control the heat generation of the heating elements A thermal control device is provided according to the temperature of one of the heating plates.

The invention will be explained in more detail with the aid of the exemplary embodiments shown in the drawing. It demonstrate:

1 is a front perspective view of a blood warmer according to the invention;

Fig. 2 is a partial section along the line 2-2 in Fig. 1, from which the relative position of the heating plates to the the bag through which the blood flows can be seen;

3 shows a perspective view of the blood warmer in FIG. 1, with the door almost closed and the cover plate the door is removed;

FIG. 4 shows a circuit diagram of the heating elements and the electrical control device for the blood warmer in FIG. 1 to 3 ? and

Fig. 5 is a circuit diagram of the heating elements in a. others Embodiment of the invention.

1 to 4 show a blood warmer 10, which zurr. Warming of chilled blood or other clinical fluids to a suitable temperature for transit is used. The blood warmer IC has a base 11 and one, stationary. Kalir.'sn 12. IT er Scckel 11 stands c? E-rrer; about cer ~. Rahrrsn. 12 ~~ c.-

0 0 9 b 4 2 ' ΙΟ 2 9 BAD

_4- 19 5 4010

and a forwardly projecting housing 13 is provided at the upper end of the frame.

A first heat conductive heating plate 21 is attached to the frame 12. The heating plate 21 has a lower portion 2lA and an upper section 2lB. A second heat conductive heating plate 22, like the heating plate 21, has a lower portion 22A and a top portion 22B. The heating plate is attached to a door 14 that is attached to the base and the Frame is hinged. Therefore, the heating plates 21 and 22 are mutually between an open position in Fig. 1 and a closed position pivotable. In the closed position, the two heating plates are parallel with a small distance arranged to one another, as can be seen from FIG. The blood warmer 10 also has a support device for detachable Holding a thin, flat bag 16 penetrated by liquid channels in a predetermined one Position on the heating plate 21. This support device consists of four pins 15A, 15B, 15C and 15D, which are attached to the Frame 12 are arranged and protrude through four corresponding openings in the bag 16. The pins 15A to 15D are aligned with four corresponding openings 17A to 17D in the heating plate 22. The support means for the bag 16 also has individual slots 18A and 18B in the heating plates 21A and 22A in which an inlet conduit 18 lies Part of the bag 16 is. Corresponding slots 19A and 19B in sections 21B and 22B of the heating plates surround the outlet conduit 19 of the bag.

When the door 14 is open (Fig.l), the heating plate is arranged at a relatively large angle relative to the heating plate 21. Therefore, the bag 16 is easily accessible, so that it can be easily installed and removed. When the door 14 is closed, the two heating plates are 21 and 22 are arranged close to and parallel to one another (Fig. 2). So when the door 14 is closed, the opposite touch Sides of the bag 16 the heating plates 21 and 22. This ensures good heat transfer from the heating plates to the:. Bag 16 guaranteed.

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1 313 4019

The heating plates 21 and 22 are provided with electrical heating elements. The arrangement and orientation of the heating elements on the heating plates is shown in FIG. The sections 21A and 21B of the heating plates have heating elements 25A and 25B in the form of electric resistance wires. The heating elements 25A and 25B are from the bottom formed differently to the top of the heating element in such a way that the heat generation upwards along the end face the heating plate 21 decreases. The heating elements are tapered so that the heat generation gradually from that part of the heating plate which adjoins the inlet 18 of the bag 16 to the outlet 19 falls, proportionally the lower heat absorption of the blood flowing from the inlet to the outlet.

To explain the heating elements 25A and 25B solij / on the heat exchange taking place will be discussed in more detail. The temperature of the blood increases gradually as it changes Inlet 1.8 flows to outlet 19. The amount of heat absorbed by the blood is proportional to the temperature difference between the blood and the heating plates 21,22. The heating plates have a high thermal conductivity by being preferably are made of heavy cast aluminum and are therefore of generally uniform temperature. That's why the blood in the vicinity of the outlet 18 absorbs less heat than in the vicinity of the inlet because of the temperature difference is much lower in the area of the outlet.

