WO1998050091A1

WO1998050091A1 - Method for controlling a blood purifying device

Info

Publication number: WO1998050091A1
Application number: PCT/IB1998/000653
Authority: WO
Inventors: Olivier Favre; Claude Droz
Original assignee: Infomed S.A.
Priority date: 1997-05-07
Filing date: 1998-04-29
Publication date: 1998-11-12
Also published as: EP0980275A1; AU6849998A; JP2001523139A; TW419385B

Abstract

The invention concerns a method for controlling a device comprising means for filtering blood (8) divided into two sections by a semipermeable membrane whereof one section (8a) pertains to the bloodstream (20, 21) wherein the flow rate is preferably imposed by a blood pump (1), and the other section (8b) receiving the extracted blood ultrafiltrate is connected to a discharge line (24) into a container supported on means for weighing (7) the ultrafiltrate. Said device also comprises several lines supplying (25, 26) a substitution product from a reservoir (15, 16) supported on means for weighing (5, 6) the product. The supply outlet of each line is connected to the blood circuit via a mixer (22). Said device further comprises electronic control means (9-14) monitoring the pumps at predetermined time intervals to adjust the instantaneous flow rate of the bloodstream, the ultrafiltrate and the substitution products respectively. The method consists in revising and, if necessary, in modifying by the electronic means (9, 12) the treatment parameters on the basis of the measured variables and the medical and/or physical knowledge data pre-stored in the electronic storing means (12) of the electronic control means so as to ensure that device operates accurately and smoothly.

Description

METHOD FOR CONTROLLING BLOOD PURIFICATION DEVICE

The present invention relates to a process for automatic control of a device for filtering and / or purifying blood applied to a patient suffering from renal insufficiency in order to eliminate one or more harmful substances from the blood. In particular, in such a device, the invention relates more particularly to a method for controlling and regulating the flow rate of the extracorporeal blood circulation, the filtration flow rate of a fluid and / or of soluble discharges from the blood and, where appropriate the injection rate of one or more physiological alternative and / or medicinal solutions. The process also applies with certain adaptations to peritoneal dialysis, which uses the human peritoneum as a filter. There are several devices each used according to the particular need.

A first device uses a filter which is a device divided into two compartments by a semi-permeable membrane. One of the compartments is connected to the patient by an extracorporeal blood circulation, and the second compartment is connected to a line for discharging the ultratfiltrate extracted from the blood and collected in a container fitted for this purpose. The operating principle of this device is based on a convection phenomenon using differential pressure in order to extract and eliminate excess water from the blood. This device is known under the name of "ultratfiltration". It is particularly suitable for the rapid elimination of water and the simultaneous elimination of a limited quantity of metabolic waste entrained by the ultrafiltrate. This allows a suitable weight to be quickly restored to the patient by eliminating excess water.

A second device called continuous or intermittent "hemofiltration" uses an installation identical to that described above except that it is completed with a natural or forced injection line of one or more physiological substitute and / or medicinal products in the circulation. of blood, which is therefore added to compensate for the amount of ultratfiltrate extracted, taking into account the possible difference in weight or volume of more or less desired liquid. This device also works on the principle of differential pressure, but the addition of the substitute product allows a substantially more extraction to be obtained. significant metabolic waste by allowing longer processing times.

A third device called "hemodialysis" is obtained by connecting the inlet of the second compartment of a filter-exchanger to a reservoir of physiological solution which is circulated in this second compartment in the opposite direction to that of the circulation of the blood. , and this while maintaining the pressures and flows in relation to the blood circulation. The flow ratio is established to create the conditions for diffusion through the semipermeable membrane from the blood to the physiological fluid. Thanks to this circulation of physiological fluid, the extraction of metabolic waste is thus obtained, and in particular the elimination of small molecules such as urea.

