Patent Application
20060064053
This invention is generally related to monitoring the amount of medical fluid delivered by a pump, and more particularly, to accurately monitoring the amount of medical fluid remaining and calculating a flow rate for complete delivery in a predetermined time period.
It is known for infusion systems that contain multiple infusion pumping modules to include a centrally managed infusion pump system in which pump and monitoring modules are selectively attached to a central management unit. The central management unit controls the internal setup and programming of the attached modules, and receives and displays information from them. Each module is capable of being detached from the central management unit.
Due to inaccuracies of the infusion system, that can be plus or minus 5% or more over long periods, and other factors such as intravenous (IV) bag overfill or interruptions in flow, a desired volume of a drug may not be infused within a desired period and the infusion may be ahead or behind schedule by, in some cases, an hour or two. The clinician, i.e. a person qualified in the clinical practice of medicine, psychiatry, or psychology, must then manually increase or decrease the flow rate in order to compensate for these factors as soon as the problem is recognized. Interruptions in receiving medication can result in inconvenience and delay for the patient and clinicians, as well as potentially negative therapeutic efficacy of the medication. Drug toxicity may also become a problem where the infusion rate is increased toward the end of the infusion to assure on-time completion.
One approach clinicians use to deal with the above problem is to weigh the IV bag to determine the exact volume of the bag. This is not a fully satisfactory approach, since the bag must be carefully weighed in the pharmacy and the empty weight of the bag subtracted from the total weight of the bag. Differences in accuracy of the scale and correction for the specific gravity (density) of the solution (which is usually not known) result in additional inaccuracies. Typically, a clinician sets an infusion flow rate based upon the derived volume of the solution. This method does not allow for accurate correction of flow rate due to interruptions in flow once the infusion is initiated and thus may not deliver the infusion medication to the patient over the desired time period. At the completion of an infusion that has been subjected to interruptions, the clinician is often left with a sizable volume of residual medication remaining in the IV bag or tubing that must be flushed or discarded. If the residual volume is discarded, the patient may not receive the full dose intended by the clinician, thus reducing the medication's effect.
Therefore, there has been identified a continuing need to provide a medical infusion system that will accurately infuse a medication over predetermined periods of time.
Briefly and in general terms, the present invention is directed to an infusion system that delivers a first infusate, preferably a medication, to an IV line, and a second infusate, preferably a neutral carrying solution, to the patient's IV line. The infusion system also includes a measurement device that determines an amount of undelivered first infusate remaining in the system. Furthermore, the infusion system includes a control system that controls delivery of the first infusate, and that enables input of a predetermined volume of the first infusate to be delivered, and input of a time period within which infusion of the first infusate volume should occur. The control system also communicates with first and second delivery devices and the measurement device to determine an optimum first infusate infusion flow rate based on the predetermined first infusate volume, the predetermined infusion time period, and the determined amount of undelivered first infusate remaining in the system, and controls the first delivery device to deliver the first infusate at an optimum infusion flow rate.
In accordance with another aspect of the invention, there is further provided an infusion system comprising a first delivery device that delivers an infusion ultra filtrate to a hemofilter, and a first measurement device that determines the amount of infusion ultrafiltrate in the infusion system. The infusion system also includes a second delivery device that receives a patient's removed ultrafiltrate from the hemofilter, and a second measurement device that determines an amount of removed ultrafiltrate in the infusion system. Furthermore, the infusion system includes a control system communicating with the first and second delivery devices and the first and second measurement units to determine optimum flow rates to and from the hemofilter, based upon the determined amounts of infusion ultrafiltrate and removed ultrafiltrate in the infusion system, and a predetermined desired pressure differential between the infusion and removed ultrafiltrates, and for controlling the first and second delivery units accordingly.
In other aspects the invention, there is provided a method of infusing a first infusate into a patient. The clinician or the system itself determines the total volume of first infusate that is to be infused into the patient. The clinician then ascertains the period of time over which it is desired that the total volume of first infusate is to be infused, such as twenty-four hours. A position sensor of a syringe pump or the weight cell of a large volume pump detects the remaining amount of first infusate to be infused. A control system constantly calculates the time remaining in the predetermined period. The large volume pump (LVP) delivers the second infusate into the patient's infusion line while either a syringe pump or a LVP and weight cell combination infuses the first infusate into the IV line. The control system preferably constantly and automatically adjusts the infusion flow rate based on the remaining amount of first infusate to be infused and the time remaining in the predetermined time period. The detecting, calculating, delivering, infusing, and adjusting steps are preferably repeated until the total volume of first infusate is infused.