The second heating plate 22 has two heating elements 26A and 26A 26B. The heating elements 25A, 25B, 26A and 26B are sinusoidal formed and each have four horizontally extending sections. As a practical matter, the end connections between the horizontal sections can be neglected. The heat generation of the heating element 25A should be along can be regarded as constant over its entire length. However, the four horizontal sections of the heating element 25A have not the same distance relative to the vertical height of section 21A of the heating plate.

0098 ^ 2/1029 ORIGINAL INSPECTED

1 9 5 · '! 01 Ü

The first or lower horizontal portion 25Al of the Heating element 25A is centered in a relatively small area A1 of section 21A of the heating plate. This Area Al is aligned with inlet 18. The next horizontal section 25A2 of the same heating element is in one slightly arranged wider area A2 of the heating plate. The next area in which the section 25A3 of the heating element is located is is even wider, and the widest of the areas of the heating plate 25A is the topmost area A4, which contains the last section A4 of the heating element. The same distribution is for each of the sections 25B, 26A and 26B of the heating elements are present. The electrical control for the blood warmer 10 is shown in FIGS. It has four thermostats 31, 32, 33 and 34, which are located under the cover plate 14 on the back of the heating plate 21 are arranged. The thermostat 31 is a control thermostat for the electric heating elements 25A and 26A. The thermostat 33 is a control thermostat for the heating elements 25B and 26B. The thermostats 33 and 34 are used to control an alarm system.

As can be seen from FIG. 4, the heating elements of the blood warmer 10 are supplied by an alternating voltage source Connections 41 and 42 supplied '. One connection 41 is connected to the series-connected thermostats 3 2 and 34, and via the thermostat 31 to the connection of the heating element 25B. The other terminal of the heating element 25B is connected via the corresponding section 26B in the other heating plate, which is connected to the connection 42 on the other hand is.

The control circuitry for the lower sections 25A and 26A is the same but is designed in a special manner to to enable higher amperage. The circuit of sections 25A and 26A is connected to the terminal 41 via the Thermostats 3 2 and 34 connected in series. The thermostat 34 is one with the input electrode electrical switching element 36 connected, whose output

009842/1029 ORIGINAL INSPECTED

_ ₇ _ 1354013

Electrode is connected to the portion 25A, which is connected in series with the heating element 26A, which is connected to the terminal 42 is in communication. The thermostat 31 is connected in series to a resistor 37, which is between the input electrode and the control electrode of the switching element are connected.

During normal operation, the thermostat arranged on the upper section 21B (FIG. 3) controls the power supply of the two upper sections 25B and 26B connected in series. Thermostat 34 is also on top section 21B arranged, but has no primary control function for the upper heating elements. It is only used for limiting control, in order to then activate an alarm device 38, if the thermostat 33 fails, or if some other fault occurs in the operation of the blood warmer which leads to a overheating of section 21B leads.

The thermostat 32 also has no control function on the Sections 25A and 26A although it is attached to section 21A of the heating plate. Like the thermostat 34 is that Thermostat 32 set for a temperature slightly above the desired working temperature of the heating plates and only takes effect if the main control is for the sections 25A and 26A (thermostat 31 and electrical switching element 36) are not working properly. The alarm device 38, which can emit an audible, visible or other alarm signal is connected in parallel to the thermostats 32 and 34. The alarm device, which is normally bridged by the two Therir.ostats, is not triggered as long as neither of the two thermostats is heated above its setting and opens, which activates the alarm device will.

From the foregoing description and from FIG. 4, it can be seen that the blood warmer 10 has two pairs of hot plate sections has, which are each controlled by a single Therir.ostat, which is attached to one of the plate sections is arranged. That is why the energy supply is too

0098-2 / '029

ORIGINAL INSPECTED

1954013

the total hot surface for each pair of hot plate sections controllable at only one point according to the conditions of thermal equilibrium. If the Heat supply exceeds or falls below the heat absorption at another point, can affect each pair of Heating plate sections result in an undesirable temperature change.

