Programmable Infusion Pump

This invention relates to a method and apparatus for infusing fluids accurately in terms of dosages or infusion rates. In particular it relates to a programmable infusion pump that receives a multiple fluid cartridge.

Infusion pumps are used to administer a variety of drug therapies to patients. Examples of two such diverse applications are the administration of chemotherapy drugs to cancer patients and the administration of heart-rate control drugs to cardiac patients.

The patient receiving drugs which are used to control his heart rate needs to have the fluid delivered at an extremely constant rate because the rate of his heartbeat is proportional (or inversely proportional, as the case may be) to the amount of drug delivered. If the rate of infusion were to decrease or increase significantly, the heart would pump more slowly or more quickly than desired. It is important for the infusion pump administering these drugs to return as quickly as possible to the proper infusion rate.

The volume of a heart rate control drug which was overinfused or underinfused does not have to be corrected for. If, for example, a volumetric correction was made to infuse an additional bolus of drug because the pump had slowed down, the patient might find his heart beating overly fast for a period of time. This would be highly undesirable and might even be dangerous for the patient. This type of therapy is referred to herein as a rate-dependent therapy, and many other examples of such therapies exist.

Another type of therapy which requires an infusion pump is the administration of chemotherapy drugs to cancer patients. A recent trend in the administration of chemotherapy is to provide for a slow, continuous infusion in place of the tradition bolus injection of a cytotoxin. It has been found by many cancer researchers and oncologists that the severe side-effects of chemotherapy, such as nausea, vomiting, diarrhea, anorexia, and lassitude, may be reduced in a significant number of patients if the drugs are administered in lower dosages over a prolonged period of time.

As an example relating to infusion pumps, the dosage of certain cytotoxins which may be administered is determined by approximating the surface area of the skin of the patient. The number of milligrams of drug to be administered for each square meter of skin per day for a given therapy is then computed. This amount of drug may then be administered by the traditional bolus injection in a few seconds or by the more advantageous continuous infusion method over a period of hours or even days.

When the more advantageous continuous infusion method is used, it becomes apparent that the infusion device must endeavor to administer the required volume (i.e., number of prescribed milligrams) of drug for a period of days. This type of therapy is referred to herein as a dosage-dependent therapy or volume-dependent therapy.

For an infusion device to perform this dosage-dependent therapy accurately, it must maintain a fairly constant infusion rate and determine if any undesired fluctuations in rate occurred. There must be a correction for the amount of drug which was underinfused or overinfused during a period of fluctuation.

For example, if the device were infusing the cytotoxins to the cancer patient too slowly for a period of time, it must determine how many milligrams of drug were not infused and it must then correct for the deficiency by infusing an additional amount of drug for a period of time. After the correction has been made, the pump must endeavor to return to the desired rate so that the prescribed amount of the remaining drug is administered to the patient in the required time period.

The small volumetric errors caused by the mechanism of conventional infusion pumps, as illustrated in the cardiac patient example, are not advantageous in the drug therapy of a cancer patient because they can build up to substantial cumulative errors over a long period of time. This is especially true when the pump is being used in an ambulatory patient who is not subject to continuous surveilance.

It is an object of the method of the present invention to provide physicians with the means for properly administering dosage-dependent therapies.

In recent times it has become increasingly desirable to provide an infusion pump which is compact and lightweight so that it may be used by an ambulatory patient. Ambulatory infusion pumps reduce the need for excess use of hospital facilities and resources. In order to provide a lightweight pump it is highly desirable that a pump require a minimal amount of electric power since power sources, such as batteries, can contribute substantially to the weight of a pump.

It is another object of this invention to provide for a compact, lightweight infusion pump which may be used by ambulatory patients.

There are also an increasing number of applications for which there is a need for a pump which can intravenously administer a plurality of drugs solutions. One such application is the use of chemotherapy to treat such diseases as cancer. Many of the drugs used in chemotherapy and other therapies cannot be mixed together prior to an infusion. Some of these drugs react to neutralize one another. Other drugs react to form precipitates which may block the catheter tube or possibly cause an embolism in the patient.

