INSERT FOR A PRESSURE TRANSDUCER

Abstract: Insert for pressure transducers in connection with a dialysis machine. The insert (10) consists of a cup-shaped container with an inner filter unit (21) accessible via a cover (25) for connection (31) to an outer apparatus such as a drip chamber. The other side of the filter unit (21) is connected with a tube (15) which passes through the bottom of the container to a pressure transducer (28) of piezoelectric type. By arranging the filter unit (21) in the cup-shaped insert, the filter unit is easily replaceable in the event of contamination.

Description: TITLE INSERT FOR A PRESSURE TRANSDUCER FIELD OF THE INVENTION The present invention relates to an insert for a pressure transducer located in a machine intended for medical treatment, such as a dialysis machine. The pressure transducer is intended for connection to an apparatus located outside the machine, such as a drip chamber in a tube-set which is used with dialysis performed by means of said dialysis machine. STATE OF THE ART With dialysis, blood is taken out of the body in an extra-corporeal closed circuit and passes on one side of a membrane located in a dialyser. A dialysis solution circulates on the other side of the membrane. A dialysis machine contains the necessary pumps and other equipment for performing and monitoring the dialysis process, which can be he odialysis, hemodiafiltration and/or hemo-filtra- tion. In order to ensure that no dangerous conditions arise for the patient, the dialysis machine is provided with several pressure transducers arranged inter alia at different positions along the extra-corporeal blood circuit. Examples of the use of pressure transducers in a similar connection are disclosed in the patent documents EP-B1-130441 as well as EP-B1-134436 which show cassettes with integrated connections to such pressure transducers positioned in the dialysis machine. Apart from the pressure transducers which are disclosed in the aforementioned patent documents, the pressure transducers used are intended for connection to tubes. Luer-couplings of male type are mounted on the front of the dialysis machine. Each luer-coupling is connected to a pressure transducer inside the machine by means of a tube, said pressure transducer converting the pressure in the tube into an electric signal. This pressure transducer is normally mounted on a circuit board. The pressure at the orifice of the luer-coupling is transmitted through the tube to the pressure transducer, with air in the tube as the pressure medium. The tube between the luer-coupling and the pressure transducer is provided with a filter, the function of which is to prevent fluid, particularly blood, being able to reach the pressure transducer. Thus the filter only allows air to pass therethrough. The apparatus, of which the pressure is to be sensed, is connected to the luer-coupling. An example of an apparatus is a drip chamber or air separator positioned on the vein side of a tube-set. From the upper end of the drip chamber leads a tube which is provided with a blood filter and a luer-coupling of female type. This luer-coupling of female type can be connected with the luer-coupling of male type positioned on the front of the dialysis machine so that the machine can .monitor the venous pressure in the drip chamber. By arranging a blood filter in the tube from the drip chamber it is ensured that blood is not able to reach the luer-coupling positioned on the front of the dialysis machine. As a means of double safety the aforementioned blood filter is positioned in the tube between the luer- coupling and the pressure transducer within the machine. When servicing dialysis machines of the type GAMBRO AK 100 we have found that sometimes it must happen that blood passes to the male type luer-coupling and into the inside of the machine. This should in principal not be possible since the outer blood filter should prevent such blood leakage. Cleaning of a machine which has been subjected to blood leakage is relatively complicated and has to be carried out by specially trained service personnel. In this case the tube positioned in the machine is replaced and the luer-coupling in the machine is cleaned. If the luer- coupling cannot be cleaned this must be replaced as well. Hopefully the blood filter within the machine has remained intact and, if so, the pressure transducer can be kept. Otherwise even this must be replaced which is very expensive. It is presumed that many of the discovered cases of blood leakage have their cause in that the dialysis machine is used with tube-sets of a basic type which lack separate blood filters. Due to the provision of double safety the dialysis machine can, despite this, be saved from costly repairs. When handling blood in an extra-corporeal closed circuit, measures have to be taken in order to minimize the