Patent ID: 12257375

DETAILED DESCRIPTION

FIGS.1,2and3show exemplifying, and non limiting, embodiments of an apparatus for extracorporeal treatment of blood. Note that same components are identified by same reference numerals inFIGS.1-3.

FIG.1shows an apparatus1designed for delivering any one of treatments like hemodialysis, hemofiltration, hemodiafiltration, and ultrafiltration.

In fact, the apparatus1comprises a filtration unit2having a primary chamber3and a secondary chamber4separated by a semi-permeable membrane5; depending upon the treatment, the membrane of the filtration unit may be selected to have different properties and performances.

A blood withdrawal line6is connected to an inlet of the primary chamber3, and a blood return line7is connected to an outlet of the primary chamber3. In use, the blood withdrawal line6and the blood return line7are connected to a needle or to a catheter or other access device (not shown) which is then placed in fluid communication with the patient vascular system, such that blood can be withdrawn through the blood withdrawal line, flown through the primary chamber and then returned to the patient's vascular system through the blood return line. An air separator, such as a bubble trap8may be present on the blood return line; moreover, a safety clamp9controlled by a control unit10may be present on the blood return line downstream the bubble trap8. A bubble sensor8a, for instance associated to the bubble trap8or coupled to a portion of the line7between bubble trap8and clamp9may be present: if present, the bubble sensor is connected to the control unit10and sends to the control unit signals for the control unit to cause closure of the clamp9in case one or more bubbles above certain safety thresholds are detected. As shown inFIG.1, the blood flow through the blood lines is controlled by a blood pump11, for instance a peristaltic blood pump, acting either on the blood withdrawal line (as shown inFIG.1) or on the blood return line.

An operator may enter a set value for the blood flow rate QBthrough a user interface12and the control unit10, during treatment, is configured to control the blood pump based on the set blood flow rate. The control unit may comprise a digital processor (CPU) and memory (or memories), an analogical type circuit, or a combination thereof as explained in greater detail in below section dedicated to the ‘control unit’. An effluent fluid line13is connected, at one end, to an outlet of the secondary chamber4and, at another end, to an effluent fluid container14collecting the fluid extracted from the secondary chamber. The embodiment ofFIG.1also presents a pre-dilution fluid line15connected to the blood withdrawal line: this line15supplies replacement fluid from an infusion fluid container16connected at one end of the pre-dilution fluid line. Note that alternatively to the pre-dilution fluid line the apparatus ofFIG.1may include a post-dilution fluid line (not shown inFIG.1) connecting an infusion fluid container to the blood return line. Finally, as a further alternative (not shown inFIG.1) the apparatus ofFIG.1may include both a pre-dilution and a post infusion fluid line: in this case each infusion fluid line may be connected to a respective infusion fluid container or the two infusion fluid lines may receive infusion fluid from a same source of infusion fluid such as a same infusion fluid container. An effluent fluid pump17operates on the effluent fluid line under the control of said control unit10to regulate the flow rate Qeffacross the effluent fluid line. Furthermore, an infusion pump18operates on the infusion line15to regulate the flow rate Qrepthrough the infusion line. Note that in case of two infusion lines (pre-dilution and post-dilution) each infusion line may cooperate with a respective infusion pump. The apparatus ofFIG.1, further includes a dialysis fluid line19connected at one end with a dialysis fluid container20and at its other end with the inlet of the secondary chamber4of the filtration unit. A dialysis liquid pump21works on the dialysis liquid fluid line under the control of said control unit10, to supply fluid from the dialysis liquid container to the secondary chamber at a flow rate Qdial.

The dialysis fluid pump21, the infusion fluid pump15and the effluent fluid pump17are operatively connected to the control unit10which controls the pumps as it will be in detail disclosed herein below. The control unit10is also connected to the user interface12, for instance a graphic user interface, which receives operator's inputs and displays the apparatus outputs. For instance, the graphic user interface12may include a touch screen, a display screen and hard keys for entering user's inputs or a combination thereof.