These devices therefore therefore comprise in common means for filtering the blood divided into two compartments by a semi-permeable membrane one of the compartments of which belongs to an extracorporeal blood circulation in which the flow is preferably imposed by a blood pump, and whose the other compartment receiving the ultratfiltrate extracted from the blood is connected to an evacuation line, line in which the flow of ultrafiltrate is also preferably regulated by an ultrafiltrate pump. When desired, these devices further include one or more lines for supplying substitute product from a reservoir. Depending on the treatment and the type of filtration means used, the power outlet of this line is either connected to the blood circulation via a mixer upstream or downstream of the filtration means, or connected to the second compartment means of hemofiltration against the flow of blood. The product flow in this line can then also be regulated by a product pump. Such a versatile device is for example described in document US 4,844,810.

Peritoneal dialysis is similar to the previous devices except that the blood circulation remains intracorporeal and that the human peritoneal membrane is used as a means of filtration.

These devices also include electronic control and monitoring means which, on the basis of measurements of the quantity of blood treated and / or of extracted ultrafiltrate and / or of product injected over a period of time control the pumps to regulate and adjust the instantaneous flow rates of the circulation or of the different lines according to the prescriptions of the doctor and the progress of the treatment. Usually, these devices also include security systems such as, for example, pressure sensors, monitoring whether the means of hemofiltration or the blood circulation or one of the lines have been blocked or broken, and trigger an alarm. visual and audible if applicable.

It is essential that the control is carried out very precisely to maintain the water balance, the calcium-phosphorus balance, or other metabolic balances in the patient. In particular, in the case of long hemofiltration treatments, it should be possible to treat no less than 40 liters of ultrafiltrate with an error of less than 200 milliliters, the equivalent of a glass of water, or to be able to comply with an overall precision less than 0.5%. However, known flowmeters measuring volumes per unit of time prove to be too imprecise.

Document US Pat. No. 4,204,957 describes such a hemofiltration device in which the measurements of the quantity of ultrafiltrate extracted and of substitute product supplied are carried out by means of weighings by means of two scales respectively supporting the receptacle for receiving the ultratfiltrate and the substitute product reservoir. To take account of the possible variation in flow rate of the incoming and outgoing liquids, the device control method consists in calculating at regular intervals the ratio between the variations in weight of products during the interval, and in comparing this ratio with a setpoint. to decide to modify this or that other flow by adjusting the setting of the corresponding pump.

Document EP 321 754 describes another analog hemofiltration device using a high precision balance to establish the balance between the quantities of products entering and leaving, a volumetric pump also of high precision to control the extraction line of the ultratfiltrate. , and a peristaltic pump to control the supply line for the substitute product. This device includes two separate electronic circuits with microprocessors exchanging data on a bidirectional channel: a pump control circuit and a monitoring circuit. The driving circuit, including a keyboard data input and a display screen, receives the measurement signals from the balance and applies control signals to the ultratfiltrate and substitute product pumps. The monitoring circuit receives flow or rotation measurement signals from each of the pumps. During the implementation of the device, the pumps are calibrated, then the treatment data, in particular the overall treatment duration T, the quantity QU _F of ultratfiltrate to be extracted and the quantity Qs _ub of substitute product, are introduced into the driving circuit through the keyboard.

The piloting process then consists in first calculating the necessary flow rates by the piloting circuit. The method then consists, at regular time intervals, on the one hand in calculating by the control circuit the theoretical remaining quantities on the basis of the calculated flow rates and the elapsed time as indicated by an internal clock, and in controlling the result of the balance, the measurement of which is also transmitted to the monitoring circuit. The method further consists, during each time interval, in monitoring the pump operations by the monitoring circuit, in comparing the quantities of products as deduced from the signal from the balance and from the signals from the pumps, and in compare them against the theoretical quantities. Finally, the method consists in adjusting if necessary the control commands of the pumps to adjust their effective flow to the theoretical value, on the other hand, if at the end of a time interval the results of the comparisons differ from a predetermined maximum limit value , an alarm is triggered.

Document WO 93/06875 describes another analogous hemofiltration device comprising a scale for measuring the extracted ultrafiltrate and the reservoir of substitute product. The piloting process consists in operating the pumps of substitute product and of the ultratfiltrate only when the blood circulation pump is in operation. At regular intervals, the weights of residual substitute product in the tank and of extracted ultrafiltrate are measured and are compared by the control circuit with predetermined theoretical weights corresponding to the given interval which have been programmed and stored in the circuit, and this in order to adjust the pumping rates of the product and of the ultratfiltrate. If necessary, the flow in the bloodstream is also modulated. Functioning in principle correctly, we note however that these devices can adopt disconcerting behaviors, in particular during transitory periods at the time of a strong evolution of one of the measures or following the introduction of a significant correction of a data. The users then have a certain mistrust vis-à-vis such automatic devices, especially if the duration of treatment is particularly long.

