Field <?£ Invention

The present invention relates to a pump intended for automatic and slow drainage of a vial containing a solution, preferably a medical solution. The drainage is performed during time period adapted and predetermined for the intended use.

Background ς>f the invention

Parenteral medicaments might be administered intramuscularly or intravenously to the patient. The intravenous treatment might be performed through a continous infusion, intermittent infusion or a so called bolus-injection.

The continous injection gives the disadvantage that the vessels are exposed for a very long time to the administered drug, which increases the risk of thrombophlebitis. Further, substances such as penicillines are unsuitable for continous ^• infus-ion because they are not stable in solution and therefor might become inac¬ tive during the infusion.

The intermittent infusion is continued for a shorter time period, e.g. 30 to 60 minutes. A bolus-injection is an injection which is continued for about 3 to 5 minutes and where the solu¬ tion injected has a higher concentration of the drug than is the case with the intermittent infusion solution. Both these methods of administration results in that pharmacokinetically high pea - concentrations are obtained in blood after a short time. The time period during which the vessels are exposed to the adminis¬ tered substance is short, which means that the frequency of thrombophlebitis is reduced.

The active drug, which is kept in a glas bottle, is in the case of the bolus-injection dissolved in sterile water by suction of the water in a first step from a glas bottle with the aid of a syringe and a suction cannula. The water is sprayed into the

glas bottle containing the active drug and a solution water-drug is obtained» In this procedure a positive pressure is often obtained in the glass bottle resulting in leakage of the active drug. This creates a great risk for the personnel from a sensi- bilisation point of view. After the mixing step, the solution is sucked back into the syringe from the the glass bottle and after the exchange of the cannula the drug might be injected in a vein during 3 to 5 minutes. This procedure gives the disadvantage that the nurse is bound to the sickbed during the injection pro- cedure.

For the performance of intermittent infusion for e.g. about 30 minutes an adapter is used in the currently used administration procedures for the transfer of a sterile powder to an infusion plastic bag with for example 100 ml phys. sodium chloride, whereupon an infusion aggregate is coupled to the patient for the administration of the dissolved drug. This way of administ¬ ration leads to high costs for the non-returnable material used in the administration, which costs often greatly exceed the cost of the drug itself.

The safety demands and a hard strive to reduce costs in the medical service has resulted in that one currently looks for less expensive drugs while at the same time the need for both effective and secure methods of administration, which at the same time offer a reduction in costs, increases.

Various devices or automatic and continous administration of drug solutions to a patient are previously known.

In US-A-2 605 765 an automatic syringe is disclosed, which con¬ tains both a medical solution and a driving device for the con¬ tinuous injection lasting for 48 to 72 hours. The device is small and is adapted to be carried by the patient during the whole injection process without much inconvenience. A driving spring biases a piston in the direction of a partition wall with a throttle valve between two chambers, whereby a viscous liquid slowly flows from the one chamber into the second. The second

chamber is restricted by a movable piston, which by the viscous liquid is forced against the medical solution, which thereby is injected slowly into the patient.

In US-A-3 474 787 is disclosed a manually managed, syringe aimed at a timely shorter injection and wherein the content of an in¬ jection vial is emptied with a speed that is manually adjust¬ able. The drainage is performed by the action of a pressure spring which biases a piston in the direction of the vial such that a pumping liquid by the piston is forced through a conduit including a valve arrangement from the front chamber in front of the piston to the back chamber behind the same. The movement of the piston is transferred to the output piston of the vial so that output and injection of the solution take place.

In US-A-4 437 859 is disclosed a driving unit of a syringe, which driving unit comprises two displaceable pistons each in one cylindrical chamber. The chambers communicate with each other though a piping, which contains a pressure regulator, a flow regulator and a needle valve. One of the pistons is connec¬ ted to a driving arm for the output piston of the syringe. When the driving unit is loaded a syringe might be placed in the dri¬ ving unit. A spring biases one of the pistons against a driving liquid, which adjustably slowly flows through the connection between the chambers and drives the other piston on in front. A special security device is arranged in order to guarantee that the driving arm of the output piston of the syringe stops in case of a leakage or the like.

The prior art devices disclosed above for the automatic and slow feeding of a medical solution to a patient all suffer from a number of drawbacks.