The embodiment ofFIG.2shows an alternative apparatus1where the same components described for the embodiment ofFIG.1are also presents and are identified by same reference numerals and thus not described again. Additionally, the apparatus1shown inFIG.2may present a further infusion line22connected, at one end, with a portion6aof the blood withdrawal line6positioned upstream the blood pump11and, at its other end, with a further infusion fluid container23, which for instance may contain a drug, or a regional anticoagulant such as a citrate solution, or a nutrients solution or other. This further infusion line is herein referred to as pre-blood pump infusion line22. A pump24, for instance a peristaltic pump controlled by control unit10, may act on a segment of the pre-blood pump infusion line to regulate a pre-blood pump infusion rate Qpbp.

The apparatus ofFIG.2, may also present a post-dilution line25(represented with dashed line) connected at one end with a further container26of infusion liquid and connected at its other end with the blood return line7. A further pump27, for instance a peristaltic pump, may act under the control of control unit10on the post-dilution line25.

A third embodiment is shown inFIG.3. The apparatus ofFIG.3is an ultrafiltration apparatus comprising a filtration unit2(in this case an ultrafilter) having a primary chamber3and a secondary chamber4separated by a semi-permeable membrane5. A blood withdrawal line6is connected to an inlet of the primary chamber3, and a blood return line7is connected to an outlet of the primary chamber3. As in the embodiment ofFIG.1, the blood withdrawal line6and the blood return line7are connected in use to a needle or to a catheter or other access device (not shown) which is then placed in fluid communication with the patient vascular system, such that blood can be withdrawn through the blood withdrawal line, flown through the primary chamber and then returned to the patient's vascular system through the blood return line. An air separator, such as a bubble trap8may be present on the blood return line; moreover, a safety clamp9controlled by a control unit10may be present on the blood return line downstream the bubble trap8. A bubble sensor8a, for instance associated to the bubble trap8or coupled to a portion of the line7between bubble trap8and clamp9may be present: if present, the bubble sensor is connected to the control unit10and sends to the control unit signals for the control unit to cause closure of the clamp9in case one or more bubbles above certain safety thresholds are detected. As shown inFIG.1, the blood flow through the blood lines is controlled by a blood pump11, for instance a peristaltic blood pump, acting either on the blood withdrawal line (as shown inFIG.1) or on the blood return line. An operator may enter a set value for the blood flow rate QBthrough a user interface12and the control unit10, during treatment, is configured to control the blood pump based on the set blood flow rate. The control unit may comprise a digital processor (CPU) and memory (or memories), an analogical type circuit, or a combination thereof as explained in greater detail in below section dedicated to the ‘control unit’. An effluent fluid line13is connected, at one end, to an outlet of the secondary chamber4and, at another end, to an effluent fluid container14collecting the fluid extracted from the secondary chamber. An effluent fluid pump17operates on the effluent fluid line under the control of said control unit10to regulate the flow rate Qeffacross the effluent fluid line. The control unit10is also connected to the user interface12, for instance a graphic user interface, which receives operator's inputs and displays the apparatus outputs. For instance, the graphic user interface12may include a touch screen, a display screen and hard keys for entering user's inputs or a combination thereof.