It is often found that when different incompatible drug solutions are used on a single patient, they are administered by using a separate catheter tube for each drug. A separate infusion pump would then be used on each individual catheter tube line and the tube would deliver the fluid solution into the patient through its respective intravascular access needle. Since a patient must pay for each catheter set and must rent a pump for use with each catheter tube, it becomes costly to use multiple catheter tubes and pumps. There is some danger of infection any time an opening is made in a patient's skin for a catheter. The likelihood of infection increases as more openings are made to accommodate multiple lines.

It is therefore yet another object of this invention to provide a single pump, with a single vascular-entry catheter set, that can deliver a multiplicity of drug solutions without mixing any of them prior to infusion. It is still yet another object of this invention to provide an ambulatory infusion pump which can administer several different drug solutions without mixing any of the fluids together.

The infusion pump of the present invention is achieved by using a unique multiple fluid cartridge assembly. The cartridge houses a plurality of flexible compartments and a pressure roller which rolls over the compartments to squeeze fluid out through their outlet opening. A plurality of access tubes connect to the openings in the flexible compartments and a multiple port connector is provided so that a single multilumen catheter can be easily connected to the cartridge for use in the infusion process. The cartridge is advantageously constructed with a resilient base to better insure that fluid does not leak behind the roller when it presses against the fluid compartments.

The cartridge may be advantageously provided with position markings along the length of the housing. These markings can be used to monitor the position of the pressure roller during the infusion process. The pump of the present invention includes an optical sensor which can read from the position markings to give a determination of where the pressure roller is. The pump is provided with a microprocessor type controller which can calculate the rate at which fluid is being delivered from the pump as a function of the time it has taken the roller to travel a measured distance. The pump of the present invention is advantageously powered by a constant force spring. Thus, the power is provided mechanically when the cartridge is inserted into the pump. There is no need for electrical power to push fluid out of the pump. A motor is provided however which controls a flow restriction valve. If the microprocessor determines that the pump is not operating at the predetermined rate, the position of the valve is changed to increase or decrease the rate of infusion. It requires very little power to occasionally operate the valve during an infusion process.

The cartridge pump of the present invention advantageously employs a novel method for maintaining highly accurate infusion rates. The optical emitter and sensor monitor the position of the pressure roller by reading the position markings. The location is fed into the programmable controller. The distance travelled from the beginning of the infusion is used in determining the total volume of the fluid which has been infused. The amount of fluid which is delivered per distance travelled by the roller is already known by the controller. The controller also determines the current rate of infusion by taking the volume of fluid infused in a predetermined distance and dividing it by the time it took the pressure roller to progress that distance. Thus the current rate and the total volume can be compared to the predetermined rate and volume. The comparison can be accomplished repetitively throughout the infusion process. By making a correction whenever the rate error or volume error exceeds a threshold value an accurate infusion rate can be maintained throughout the infusion process. This method is thus highly advantageous for use in dosage dependent and rate dependent therapies.

Other objects and advantages of the present invention will become apparent during the following description of the presently preferred embodiment of the invention taken in conjunction with the drawings.

FIG. 1 illustrates a multilumen infusion system using the pump and cartridge of the present invention.

FIG. 2 is a perspective view with portions cut away of the cartridge of the present invention.

FIG. 3 is an exploded view of the base portion of the cartridge housing of FIG. 2.

FIG. 4A is a cross-sectional view of the flow restrictor valve of FIG. 2 in an open position.

FIG. 4B is a cross-sectional view of the flow restrictor valve of FIG. 2 in the fully closed position.

FIG. 5 is a magnified view of a portion of the position indicating strip of the present invention.

FIG. 6 is an illustration of a cartridge of FIG. 2 in the process of being filled with fluid.

FIG. 7 is a perspective view partially cut away of the pump of the present invention.

FIG. 8 is a side view in cross-section of the pump of FIG. 7.

FIG. 9 is an end view in cross-section of the pump of FIG. 7.

FIG. 10 provides an enlarged view of the optical sensing mechanism of the present invention.