In yet other aspects, there is provided a method of infusing an ultrafiltrate into a patient comprising the steps of delivering an infusion ultrafiltrate to a hemofilter, measuring the amount of infusion ultrafiltrate in the infusion system, receiving a patient's removed ultrafiltrate from the hemofilter, measuring the amount of removed ultrafiltrate in the infusion system, and adjusting flow rates of the delivering and the receiving steps based upon the measured amounts of infusion and removed ultrafiltrate in the infusion system and a predetermined desired pressure differential between the infusion and removed ultrafiltrates.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description.
Referring now to the drawings with more particularity, in which like reference numerals refer to like or corresponding elements among the several views, the multichannel coordinated infusion system according to the invention infuses a predetermined volume of medication over a specific predetermined time period, such as 1000 ml of a chemotherapeutic agent over a 24 hour period.
The present invention will be explained by way of example whereby a patient undergoes a chemotherapy medication or other medication infusion. It should be understood that such an example is for illustrative purposes only.
Typically, a chemotherapy medication is infused over multiple sessions lasting many days. Due to inaccuracies in some infusion systems or interruptions in the delivery of an infusion, the infusion may be early or late by many hours by the end of the infusion session. The present invention addresses this problem and illustrative embodiments are provided below. In one embodiment, an accurate fluid transferring device, for example a weight cell in combination with a large volume infusion pump (“LVP”) is used where the fluid transferring device is controlled by an intelligent control module.
Syringe pumps typically consist of a cylinder that holds a fluid that is expelled by an advancing plunger. The plunger is usually advanced into the cylinder by a drive mechanism that includes a motor connected through a gear or gears to a driver head to provide a relatively constant pulse-free flow. In accordance with an aspect of the present invention, a means is provided for accurately infusing a predetermined volume of fluid over a predetermined period. Rather than programming a specific flow rate, a clinician may program a specific volume to be infused over a specific period and the system automatically adjusts the flow rate, within certain parameters, based on the remaining volume to be infused and the remaining period for infusion. The system also accommodates for any changes in starting and stopping of the system due to circumstances that might occur during infusion such as an occlusion or air in the infusion line or for some other reason where the infusion needs to be momentarily stopped.
Typically, medication solutions are provided in concentrated form, and must be diluted prior to infusion into the patient. As syringes generally contain relatively small volumes of fluid, as compared to IV drip bags, many syringe-borne medications are provided in concentrated form and must be diluted during administration. The present invention allows concentrated medications in a syringe to be diluted on a continuous basis by a neutral carrying solution such as normal saline solution supplied via a large volume pump (LVP).
Again referring to
The first functional unit 16 is preferably an infusion pump or the like. More specifically, the first functional unit 16 is preferably a large volume parenteral pump (“LVP”) with a flow rate of approximately 1000 to 2000 ml/hr, or more. The primary task of the first functional unit 16 in this embodiment is to deliver a dilution solution 32 into an IV line 34 inserted into a patient via a dilution infusion channel (Channel A), in this instance, the LVP 16. The dilution solution may be any neutral solution such as a normal saline solution, and is typically contained within a receptacle such as an IV bag 36.
The second functional unit 14 is preferably a low-volume timed infusion pump, such as a syringe pump. The primary task of the second functional unit 14 in this embodiment is to deliver a concentrated medication into the IV line 34 via a medication infusion channel (Channel B), in this instance, a syringe pump 14. The medication may be any type of drug in fluid form, for example a chemotherapeutic agent.