The object of the present invention is an automatic method of piloting and monitoring a blood treatment device which is precise and reliable whatever the type of treatment carried out, and which, moreover, is easy to implement by requiring the least amount of intervention liable to user error, and which should be of a consistent behavior to inspire the confidence of patients and treating physicians.

These aims are achieved by a method of controlling a device comprising - means for filtering the blood divided into two compartments by a semi-permeable membrane one of the compartments of which belongs to a blood circulation in which the flow is preferably imposed by a blood pump or the heart, and the other compartment receiving the ultratfiltrate extracted from the blood is connected to an evacuation line in a container, line in which the flow of ultrafiltrate is measured by weighing means or for measuring the volume of the ultrafiltrate and / or by direct flow measurement means, a line in which the flow of ultrafiltrate is also preferably regulated by an ultrafiltrate pump,

one or more lines for supplying a substitute product from a reservoir, the flow rate of which is measured by means of weighing or measuring the volume of product and / or by means of direct measurement of flow rate, the outlet supplying this line being either connected to the blood circuit via a mixer upstream or downstream of the filtration means, or connected to the second compartment of the filtration means against the flow of the blood circulation, or connected to the circuit blood via a flow divider upstream and downstream of the filtration means, the flow rate in this product line is preferably controlled by a product pump, - electronic control means which, on the one hand on the basis of parameters established for the treatment and on the other hand on the basis of variables measured by sensors, control the pumps at predetermined time intervals to adjust the instantaneous flow rates respectively circulation of blood, ultratfiltrate and substitute product, characterized in that it consists in, during the implementation of the device and during its operation, to revise and if necessary to modify by means of control the treatment parameters as a function of the measured variables and of medical and / or physical knowledge data previously stored in electronic means for storing electronic control means in order to maintain precise and flexible operation of the device.

By maintaining precise and flexible operation of the device is meant, for example, the fact of automatically correcting errors appearing in the measurements of a sensor following a jolt or a shock, or the fact of correcting errors occurring during the introduction of medical parameters, or the fact of automatically attenuating a too strong control command of pump due to a too large correction calculation result, or the fact of automatically damping oscillations of control order of pump due to a measured value oscillating around a predetermined critical value, or other automatic adjustment of parameters maintaining consistent behavior to the device.

By treatment parameters is meant on the one hand parameters of medical prescription for the treatment to be carried out according to the patient's particularities such as the duration T of treatment, the overall quantity Q _UF of ultrafiltrate to be extracted and / or its flow rate, the overall quantity Q _Sub of substitute product and / or its flow rate, but also the quantity q _Med of an injected medicament, such as heparin, or a set temperature of means of heating the blood before reintroduction into the body of the patient. We also mean the hardware configuration of the device, for example the type of tubing used. By treatment parameter, we mean on the other hand the operating parameters of the device, in particular the calibration values (gain G, initial offset do) of each of the sensors present: balance or load cell of weight measurement, pressure gauge of pressure, peristaltic pump rotation sensors, but also the time interval Δt between two adjustment cycles, the flow setpoint parameter D, _j applied to the circulation or line pump j, the percentage of correction allowed , the maximum acceptable difference between theoretical and measured values, or others.

According to a first example of application, the method according to the invention consists, when changing a container on a scale, for example changing an empty substitute product tank for a full tank or a container of reception of full ultrafiltrate for a vacuum, to read and record the measured weighing values before, during and after the change, to detect stable measurements corresponding to the initial state, to empty and to the final state, and to recalculate the gain G and shift offset parameters of this balance.

Thus, if a balance is distorted following a shock or a jolt, it is recalibrated as of the next change of container, which avoids taking into account erroneous values over a long period. In the event that the no-load value proves to be outliers, meaning that the damage to the balance is too great to be corrected, an alarm can be triggered. The technical calibration knowledge thus prerecorded makes it possible to trigger an automatic calibration dynamically throughout the treatment and no longer only at the start.