risk of infection, particularly with hepatitis and AIDS. Blood which leaks into the machine and remains there can be a source of infection for the next patient, for which reason a machine where leakage has occurred must be attended to immediately. The insert according to the present invention can also be used in connection with sensing of pressure in circuits which contain fluids other than blood, such as in machines intended for other medical use, for example in connection with infusion or peritoneal dialysis. SUMMARY OF THE INVENTION The object of the present invention is to provide an insert or a pressure transducer in connection with a dialysis machine or the like. The insert contains a filter unit which provides said double safety. By placing the filter unit in the insert a simple replacement of the filter unit is possible, without the costly intervention of service technicians. A further object of the present invention is to provide an insert for a pressure transducer which contains a filter unit, whereby at the same time an additional filter unit is provided within the machine in order to achieve triple safety. An additional object of the invention is to provide an insert for a pressure transducer provided with a cover. The cover contains a luer-coupling of male type for connection to previously used apparatus provided with a luer-coupling of female type. An insert which meets the aforementioned objects is defined in the appended claims, to which reference is made. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail below with the help of the embodiments of the invention depicted in the drawings. Fig. 1 is a cross-section view which shows a pressure sensor with luer-coupling according to the state of the art. Fig. 2 is a sideview in partial cross-section, of an insert according to the invention. Fig. 3 is a cross-section view through the insert according to Fig. 2 provided with a filter unit according to the invention. Fig. 4 is a cross-section view similar to Fig. 3 and shows an alternative embodiment of the insert according to the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 shows a cross-section through a pressure transducer according to the state of the art such as that used presently on the dialysis machine GAMBRO AK 100. The dialysis machine is shown only in the form of a front panel 1. A luer-coupling 2 of male-type extends through the front. The coupling is attached to the front 1 by means of a holder 3. Within the dialysis machine, to the left of the front in Fig. 1, the luer-coupling 2 is connected to a pressure transducer 5 by means of a tube 4 containing a blood filter 6. The pressure transducer 5 is mounted on an electric circuit board which is normally located at a distance from the front 1. A blood filter 6 is arranged on the tube 4. The blood filter 6 is a disc filter with a pore-size of circa 0,2 μm. The membrane of the filter is manufactured of a hydrophobic material such as PTFE (teflon) . In this way the membrane allows air to pass through it but cannot allow fluid, particularly blood, to pass therethrough. The membrane further forms a barrier for particles larger than circa 0,2 μm, such as bacteria and most viruses. Other types of filter can of course be used. The filter can be positioned anywhere on the tube but is preferably arranged as close to the front 1 as possible, i.e. immediately behind the luer-coupling 2, as shown in Fig. 1. The apparatus, of which the pressure is to be measured, is coupled to the luer-coupling 2 by means of a tube 9 which ends in a luer-coupling 7 of female type. In the embodiment shown in Fig. 1, the luer-coupling 7 is integrated with a blood filter of disc type 8. The disc filter is of known construction and can be the same filter as the filter 6 within the apparatus. The apparatus in question is connected to the filter 8 by means of the tube 9. The apparatus can be a drip chamber in a tube-set for extra-corporeal transport of blood in connection with hemodialysis. The venous pressure is measured in the drip chamber. If a simpler tube-set, which has no filter 11, is used, there is a risk that blood will pass through the luer-coupling 7 to the luer-coupling 2 and further into the inside of the machine into tube 4 and up to the blood filter 6 positioned therein. In order to clean a machine contaminated in this way, the casing of the machine has to be opened and the tube 4 with filter 6 replaced, as well as the luer-coupling 2 being replaced where necessary. In order to facilitate such a replacement of the inner blood filter it is, in accordance with the invention, placed in a separate insert mounted on the front of the machine. Such is shown in more detail in Fig. 2. Fig. 2 shows the front 1 of the machine provided with an insert according to the present invention. The insert consists of a cup-shaped container 10 with an outer flange 