Referring now to FIG. 1, the various pieces of a multilumen infusion system using the present invention are shown. The present invention includes a constant pressure infusion pump 10 which receives a multiple drug cartridge 20. The pump 10 of the preferred embodiment is powered by a constant force spring. A position indicating strip 22 is located on the multiple drug cartridge 20 for use by the pump 10 in monitoring the rate of infusion. The total volume of drug to be infused and the desired length of time for the infusion is programmed into the pump by a detachable programming unit 30.

The multiple drug cartridge 20 includes a multiple port connector 24. The multiple port connector 24 provides an outlet for each of the fluids being pumped from the cartridge 20. The multiple port connector 24 is adapted for connection to a connector 32 on a multilumen catheter 34. In the embodiment shown, the multiple port connector 24 and connector 32 snap-fit together. Of course, other multilumen connectors could be substituted for the snap-fit connectors. For example, at the other end of multilumen catheter 34 is a multilumen catheter connector with a threaded locking ring. Such a multilumen locking connector is disclosed in U.S. Pat. No. 4,581,012, issued Apr. 8, 1986, the disclosure of which is incorporated by reference herein. The multilumen locking connector is used to connect multilumen catheter 34 to an implantable multilumen catheter 40. The implantable multilumen catheter includes a tissue cuff 42 for forming a seal with the skin of a patient.

The multilumen infusion system of FIG. 1 provides for a simple and controlled infusion of a plurality of fluid solutions into a patient. Although the invention as described herein derives significant advantages from providing a plurality of fluid solutions through a multiple lumen catheter set, the infusion pump and cartridge of the present invention may also be made for use with a single fluid cartridge and conventional single lumen catheter.

Referring now to FIGS. 2 and 3, the multiple drug cartridge 20 of the present invention is shown in greater detail. The cartridge 20 is contained by a housing 21 which carries a plurality of flexible fluid containing compartments 36. Each compartment 36 has an outlet 37 connected to an access tube 38. A pressure roller 28 is provided inside the cartridge for rolling over the flexible compartments 36 in order to squeeze fluid out through the access tubes 38. The access tubes 38 extend into the multiple port connector 24. The pressure roller 28 includes a knob 29 on either side which extends from the cartridge for engaging a drive mechanism in the pump 10. The drive mechanism of the present invention is a sliding member pulled by a constant force spring. In accordance with the presently preferred embodiment, the knobs 29 extend from both ends of the pressure roller and ride within a pair of slots or tracks 31. It may also be possible to provide an open faced cartridge for use in a pump which already contains a pressure roller. However, the presently preferred arrangement is to include the roller 28 within the cartridge.

In order to control the rate of infusion of fluids from the cartridge 20, a flow restrictor valve 50 is provided for interaction with the access tubes 38. The valve 50 is controlled by an external gear 26 which is engageable with a mating gear inside the pump 10. Turning the gear 26 will change the pressure exerted upon the access tubes 38 by the valve 50. The more pressure which is applied by the valve 50 to the access tubes 38 the more restricted the flow of fluids therethrough. The valve 50 can be wound entirely down against the access tubes to completely close off fluid flow when desired.

The bottom of the cartridge housing 21 is a solid base member 44. Overlaying the solid base member 44 is a resilient layer 46. The resilient layer 46 is compressible by the pressure roller 28. Thus, as the pressure roller 28 is moved along the slots 31 through the cartridge a tight seal is formed between the roller 28 and the resilient layer 46 to prevent fluid from escaping behind the roller within a flexible compartment 36. All fluid is forced out through the access tubes 38. It is the resiliency of the layer 36 which causes it to push up against the roller 28 as the roller is held within the slots 31 down against the layer 46 thus forming the tight seal. The flexible compartments 36 are formed on the resilient layer 46 by a plastic molded layer 48. Layer 48 is molded in the shape of a plurality of compartments with an access tube 38 leading from each compartment. It would of course be possible to practice the invention using flexible bags to contain fluids instead of the multilayer construction described herein. In the presently preferred embodiment, both layer 46 and layer 48 are made of silicone, such as Dow Corning Silastic.