According to a second application example, the method consists in establishing at time i the parameter Δt, _j of the time interval between two piloting operations for adjusting the flow rate of a pump j inversely proportional to the last variable pd of weight or db, _j of flow rate actually measured from this pump. In other words, if the flow rate of a pump is low, the duration of the interval between two settings is long, while if the flow rate of the pump is large, the interval is short and the settings are very close . For example, an adjustment of the pump j is only triggered when the variation in weight measured (pd _{i + 1 j} - pd ,,) / Δt ,, of the corresponding liquid is greater than a parameterized value M, notably dependent on the resolution balance; or once the predetermined maximum interval duration D has been reached. This knowledge pre-recorded of a better adaptation of the time interval between adjustment cycles thus makes it possible to control transient situations much better.

According to a third example of application, the method consists, during piloting at the interval Δt _M , and following either on the one hand a measurement of a weight value pd | _jrτ , es or debit db |, _mes carried out in traffic or line j leading to the observation of a significant error εij between the theoretical weight pd _IJth expected at time i and the weight actually measured pd _ljmes , (ie εij = pd _IJtn - pd _ljmes or according to the measured flow db _IJth - db _ljmes ), or on the other hand to a calculation following a manual entry in the device of the value of an exceptional contribution or loss, implying a correction important ΔDbt = Db _π - Db,. ^ of the new setpoint parameter Db, _j of the corresponding pump j, to limit this setpoint parameter of the pump j to a value Db | _Jcorr so that the increase ΔDbt _corr is limited to a predetermined percentage P% stored as data for knowledge of coherent operation.

For example, it may be that, everything else being normal, the extraction of ultratfiltrate is momentarily weaker because the filter becomes clogged. In another example, it sometimes happens that the pumps are stopped during an intervention on the device while the patient remains on an infusion. After one hour, the patient may have "swelled" by 300 milliliters. This large volume must therefore be deducted during the following adjustments, the values of which are appreciably modified. Then, this piloting process avoids immediately packing the pump of the ultrafiltrate line in an exaggerated manner, but makes it possible to increase the flow rate of this pump gradually. By thus avoiding apparently irrational behaviors, one appreciably increases the confidence of the personnel towards the device. This process can also take place following the introduction of information on the patient's absorption of an amount of oral water which temporarily upsets the theoretical water balance, which imbalance may very well be remedied over a long period of time. preferably a short period leading to a runaway of one of the pumps. Preferably, this process is optional so that it can be disengaged if the staff knows in advance that particular processing conditions are about to occur. This process can be supplemented by a method of controlling the convergence of water balance towards its theoretical value.

Unlike the previous state, the adjustment of a flow Dbj, is no longer made solely on the basis of a measured value, but in combination with knowledge data, in this case capping data. preferred acceleration previously established during the implementation of the device.

According to a fourth example of application, the method consists, during the introduction of a parameter into the electronic control means, of comparing the entered value of the parameter with a range of tolerable values contained in the prerecorded knowledge data, and to keep this parameter at the initial value if the new value is outside the range.

For example, during the implementation of the device, treatment parameters are introduced such as parameters q _Med of quantities of drugs to be injected during the duration T of the treatment. The method therefore consists in verifying that the value entered belongs to a safety range (qe Min - _{. Ed} a _x ) for example defined by the manufacturer of the medicament and previously stored in the memory. According to another example, the user manually enters the value of a loss or of a contribution making it possible to take it into account in the entire water balance of the patient. However, it is easy to make a mistake by a factor of 10, for example by writing 1000 ml instead of 100 ml. The 900 ml difference is then added or removed automatically from the patient by the subsequent operation of the device modifying his water balance in a dangerous way. This pre-recorded knowledge of medical risks makes it possible to automatically avoid crisis situations.