The syringe pump 14, according to one embodiment, includes a syringe size detection system having a sensor 38, such as a linear actuator, to measure the syringe diameter that is then used to determine, using a look-up table or the like, the type of syringe that is being used. For example a syringe having twenty mm diameter may have a fifty ml volume. There may however be other syringes with the same diameter, so, according to one embodiment, a clinician is prompted to confirm the syringe size as will be discussed in relation to
The syringe pump 14 may furthermore include a measurement device 40 such as an accurate linear position sensor that ascertains how far a plunger 42 of a syringe has traveled and how much farther the plunger 42 must travel to reach the end of its delivery stroke. The plunger position taken together with the syringe size, enable a processor within the multichannel coordinated infusion system 10 (see U.S. Pat. No. 5,713,856) to accurately determine the volume of medication remaining in the syringe. Such a determination can be made continuously in real time if desired.
In use, the control system of the PCU 12 communicates with the functional units 14 and 16, and the measurement device 40 to determine an optimum first infusate infusion flow rate based on a determined amount of undelivered first infusate remaining in the system, a predetermined volume of fluid to be infused, and a predetermined infusion time period. The control system of the PCU 12 then controls the flow rates of the functional units 14 and 16 accordingly.
Options 74 more particularly relevant to infusion are presented in
The clinician is prompted to enter the medication infusion flow rate, which may be entered via the numerical hard keys. If the clinician would prefer to infuse a specific volume or the entire volume of the syringe, the soft key S2 next to “VTBI” may be pressed. The clinician may either enter a volume to be infused, or, by either pressing the hard up or down keys (numeral 208 of
According to this embodiment of the invention, the clinician typically requires infusing a predetermined volume of medication over a predetermined time period. As described in relation to
In
As described above, the medication typically must be diluted with a neutral solution, such as saline, prior to infusion into the patient. To set up the dilution channel the clinician presses the S12 soft key associated with “DILUTE”, which displays the dilution interface screen shown in
In use, a receptacle 118, such as an IV drip bag, of unknown volume but having a known empty or tare weight containing a medication 120 is suspended from weight cell 116. A clinician typically identifies the receptacle to be suspended from the weight cell (e.g. a commercially available 250 ml plastic solution bag), and enters this information together with the approximate volume and duration of the infusion into the PCU 12. The type of receptacle and hence its tare weight may be determined automatically by a receptacle detection system 122. The tare weight may be determined from a database in the PCU programmed with the names of manufacturers of receptacles and the tare weight of their receptacles, or the manufacturer may include a bar code or another information device on its receptacle that the PCU may be able to read. The pharmacist may weigh the dry bag and put in a bar code or other electronic tag, or the manufacturer may include an identifier on the receptacle including the manufacturer's name, model number, and weight of the bag in grams. The weight of the fluid in the receptacle is calculated by subtracting that specific container's known tare weight from the receptacle's net weight measured by the weight cell. A tube 100 delivers the medication of the bag through the LVP 114 (Channel B) to connect with the IV line 34.
The processor within the multichannel coordinated infusion system 110 (control system) automatically determines a precise infusion flow rate based on the predetermined total volume to be infused, the measured fluid weight, and the time remaining in the period allotted for the infusion. This determination may be made continuously and in real time if desired. Inaccuracies due to different specific gravities of fluid are generally minimal (as most medication fluids have specific gravities close to one, i.e. a similar mass to water which is used as a standard) but may be taken into account by the multichannel coordinated infusion system 110. The system therefore automatically determines the weight change of the receptacle 118 and adjusts the medication infusion rate via Channel B accordingly, to insure complete delivery of the contents of the receptacle, or a specified volume, in the predetermined time period allotted for the infusion. In doing so, the system automatically adjusts for periods of no flow due to alarms, pause conditions, etc.
The functional units 16 and 114 are preferably removably attached to the interface unit PCU 12 and may be interchanged with other functional units, as described above. It is to be understood that although two functional units are shown in
Typically LVPs need a positive head height to operate accurately. In the weight cell embodiment discussed above, the constant control of the flow rate through Channel B negates the need for a positive head height. The arrangement above permits the delivery of the entire contents of an unknown volume in an exact predetermined period of time. It also results in the ability to deliver jointly controlled dilution and infusion solutions.