The relative infusion rate of the fluids in the compartments is determined by the geometry of the compartment. When the compartments are all the same size then the fluids in each are infused at the same rate. It is preferable that each compartment has the same length but varies in width or height to provide a different volume compartment. With all compartments the same length those with a larger width and/or height will have a larger volume. Thus when the roller moves a certain distance along the lengths of the compartments those with a larger width and/or height will have expelled a greater volume of fluid. Hence, the infusion rate is faster for the larger volume compartment. The infusion rate is proportional to the relative volume of the compartment.

In accordance with an alternative embodiment of the invention, the fluid containing compartments may be syringe barrels each with a piston for pushing fluid out of the syringe barrel. The pressure roller may be replaced by any slidable member attached to the constant force spring. The slidable member is pulled by the constant force spring against the syringe pistons to push fluid out of the syringe barrels.

The valve 50 of the present invention shall now be described in greater detail. The external gear 26 is directly connected to an internal gear 27. The internal gear 27 meshes with a second internal gear 52. Referring now to FIGS. 4A and 4B the second internal gear 52 is connected to a threaded cylindrical member 54. The threaded cylindrical member 54 engages a threaded hole within a non-rotating valve housing member 56. As shown in FIG. 2, the non-rotating member 56 is approximately square shaped and is prevented from rotating by the wall of the housing 21. The non-rotating member 56 acts to push against a coil spring 58. The spring 58 is held between the non-rotating housing member 56 and a lower housing member 59. At the bottom of the lower housing member 59 there is a compression member 60. As the threaded cylindrical member 54 is turned to force the non-rotatable housing member 56 against the coil spring 58 pressure is exerted downwards against the lower housing member 59 and the compression member 60. Thus the compression member 60 pushes against the access tubes 38 to restrict the flow of fluid therethrough. The compression member 60 can be pushed tight enough against the resilient member 46 so that the access tubes 38 are squeezed shut therebetween.

As shown in FIG. 4B, a positive mechanical seal can be achieved by further rotating the threaded cylindrical member 54, until there is direct contact between the non-rotating housing 56 and the lower housing member 59. This is desirable for situations that require a guaranteed seal, such as when the cartridge is prefilled at a pharmacy and transported to the physician. The threaded cylindrical member 54 may be turned in the opposite direction to relieve the pressure between the compression member 60 and the resilient base 46 so that fluid may flow through the access tubes 38. Thus, the rate of fluid flow through the access tubes 38 can be controlled by merely turning the external access gear 26 to give a variable degree of flow restriction to the fluids which are subjected to a constant force by the pressure roller 28 within the pump 10. It is also possible to use other types of flow restriction valves, such as needle valves.

The position indicating strip 22 is provided so that the location of the pressure roller 28 relative to the fluid compartments 36 can be detected through an appropriate sensing system. The position indicating strip 22 is oriented lengthwise in the direction of movement of the pressure roller 28. The strip 22 can be simply a plurality of equally spaced lines for which a simple sensing mechanism in the pump 10 can determine relative position by counting the number of lines crossed by the pressure roller 28. It is preferable, however, to provide the position indicating strip with coded information indicating the absolute position of the roller. The strip may appear something like that shown in FIG. 5. Access to absolute position from coded information has the advantage of allowing for determination of the position of the roller despite occasional, vibration-induced backward movement of the roller which could be interpreted by a line counter as an additional forward movement. In order to provide highly accurate infusion rate and volume information, the coded patterns on the position indicating strip 22 may be placed very close to one another, such as 10 microns apart. Depending upon the resolution desired, other greater distances between the coded patterns may suffice. The strip 22 is preferably reflective to make it easier to optically sense position. Knowing the position of the roller, the volume of fluid which has been infused into a patient can be readily determined.

The volume of the fluid which has been infused may be determined by multiplying the cross-sectional area of each flexible compartment 36 by the value assigned to each linear position of the roller. The flexible compartments 36 of the presently preferred embodiment have tapers near the starting and ending positions of the roller. These tapers, and the corresponding changes in cross-sectional area, are known functions of the shape of the mold that is used to manufacture the molded layer 48. This geometric information is stored in the microprocessor used to compute the infusion rate.