According to a fifth application example, the method consists, when measuring a value located outside of a range of accepted values, in modifying a data item indicating the presence of error in the knowledge data prerecorded, to record the suspect value in data storage means, and to restart a new measurement. This also applies to an order that has not been followed. Thanks to this process, the operating incidents recovered by a simple repetition of the instruction are nevertheless recorded in means of memorization of the piloting circuit, the history of these incidents thus accumulated making it possible to better distinguish and diagnose a failure occurring by the after. Typically, weight or pressure sensors may first have intermittent failures which are undetectable thereafter, but the accumulation of which makes it possible to conclude that said sensor is aging, requiring replacement preferably in advance.

The knowledge data established during the construction of the device can be revised and improved periodically, for example during a revision of the device or following the appearance of new drugs or the discovery of new medical results.

The invention and its advantages will be better understood on reading the following detailed description, made with reference to the appended block diagram of a blood purification device, taken by way of illustration and in no way limiting.

In the figure is illustrated a patient 19 suffering from renal insufficiency and whose purification of the blood must be carried out extracorporeally. As such, this patient is connected to an external blood circulation subsequently comprising a conduit 20 for collecting and removing blood, a blood pump 1 which may be a peristaltic pump, hemofiltration means 8 and a return conduit 21 blood to the patient.

The blood filtration means 8 are in the form of a chamber separated into two compartments by a central membrane: a compartment 8a traversed by the bloodstream and a compartment 8b in which the ultrafiltrate extracted from the blood appears. This compartment 8b is connected by a line 24 to a pump 4 for extracting the ultrafiltrate, which line is then directed towards a collection container 17. By adjusting the flow rates of pumps 1 and 4, pressure can be created differential between the compartments 8a and 8b causing a displacement by convection of the ultrafiltrate through the membrane of the means 8. The pump 4 can be a peristaltic pump or a positive displacement pump, but remains optional. The device further comprises a reservoir 15 for a first substitution product and / or medicament, which product is injected into the bloodstream upstream of the hemodialysis means 8 through a line 25 inside which the flow rate is preferably controlled by a pump 2. In the case of hemofiltration, the supply end of line 25 is connected via a mixer 22 'to the conduit 20 of the blood circulation, for example downstream of the pump 1, this product then passing into the compartment 8a of the filtration means. In the case of a hemodialysis treatment, the supply end of the line 25 is deflected along a line 25 ′ to be connected in the second compartment 8b of the filtration means 8 for purifying the blood.

This device may further comprise a second reservoir 16 for a second substitution and / or medicinal product intended to be injected into the bloodstream downstream of the filtration means 8. For example, this second product is brought in through a conduit 26 and a product pump 3 to a mixer 22 interposed in the conduit 21.

In another configuration not illustrated, the product can be brought in from the container 15 by means of the pump 2, a flow divider adjusting the proportion between the flow of substitution product injected into the bloodstream upstream of the filtration means 8 and the flow of substitution product injected into the bloodstream downstream of the filtration means 8.

One or more pressure sensors 30 installed on line 21 makes it possible to monitor the proper functioning of the device, in particular the filtration means 8, the condition of the tubes and their connections as well as that of the patient and to anticipate possible problems, in particular a coagulation of blood at the level of the membrane, or an obstruction of the upstream line 20. A sensor not illustrated and connected to the line 24 can monitor the desired absence of blood in the ultratfiltrate.

In order to rigorously maintain the hydric and metabolic balances of patient 19, this device is controlled by electronic means 9-14 which, on the basis of measurements from sensors 2'-3'-4 ', 5-6-7 control exactly the flows applied by pumps 1-4 in the blood circuit and their corresponding line.

The electronic means comprise a central control circuit 9 including a microprocessor, this circuit being accessible by a keyboard 14 and displaying data on display means such as a screen 13. This central control circuit 9 is duplicated by a circuit monitoring system 10 also comprising a microprocessor with which it is connected on a bidirectional data transfer line, and exercising direct control over the motors and the sensors. This control circuit 9 is also connected through a data transfer bus with on the one hand first electronic means for storing parameters 11, for example RAM circuits for storing parameters specific to the processing and software for the implementation of the device control method, and on the other hand with a second electronic storage means 12 for general knowledge data, for example in the form of an EPROM or Flash-PROM circuit. The data from these two storage circuits 11 and 12 can be accessible to the monitoring circuit 10 through the bidirectional channel.