In all cases the output is performed by spring bias, which means that if leakage or other breakage should occur in the apparatus a non-supervised output and drainage of the con¬ tents of the syringe into the patient will occur. This could lead to a catastrophy for the patient. In order to

avoid this risk of accidents the apparatus must be comple¬ mented with certain complicated and expensive security de¬ vices.

Feeding with springs leads to the drawback that the power of feeding is not linear, which gives a non-uniform pres¬ sure on the piston.

The constructions are complicated and so expensive to manu- facture that they do not form a realistic alternative for the currently used and above disclosed disposable equip¬ ment.

Time consuming adjustements by the hospital personnel is necessary for the prior art devices for the adjustment and regulation of the flow in order to obtain the desired in¬ jection or infusion time.

Basic concept of the invention.

The object of the present invention is to solve the above prob¬ lems by an infusion pump, which provides a safe, controlled, automatic and slow drainage of a liquid-containing vial. More¬ over, the infusion pump, thanks to its simple constructive de- sign, offers an administration method preferably for intermit¬ tent infusion, which offers reduced costs for the medical ser¬ vice.

These objects are attained through an infusion pump of the kind discussed in the preamble of this application, which is charac¬ terised in that the pump comprises a closed pump housing within which a pumping liquid is arranged to flow through a throttle valve provided between a first and a second chamber in the pump housing. The first chamber is on the one side restricted by one side of pump piston, which is reciprocable within a piston cy¬ linder, and which pump piston for the discharge of the solution is arranged to be driven by a vacuum on the other side of the pump piston.

Further advantageous characterising features of the invention appears from the following specification of embodiments and from the subclaims.

The pump piston of the infusion pump is thus driven by a vacuum formed behind the piston when the pump is loaded. The pump hou¬ sing is thus on the oppoosite side of the piston divided into two chambers, both of which are filled with pumping liquid, which might flow through a control valve in both directions bet¬ ween the chambers. The wall of one of the chambers is restricted by a flexible membrane, which creates a variability of the inner volume of the chamber and thus a variability of the amount of pumping liquid contained in the chamber. Upon loading the inner volume of said chamber increases while the chamber volume gradu¬ ally decreases during the drainage phase.

The pump according to the invention has the advantage, in oppo¬ site to previous constructions, of being completely safe if a leakage or breakage should occur in the construction. In such a case the vacuum built up behind the piston during the loading will be balanced. This will result in that the pump stops and the infusion is interrupted. The same situation will occur, i. e. the pump stops automatically, when the syringe or the vial is empty and the complete dosage of medicament is injected.

The pump can cooperate with an ordinary syringe, which is well known by medical staff both from a functional as well as from a handling point of view, but also other types of vials are pos- sible for cooperation with the pump. With the syringe or with any other suitable vial mounted in the loaded infusion pump, an infusion tube with cannula is attached from the syringe to the patient, whereby the infusion is started. When using a syringe or vial with scale marks the personnel at any time might read how much of the medicament is given.

With "vial" is ment different types of closed containers, con¬ taining a solution, with or without a piston reciprocable in the container for output the solution.

The time consumed for drainage of the syringe or the vial is de- termined by the form of the low valve and the size of the valve body. Different valve body sizes corresond to different infusion times, which means that no work is demanded from the medical staff for adjusting of the output flow, unlike the systems cur- rently used, which demand a considerable effort from the person¬ nel in order to obtain an intended infustion rate. A system which according to the invention does not have to be adjusted leads a safe system, since no adjustement errors can occur be¬ cause of the human factor. The drainage might suitably be per- formed during a time period of 30 och 60 minutes but also infu¬ sion periods of abot 24 hours are of intetrest, e.g. in aneste- sia.

The pump might be used without an external source of energy, which is an advantage when moving patients or if the patient stays at home. The pump is easy to handle and to load and the infusion can easily be stopped by removing the syringe from the pump.

The infusion pump according ^* co the present invention is suitable for autoclave treatment or sterilisation with damp, which is a great advantage regarding to infectious deseases, e.g. in an in¬ fectious clinic.

Short description of the drawings.

One embodiment of the invention and modifications thereof are described in detail below with reference to the attached dra¬ wings, wherein

Fig. 1 shows a side view of the infusion pump in unloaded po sition without any mounted vial or syringe;

Fig. 2 shows a sectional view of the infusion pump according to Fig. 1 with the pump in loaded position and with mounted syringe therein;

Fig. 3 shows the infusion pump according to Fig. 2 in a posi tion of current output;

Fig. 4 shows the infusion pump according to Fig. 1 from above;

Fig. 5 shows the infusion pump according to Fig. 1 from be¬ low; and

Fig. 6 shows a sectional view of an alternative embodiment o the infusion pump.