The design of the heating elements can not be optimal for more than one flow rate as long as the Heating plates cannot be divided into differential areas, each of which has its own heating element and its own

fc control. However, good results can be achieved with two balanced, separately controlled heating areas as in the blood warmer 10 can be achieved. The heating elements for the Both sections of the heating plates can be proportioned so that the heat input equals the heat demand in each Area at a maximum flow rate becomes. A maximum flow rate is used as a control criterion chosen because of the risk of shock to a patient receiving a blood transfusion below body temperature increases with the flow rate and because of the rise in temperature of the blood in the blood warmer decreases with increasing flow velocity. This means that through an optimal arrangement of the heating elements

ψ for the maximum permissible flow rate, the temperature rise in the blood takes place with a maximum control.

In the blood warmer 10 and in any comparable heat exchanger in which a liquid is in one thin thermally conductive pouch is heated between relatively closely spaced heating plates, the following relationship can be be set up:

ti \ JU- KAP (To-T) dt
(ij cm - ^

thereby means

009842/1029

- 9 - 1954010

dH = heat differential

T ₀ = temperature of the heating plates in degrees Celsius

above the starting temperature of the liquid. speed

T '= temperature of the liquid at a given time

dt = time differential

D = thickness of the bag

K = thermal conductivity of the bag

A = contact surface of a plate

P = ratio of the effective contact area to the actual plate area

The increase in temperature dT during the period dt is:

(2) dT = ^dH

where dT = temperature increase in time dt V = volume of liquid in the bag.

Approximately it can be assumed that the specific Weight of the liquid to be heated = 1, and that the specific heat also = 1. All of these take place Figures in cgs units. Under these conditions and the further assumption that the volume of the bag 16 is proportional to its surface area, equations (1) and (2) can be used to establish a heat exchange equation

for the blood warmer 10 at a maximum flow rate S can be used:

(3) T = To

In a typical construction it can be assumed

2 that the total surface of the bag 16 is 400 cm and that the

2
effective bag surface is 200 cm for each of the heating plates, the reduction being due to the formation of the bag with flow channels (Fig.2). For a typical one suitable for the manufacture of the bag 16

009842/1029

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Plastic, the thermal conductivity is about 0.00035, the thickness of the bag is about 0.0254 cm and the maximum flow

3 '3

speed 150 cm per minute or 2 cm per second - With this assumption and with the assumption that the cooled to 4 ° C If blood is to be heated to the transfusion temperature of 37 ° C, the temperature rise is T for the lower heating plate sections 21A and 22A according to equation (3) 22 ° C. A quarter of this total temperature rise is to be assigned to each of the sub-areas A1 to A4. When equation (3) is solved for the area A, it becomes the expression

ιλ \ τ » DS , To ^{(4) Α =} 2PK ^ln

and the individual areas A1 to A4 can be calculated in the following way:

(5)

Al =

_ln

To I To - T ¹ J

Al + A2 =

DS 2PK

In

To

To - 2Τ ¹

Al + A2 + An =

DS 2PK

In

To

To - ηΤ ¹

where T '= increase in liquid temperature per section

Al An = section areas, inlet - to outlet end-for the construction shown in FIGS. 1 to 4 results in the following calculation with the parameters assumed above of the sub-areas Al to A4:

Al = 182 in

33

33-5.5

Al + A2 = 182 in

= 33.2 cm

³³ = 73.7 cm ²

33-11

Al + A2 + A3 = 126 cm ²
Al + A2 + A3 + A4 = 200 cm ²
so that the following areas result:

00 98 42/1029

_ _n _ 1954013

Al = 33.2 cm ² A2 = 40.5 ση ² A3 = 52.3 cm ² A4 = 74 cm ²

With the same assumptions and calculations on the same basis, the partial areas of the upper heating plate sections are :

A5 = 33.2 cm ² A6 = 40.5 cm ² A7 = 52.3 cm ² A8 = 74 cm ²

Although the areas A5 to Ä8 are equal to the areas A1 to A4, the heating element 25B is not formed the same as the heating element 25A because only one is required Generate third of the heating energy of the heating element 25A. This means that the heating element 25B is only one third contributes to the overall temperature rise caused by the heating element 25A.