In order to be able to follow the progress of the treatment, the device comprises, on the one hand, scales, respectively a scale 5 supporting the reservoir 15 of the first product, a scale 6 supporting the tank 16 of the second product and a scale 7 supporting the can of reception 17 of the ultrafiltrate. These scales can be of strain gauge and with electronic processing emitting electronic measurement signals p transmitted to the central control circuit 9 through a preamplification and adaptation (input / output) circuit 9 '. Similarly, rotation encoders or other flow sensors 2 ', 3' and 4 'respectively in relation to the pump 2 for injecting the first product, with the pump 3 for injecting the second product and with the pump 4 extraction of the ultrafiltrate, generate electrical signals dbj _j which are transmitted to the monitoring circuit 10 through a preamplification and adaptation (input / output) circuit 9 '". The control circuit 9 applies instructions to a 9 "interface card sending instructions D to each of pumps 2, 3 and 4. Thus, on the basis of the measurements of weight pd and of flow rate db, the control circuit 9, under the control of a procedure as transcribed by a software loaded in the memory 11, performs at regular intervals Δti adjustment cycles, c that is to say that during this cycle it acquires the measured values and PDY dbi _j P ° ^ur compare them to theoretical values corresponding to the time i, and in case of drift, applies new instructions D to the corresponding pump. In particular, this control method comprises a start-up sequence then, during each cycle, a value acquisition sequence, a setting calculation sequence and a safety verification sequence.

More particularly according to the invention, this device control procedure is not only carried out on the basis of the processing parameters recorded in memory 11 and the measured values of sensors, but also under the monitoring and intervention of general knowledge data. of a medical type relating to the methods of treatment and to the products used, and of technical knowledge relating in particular to the technical characteristics of scales and pumps, this in order to ensure both reliable operation, that is to say without risk of provoke a fatal crisis for the patient due to dysfunction of the device but also a so-called flexible operation, that is to say not triggering apparently aberrant behaviors although justified.

In a first start-up sequence, the central circuit 9 carries out an electronic test of the various components of the device, that is to say it checks whether it obtains effective access to the scales, the encoders, the pumps, or even to several safety pressure sensors such as, for example, the sensor 30 verifying that the blood circulation is not obstructed or is not broken.

The circuit 9 then proposes on the screen 13 treatment choices whose answers will be introduced by the user by means of the keyboard 14. The user can then choose the duration T of the treatment, the quantity Q _uf of ultrafiltrate to be extracted , the quantity Q _sub of substitution and / or medicinal product to be added. More particularly according to the invention, each of the choices expressed by the user is checked against medical knowledge recorded in the memory 12. In particular, if, as a function of the quantity Q _uf introduced, the user introduces a quantity Q _{sub that is} too large, the circuit 9 finds that this value introduced lies outside a predefined range in general knowledge and refuses to validate this entry, that is to say that it does not write it in memory 11 by signaling it to the user.

It should be noted that entering parameters can also occur during treatment, for example when you want to introduce an exceptional fluid intake or loss of the patient. Then, circuit 9 also compares these values with respect to a range of probable values contained in the general knowledge situated in the value 12. This thus avoids introducing an outlier, for example 1000 milliliters instead of a value of 100 milliliters corresponding to a glass of water normally absorbed by the patient.

The start-up sequence then continues with a procedure for rinsing the blood circuit and the supply and evacuation lines, then, after connecting the patient, the treatment itself is launched.

Frequently, during treatment, one of the empty product tanks and / or the receiving container full of ultrafiltrate must be changed. More particularly according to the invention, the control circuit 9 takes advantage of this change to carry out a verification of the calibration of the corresponding balance. In particular, this control circuit begins by triggering an alarm when it finds that the measured weight of a tank drops below a lower limit or that the measured weight of the container exceeds a predetermined upper limit. It then triggers a continuous acquisition phase of the measured weight value which value is accumulated in a memory. After the user has changed the tank or canister, the control circuit 9 detects significant variations in measured weight values and analyzes the sequence to recognize the last measured value from the old tank or canister, the no-load value of the balance and the new value of the tank or can. If the no-load value proves to be too large, the control circuit 9 then declares this balance as too unbalanced and requires recalibration by a technician. If the no-load value has remained below the predetermined value, the control circuit re-determines the no-load offset dO to subtract from the measured value as well as the calibration gain G to apply to obtain a corrected measured value. The control circuit, noting that the conditions are met again for the treatment, restarts the latter automatically. Thus, thanks to the technical knowledge stored by the memory 12, the control circuit 9 was able to minimize the intervention of the user to a simple replacement of container while taking advantage of this change to increase the measurement accuracy by recalibration. The harmful effects of a shock or a shock to the balance are then periodically eliminated.

