APPARATUS FOR FEEDING METERED AMOUNT OF LIQUID

Abstract: Pumping apparatus for administering anaesthetic agent to a patient on a regular basis, comprises a motor drive pump which permits actuation of the pump at adjustable periodic intervals with the duration of actuation also being adjustable. The pump may be of paristaltic type (28) having equiangular distributed lobes (32) on a rotary driven member (30). The flexible tube (34) which is held in tension relative to the lobes (32) is detachable. The unit is controlled by setting adjustable knobs for the periodic interval of actuation (T1) and the duration of each actuation (T2). T1 may be adjusted from under 30 minutes to over 4 hours (1/2 - 4 hours being preferred for performing epidural block) at dose delivery rates of about 10 ml within 5 minutes. The T2 knob is calibrated in units of dose. A remote transmitter may be used to indicate stages of operation or malfunction of the unit.

Description: "APPARATUS FOR FEEDING METERED AMOUNT OF LIQUID" This invention relates to a method of and apparatus for feeding a metered amount of liquid, and has particular, but not exclusive, reference to a method and apparatus for feeding a metered amount of an appropriate liquid anaesthetic during the performance of the procedure known as an "epidural block". In performing an epidural block, an anaesthetic agent is injected into the epidural space of the spinal cord to produce regional anaesthesia, particularly in situations such as during childbirth where general anaesthesia is not required. The epidural space or cavity is a space adjacent to the spinal duramater, the tough, fibrous membrane forming the outermost of the three coverings of the spinal cord. Administration of a local anaesthetic into the epidural space has the effect of blocking pain from the spinal cord, and for this reason is widely used during childbirth. Since the anaesthetic used is a local anaesthetic, it is found that an epidural block is usually effective for approximately Ik to 2 hours, and accordingly repeated administration of the anaesthetic is required for long-term performance of the epidural block, particularly in prolonged childbirth or in post operative pain. One of the major disadvantages in performing an epidural block by manual procedures is that larger volumes of anaesthetic have needed to be administered so as to prolong the period during which the anaesthetic is effective, and thereby minimise the number of times that the manual injection must be given. It will be appreciated, however, that the use of large volumes of anaesthetic can give rise to complications, particularly since each injection initially gives rise to a greater degree of anaesthesia than is actually required. There is therefore a need for a method whereby lower doses of anaesthetic can be administered on a more regular basis so as to provide a more effective and safer method for performing an epidural block. This need can be readily appreciated when it is understood that in some situations, for example, in treatment of post operative pain, the epidural block may need to be maintained for an extended period of many days. Whilst the present invention will be described with particular reference to the administration of anaesthetic in a procedure such as the performance of an epidural block, it will be readily appreciated that the- apparatus of the present invention has general application in feeding metered amounts of liquids other than anaesthetic, for example the administration of other drugs such as cancer toxic drugs which need to be administered in such a way as to maintain a constant dosage level. According to the present invention, there is provided apparatus for " administering liquid to a patient comprising a motor-driven pump for feeding a metered amount of liquid, and a control system for controlling the operation of the pump, said control system comprising first control means for effecting actuation of the pump at periodic intervals, and second control means for controlling the length of each actuation of the pump whereby the pump is able to deliver a variable dose of liquid at each actuation, the first control means being adjustable to vary the time interval between successive actuations of the pump such as to permit at least about 30 minutes between each actuation. In another aspect of the present invention, there is provided a method for administering a liquid anaesthetic to a patient, which comprises the use of an apparatus as broadly described above to deliver metered amounts of said liquid anaesthetic at regular time intervals to the patient thereby maintaining a desired level of anaesthesia in said patient. As previously mentioned, •one particular application of the present invention lies in the performance of. an epidural block; it is found that in performing such a procedure, the dose of local anaesthetic which needs to be administered to a patient at each time can be significantly reduced, for example to a level of one-half to one-third of the dose normally administered by hand in the manual procedure. Of course, in order to maintain a substantially constant level of anaesthetic, the interval between administration of such doses can be significantly reduced also, again to approximately to one-half, to one-third of the normal time interval. The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a rear perspective view of pump apparatus in accordance- with a preferred embodiment of the inventio ; Figure 2 is an enlarged front perspective view showing a pumping element of the apparatus; and Figure 3 shows schematically the general layout of the apparatus. More particularly, as shown in the drawings, the pump apparatus of the preferred embodiment comprises a casing 2 containing a control, motor M and a control system S. The motor is preferably powered by batteries B so as to be operable independently of a mains supply, the batteries being housed within the casing. Externally, the casing 2 carries control knobs 4, 6 for- timing control means T.., T 2 for setting the periodic interval of actuation, and the duration of each actuation. The timing control means may be infinitely variable or variable stepwise. The casing also carries an on-off switch 8 and an indicator 10 which indicates a low battery condition. To enable the apparatus to perform an epidural block, I have determined that at each actuation, the apparatus should be capable of delivering a dose. of up to 10ml of liquid anaesthetic. The timing control means T 2 which controls the period of each actuation is adjustable to permit a dosage range of from 0 to 10ml in 0 increments preferably of 0.5 ml, the control knob 6 for this timing control function being calibrated as a dosage, rather than a time. It will be appreciated that the time required for the pump apparatus to deliver a particular dosage will be dependent on the output of the 5 particular pump used in the apparatus. However,. for typical applications, the pump should have such a capacity that it is able to deliver a 10ml dose within about 5 minutes. I have also determined that it is necessary for the timing control means T. which controls 20 the interval between actuations is able to provide an adjustable interval of at least about 30 minutes between successive actuations, and preferably is able to provide an adjustable interval at leas -over a range of from about 30 minutes to 4 hours, preferably at increments of 2530 minutes. It will be appreciated that the timing control means T. may be capable of permitting adjustment over a wider range, say from under 30 minutes to over 4 • hours, but the range of from about 30 minutes to about 4 hours is considered to be a useful range for the 30intended application of the apparatus. The casing 2 is adapted to be mounted on an upright stand of the type used for supporting a drip feed, and for this purpose one wall 12 of the casing carries a clamp 14 for attachment to the stand. An opposite wall 16 of the casing 2 carries the pumping element (see Figure 2) which is driven by means of the electric motor within the casing 2, and associated components. More particularly, there .is shown in Figure 2 an inlet connection 18 adapted for connection to tubing 20 leading from a supply of anaesthetic or other liquid suitably within a container also supported by the stand, an outlet connection 24 adapted for connection to tubing 26 leading to a catheter or the like for administration of the liquid to a patient, and the pumping element 28 for inducing a metered flow between the inlet and outlet connections 18, 24. Although the pumping element 28 may take various forms, in the preferred embodiment of the invention, the pumping element comprises a driven rotary member 30 having an plurality of lobes 32 equi-angularly distributed about the axis of the member. A flexible tube 34, for example of a flexible plastics material, extends from the inlet connection 18 to an outlet connection 24 around a part of the circumference of the rotary member 30. The inlet and outlet connections 18, 24 are removably clipped into a holder 36, mounted on the wall 16 of the casing 2 with the flexible tube 34 being of such a length that it is under tension between the inlet and outlet connections 18, 24 and thereby tends to flatten in the area of contact with each of the lobes 32 during rotation of the rotary member 30. The flattening action tends to block or to at least substantially restrict the cross section of the tube 34 in the area of contact with the lobes, whereby discrete volumes of liquid are pushed through the tube 34 during the rotation of the rotary member 30. The construction of the pumping element of the preferred embodiment is advantageous in that the flexible tube 34 forms, together with the associated inlet and outlet connections 18, 24, and the tubing 20, 26 attached to the connections for feed and supply of the liquid, a unit which can be removed simply by unclipping the inlet and outlet connections 18, 24 from the holder 36, to be replaced by a fresh sterile unit thereby permitting the maintenance of a sterile flow path for the liquid. One particular advantage of•performing an epidural block by the method described herein using the apparatus of the present invention lies in the fact that the procedure can be•performed by topping up the dose of local anaesthetic before the previous dose has worn off. In contrast, however, when an epidural block is performed by the manual procedure a new dose of anaesthetic is often administered after the previous dose has worn off or when the level of analgesia has diminished substantially. The maintenance of substantially constant levels of analgesia is, of course, a most desirable result since " it avoids both patient discomfort due to the wearing off of the analgesia, as well as the risk of possible complications where higher doses are administered. It will be appreciated that the mode of operation of the apparatus of the present invention is such as to deliver a predetermined dose of a liquid such as an anaesthetic liquid on an intermittent basis, the dosage delivered and the time intervals at which the dosage is delivered being determined according to the setting of the timing control means which actuate operation of the motor. It will also be appreciated that many modifications and variations can be made to the device which is particularly described herein, in order to enhance its utility. In particular, indicator means such as an indicator light on the battery casing or means to actuate a remote indicator, may be provided so as to indicate when the pump is starting and/or operating. The remote indicator may for example be an indicator light at a nursing station or a remote "beeper" type portable paging unit, operated by an FM transmitter „ responsive to the operational state of the apparatus, to alert a nurse as to the actuation or alternatively malfunction of the pump. Similarly, further indicator means such as liquid crystal or other display means may be provided so as to display, for example, the total volume of liquid delivered by the pump, the time interval remaining before the next dose of liquid is due to be delivered, and so on.