At the maximum flow rate through the blood warmer IO, the two lower heating elements require 25A and 26A about 23Ο watts. However, it is necessary to compensate for heat losses and possible voltage drops in the electrical voltage source that occur along the circumference. In a practical construction, 450 watts were found to be suitable for the two heating elements 25A and 26A. The two Upper heating elements 25B and 26B only need a third of this, i.e. about 15Ο watts. These heat outputs are the same Way distributed to the two heating element sections of each pair.

The division of the section 21A into four subsections A1 to A4 is done for practical reasons and is therefore not necessary feature of the invention. The total number of transversal

009842/1029

running subsections of the heating element section 25A can therefore be selected differently. For example in a given construction it may be desirable to use six sections for the heating element, which have an increasing width from the bottom to the top of the heating plate section should. According to the above equations, the following partial areas would result:

All = 21.5 cm ²
A12 = 24.2 cm ²
A13 = 28.0 cm2
A14 = 33.3 cm ²
A15 = 40.8 cm ²
A16 = 52.2 cm ²

According to the above embodiments formed heating elements 25A, 25B, 26A, 26B have one between the lower or inlet end and the upper or outlet end so different width that the heat generation of the two heating plates from the inlet end to the outlet end gradually proportional to the decreasing heat absorption the liquid flowing through the bag 16 decreases. This is achieved through the thermal control, in particular by the thermostats 31 and 33, even by the thermostat control of the heating elements accordingly the temperature of just one heating plate. Relatively precise control is possible because of the equilibrium conditions are practically identical at corresponding points on the front and rear heating plates. Since the Bag 16 is filled with a liquid, there is also a good heat transfer through the bag and the liquid between the front and rear heating plates.

009842/1029

- 13 - 1954010

If the heating elements correspond to the basic relationship according to equation (3), they can basically the same operating properties can also be achieved in a construction in which the transverse section the heating elements are arranged in sections of the same size. A construction of this kind is shown in Fig. 5, in which a heating plate 121, lower and upper sections 121A and 121B with heating elements 125A and 126A having. The partial areas A21 to A28 of the heating plate 121 are all the same size and each contain a single one Heating element.

From the equations (1) to (3), it can be calculated that the construction shown in FIG. 5 has the same operational characteristics as the construction in Fig. 4 results when the performance of the individual heating element sections accordingly is determined by the following relationships:

(6) Wl = 4.18 LSTl,

W2 = 4.18 LST2, ...
Wn = 4.18 LSTn
and

(7) Tl = ToM,

T2 = (To - Tl) M, ...
Tn = (To - Tl - ... Tn- I) M wöbe i

η = total number of sections (8 in Fig. 5)

Tl ... Tn = increase in liquid temperature in each segment

L = constant for the compensation of low line voltages and thermal losses

Wl · .. Wn = input power of each section

-u ■ -2KPA

and where ~ ^ ~

(8) M = 1 - e

Although this construction is well suited for practical purposes, it is trained differently Heating element sections required, which is why a larger number

009842/1029

of individual parts than in the construction according to Fig. 4 is required.

When the above-mentioned parameters are applied to the construction according to FIG. 5, the performances are as follows required for the eight heating element sections in plate areas A21 to A28 (Fig. 4):

Wl = 162 watt W2 = 123 watt W3 = 94 watt W4 = 71 watt W5 = 54 watt W6 = 41 watt W7 = 31 watt W8 = 24 watt

It should be noted that the power requirement W1 to W4 for the first four sections (A21 to A24) is 450 watts and that the power requirement W5 to W8 for the next four sections (A25 to A28) is 150 watts. Therefore the power requirement is the same for the construction in Fig. 5 as for that in Fig. 4, as long as the basic Operational requirements remain unchanged. It can also be shown that the temperature rise and the thermal Conditions for the heating platens are essentially the same for both heating element designs.

The blood warmer according to the invention can therefore be used in an expedient manner. The bag can be used very quickly and easily replaced by opening the door 14, removing the bag 16, and replacing it with a new bag is replaced, after which the door only has to be closed again. Only these measures are required to connect the blood warmer from one pump system to another. If there is any leakage from the bag or any contamination "has occurred

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all heating surfaces are easily accessible so that they can be cleaned easily. It therefore results in this Regarding no difficulties, which is of particular importance in an operating room.

