DE3838689C1 - Method for the continuous measurement of the pressure in a flexible fluid line for medical purposes, as well as a device for carrying out the method - Google Patents

Abstract

Method and device for monitoring the pressure in a fluid line, in particular in an infusion pump, the fluid hose (12) being deformed with the aid of an actuation member (72), the deflection of the actuation member (72) being subsequently determined by resetting the fluid line (12) as a result of the conveying pressure, and an alarm being triggered, where appropriate. <IMAGE>

Description

The invention relates to a method for continuous measurement of pressure in a flexible Fluid line for medical purposes and a Device for performing the method.

In particular when administering medical liquids, such as IV solutions, to humans by means of pumps, monitoring the fluid line with which the IV solution is supplied to the patient is of considerable importance. An essential feature of this device is a pressure measuring device arranged at the outlet of the pump - usually a peristaltic pump - with which the pressure in the fluid line is continuously monitored. Usually, when the current pressure value deviates from a predetermined target value, the entire pump arrangement is brought into the safe state with the formation of an alarm.

To measure this pressure are in medical In practice two methods are known:

It is based on the principle of pressure communicating tubes in a side leg of the infusion system, that for the better Readability is attached to a ruler. It this is the so-called ZVD measurement (central venous pressure).

Furthermore, by means of a pressure measuring device (Pressure cell) an integration into the Infusion system. It will Measuring signal evaluated by a device that the ZVD measurement as a so-called "bloody blood pressure measurement" allowed.  

A device of the first type is known for example from DE 32 09 721 A1, at a pressure measuring device at the outlet of the pump is present, which is connected to an evaluation unit is. In this measuring device a special Fluid hose needed, one side Has bulge in which the respective level is registered, which is a mark for the im Hose serves pressure. Quite apart from the fact that a certain expensive disposable this arrangement is relatively imprecise and difficult to adjust because of the inside the meniscus forming the recess desired accuracy contributes.

Furthermore, EP 66 607 A1 describes a pressure detector known for an infusion pump in which the Pressure measurement inside the infusion pump takes place. For this purpose, the hose system of the A small circular capsule integrated, one wall stiff and the other Side is designed as a movable membrane. The diaphragm that bulges when overpressure occurs mechanically a signal generator that is caused by friction has a certain hysteresis, whereby the ZVD measurement was carried out only relatively imprecisely can be. In contrast to the one mentioned at the beginning Therefore, only one method can be used with this arrangement Measurement accuracy of approx. 10% can be guaranteed. In addition, by integrating the Pressure measuring capsule in the infusion tube the price of the entire disposable is considerably more expensive.  

DE 30 35 703 A1 describes an infusion device in which monitors an undisturbed flow through a hose system shall be. This is u. a. provided the hose between a rigid abutment and an elastic element and deform. The pressure built up in the hose leads to a deformation of the elastic element. This device serves as a safety device, which egg triggers an alarm or switches off the device if that as Switch trained elastic element a certain Ver degree of shaping exceeds. It turns out with this Ausge staltung as disadvantageous that only a safety shutdown can be made, or an alarm after exceeding an alarm threshold can be triggered.

The invention is therefore based on the object to further develop the above-mentioned methods and a  To provide device for this at which using a normal flexible Hose a pressure measurement with a measuring accuracy can be carried out below 10%.

The task is solved by in the claims 1 and 4 specified features. The subclaims show advantage adhesive developments of the invention.

The pressure measurement according to the invention initially shows the Advantage on that a conventional hose system as Disposable can be used, d. H. no additional pressure measuring elements in the hose system need to be integrated into the disposable price drive up.

In addition, the inventive method with a relatively high measuring accuracy, for example 5% and below will. So with one to be determined Deflection of the measuring device of 1 mm still steps from 30 to 70 µm, in particular approximately 50 µm, without every difficulty can be measured.

The pressure measuring device according to the invention is located itself within the entire pumping arrangement downstream of the usually peristaltic pump. To Pressure measurement is the radial expansion of the usually designed as a silicone tube Pump tubing used, of which a section the special pump element in peristaltic pumps forms. When measuring pressure, the elastic  Hose opposite its untensioned circular Starting position deformed elastically, the Hose cross section takes an oval shape. For this are the elastic restoring forces of the hose to overcome, taking care that the Tube is not completely occluded. Since the Restoring force is substantially linear, the Pressure of a supplied fluid, especially one IV fluid, essentially linear using the measuring device according to the invention can be measured.

For this, the elastic hose with a Actuator connected to the one hand Tube deformed, on the other hand the Deflection of the actuator is a measure of pressure inside the hose represents. With increasing pressure, the Hose strives to be out of its oval deformed state into its optimal circular shape to return. This leads to a radial Deflection of the hose and thus to one Actuation of the actuator, d. H. to an um a certain amount of displacement that using a detector of the above Accuracy can be determined.