The operation of the cartridge shall be discussed with reference to FIG. 6. It is expected that cartridges would be generally supplied with their fluid containing compartments in an empty condition. A fill adapter 64 is used in the process of filling the compartments 36 with fluid. The fill adapter 64 has a connector which snaps onto the multiple port connector 24 and includes a plurality of single lumen tubing 66 through which fluid may be injected. The external gear 26 is turned to open the access tubes 38. For each fluid, a syringe is filled with enough drug and solution to fill each fluid containing compartment 36 to capacity. The syringes containing the fluids are attached to the open ends of the tubing 66. The syringes are squeezed to expel fluid through the fill adapter 64 and into the fluid containing compartments 36. After each of the compartments has been filled in this manner, the cartridge 20 is held vertically with the connector 24 on top. The roller 28 is gently shaken in order to displace any air bubbles in the fluid containing compartments. The syringe stems are withdrawn slightly to see if any air bubbles are present. If any air bubbles appear near the multiple port connector 24, which may advantageously be made of a clear plastic material such as polycarbonate, the respective syringe stem should be slowly withdrawn until the bubble is inside the syringe. The syringe is then held in an inverted position so that the fluid may be returned to the cartridge, but the air remains in the fill adapter. Each line is double checked for air bubbles and air bubbles are pulled out of the cartridge with the syringe stems wherever necessary. After it has been ascertained that there are no air bubbles remaining in the fluid compartments within the cartridge 20, the external valve gear 26 is turned to close off the access tubes 38 as shown in FIG. 4B. The use fill adapter 64 is removed and discarded. A fluid filled cartridge is now available for use in the pump.

Referring now to FIGS. 7, 8 and 9, the infusion pump 10 of the present invention is contained within a housing 11. The housing has an opening 71 through which the multiple fluid cartridge assembly is inserted. A locking device of any type may be used to hold the cartridge 20 inside the pump 10. A sliding peg 74 is shown in the drawings for use in locking the cartridge 20 within the pump 10. The peg 74 can slide back and forth within its mount 75, but the mount 75 maintains the peg captive so that it does not fall off of the device. On the inside, the pump 10 includes a sliding member 76 attached to a constant force spring 78. A constant force spring differs from a traditional tension or extension spring in that the output of the traditional spring increases (or decreases) linearly with position changes. The constant force spring provides a relatively stable output force regardless of position. Such springs are available from Stock Drive Products (New Hyde Park, N.Y.), model number SH08J28, as well as many other manufacturers. The constant force spring 78 is a metal coil. The metal coil constant force spring 78 is mounted on an idler spool 80. In accordance with the presently preferred embodiment there are two constant force springs, one on either side of the pump. The invention may just as well be made with one or any other number of constant force springs. The idler spools 80 are mounted to the pump housing 11. The spools 80 allow the coil spring 78 to rotate but prevent the springs from translational movement within the pump. The free end of the coil springs 78 are attached to the sliding member 76. The sliding member 76 has a channel 82 on its inner portion on either side of the incoming cartridge. The channels 82 do not go all the way through the sliding member 76. Rather, the channels 82 have a stop 83 which will butt against the knobs 29 of the pressure roller 28 on the cartridge 20. When a cartridge filled with fluid is inserted into the pump 10 the knob 29 on the pressure roller slide into the channel 82 of the sliding member until they hit the stops 83. Then further insertion of the cartridge pushes the sliding member to the rear of the pump unwinding the constant force spring 78. The sliding member 76 is pulled by the springs 78 against the pressure roller 28. The pressure roller pushes against the fluid filled compartments but is prevented from movement since the flow restrictor valve 50 is closed thereby preventing fluid from exiting from the compartments. The sliding member 76 includes a groove 84 on the outer side facing the wall of the pump housing. The grooves 84 are provided for riding within a track 86 on each side of the pump housing. The grooves 84 and track 86 maintain the sliding member in proper alignment on its movement through the pump. The pumping action begins when the flow restrictor valve 50 is opened from its closed position to allow fluid to flow out through the access tubes 38. Hence, the substantially constant force provided by the spring 78 pulls the sliding member 76 and consequently the pressure roller 28 against the fluid filled compartments to push fluid out of the pump.