The explained arrangement of the electrical heating elements enables the blood warmer to have a constant end temperature within a wide range of flow rates. Laying out the electrical heating elements accordingly the heat absorption of the blood or other clinical fluid enables an accurate thermal Control, which makes the blood warmer a very reliable device without the need for expensive Thermostat circuits or other complex control circuits are required.

Claims

0098 ^ 2/1029

Claims (1)

Claims (l.y heating device for heating clinical fluids at transfusion temperature, in particular blood warmer, characterized in that a first and a second thermally conductive heating plate (21; 22) hinged to one another so as to be pivotable along a side edge are so that the two heating plates can be pivoted into a closed position in which they are close and parallel to one another lie, as well as in an open position in which they enclose a relatively large angle that a h thin, flat bag 16 provided with flow channels on one of the two heating plates with a support device (15) is releasably connectable, that the bag (16) at opposite ends has an inlet line (18) and an outlet line (19) that the opposite sides of the Bag rest on the two heating plates when the heating plates are pivoted towards each other and the bag is filled with liquid, that first and second electrical heating elements (25-26) are individually assigned to the two heating plates, that each of the heating elements from its end adjacent to the inlet line the end adjacent to the outlet conduit of the bag in accordance with the decrease in heat absorption from the inlet conduit f the outlet line of the bag is formed flowing liquid, and that a thermal control device (31-37) is thermally connected to at least one of the two heating plates and electrically to the heating elements in order to control the energy supply to the heating elements according to the temperature of the heating plate. 2. Heating device according to claim 1, characterized in that that the pivot axis of the heating plates is arranged vertically, that only one of the two Heating plates (22) is pivotable, and that the inlet line (18) on the lower side of the heating plates and the outlet pipe (19) is arranged on the upper side of the heating plates. 009842/1029 1354019 3. Heating device according to claim 2, characterized in that each electrical heating element has at least two superimposed sections (22A, 22B; 25A, 25B), and that the thermal Control device for each heating element section in each case has a thermostat. 4. Heating device according to claim 1, characterized in that the formation of the heating elements by the equation -KA P DS
T = To 1 - e is determined, where T = temperature of the liquid at a given Time
To = plate temperature above the original Liquid temperature K = thermal conductivity of the bag A = contact surface of a plate D = thickness of the bag
S = maximum flow velocity P = ratio of the effective contact area to the actual plate area. Heating device according to claim 4, characterized in that each heating element has one Series of η transverse sections, each of which is in a subsection of the associated plate is arranged between the region of the inlet line and the outlet line, and that the partial surfaces of the Plates through the relationship Al = Al + A2 = 0098A2 / 1Ö29 Al + A2 ... + An = ^ = In TO To - nT are determined, where Al = first partial surface of the plate in the area of the A discharge line A2 = second sub-area of the plate An = last sub-area of the plate in the area of the Outlet pipe T '= increase in liquid temperature per part ~ section. 6. Heating device according to claim 4, characterized in that each of the heating elements has a series of η transverse parts, which are assigned in n-sub-areas of the same size on the Plate between the inlet pipe and the outlet pipe of the bag are arranged, and that the conduction of the "heating element sections through the relations Wl = 4.18 LST 1,
W2 = 4.18 LST2,
Wn = 4.18 LSTn
and Tl = ToM, T2 = (To - Tl) M, ... Tn = (To - Tl - ... Tn-I) M certainly are, whereby
-2KPA M = I nDS
- e and where Tl .. . Tn = Ans Tn = increase in liquid temperature in each segment L = constant to compensate for too low supply voltage and thermal losses Wl ... Wn = power requirement of each segment. 009842/1029 - 19 - 195401 Q Heating device according to claim 5 or 6, characterized indicated that each electrical heating element has two superimposed sections, that each heating element section is arranged according to these relationships, and that the thermal Control device a first thermostat (31) for controlling the two lower heating element sections and a second thermostat (33) for controlling the two upper heating element sections. 0 0 9 8 L 2! 1 0 2 9 Blank page