Blood-heating Apparatus

Abstract

Apparatus for heating blood required for transfusion purposes which enables blood newly drawn from the cold store to be used immediately and without waste. A water tank is provided with a submerged broad based chimneylike convection device having a removable blood-heating coil wound round its outside. An electric heater below the convection device causes heated water to rise up the center and fall around the blood-heating coil. A thermostatic control ensures that the blood is heated to the correct temperature and indicating and other safety devices ensure correct functioning and immediate indication of any failure.

Description

This invention relates to apparatus for heating blood required for transfusion purposes and the principal object of the invention is to provide apparatus which may be brought into use very quickly, is completely automatic in use, and has a high factor of reliability.

Blood required for transfusion is generally stored in bottles and is kept at a temperature of 4.degree. C. Immediately prior to use the blood must be heated to approximately 36.degree. C. (96.8.degree. F.), and having once been heated it must be discarded if not used, as it cannot be cooled again and stored for subsequent use. At present, when blood is required, it is necessary to withdraw it from the cold store and, in view of the time required for heating, to ensure that a sufficient quantity is heated in advance. Where a major operation, which may require a substantial amount of blood, is involved the amount of blood heated may exceed the amount actually used, and this results in waste.

The apparatus according to the invention provides for the blood to be heated continuously immediately before being supplied to the patient, the containers remaining in cold storage until the blood is actually required for use. The apparatus delivers the blood to the patient at a constant and automatically controlled temperature, thereby eliminating the risk of the patient receiving underheated or overheated blood as the result of human error. A further important feature of the invention is that it minimizes the time required to prepare for a transfusion, which may be a very important factor in emergency treatment.

The invention consists of apparatus for heating blood required for transfusion purposes comprising a tank to contain a quantity of water, an electric heating unit disposed substantially centrally in the lower part of the tank, a convection guide placed above the electric heater in the tank, the convection guide comprising a broad conical lower portion and a chimneylike upper portion, means for removably attaching a blood coil to the outer surface of the chimney portion of the convector guide, and an automatic temperature control in the tank arranged to control the heating unit.

Conveniently a second automatic temperature control is provided, set to a temperature slightly above that of the said temperature control, to operate in case the normal temperature control fails.

Indicator lamps may also be provided to show whether each part of the apparatus is functioning as it is intended to function.

The tank may be built in a unit with an electrical control box containing all the control and indicating equipment, and a drip stand clamp may be provided to enable the apparatus to be clamped on to a standard drip stand normally used for blood transfusions.

A preferred embodiment of the invention will be described with reference to the accompanying drawings in which

FIG. 1 is a sectional elevation of a blood-heating apparatus according to the invention;

FIG. 2 is a plan view of the apparatus of FIG. 1; and

FIG. 3 is a circuit diagram showing how the heating is controlled.

Referring first to FIGS. 1 and 2, the apparatus comprises an outer tank 11. This could be in the form of a casting or might be made from sheet metal but it is preferred to make it of a strong material having comparatively poor heat conduction properties, such as fiberglass. The use of this material is also beneficial in keeping the weight to a minimum. The tank II may be circular when viewed in plan but it is preferably provided with a flat side 12 in order that a control unit, generally indicated at 13, may be attached. Located centrally in the bottom part of the tank is an electric heater 14 which may conveniently be of the kind commonly used in electric kettles, and this is secured to the flat side 12 by the usual mounting consisting of a flange 15, sealing washer 16, flat washer 17 and nut 18. Mounted above the heater 14 is a convection guide, generally indicated at 19, consisting of a lower wide conical portion 20 and an upper chimneylike portion 21, the portion 21 preferably being also slightly conical. The parts are so dimensioned that the upper end 22 of the convection guide 19 is well below the level of the top of the tank so that when the tank is filled with water there is a good depth of water above the top of the convection guide. The convection guide may stand on legs 23 so that it is readily removable. It is preferably made of a light, strong thermally nonconductive material, such as fiberglass.

A blood coil 24 is made of flexible tubing and is carried on the chimney portion 21 of the convector guide. It may be wound on a small frame which is slipped over the outer conical diameter of the chimney portion, or it may be wound directly on the chimney portion, or it may be merely clipped thereto. A certain amount of variety is possible in the mode of attachment. It is, however, desirable that the convolutions of the blood coil be evenly spaced in the longitudinal direction and preferable that they stand clear for a small distance from the chimney portion 21 to allow free circulation of water.

Attached to the flat wall 12 of the tank 11 is a casing forming an electrical control box, generally indicated at 25, which is provided with a cover 26 and a sealing washer 27 so that it may be hermetically sealed to prevent the ingress of explosive vapors which may be met with in an operating theater. This avoids the possibility of an explosion which might be caused by an electric spark in the casing 25 resulting from the operation of the electrical control gear.

Two thermostats, respectively 28 and 29, attacked to the wall 12 project into the tank 11.

A drip stand clamp, generally indicated at 30, comprises a base portion 31 a clamp member 32 and two eyebolts, respectively 33 and 34, which can be swung into slots in the clamp member 32 and secured by means of knurled nuts, respectively 35 and 36. This enables the blood-heating apparatus to be attached to the standard drip stand. The drip stand clamp is attached to a bracket 37 which is fixed to the bottom of the tank 11 by two studs 38. The studs 38, with a third stud 39, also form feet for the apparatus. The bracket 38 is provided with a central pad 40 to support the bottom of the tank.