11 which is sealingly located in a hole 14 in the front 1. The insert is maintained therein by means of hooks 12 and 13 which grip behind the front 1 when the insert 10 is inserted through a hole 14 in the front. At its bottom, to the left in Fig. 2, the container is provided with an integrated horizontal tube 15 which is concentrically positioned in the container 10. The tube 15 is provided with a through-hole 16 which is connected to a holder 17 for a pressure transducer (see Fig. 3) via a projecting stud 18. The hole 16 is connected with a transverse hole 19 positioned in a tube-coupling 20. The function of this hole 19 will be explained in more detail below. The orifice of the insert 10, to the right in Fig. 2, is covered by a cover which is shown in more detail in Fig. 3. Fig. 3 shows the insert 10 according to a preferred embodiment of the invention. A filter unit 21 is mounted on the tube 15, said filter unit consisting of a blood filter 22 and thick-walled tube pieces 23, 24 arranged on either side of the filter. The tube piece 23 connects the filter 22 with the tube 15. The tube piece 24 cooperates with the other end of the blood filter and extends to the right in Fig. 3 up to a cover 25 which covers the open end of the insert 10. The cover 25 has a cylindrical portion 26 which extends into the insert 10 and cooperates with the tube piece 24. The cover 25 is additionally provided with a hole 27. The hole 27 is positioned just in front of the tube piece 24 so that the outer end of the tube piece is accessible from the outside through the hole. A pressure transducer 28 located in the holder 17 is shown to the left of the insert 10, seen as in Fig. 3. The pressure-sensitive surface of the pressure transducer is positioned directly in front of the hole 16 in the tube 15 and against the projecting stud 18. A seal 29 ensures that the stud 18 is sealed with respect to the pressure transducer 28. The pressure transducer 28 is electrically connected with a circuit board positioned at a distance from the insert 10 by means of conduits 30. The conduits and the electrical contacts are well insulated in order to be properly protected. The pressure transducer 28 is of a conventional construction and comprises for example a piezoelectric crystal as the active element. The pressure transducer 28 can sense over-pressure as well as under- pressure with respect to the surrounding atmosphere. The insert according to Fig. 3 is intended to cooperate with a drip chamber having a specially shaped head which is provided with an integrated blood filter as well as an outlet connection stub 31, of which only the connection stub 31 is shown in Fig. 3. The exact design of the drop chamber head is disclosed in the International patent application no. ... (corresponding to Swedish Patent Application No.94.02721-6) filed concurrently herewith, to which reference is made. The drip chamber is attached at the front 1 by means of holding means intended therefor, which are so placed that the stub 31 is positioned directly opposite the insert 10. When putting the drop chamber into place the stub 31 passes through the hole 27 in the cover 25 into cooperation with the tube piece 24 which seals against the stub 31. In this way a sealed connection is achieved between the upper part of the drip chamber and the pressure transducer 28 via the blood filter 22 and the blood filter integrated into the drip chamber head. In this way double safety is obtained. If, in spite of this, leakage of blood should occur through the blood filter integrated in the drip chamber head, the blood reaches no further than the blood filter 22 in the insert. When the leakage is noticed, the cover 25 is removed and the insert 21 is replaced. This is a relatively simple operation and can be carried out without interfering in the machine itself and without the assistance of service-personnel. When using the insert according to the invention in connection with a drip chamber, an over-pressure is present in the connection stub 31 and the hole 16. It is desirable to be able to adjust the level in the drip chamber by regulating the amount of air contained in the drip chamber. This occurs by means of the aforementioned transverse hole 19 and tube coupling 20 (only the hole 19 being visible in Fig. 3) . The tube coupling 20 and the hole 19 are connected to a pump, by means of which air can pass through the hole 16 to or from the drip chamber, whereby the level in the drip chamber is adjusted. If this function is not required, the transverse hole 19 (see Fig. 2) can be closed with a cover. Alternati¬ vely, two embodiments of the insert 10 are made, where the hole 19 is closed in one of them. The latter embodiment can for example be used in connection with a pressure trans¬ ducer for artery pressure. The insert 10 according to the invention can also be adapted for