To measure such a deflection, all, continuously registering Measuring devices are used that the input have mentioned accuracy. Usually namely a hose to get out of its unpressurized Initial situation in its circular optimal position to be able to be transferred at about 1 bar, just to be deflectable about 1 mm. In this respect they are Stretch about 1 mm with the required To determine accuracy.  

Optical or electrical measuring systems can be used for this are used, the use of a Strain gauge is particularly preferred. As is known, the electrical resistance of a Strain gauge depending on the strain or compression changed so that the actuation of a strain gauge on a leaf spring (Bending beam) by bending it into one Changes in the measurement signal leads. Here is the Measurement in the desired range so precisely that the Administration of IV solutions easily and cheaply can be monitored.

This can be effective by monitoring the Pressure can be determined whether the hose kinked or detached from the infusion needle whether it is blocked or even torn.

In addition to monitoring IV infusion systems can of course also other hose systems, for example blood tubing systems in blood pumps and the like. are monitored with this device.

The inventive method is only very low hysteresis effects that result from the friction between the hose, one elastic separating layer and the bending beam surrender. However, it is not so large that it does so the measurement is permanently influenced. To that extent the measuring range can be divided into three measuring sections will.

The first section concerns the measurement of the tubeless device, d. H. with one in peace bending beam. The result is a  characteristic output signal of the Strain gauge.

In the second section, this signal significantly changed that unpressurized (filled or empty) a hose is inserted into the measuring arrangement and is deformed there. The resulting measurement signal becomes the initial and adjustment measures that take place automatically later used.

A third section will build on this Zero point value the actual measurement on the hose carried out by now the to be funded Pumped liquid with a certain pressure becomes. The resulting system pressure, the adjusts itself to the infusion is through The flow resistance of the infusion solution is affected, can have the following reasons:

Long catheters with small inner diameters, Small lumen cannula, infusion filter with higher flow resistances (through small pores), and kinked infusion lines between pump and Patient can sustain flow resistance influence.

At the beginning of the infusion, the pressure measuring device according to the invention fixes the pressure, which results from the so-called normal flow resistance returns and stores the resulting value as "Normal value". By storing this Normal value gives the first possibility of one so-called comfort alarms when you have certain Maximum deviations (e.g. 25%) are still permitted  with values beyond that a Trigger staff call. In this respect, the Pressure measuring device first a normal value and calculated based on predetermined relative Measuring limits determined above or below this Limits lying in normal value. All values are stored in a memory, the resultant respective current measured value with these upper and lower limits are compared.

According to a further preferred embodiment can be achieved that the nursing staff will not only when the infusion is stopped due to a dangerous limit pressure is called, but rather when a dangerous tendency is recognized can already take countermeasures. A Such a tendency can be determined by the fact that the current measured values are saved continuously and each the differential with the previous ones Measured values is formed. It is imagined Gradient factor over a predetermined period of time, which is gradually becoming for the presence of one constructive disorder can be characteristic. In this respect, there is a permissible upper one in the register Slope factor with which the continuous formed slope factor is compared. As soon as the current slope factor above this limit a staff call is triggered again.

After all, for security reasons it is an absolute Limit value, for example approx. 1 bar overpressure, in Stored in conjunction with the Fact that the infusion pump is physical Reasons can not generate more than 1.5 bar, the Protection of the infusion system is used. This is supposed to  tubing rupture or disconnection be prevented at the glue points.

The zero point value can be in the following way be determined.

In the factory or through the service are successively eight different hoses or one standard hose in the pump is inserted. The measuring device sets these eight measured values in the memory, so that on this way a statistically verified zero point is guaranteed.

On the other hand, the user of the infusion pump also this statistic by a special one Procedure on his, for example, specifically soft or hard infusion tubing determine. To do this, he repeats those in the factory procedure followed by turning the pump open Turn on the door, insert the hose, then the door closes and the pump by pressing the Start button causes the determined Zero point value in said register take over. With each of these readjustment steps he sets one of the eight zero-point values new, so that the pump after eight such steps saved a new individual zero point value Has.

This method of storing Zero point measurements offer the advantage of a statistically verified reference point for the Measurement of the system pressure and is also suitable adapt to changed disposables.  

Other benefits are shown by described by exemplary embodiments.

Show it

Fig. 1 shows a basic diagram of a device according to the invention,

Fig. 2 is a sectional view of a preferred embodiment along the line III-III of Fig. 3 and

Fig. 3 is a bottom view of the embodiment of FIG. 2.