FIG. 3 shows the circuitry of the control equipment in the control box 25. A flexible cable-containing line, neutral and earth conductors is brought into the control box 25 through a conventional gland and connected to a connecting block indicated in dotted lines at 41. A neon lamp 42 is connected between the line terminal and the earth terminal to indicate, when illuminated, that the earth continuity is in order. A further neon lamp 43 connected between the line and neutral lines indicates that the line and neutral circuit is in order. Leads from the line and neutral terminals pass to a double-pole switch 44. A lead from the live pole of switch 44 passes to a fuse 45 having a neon lamp 46 in series with a resistor 47 connected across it, so that if the fuse 45 should blow the neon lamp 46 will light up. From the fuse 45 a live wire leads to one side of a "normal" thermostat 48 having its casing connected to earth by a lead 49. A capacitor 50, conveniently of 0.1 .mu.f. capacitance, is provided to quench any sparks which may occur when the contacts of the thermostat 48 open. A lead 51 from the other side of the thermostat 48 passes to a terminal 52 of the connecting block and from terminal 52 a further lead 53 passes to one side of a "high" thermostat 54. This high thermostat is similar to the thermostat 48 having its casing earthed and a capacitor 55 connected in parallel with its contacts. From the other side of the thermostat 54 a lead 56 passes to one terminal of the heating element 57 the other terminal of which is connected through a fuse 58 and the neutral pole of switch 44 to the neutral terminal of the terminal block. A neon lamp 59, in series with a resistor 60, is connected across the fuse 58 and this will light up if the fuse blows. The heater 57 has its casing connected to earth by a line 61 and a neon lamp 62 in series with a resistor 63 is connected across the terminals of the heater 57. A further neon lamp 64 is connected between the terminal 52 and the neutral line and still another neon lamp 65 is connected in parallel with the contacts of the "high" thermostat 54.

The apparatus is intended to supply blood to a patient at a temperature of 36.degree. C. (96.8.degree. F.). When the apparatus is to be placed in operation the blood coil 24 is mounted on the chimney portion of the convection unit and the convection unit and blood coil assembly is lowered into the water tank, which is filled to a point very near its top so that the blood coil and convection unit are completely submerged. The outlet from the upper end of the drip coil is connected to an extension tube carrying the vein needle through which the blood is supplied to the patient and the lower end of the blood tube 24 is connected to the container which contains the cold blood which has been brought from the cold store. The heater is switched on by closing the main switch 44. Before this switch is closed the two neon lamps 42 and 43 are alight to show that power is available and the neutral and earth continuity lines are in order. Since the water is initially cold the thermostats 48 and 54 are both closed, and because the thermostat 48 is closed the neon lamp 64 is alight to indicate that heating is proceeding. Neon lamps 46, 59, 62 and 65 are not illuminated and only come into operation if something is wrong.

Heating proceeds until the temperature within the tank reaches 38.degree. C. (100.4.degree. F.) at which point the thermostat 48 is set to cut out. As soon as the neon lamp goes out it is known that a supply of hot water is available and the blood in the blood coil 24 will have been raised to the desired temperature of 36.degree. C. (96.8.degree. F.) or slightly above that temperature. Transfusion may therefore commence as soon as cold blood still in the extension tube and the vein needle has been allowed to run away. Thereafter blood flowing through the blood tube will be heated to the required temperature. As soon as the water temperature in the tank drops to 37.degree. C. (98.6.degree. F.) the thermostat 48 cuts in again and the further heating is indicated by the neon lamp 64.

If for some reason the "normal" thermostat 48 should fail to operate to cut off the heating when the desired temperature is reached the temperature will continue to rise until it reaches 40.degree. C. (104.0.degree. F.), at which level the "high" thermostat 54 operates to cut off the supply. Opening of the contacts of thermostat 54 places the supply voltage across the neon lamp 65, which immediately lights up to indicate that a fault has developed.

If for any reason the heater 57 should fail it will cease to take current and the supply voltage will accordingly be placed on the neon lamp 62 and its series resistor so that the neon lamp 62 will light up to indicate a heater failure.

In the foregoing specification, certain specific temperatures have been mentioned but it is known that the temperature of the blood at the point of entry to the patient does not necessarily have to be what is frequently considered as blood heat (37.degree. C. -98.6.degree. F.), but may lie anywhere within the range 36.degree. C. -39.degree. C. inclusive. The factors governing the blood temperature may be, for example, ambient temperature, the condition of the patient, and the type of operation being carried out.

It will therefore be apparent that the temperatures stated in this specification are exemplary, and simple adjustment of the automatic temperature control will quickly permit the above-mentioned range of temperatures to be achieved.

Claims

I claim:

1. Blood-heating apparatus, comprising a vessel to contain a heating liquid to a predeterminable minimum level, a coil of tube extending in the vessel between an inlet from the exterior of the vessel and an outlet to the exterior of the vessel, an electric heater in the vessel, and a thermostat in the vessel to control the electric heater and thereby the temperature of heating liquid contained by the vessel, wherein the electric heater is lowermost in the vessel, a tubular convection guide is positioned in the vessel above the heater, the tubular convection guide consists of a chimney open at its upper end below said predeterminable minimum level and having an outwardly and downwardly flared lower end, the periphery of said lower end being the upper boundary of a lower entry to the tubular convection guide, the coil of tube is coaxial with and outside the chimney above the lower end of f the convection guide, and the outwardly, downwardly flared lower end of the convection guide extends radially beyond the coil and the electric heater.

2. Blood-heating apparatus as claimed in claim 1 wherein the convection guide is formed of thermally nonconductive material.