use together with a pressure transducer 5 according to the embodiment in Fig. 1. In this connection, the holder 17 is replaced by a tube coupling 32, such as shown in Fig. 4, which by means of an air tube 4 is connected with the pressure transducer 5. In order to obtain triple safety, the tube coupling 32 can be provided with an integrated blood filter 33, such as shown in Fig. 4. This blood filter can however normally be omitted. Fig. 4 additionally shows the insert 10 provided with a luer-coupling of male type 34 corresponding to the coupling 2 in Fig. 1. Once provided with this coupling 34, the insert 10 can be used for blood tubes or tube-sets according to known technology. The luer-coupling 34 of male type is fixed to a cover 36 or formed in one piece with the cover 36 on the insert 10. The cover 36 is fixed to the front 1 and the insert by means of a bayonet coupling 35. The luer-coupling 34 is thus fixed with respect to the front of the machine. The insert 10 according to the invention is provided with a blood filter 22 similar to that in Fig. 3. By connection to a luer 7 of female type according to Fig. 1, the same function as in Fig. 1 is achieved. By using both the filter 22 and filter 33, an outer blood filter 8 can be omitted in certain applications if such is desired. It is possible to manufacture the cover 36, the coupling 34 as well as the blood filter 22 in a single piece, whereby this complete component is replaced in the event of blood leakage. Instead of coupling the pressure transducer 28 to a circuit board positioned at a distance by means of conduits 30, the circuit board can be positioned at the bottom of the insert 10 in connection with the pressure transducer. The invention has been described above with referen¬ ce to preferred embodiments of the invention. These em¬ bodiments can be modified by a skilled man in many ways and such modifications which are obvious for a skilled man are intended to be encompassed within the scope of the in¬ vention. The various components described, can be combined in different ways to those shown in the drawings. The invention is only limited by the appended claims.

Claims: CLAIMS 1. Insert for a pressure transducer positioned in a machine intended for medical use, such as a dialysis machine, for connection to an apparatus located outside the machine, such as a drip chamber in a tube-set, character- ized by a substantially cup-shaped container (10) , which is arranged at the front (1) of the machine; a tube (15) arranged in the container, one end of which is connected to a pressure transducer (28) or a coupling (32) to a pressure transducer; a filter unit (21) positioned in the container, one side of which is connected with said tube (15) and the other side of which is provided with a coupling (24, 34) for connection to said apparatus. 2. Insert according to claim 1, characterized in that a pressure transducer (28) is fixed to the outside of the container (10) within the machine and in that the tube (15) extends from the pressure transducer (28) , through the container to the inside of the container (10) . 3. Insert according to claim 1, characterized in that the tube (15) extends from the inside of the container and through its bottom and finishes with a tube connector (32) for connection via a tube with a pressure transducer (5) positioned at a distance therefrom. 4. Insert according to any one of the preceding claims, characterized by a cover (36) which covers the orifice of the container and is provided with said coupling in the form of a luer-coupling (34) of male type, which is connected with said filter unit (21) . 5. Insert according to any one of claims 1-3, characterized by a cover (25) which covers the orifice of the container and is provided with a central hole (27) , through which said coupling (24) is accessible. 6. Insert according to claim 5, characterized in that said coupling (24) is constituted by a tube with a relatively thick wall and with an inner lumen dimensioned to receive a connector (31) to said apparatus. 7. Insert according to any one of the preceding claims, characterized by an additional filter unit (33) arranged outside of the insert (10) between the insert and the pressure transducer (5) . 8. Insert according to any one of the preceding claims, characterized in that the container (10) is essentially cup-shaped and in that the container is fixed to the front (1) at its outer open end. 9. Insert according to any one of the preceding claims, characterized in that the tube (15) is concentri- cally arranged in the bottom of the container and extends through the bottom for connection to the pressure trans¬ ducer (28) .

Inventors: CARLSSON PER-OLOV, CARLSSON, PER-OLOV
Applicants: CARLSSON PER OLOV, GAMBRO AB, CARLSSON, PER-OLOV
Application year: 1995
Main classification: G01L19
IPC codes: A61M1, A61M39, G01L7, G01L19