In Fig. 1, 10 denotes the device according to the invention. It has an elastic hose 12 which is fixed relative to a fixed wall 14 with the aid of the actuating member 16 . This actuator 16 consists of a pressure plate 18 which is linearly deflected by means of a spring member 20 and fixed against the hose 12 , this hose 12 being converted from its circular shape into an oval shape, as shown in FIG. 1. The actuator 16 is connected to a measuring device 22 which can determine the deflection of the spring 20 , as shown by the arrow in FIG. 1. The measuring device 22 is advantageously connected via an electrical line 24 to an analog / digital converter 26 , which converts the analog signal emitted by the measuring device 22 into a digital signal. The A / D converter is connected to an evaluation unit 30 via a further line 28 .

This evaluation unit 30 is also connected via a line 32 to a start button with which the device 10 is put into operation. Furthermore, the evaluation unit 30 can be connected to a further line 36 with a switch 38 which indicates that the hose is inserted or which indicates that - as is shown in the explanation of the embodiment shown in FIG. 2 - one Door is closed, which corresponds to the wall 14 in the present case.

Finally, the evaluation unit 30 is connected via a line 40 to a memory 42 , in which measured values can be stored and also deleted again in accordance with a predetermined procedure.

Finally, a line 44 leads from the evaluation unit 30 , which is connected to an alarm unit 46 , with which the entire arrangement can be brought into the safe state or an optical and / or acoustic operator call can be triggered. Furthermore, the evaluation unit 30 is connected via a further line 47 to a motor switch 48 , which triggers the operation of a motor, not shown, for operating the infusion pump.

The embodiment of FIG. 1 is operated as follows.

First, the hose 12 is oval-shaped between the fixed wall 14 and the resilient actuator 16 . With the switch 38 closed and the start button 34 actuated, the measuring device 22 generates a measurement signal which is compared as the zero point value with the zero point values present in the memory or is written into the memory 42 as the new zero point value. Only after a comparison of these values, which stand for a pressure-free hose, is the entire arrangement released and then the motor switch 48 is activated by the evaluation unit 30 as a control unit.

As the liquid to be infused is conveyed, the deflection of the pressure plate 18 , which is measured with the aid of the measuring device 22 , changes. The evaluation unit 30 forms a normal value at the beginning of the funding, as has been described above. This normal value is stored in the memory 42 and, in accordance with a predetermined program, a proportional deviation (for example ± 25%) from this normal value is also calculated by the evaluation unit 30 , the upper and lower limit values in turn being stored in the memory 42 . A constant comparison of the current measured values with the upper or lower permissible limit value is then carried out while the liquid is being conveyed.

According to a further embodiment, the respective current measured value is stored in succession in the evaluation unit over a certain period of time, the differential being formed via this measured value sequence and a slope resulting therefrom being calculated. This slope factor is compared with a predetermined limit value, designated as permissible, in the memory 42 , an operator call or alarm being triggered in the alarm unit 46 when the limit value is exceeded. This can bring the entire arrangement into the permissible state, for example by stopping the engine.

Finally, an absolute limit value is stored in the memory 42 , which corresponds to a deflection which is generated in the hose 12 at a pressure of 1 bar. When this limit is reached, an alarm is triggered immediately.

A preferred embodiment of the device is designated by 50 in FIGS. 2 and 3. This device 50 has a frame 52 , shown in part, on which a housing 53 with two housing parts 54 and 56 is arranged, which form a channel 58 which is open at the top and bottom. The upper and lower openings are designated 57 and 58 , respectively. This channel 59 is dimensioned such that it can accommodate a deformed hose 60 in its width and an undeformed hose 60 in its height.

The housing parts 54 and 56 are fastened to the frame 52 in a conventional manner and covered with an elastic separating layer 62 which also lines the channel 58 . This separating layer 62 is advantageously a silicone rubber mat that separates the outside from the inside of the infusion device 50 . Because of its high elasticity, it hardly influences the deformation process of the hose 60 .

Furthermore, a door 66 is articulated on the frame 52 via a joint 64 , which overlaps the two housing parts 54 and 56 in the closed state and interacts with a lock 68 , which is also connected to the base plate 52 . This closure 68 has a switch or closure sensor 38 from which the line 36 goes.

The inside of the door 66 is provided with a projecting pressure element 70 which, when the door 66 is closed, projects into the channel 58 and serves as a rigid contact wall which corresponds to the wall 14 according to FIG. 1.

A bending beam 74 is provided as the actuating element 72 and is fastened to the housing part 74 by means of a connecting screw 76 . The other end of the bending beam has a hammer 78 which can be adjusted in its longitudinal axis by means of an adjusting screw 80 . In a state in which no hose 60 is inserted, this hammer 78 protrudes from below through the lower opening 58 into the channel 59 .