In a similar manner to that described in relation to
The Channel A dilution infusion is then set as described in relation to
The method of infusing a medication into a patient in accordance with the infusion system of
Patients with chronic renal failure usually make use of a normal hemodialysis procedure. Hemodialysis is often very difficult for the patient, as there is a large amount of fluid shifts and electrolyte changes as well as many physiologic changes that occur while the patient is having his or her blood cleansed by a hemodialysis machine. The procedure generally drains the patient's energy making him/her tired and weak. Such side effects are even more pronounced with patients who are critically ill. Patient's bodies often cannot tolerate the procedure as their blood pressure drops and they have other physiologic problems. To overcome the extreme nature of hemodialysis, the CRRT (CAVH and CAVHD) procedures were developed. CRRT is similar to hemodialysis, except that the patient is on the machine (the filter system) continuously rather than for several hours at varying increments of time. In CRRT, it is important to keep accurate records of dialysis liquids and intravenous liquids entering the patient and the amount of liquids leaving the patient. That is, a mass balance must exist when liquids are drawn and replaced from a patient. Severe clinical problems, and even death, may occur if these fluid balances are not carefully regulated. The advantage of these therapies is that they are less stressful on the body and provide continuous treatment as opposed to three to four hour hemodialysis sessions.
The goal of these procedures is the same as hemodialysis, to clean the blood, but the process is more gradual. CAVH typically uses the patient's arterial blood pressure to deliver blood to a low-resistance hemofilter. To maintain systemic blood pressure, the patient receives replacement fluids. CAVHD is a modification of the CAVH method that uses an infusion pump to move a dialysate solution countercurrent to blood flow, adding the ability to continuously remove solute while removing fluid.
Both CAVH and CAVHD provide continuous renal replacement therapy, thus allowing removal of solutes and modification of the volume and composition of the extracellular fluid to occur evenly over time. Unstable patients, who are often intolerant of the abrupt fluid volume and solute concentration changes that accompany standard hemodialysis treatments, can usually be treated safely with CAVH or CAVHD.
The hemofiltration system utilizes a small filter that is highly permeable to water and small solutes, but impermeable to plasma proteins and the formed elements of the blood. The filter is placed in an extra corporeal circuit. As the blood perfuses through the hemofitter an ultrafiltrate of plasma is removed. The ultrafiltrate is concurrently replaced using a fluid with an electrolyte composition that is either similar to that of normal plasma or specifically designed to correct abnormalities in the individual patient. The hemofiltration circuit connects a large artery and vein. Blood is typically pumped through the circuit by the heart, allowing the patient's arterial-to-venous pressure gradient to provide the pressure to drive the system. This system however does not accurately control the fluid mass balance discussed above.
In the present invention, a dialysis filter 144 is connected between an arterial venous (“AV”) shunt on one side and two weight cells and LVP combination modules 146 and 148 on the other. The LVP combination modules are both controlled by a single PCU 150. Blood 152 from the patient enters the filter and an ultrafiltrate 154 is removed and contained in receptacle 156, leaving only blood cellular components, and blood plasma proteins. A replacement ultrafiltrate 158 enters the filter 144 via a conduit 160 and is mixed with the separated blood plasma proteins before returning 162 the blood to the patient. The flow rate of the ultrafiltrate 154 removed from the patient is monitored by PCU 150 that controls the LVP module 146. Likewise, the flow rate of the ultrafiltrate 158 replaced into the patient is accurately controlled by the PCU 150 that controls the LVP module 104.
By doing so, the PCU 150 controls the LVP module 148 to accurately deliver an infusion into an IV line based on the flow rate desired. The LVP module 146 is programmed to accurately withdraw fluid from the line by measuring the amount of fluid withdrawn. The system can be programmed to maintain a preset difference between the two infusions to result in an accurate positive or negative balance. Similar to the embodiments described above, since the two infusion modules 146 and 148 are programmed by the same PCU 150, when one infusion module stops for any reason, the second module will also stop.
Improved accuracy, control and the ability to program either a positive or negative pressure differential in a CRRT system may be achieved using the multichannel coordinated infusion system 140 with weight cell capability and central PCU 150 control. The multichannel coordinated infusion system 140 is also able to overcome conditions such as high intake and output pressure differences that significantly affect volume of delivery or withdrawal.
While the particular infusion systems and methods as herein shown and disclosed in detail are fully capable of performing as indicated and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention, and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
