WO1995008359A1

WO1995008359A1 - Medication administration apparatus

Info

Publication number: WO1995008359A1
Application number: PCT/GB1994/001831
Authority: WO
Inventors: Timothy Johnson
Original assignee: Timothy Johnson
Priority date: 1993-09-18
Filing date: 1994-08-22
Publication date: 1995-03-30
Also published as: AU7502194A; GB9319371D0

Abstract

Patient-controlled analgesia apparatus has a pump (10) comprising a resilient sleeve (20) exposed on all sides for actuation between the fingers and thumb of a patient. The inlet to the pump (10) has a flow restrictor (23) and is connected to an infusion bag (1) via tubing (6), a flow limiting valve (7) and a spike (5). The outlet of the pump (10) has a one-way valve (29).

Description

MEDICATION ADMINISTRATION APPARATUS

This invention relates to medication administration apparatus of the kind by which a patient can administer medication to himself, the apparatus comprising a container of medication connected to an inlet of a manually-operable pump the output of which is connerted to a region of the patient to be treated with the medication.

The invention is more particularly concerned with patient-controlled analgesia (PCA) apparatus or similar apparatus by which a patient can administer medication to himself as desired.

PCA has been found to be extremely useful in the management of pain. Using PCA apparatus, the patient can administer an analgesic when he perceives pain and, after doing so, experiences relief. The apparatus is designed to prevent administration of harmful doses and often results in a reduction in the overall amount of analgesic administered. Because the apparatus is self-controlled, it reduces the workload on clinical staff and can, therefore, reduce costs as well as increasing patient well-being.

A review of PCA apparatus is given in "Patient-Controlled Analgesia: A review of Effectiveness of Therapy and a Evaluation of Currently Available Devices" by R. P. Rapp et al., DICP, The Annals of Pharmacotherapy, November 1989, Volume 23, pages 899 to 903. Some presently-available apparatus have a pump controlled electrically and employ a computer to monitor the dose of medication administered. Examples of this form of apparatus are described in: "Patient controlled analgesia - Assessment of machine feedback to patients" by T. W. Johnson and F. E. Luscombe, Anaesthesia 1992, Volume 47, pages 899 to 901 and US-A- 5,069,668. This form of apparatus is complex and expensive and can be difficult to set up. An alternative form of apparatus relies solely on mechanical means to administer medication. Examples of such apparatus are described in WO- A-91/08002, EP-A-231371 and WO-A-93/00944. In order to produce the necessary reliability and safety, these apparatus tend to require rather complex interconnection arrangements and can be difficult for the patient to use. They are also too expensive to be used as widely as would be desirable. Some apparatus is designed specifically to be implanted under the skin of the patient so that the medication reservoir has to be refilled by injection through the skin. The medication pump, is activated by pushing down the skin over the pump. In many cases patients can have difficulty in locating the correct location, especially elderly patients with poor manual dexterity. Also, it is difficult for the patient to know whether or not he has successfully actuated the pump, because the design of the pump and the thickness of the overlying skin reduces any tactile feedback from the pump. Examples of implantable apparatus are described in EP-A-168675, EP-A-143503 and US-A-4,857,059.

It is an object of the present invention to provide improved PCA apparatus and other medication administration apparatus.

According to one aspect of the present invention there is provided medication administration apparatus of the above-specified kind, characterised in that the inlet of the pump is connected to the container via first length of tubing and a spike connection at one end of the tubing, that the pump has a tubular resilient member that is, in use, exposed on all sides for actuation between the fingers and thumb of the patient, that the pump has a flow restrictor between its inlet and the first tubing to limit flow of medication into the pump to a safe level, and that a second length of tubing extends from the outlet of the pump via a one-way valve allowing flow of medication out of the pump on actuation but preventng flow from the second tubing into the pump. The apparatus preferably includes a flow limiting valve between the container and the inlet of the pump. The tubular resilient member is preferably of circular section before actuation and may be of a translucent plastics material. The flow restrictor is preferably a capillary bore, which may open into a flared region within the pump. The one-way valve may include a duck-bill valve. The apparatus may include a manually-operable clamp that is operable to prevent flow of fluid through the apparatus. Preferably, the second length of tubing is connected to the patient via one arm of a Y-coupling and there is an air filter between the pump and the patient.