The central control circuit 9 also includes an internal clock whose pulse count allows it to determine the time i elapsed since the start of the treatment. At time intervals Δ _ti , this control circuit initiates an adjustment cycle. This cycle begins with the acquisition of the measured values of weight pdj _j at this time i for each of the balances j of first product, second product and ultrafiltrate. The circuit can then calculate the mass variation Δp during the last elapsed interval Δ _ti . At the same time, the control circuit calculates from the flow parameters entered Q _uf / T or Q _sub / T the theoretical variation in expected mass, and this taking into account the assessment of the evaluation at the previous interval. The flow D is then accelerated or slowed down as a function of the difference between the expected mass and the measured mass. The modification of a parameter by the user is taken into account immediately, without the need to wait for the next adjustment.

In parallel, the monitoring circuit 10 acquires on its input / output circuit 9 "the values measured dj _j from the transducers 2 ', 3' and 4 '. This monitoring circuit can, by combining the time interval Δ _ti , also measure in a second way the variations in mass of product and / or ultrafiltrate. An exchange of data between the control circuit 9 and the monitoring circuit 10 makes it possible to verify that the variations in mass measured from the balances are equivalent to the mass values measured from the transducers with the imprecision close to these last results. In the positive case, the decision of adjustment of corresponding flow rate is validated. In the opposite case, one considers that the important difference between the mass variation value from the scales and from the encoders means that one or the other of these elements present a significant fault requiring the triggering of an alarm for verification by a technician.

More particularly according to the invention, this new flow rate setpoint D is moreover reassessed according to the general knowledge stored in the memory 12 which imposes a ceiling at a value Db _max , for example of 40% of the theoretical value, knowing that a larger correction, although justified, may cause concern for the patient and / or the user, at the risk that it will be performed incorrectly. Thus, the application of this general knowledge tends to limit the correction for the following interval for example to a maximum of 40% of the last known value of the flow rate, this correction then being automatically spread over time.

Preferably, this knowledge also triggers an alarm in the event that this correction limitation occurs beyond a predetermined number of time intervals, and this to prevent this capping causing a divergence in the weight difference observed. . The user can then manually choose to disengage this security knowingly.

According to another important aspect of the invention, the usually constant time interval Δ _ti is, in this device, re-evaluated according to a function belonging to the general knowledge stored in memory 12. More particularly, the following time interval Δ _ti is established inversely proportional to the last variable of flow rate dby measured, or preferably to the last evaluation of the variation in weight divided by the last time interval actually measured for traffic or line j. In other words, an adjustment is only triggered when the variation in weight Δ _m reaches a predetermined value M according to a more or less long interval of time Δ _ti . Then the adjustment cycles are more widely spaced at long intervals Δ _ti for a line with a slow flow, and much more closely spaced for a line with a high flow. This allows better control of transient situations in one direction as in another.

In particular, according to a method of the invention implemented by the control circuit 10, an adjustment cycle of the pump j is only triggered when the weight variation pdy / Δ _tl measured since the last adjustment becomes greater than a parameterized M value depending in particular on the resolution of the balance. This avoids causing adjustment oscillations due solely to the measurement uncertainty of the balance around this measurement. Preferably, this expectation of variation in weight over time is limited to a duration D configured in the general knowledge data stored in the memory 12. Thus, the knowledge of oscillatory phenomena in the control of the device due to measurement uncertainties is damped in the process according to the invention.