It would be possible to have two sliding members, one on either side of the cartridge, however, a single sliding member connected by a bar over the top of the cartridge is preferred to provide a constant force across the fluid compartments and to provide a convenient location for the optical sensing system of the present invention.

In order to control the amount of pressure exerted by the flow restrictor valve 50 on the access tubes 38 the pump 10 is provided with a motor 88. The motor 88 is provided for turning a motor gear 90. The motor gear 90 engages the external cartridge gear 26 when the cartridge is fully inserted into the pump. An electrical button switch 92 can be provided on the outside of the pump to allow a user to turn the pump on or off. The pump has the indication "STOP" on the outside of the pump next to the button so that the patient knows that he can turn the pump off by depressing the button. When the pump is started by depressing button 92 the motor 88 will cause the gear 90 to turn. This causes gear 26 to likewise rotate thereby opening the valve 50 to allow fluid to begin flowing through the access tubes 38. In order to stop the pumping action, the motor will cause gear 90 to rotate in the opposite direction so as to cause valve 50 to close upon the access tubes. A battery 94 is provided for operating the motor 88. The battery 94 is also used for providing power to the microprocessor controller of the pump for operating the optical sensing system. Only a lightweight battery 94 is required because the motor is only needed from time to time after the proper flow rate has been established. A duty cycle for the motor of less than 2 seconds every 5 minutes is possible with the present invention. The electronics and optics also use only a small amount of electric power. It is highly advantageous that the power for pumping is provided by the mechanical spring 78. This advantageously avoids the need for the heavy power packs that are typically used with motor-driven pumps and avoids the fear that the power might run out during the infusion process.

A microprocessor based controller 96 is provided on a circuit broad. An electrical connector 98 is provided so that the detachable programming unit 30 can be used to set the infusion rate in the infusion pump 10. Other parameters of the infusion process may also be set by the programming unit 30. In addition, the programming rate may be a sequence of different rates which change from one to another over a long infusion process.

In accordance with the present invention, a unique control system is provided for regulating and maintaining an infusion rate delivered by an infusion pump to a patient. The control system includes the microprocessor controller 96 and the detachable programming unit 30. It will be understood that the detailed embodiment of the control unit 96 and the programming unit 30 itself form no part of the present invention, except to the extent that it provides one programmable control means available to those of ordinary skill in the art suitable for use in carrying out the steps of the present invention, the programming techniques for adapting a microprocessor controller to such steps being well known in the microprocessor and programmable control means art.

Before turning to the steps of the infusion dosage control method of the present invention, the optical sensing system shown in FIG. 10 shall be described. An optical emitter 100 and optical detector 102 are carried on the sliding member 76 of the pump 10. Power is supplied to these devices through a flexible cable 104 connected to the control unit 96. Ultimately, of course, the power is supplied by the battery 94. The flexible cable 104 is also used to transmit information back and forth between the optical sensing system made up of the emitter 100 and detector 102 and the control unit 96. The emitter 100 may consist of a common LED or laser diode. A lens 101 may be provided to focus the light emitted by the emitter 100. The light illuminates a spot on the position indicating strip 22. Light reflected from the strip 22 is detected by a sensor which is used as the detector 102. For a simple strip 22 which contains a plurality of equally-spaced stripes, the detector 102 may be a phototransistor which is masked with a striped pattern similar to that on the position strip 22. The photo masking of the detector causes the detected spot to turn on and off as the sliding member 76 carries the emitter 100 and detector 102 across the strip 22. Commonly available NPN-Si Phototransistors such as the NTE3037 distributed by NTE Electronics, Inc. (Bloomfield, N.J.) may serve as such sensors. Equivalently, the emitter 100 could be masked with the striped pattern so that almost any light detector could easily identify moving the distance between two stripes. Alternative emitters and detectors may be readily selected by those of ordinary skill in the art.