Patient-controlled analgesia apparatus in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic side elevation view showing the layout of the apparatus;

Figure 2 is an enlarged sectional elevation of the pump of the apparatus;

Figure 3 is a lateral section of the pump, before actuation, along the line III - III of Figure 2;

Figure 3 A is a section of the part shown in Figure 3 after squeezing; and

Figure 4 is a perspective view of a modified part of the apparatus. The apparatus comprises a 100ml infusion bag 1 containing a saline and analgesic medication solution and supported by a hanger 2 either above or below the height at which the medication solution enters the patient. The bag 1 has two ports 3 and 4 on its lower edge. One port 3 is a self-sealing port through which the analgesic is injected into saline within the bag. The other port 4 is a longer, self-sealing port by which the solution in the bag flows out to the patient. Connection to the second port 4 is made by means of a spike connertor 5 at one end of a first length of tubing 6. The spike connector 5 also includes a conventional flow-limiting valve 7 that is normally open but shuts off, to prevent flow out of the bag 1, if pressure in the bag increases beyond a safe limit.

The tubing 6 extends to the inlet of a pump 10, which is described in detail later. A normally-open clamp 11 is mounted on the tubing 6 so that the tubing can be closed as desired.

The outlet of the pump 10 is connected to one end of a second length of tubing 12. At its other end, the tubing 12 is bonded to one arm of a Y-coupling 13. The Y-coupling 13 serves to make connection of both the tubing 12 and an intravenous fluid line 14 with an intravenous catheter 15 that extends into a vein of the patient. The line 14 includes a one-way valve 16 that allows flow of liquid down along the line, into the patient, but prevents passage of medication up the line from the pump 10 when this is actuated. The intravenous fluid line 14 is optional and can be used for continuous saline administration, pressure monitoring or the like. When the intravenous line 14 is not used, its side arm on the Y-coupling 13 is simply capped closed. The outlet tubing 12 may include an air filter 17 to prevent passage of air bubbles to the patient. The air filter 17 would be of the kind including a gas-permeable/liquid- impermeable membrane that allows air to vent to atmosphere. Alternatively, the air filter could be positioned at the inlet end of the tubing 6. The pump 10 will now be described in more detail with reference to Figures 2 and 3. The pump 10 comprises a resilient, tubular sleeve 20 of a translucent siliconized PVC. The sleeve is about 5cm long with a circular section having an external diameter of 12mm and an internal diameter of 8mm. At its upper, inlet end, the sleeve 20 is bonded to the outside of an inlet termination 21 moulded from a rigid plastics. The termination 21 has a central capillary bore 23, which is about 10mm long and 0.05mm in diameter. The bore 23 forms a flow restrictor for fluid entering the pump 10. At its upper, outer end, the capillary bore 23 opens into an enlarged recess 24 that receives the lower end of the tube 6 and into which the tube is bonded. At its lower end, the bore 23 opens into a flared region 25 so that fluid entering the pump 10 can flow smoothly from the bore.

The lower, outlet end of the sleeve 20 is bonded to an outlet termination 26 formed from two rigid plastics mouldings 27 and 28 that are bonded together trapping between them a one-way valve 29, such as a duck-bill valve. The upper moulding 27 has a flared passage 30 that allows a smooth flow of liquid to the valve 29. The lower moulding 28 has a fluid passage 31 extending axially through it, the passage opening into a recess 32 at its lower end that receives one end of the tubing 12 and to which the tubing is bonded. The valve 29 is normally held closed by pressure in the tubing 12, which is at venous pressure exceeding the pressure in the unactuated pump.

In operation, the spike 5 is pushed into the port 4 to make fluid connection with the contents of the bag 1. The apparatus is then primed to expel air and draw in fluid from the bag. This is done by inverting the pump 10, so that the valve 29 is uppermost, and repeatedly squeezing the sleeve 20. The resilience of the sleeve 20 is such that, when it is released after having been squeezed, the sleeve applies a negative pressure within the pump as it tends to recover its initial shape. Because the capillary bore 23 provides a relatively low resistance to the flow of air compared with the flow of liquid, the air in the inlet tubing 6 is expelled quickly. The capillary 23 provides a greater resistance to air flow then does the valve 29 so that the air is expelled only in this direction and fluid is drawn into the pump. When liquid reaches the capillary bore 23, the priming rate falls to about 12ml hr. The volume of the pump 10 and outlet tubing 12 is less than about 3 ml and the time to prime the pump is only about ten minutes. Because fluid enters the pump 10 at its lower end during this priming operation, there is little risk of air bubbles collecting. After priming, the pump 10 can be used in any orientation. The priming operation is carried out either before connecting the Y-coupling 13 to the catheter 15 or before the catheter is introduced to the patient.