Furthermore, it may happen that a measured value of balance, encoder, flow transducer or pressure sensor is a manifestly outlier. Usually then, the control circuit rejects this value and triggers a new measurement so as to ignore these parasitic measurements due to a momentary defect in the corresponding sensor. More particularly according to the invention, the moment i and the outlier pd _ab are stored in a device history file making it possible, during a revision of the device, to detect intermittent failures as well as their frequencies for a given sensor facilitating its replacement before complete failure. In particular, an increasing repetition in time of the appearance of outliers can be noted by the control circuit 9 according to a procedure stored among the knowledge data of the memory 12. This detection of repetition of error makes it possible to trigger a message warning of risk of failure.

The general knowledge data are preferably developed for a plurality of families of elements: families of scales, pumps, membranes of hemofiltration means, and this by collection of the data supplied by the respective manufacturers so that the change of elements by another of his family is facilitated.

Claims

1. Method for controlling a device comprising

- blood filtration means (8) divided into two compartments by a semi-permeable membrane

5 of which one of the compartments (8a) belongs to a blood circulation (20,

21) in which the flow rate is preferably imposed by a blood pump (1), and the other compartment (8b) of which receives the ultratfiltrate extracted from the blood is connected to an evacuation line (24) in a container ( 17), line in which the ultrafiltrate flow is measured by weighing means (7) or volume measurement of the ultrafiltrate and / or by direct flow measurement means, line in which the flow of ultrafiltrate is also preferably regulated by an ultrafiltrate pump (4),

- one or more supply lines (25, 26) of substitute product from a reservoir (15, 16), the flow rate of which is measured by weighing means 5 (5, 6) or by volume measurement of product and / or by direct flow measurement means, the supply outlet of this line being either connected to the blood circuit by means of a mixer (22) upstream or downstream of the filtration means (8 ), either connected to the second compartment (8b) of the filtration means against the flow of the blood circulation, or connected to the blood circuit by means of a flow divider upstream and downstream of the filtration means (8), the flow rate in this product line being preferably regulated by a product pump (2, 3),

- electronic control means (9-14) which, on the one hand on the basis of parameters established for the processing and the machine and on the other hand on the basis of 5 variables measured by sensors (5,6,7 , 2 ', 3', 4 '), control the pumps at predetermined time intervals to adjust the instantaneous flow rates of the circulation of blood, ultratfiltrate and substitution products respectively, characterized in that it consists, during the implementation of the device and during its operation, to revise and if necessary to modify by electronic control means (9, 12) the parameters of the treatment as a function of the variables measured and of data of medical knowledge and / or physics previously stored in electronic storage means (12) electronic control means in order to maintain precise and flexible operation of the device.

2. Method according to claim 1, characterized in that, when changing a container (15,16,17) on a balance (5,7,6), to read and save the values

5 weighing measurements before, during and after the change, to detect the stable measurements corresponding to the initial state, to no load and to the final state, and to recalculate the gain and offset parameters of this balance.

3. Method according to claim 1, characterized in that it consists in establishing at a given moment the parameter of the time interval between two operations of o piloting adjustment of the flow rate of a pump inversely proportional to the last variable actually measured from this pump or at a given flow setpoint.

4. Method according to claim 1, characterized in that it consists in triggering an adjustment of a pump only when the measured variation in weight of the corresponding liquid is greater than a parameterized value or when a maximum interval duration has been reached.

5. Method according to claim 1, characterized in that it consists, following a measurement, in a calculation of a weight or flow value carried out in traffic or a line leading to the finding of a significant error between the theoretical mass 0 expected at this time and the mass actually measured implying a significant correction of the new flow setpoint parameter of the corresponding pump, to limit this pump setpoint parameter to a corrected value so that the flow increase is limited to a predetermined percentage stored as coherent operating knowledge data.

6. Method according to claim 1 characterized in that it consists, during the introduction of a parameter into the electronic control means, in comparing the entered value of the parameter with a range of tolerable values contained in the knowledge data , and keep this parameter at the initial 0 value if the new value is outside the range.

7. Method according to claim 1 characterized in that it consists, during the measurement of a value located outside of a range of accepted values, in modifying a datum of indication of presence of error in the pre-recorded knowledge data, to record the suspect value in data storage means, and to relaunch a new measurement.

8. Method according to claim 1, characterized in that the medical and / or physical knowledge data previously stored in electronic storage means (12) can be modified or acquired during the treatment.