A more accurate strip 22 would have a pattern encoded onto the surface, as shown in FIG. 5, to allow the actual position of the roller to be determined. This encoded strip 22 would require an array sensor to serve as the detector 102. Such array sensors are manufactured by Micron Technology, Inc. (Boise, Idaho), Models IS32 OpticRam and IS6410 OpticRam. Other array sensors are also commercially available. These array sensors require the lens 101 which focuses the pattern on strip 22 onto the active detection area.

The information received by the detector 102 whether it be a coded pattern or a simple series of on-off pulses is transmitted over the cable 104 to the control unit 96 where it is interpreted by the microprocessor unit. The interpretation may be a simple matter of counting the number of lines which are passed by the sliding member 76 as it is moved or it may be a more complicated algorithm which reads the patterns inscribed on the position indicating strip 22 to determine the absolute position of the sliding member 76 and thus the location of the pressure roller 28.

As with any measurement instrument, it is necessary to calibrate the sensing mechanisms so that it can determine the amount of volume which is displaced by the pressure roller 28 as the sliding member 76 moves a certain distance. This calibration is achieved in the present embodiment of the invention, by storing position and volume profiles in the microprocessor. For any given cartridge, the relationship between the position of the sliding member 76 and the volume expelled from the compartment 36 is measured and stored in the programming unit 30. The position and volume profile for the cartridge type being used in the pump 10 is transferred into the control unit 96 of the pump 10 when a physician initializes the pump for determining its treatment regimen. The physician indicates the type of cartridge and the programming unit 30 transfers the appropriate profile to the control unit 96.

The method of the present invention for maintaining a controlled flow rate shall now be described. The unit dosage for the therapy is determined by the physician. The physician then calculates the number of milliliters, cubic centimeters or milligrams of drug or drugs which are to be administered over a given infusion time period. The volume of fluid is then determined which corresponds to the required dosage for each drug. A diluting solution may be used in the preparation of this volume, if desired by the physician. The volume of fluid is accurately measured in a measuring device, such as a syringe or graduated cylinder. Separate measuring devices are more advantageously used in the case of multiple drugs to prevent mixing. The fluids are loaded into the storage compartments of the cartridge in accordance with common safety procedures, such as air bubble removal discussed above. Then the detachable programming unit 30 is attached to the electrical connector on the pump. The programming unit will then issue prompts so that the doctor may input the identity of the cartridge and the desired regimen which the pump is to follow with respect to duration and infusion volume. Thus, the pump is informed of the volume of fluids contained in the compartments and the length of the time period over which the infusion is to take place. The pump is attached to the patient and started. The detachable programming unit 30 is then disconnected.

The programmable controller 96 in the pump receives position information from the position indicating strip 22 through the optical sensing system and the position data is interpreted. When the pressure roller reaches the end of the cartridge, the pump is stopped and the end of the cycle is indicated througn a visual or audible signal. The end of this infusion cycle may also be indicated by expiration of the infusion time period. The doctor can set a certain amount of time for the infusion to take place and at the end of that time the infusion process will be stopped and the flow restrictor valve will be closed.

The controller determines whether any change in position has occurred. If the pressure roller stops moving then the controller checks to see whether there is an occlusion. A test is performed to determine the presence of an occlusion by opening the valve slightly. If the roller still does not move, an occlusion is assumed. If it is determined that there has been an occlusion, the flow restrictor valve is closed to stop the pump and an alarm is set off visually or audibly. If no occlusion is determined to exist, then the controller returns to its program to adjust the valve for obtaining the appropriate flow rate. Other types of occlusion tests may be performed, such as measuring the pressure changes which occur in the fluid lines during the occlusion formation, but the presently preferred test is based upon an interpretation of pressure roller motion.