Claims: CLAIMS : - 1. Apparatus for administering liquid to a patient comprising a motor-driven pump for feeding a metered amount of liquid, and a control system for controlling the operation of the pump, said control system comprising first control means for effecting actuation of the pump at periodic intervals, and second control means for controlling the length of each actuation of the pump whereby the pump is able to deliver a variable dose of liquid at each actuation, the first control means being adjustable to vary the time interval between successive actuations of the pump such as to permit at least about 30 minutes between each actuation. 2. Apparatus according to claim 1, wherein the . first control means is adjustable to vary the time interval between successive actuations at least over a range of from 30 minutes to 4 hours. 3. Apparatus according to claim 1 or claim 2, wherein the second control means is adjustable to permit a dose of at least up to 10ml to be delivered at each actuation. 4. Apparatus according to any one of claims 1 to 3, further comprising transmitter means responsive to the operational state of the apparatus to signal to a remote location, actuation and/or malfunction of the apparatus. 5. Apparatus according to any one of claims 1 to 4, wherein the pump comprises a removable deformable tube defining a liquid flow path, and a pumping element engageable externally with the tube to deform the tube and provide the metered flow. 6. A method for administering a liquid anaesthetic to a patient, which comprises the use of an apparatus according to any one of claims 1 to 5, to deliver metered amounts of said liquid anaesthetic at regular time intervals to said patient, thereby maintaining a desired level of anaesthesia in said patient.

Inventors: SCHWEITZER STANLEY ALEXANDER, SCHWEITZER, STANLEY, ALEXANDER
Applicants: SCHWEITZER STANLEY ALEXANDER, SCHWEITZER, STANLEY, ALEXANDER
Application year: 1985
Main classification: A61M5
IPC codes: A61M5