Detailed description of preferred embodiments of the invention

Figs. 1 - 5 show a first embodiment of the infusion pump accor- ding to the invention, which comprises a pump housing 2 in the extension of which is provided a loading housing 4 with two dia¬ metrically opposed and longitudinal openings 6. The outer end of the loading housing is externally provided with a groove 8 for the cooperation with an internal fold 10 on a removable and exchangeable syringe adapter 12. The syringe adapter 12 is a carrier for an ordinary syringe, whereby an internal gripping groove 16 is of a size and has a diameter corresponding to the gripp 18 of a specific syringe so that the syringe might be fixed in the syringe adapter, when it has been introduced through the open part of the adapter and the grip of the syringe has been placed in the gripping groove 16. The cross section of the adapter 12 has an extension which is less than half a circle in order to be able to lock the oval gripp 18 of the syringe in the adapter. In order to insert the syringe 14 into or to loosen the same from the adapter 12 the oval grip 18 thus has to be turned a little to be able to pass through the opening in the adapter, since the maximum width of the grip 18 is larger than the opening of the adapter.

A number of syringe adapters 12, which are identical besides the size of the gripping groove 16 exists as accessories to the in¬ fusion pump in order to be exchangeably mountable on the loading housing 4. The infusion pump can be adapted to another size of syringe by a mere exchange of the adapter 12.

The pump housing 2 comprises a piston cyinder 20 in which a pump piston 22 with a surrounding piston gasket 24 is reciprocable. The pump piston 22 is on one side provided with a piston rod 26, which passes through an inlet 28 in the bottom of the piston cy¬ linder. A shaft gasket 30, preferably an O-ring of teflon, is provided in the inlet 28 in order to sealingly abut the piston rod 26 at its movement back and forth through the inlet 28. In the end of the piston shaft 26, which in all possible positions of the piston is located outside the piston cylinder 20 in the loading housing 4, is mounted a threaded adjustment screw 32.

The adjustement screw 32 shall after adjustement and fine set- ting abut the thumbplate 34 of the syringe onuted in the infu¬ sion pump. The adjustement screw 32 is fluted around the peri¬ phery and is easily accesible for adjustement from both ways through the longitudinal openings 6. A strap 62 is stretched from the adjustement screw 32 around the pump housing 2 and back to the adjustement screw 32 and thereby forms an aid for the loading of the pump, which will be described in more detail be¬ low.

The pump housing 2 further comprises, on the side of the pump piston 22 opposite the piston rod 26, a first 36 and a second 38 chamber, which both are filled with a pumping liquid 40, prefer¬ ably silicon oil, and which chambers 36, 38 are separaed by a throttle valve 42. The internal volume of the first chamber 36 varies from a minimum to a maximum by the displacement of the pump piston 22 in the piston cylinder 20. The internal volume of the second chamber 38 varies in that one of the walls of the chamber 38 is formed by a flexible membrane 44, so that a mini¬ mum volume is obtained when the membrane wall is concave and a

maximum volume is obtained when the membrane wall is forced out to a convex position. In order to protect the membrane wall 44 and in order to create a planar surface, which can be placed steadily against a support, the outer end of the pump housing 2 is covered by a protective cover 46, in which an air opening 48 is provided for air flowing in and out upon changing of the form of the membrane wall 44. A suspension clamp 50 is fastened bet¬ ween the outer end of the pump housing 2 and the protective co¬ ver 46, whereby the clamp in one position is retracted against the protective cover inside the outer edge of the pump housing and in an extended position perpendicular to the protective co¬ ver is meant to be an aid for the suspension of the pump above the patient.

The throttle valve 42 comprises a valve housing 52 with a cy¬ lindrical valve chute 54, the valve chute being provided with a first opening 56 towards the first chamber 36 and a second ope¬ ning 58 towards the second chamber 38. A cylindrical valve body 60, one end of which being planar and the other end being co- nical, is slideably arranged in the valve chute 54 between two extreme positions (I and II) . The diameter of the cylindrical valve body 60 is less than the diameter of the valve chute 54, which means that a narrow cylindrical gap 64 is formed around the valve body when it is situated in position I. It is the size of this gap 64 that determines the time consumed for the drai¬ nage of the content of the syringe 14. A. stop means (not shown) is arranged in the valve chute 54 at the planar end of the valve body in position II. Because the valve body is stopped in this position (II) a space is formed for pumping liquid 40 behind the planar end portion of the valve body.