The controller determines the current flow rate at which the pump is operating by counting the time which has elapsed as the pressure roller moves a predetermined distance. The programmable controller has a built in time clock as is typical in the art for microprocessors. The programmable controller is provided with a program that allows it to correlate the linear position of the pressure roller to the volume of fluid which has been expelled through or from the infusion pump. As long as the microprocessor is informed of the proper position and volume profile for the particular construction of the cartridges and molded layers which will be used in the pump, the pump will function properly. When the detachable programming unit was attached to the infusion pump for setting the parameters of the infusion, the type of cartridge which was being inserted into the infusion pump was indicated to the pump. In this manner, the programmable controller of the pump will know which set of data to refer to in determining the correlation between the linear position of the pressure roller and the volume of fluid expelled from the flexible fluid filled compartments.

In accordance with the present invention, the calculated current flow rate is compared with the desired flow rate as was indicated to the control unit by the detachable programming unit 30. The error in the flow rate is determined and compared with a predeterminedd allowable error. If the allowable error has been exceeded, the controller will instruct the flow regulator to make a correction. The type of correction depends on whether a rate-dependent therapy or a dosage dependent therapy is being followed. For a rate dependent therapy, the flow restrictor valve is adjusted a small amount. The valve will continue to be adjusted until the rate error has been reduced to an acceptable level. For a dosage dependent therapy, the flow restrictor valve is adjusted opened or closed until any volume error has been substantially eliminated. The valve is then readjusted to more closely approximate the desired rate of infusion.

Further in accordance with the invention, for dosage dependent therapies in addition to checking the current flow rate for error, the controller compares the total volume which has been infused with the volume which should have been infused according to the programmed infusion regimen. If the volumetric error exceeds a predetermined limit, the flow restrictor valve is instructed to open or close until the volume error has been substantially eliminated. In the presently preferred embodiment, the maximum allowable volumetric error is 1.0 cubic centimeter of drug for the cartridge. If for example the cartridge has four 20 cc. chambers, the volumetric accuracy for each individual chamber is 0.25 cc. This corresponds to an accuracy of 1.25% for the total infusion process, regardless of the duration of the infusion. When a volumetric error has been corrected, the valve is readjusted so as to approximate the desired rate of infusion. When the infusion process progresses at the desired rate and is within the volumetric tolerances, the controller continually loops through its program checking the position being sensed, the change in position, the change in time and determining whether a rate or volumetric error exists. Most of the time no adjustment will be necessary and therefore very little electrical power is consumed. The process continues until the end of the infusion at which time the flow restrictor valve is closed.

Sample computer programs for implementing the control method of the present invention on an Apple II computer (manufactured by Apple Computer Co., Inc.) equipped with A6 T/D Timer Driver Board and A32 I/O Optically Isolated I/O Board (manufactured by Rogers Labs, Inc., Santa Ana, CA) are attached as Appendix A. A similar program may be written by one of ordinary skill in the art to operate the microprocessor selected for the controller of the device of the present invention.

In the presently preferred embodiment, an electronic control system with optical sensing capability monitors the infusion process volumetrically and any deviation from the desired rate is derived from the changes in volume that are sensed by the system. It is possible for one of ordinary skill in the art to devise other feedback sensors to accomplish the same volumetric measurement, such as by attaching strain gauges to a syringe barrel and measuring the position of the plunger.

In the presently preferred embodiment, a cartridge with a roller and one or more elastomeric chambers which can independently store a multiplicity of fluid solutions is used to hold the fluids as the roller position is being measured. Other chambers could be devised by one of ordinary skill which could be used to accomplish the same type of measurement, such as by mounting one or several syringes in a manifold and using the position of the plungers to measure the volume.

In the presently preferred embodiment, an electronic controller is used to determine if any substantial errors exist in the rate or volume of fluid delivered. Other controllers, such as a mechanical controller comprised of gears and cams, may be adapted to measure fluid delivery errors and correct for them.

Of course, it should be understood that various changes and modifications to the preferred embodiment detailed herein and to the method of administering a dosage-dependent therapy as described herein will be apparent to those skilled in the art. These changes described above and other changes can be made without departing from the spirit and scope of this invention and method, and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the following claims. ##SPC1##