Once the apparatus has been primed and connected to the catheter 15, analgesic liquid can be administered by the patient. When the patient feels pain he actuates the pump 10 by squeezing it between finger and thumb to administer about 1ml of solution. Squeezing the pump 10 causes the pressure within the pump to rise above venous pressure so that the solution is forced through the one-way valve 29 and into the outlet tubing 12. The resistance to flow provided by the capillary 23 exceeds that of the valve so there is no flow of solution back through the capillary. This avoids the need for any one-way valve at the inlet of the pump. The dose of drug is easily altered by changing the concentration of the solution in the bag. After actuation, the patient will be able to feel that fluid has been expelled because the pump 10 is exposed around its entire circumference and the flattened shape shown in Figure 3 A is readily felt. This gives a useful tacile feedback reassuring the patient that the apparatus is functioning correctly. When the pump 10 is released, the sleeve 20 begins to recover its original, circular shape and draws solution from the bag 1 to fill the pump again. The rate at which this filling is achieved is about 12ml/hr although the rate of filling will initially be greater than this and will reduce below this as the pump fills. - 1 -

The capillary flow restrictor 23 provides a safety feature by limiting the maximum filling rate of the pump. Thus, even if the patient were repeatedly to actuate the pump 10, the rate of administration of solution to the patient could not exceed the maximum set by the flow restrictor. Even if the valve 29 were to fail, there would still not be a dangerous flow of drug into the patient. The fact that the pressure at the inlet to the pump 10 is less than that at the venous outlet, ensures that the pump must be actuated before solution can be administered and that there is no continuous flow of solution to the patient.

Instead of hanging the bag 1, it could simply be placed on the bed next to the patient or be worn in a holster by a patient. If the bag were to be squeezed inadvertently, such as by the patient lying on it, the excess pressure this would produce would cause the flow-limiting valve 7 to close and block all flow of liquid from the bag. This reduces the risk that medication might be forced through the flow restrictor 23 at an increased rate. Alternatively, excess pressure can be avoided by enclosing the bag 1' in a rigid box 40 such as shown in Figure 4, so that the bag cannot be squeezed.

The rate at which medication is administered can be monitored by periodically weighing the bag, such as by suspending the bag beneath a spring balance 50.

When the bag 1 needs to be replaced, the tubing 6 is closed by the clamp 11, to prevent entry of air, and the spike 5 is removed from the old bag and is reinserted in a new bag.

The present invention enables very simple apparatus to be provided that offers a high degree of safety but at a cost low enough to be entirely disposable after use on one patient. The apparatus can be used very easily by the patient with a high degree of confidence because of the good tactile feedback provided by the pump. The pump can be used to give a dose of variable amount since, by applying less pressure to the sleeve 20, a smaller amount of medication will be administered. The high level of confidence given to users of the apparatus means that they will only administer sufficient analgesic to provide the desired degree of pain relief, thereby reducing drug consumption.

Claims

CLATMS

1. Medication administration apparatus by which a patient can administer medication to himself, the apparatus comprising a container of medication connerted to an inlet of a manually-operable pump the outlet of which is connerted to a region of the patient to be treated with the medication, characterised in that the inlet of the pump (10) is connected to the container (1) via a first length of tubing (6) and a spike connection (5) at one end of the tubing, that the pump (10) has a tubular resilient member (20) that is, in use, exposed on all sides for actuation between the fingers and thumb of the patient, that the pump has a flow restrictor (23) between its inlet and the first tubing (6) to limit flow of medication into the pump to a safe level, and that a second length of tubing (12) extends from the outlet of the pump via a one¬ way valve (29) allowing flow of medication out of the pump (10) on actuation but preventing flow from the second tubing (12) into the pump.

2. Medication administration apparatus according to Claim 1, characterised in that the apparatus includes a flow limiting valve (7) between the container (1) and the inlet of the pump (10)

3. Medication administration apparatus according to Claim 1 or 2, characterised in that the tubular resilient member (20) is of circular section before actuation.

4. Medication administration apparatus according to any one of the preceding claims, characterised in that the tubular resilient member (20) is of a translucent plastics material.

5. Medication administration apparatus according to any one of the preceding claims, characterised in that the flow restrictor is a capillary bore (23).

6. Medication administration apparatus according to Claim 5, characterised in that the capillary bore (23) opens into a flared region (25) within the pump (10).

7. Medication administration apparatus according to any one of the preceding claims, characterised in that the one-way valve includes a duck-bill valve (29).

8. Medication administration apparatus according to any one of the preceding claims, characterised in that the apparatus includes a manually-operable clamp (11) that is operable to prevent flow of fluid through the apparatus.

9. Medication administration apparatus according to any one of the preceding claims, characterised in that the second length of tubing (12) is connected to the patient via one arm of a Y-coupling (13).

10. Medication administration apparatus according to any one of the preceding claims, characterised in that apparatus includes an air filter (17) between the pump (10) and the patient.