The infusion pump according to Figs. 1-5 works in the following way:

The infusion pump is loaded by the user pulling the strap 62 at the protective cover 46 so that piston rod 26 and pump piston 22 is forced into the piston cylinder 20. The pump piston 22 thereby forces pumping liquid 40 from the first chamber 36

through the first opening 56 in the valve housing 52. The pum¬ ping liquid urges the valve body 60 from position I to position II where it is stopped against the stop means in the valve chute 54. The pumping liquid 40 now might flow further past the co- nical end of the valve body 60 and out through the second ope¬ ning 58 to the other chamber 38, into which the flexible mem¬ brane 44 is pushed. When the pump piston has reached its end po¬ sition in the piston cylinder the pump is completely loaded and the injection syringe 14 can be mounted.

The syringe adapter 12 suitable for the syringe 14 is put on the groove 8 of the loading housing and the oval grip 18 of the sy¬ ringe is tilted a little and is introduced into the adapter ope¬ ning and is locked in the gripping groove 16. The adjustement screw 32 is adjusted so that it abuts the thumbplate 34 of the syringe, the syringe is connected through a tube and a cannula to the patient and the complete equipment is suspended in the suspension bracket 50.

The device is now iready for administration of the drug solution, which is contained in the syringe, by an output operation driven by the vacuum pressure formed behind the pump piston during the loading of the infusion pump. The pumping liquid 40 thereby tends to flow from the second chamber 38 via the second opening 58 where the liquid pressure acts on the end portion of the valve body 60 so that the complete valve body 60 is displaced to position I. The pumping liquid 40 thereby flows slowly through the cylindrical gap 64 and out through the first opening 56 to the first chamber 36. The pump piston 22 is pressed by pumping liquid equally slow outwards in the piston cylinder 20, whereby this movment is trans erred via the piston rod 26 to the piston of the syringe 14, which expels the drug solution. When the sy¬ ringe has been emptied of its contents the infusion pump will stop automatically. The device is freed from the patient where- upon the adjustement screw is threaded inwardly for a short dis¬ tance in order to facilitate the release of the empty syringe. The grip of the syringe is tilted slightly in order to be able

to be passed through the opening of the adapter of the syringe, whereupon the syringe is taken out of the loading housing.

In Fig. 6 an alternative embodiment of the infusion pump is il- lustrated, which only differs from the embodiment shown i Figs. 1 - 5 by a rapid adjustment device 66, which is an alternative to the adjustement screw. The rapid adjustement device 66 com¬ prises a control button 68, which is displaceable in a sleeve 7 in the pump housing 2. The back end of the control button protrudes a short distance beyond the sleeve 70 and its inner end is provided with a magnetic part 72. In the sleeve 70 and around the front part of the control button a pressure spring 7 is provided against which bias the control button 68 might be pushed so that the magnet 72 abuts the wall of the valve housin 52. In this position the force of the magnet affects the valve body 60, which is made of metallic material so that it is main¬ tained by the magnet 72 in position II instead of being displa¬ ced by the pumping liquid to position I in the valve chute 54.

As long as the control butten 68 is pressed the pumping liquid 40 passes fairly quick from the second chamber 38 and through the valve housing 52 to the first chamber 36 so that the end of the piston rod 26 rapidly can move to the position for the thu bplate 34 of the syringe 14. In this position the control button 68 is released and is biased out by the force of the spring, whereby the magnetic force releases the grip of the valve body 60, which immediately is displaced to position I by the liquid pressure, whereby the slow feeding starts.

The invention is in no way restricted to the above described em¬ bodiments, instead several modifications of the inventionen is possible within the scope of the claims. For example, scale marks might be provided along the loading housing to make pos¬ sible a succesive reading of the remaining or already injected solution. The loading housing might also be provided with one o more lock means, which adjustably might provide a locking func¬ tion for the movements of the thumb plate at the output. By suc a locking function different aomunts of the contents of the sy-

ringe be feed out automatically instead of the complete content of the syringe. Instead of being cylindrical the valve body might for example be spherical.