A strain gauge 82 (two strain gauges 82 are shown in FIG. 3) is attached to the bending beam 74 , from which (as shown in FIG. 3) electrical leads 84 lead to a circuit board 86 which is attached to the right housing part 54 . This circuit board contains a conventional resistance measuring bridge, from which the line 24 to the evaluation unit 30 according to FIG. 1 goes.

The device according to FIGS. 2 and 3 is operated as follows:

First, the hammer 78 is adjusted such that it projects into the channel 58 when the hose is not inserted. This position is extended in FIG. 2 with a dashed bending beam marked with a.

When the empty hose is inserted, as shown in FIG. 2, the bending beam is in position b, while the conveyed state, which is also shown in broken lines, is shown by c.

All states result in a specific signal which is evaluated as explained in the description of FIG. 1.

A microprocessor which can be loaded again (EPROM) is advantageously used as the evaluation unit 30 and memory 42 .

Finally, the use of the analog / digital converter 26 is advantageous since digital values can be monitored particularly easily over analog values over a long infusion period.

Claims (8)

1. A method for continuously measuring the pressure in a flexible fluid line for medical purposes, in which the fluid line is filled in infusion mode with a fluid whose flow pressure is to be monitored, in which the fluid line is deformed radially by a certain amount by compression and thereby against an elastic element is prestressed and in which the radial expansion of the fluid line resulting from the flow pressure is monitored, characterized in that when the fluid is conveyed, the deflection of the elastic element is measured as a function of the return of the fluid line to its initial shape . 2. The method according to claim 1, characterized in that for pressure monitoring the one that is not under fluid pressure Fluid line against a predetermined biasing force the elastic element is determined, its deflection determined at the start of funding as normal value becomes, at the same time, a predetermined deviation from this Normal value is set and it is continuously checked whether the current value within the defined as permissible  Range and an alarm may be triggered and the pressure in the fluid line is adjusted. 3. The method according to claim 2, characterized in that to determine a tendency to change differentiates the Increase in fluid pressure within a predetermined Checked during the funding period and at About a predetermined pressure increase factor alarm rise is triggered. 4. Device for performing the method according to one of claims 1 to 3 with a rigid wall ( 14 , 66 ) and an actuator ( 16 , 72 ) which is movable in dependence on the pressure in the fluid line, the distance between the wall ( 14 , 66 ) of the actuator ( 16 , 72 ) is smaller than the outer diameter of the fluid line ( 12 , 60 ), and the actuator ( 16 , 72 ) has such a spring force that the inserted fluid line ( 16 , 72 ) without occlusion is deformed, characterized in that the actuator ( 16 , 72 ) is connected to a device for the continuous determination of the deflection of the actuator ( 16 , 72 ), that the actuator ( 16 , 72 ) is a resiliently deflectable bending beam ( 74 ) and that the device for continuously determining the deflection of the actuating member ( 16 , 72 ) has a strain gauge ( 82 ) on the bending beam ( 74 ) BEFE, the output signal of which r evaluation unit ( 30 ) is supplied. 5. The device according to claim 4, characterized in that the wall ( 14 ) in the form of a on a frame ( 52 ) is steered door ( 66 ) which, in the closed state, represents the contact surface for the fluid line ( 12 , 60 ). 6. The device according to claim 4 or 5, characterized in that the evaluation unit ( 30 ) with a door switch ( 38 ), a start button ( 34 ), a measured value memory ( 42 ), an alarm unit ( 46 ) and a motor switch ( 48 ) connected and with the door ( 66 ) closed and the motor switch ( 48 ) not actuated checked whether the signal transmitted by the actuator ( 72 ) corresponds to a value stored in the memory ( 42 ) which corresponds to an inserted fluid line ( 12 , 60 ), and when the motor switch ( 48 ) is actuated, it forms a normal value which corresponds to a fluid line ( 12 , 60 ) under a certain delivery pressure, stores this normal value in the measured value memory ( 42 ), specifies a predetermined deviation from this normal value and compares the lower permissible measurement limits and, if necessary, Alarm triggers. 7. The device according to claim 6, characterized in that an allowable maximum pressure value is stored in the measured value memory ( 42 ). 8. The device according to claim 6 or 7, characterized in that the evaluation unit ( 30 ) has a unit for differential formation, which differentiates the current measured values from the normal value and calculates the increase factor therefrom within a predetermined period and this increase factor with a predetermined , compares the value stored in the measured value memory ( 42 ) and triggers an alarm when the predetermined value is exceeded.