In each one of the above described embodiments an ultrafiltration actuator, comprising the effluent fluid pump17, is inserted into the effluent fluid line13and configured to cause a transfer of fluid from the primary3to the secondary chamber4; in practice, in the embodiment ofFIG.1the control unit may drive the dialysis liquid pump21, the infusion pump18and the effluent pump17such that Qeffis equal to Qdial+Qrep1+Qpfr; in other words, the control unit drives the mentioned pumps so that the total flow rate flowing through the effluent line is made equal to the sum of the flow rate through the fresh dialysis liquid line, the flow rate through the replacement fluid line and the patient fluid removal rate which is to be imposed on the patient. In the embodiment ofFIG.2the control unit may drive the dialysis liquid pump21, the infusion pumps18and27, the pre-blood pump infusion pump24and the effluent pump17such that Qeffis made equal to Qdial+Qrep1+Qrep2+Qpbp+Qpfr; in the embodiment ofFIG.3, the flow Qeffequals Qpfras there is no dialysate or infusion line. Although this is not shown in the enclosed figures, note that the extracorporeal blood treatment apparatus1(e.g. the apparatus1ofFIG.1or2or3) may include one or more syringe pumps: for instance a syringe pump connected to the blood withdrawal line6and a syringe pump connected to the blood return line7; of course only one syringe may be used either connected to line6or to line7. In this case, Qeffwould be controlled to account for the flow rate delivered by said syringe pump(s). InFIG.1,2,3, Qeffrepresents the ultrafiltration flow rate, namely the flow rate passing through the semi-permeable membrane5(Qpfr=Qufin the case where there is pure ultrafiltration or pure hemodialysis, while Quf=Qpfr+Qrep1and/or +Qrep2in case there are one or more infusions through respective fluid replacement lines).

In order to measure the quantity of fluid delivered or collected in each container, appropriate sensors are used. For instance, referring toFIGS.1and2, the apparatus1also comprises a first scale33operative for providing weight information W1relative to the amount of the fluid collected in the effluent fluid container14; a second scale34operative for providing weight information W2relative to the amount of the fluid supplied from the infusion fluid container16; a third scale35operative for providing weight information W3relative to the amount of the fluid supplied from dialysis fluid container20. In case more infusion lines would be present, as infusion lines22and25inFIG.2, then a respective fourth and fifth scales36and37could be present to provide weight information W4, W5relative to the amount of fluid supplied from infusion container23and from infusion container26. In the apparatus ofFIG.3, a single scale33is present which is operative for providing weight information relative to the amount of the fluid collected in the effluent fluid container14. The scales are all connected to the control unit10and provide said weight information Wifor the control unit to determine the actual quantity of fluid in each container as well as the actual flow rate of fluid supplied by or received in each container. The control unit may also be configured to receive weight information Wifrom the first scale and, depending upon the selected treatment and type of apparatus, from one or more of the other the scales and to control the flow rate through the effluent fluid line, the infusion fluid line (if present), the dialysis fluid line (if present) by controlling the respective pumps based on said weight information Wi, and on initial set values.

From a structural point of view one or more, all containers14,16,20,23may be disposable plastic containers, for instance bags which are hang on a support carried by the respective scale. All lines and the filtration unit may also be plastic disposable components which may be mounted at the beginning of the treatment session and then disposed of at the end of the treatment session. Pumps, e.g. peristaltic pumps, have been described as means for regulating fluid flow through each of the lines; however it should be noted that other flow regulating means could alternatively be adopted such as for example valves or combinations of valves and pumps. The scales may comprise piezoelectric sensors, or strain gauges, or spring sensors, or any other type of transducer able to sense forces applied thereon. Although the examples in the figures show use of scales for determining the amount of fluid in the respective containers and for allowing calculation of the respective flow rates through the various lines, it should be noted that volumetric sensors for determining flow rates or combinations of mass and volumetric sensors may alternatively be adopted.

Operation

Reference is made by way of non limiting example to the flowchart ofFIG.4. The control unit10is configured to control the ultrafiltration actuator (e.g. by controlling at least the effluent pump17) based on a set value Qpfr_setand to control the other pumps (such as pumps18,21,24,27and the syringe(s)) if present) based on set values initially set by an operator or pre-stored in the machine or received from a source external to the machine; for instance, with reference toFIG.4, the control unit10may receive (step100) set values for one or more of the flow rates Qrep_setto be imposed through the infusion lines (when present), the set value Qdial_setto be imposed through the dialysis liquid line (when present) and the set value Qpfr_setfor the patient fluid removal rate which is a desired value for the rate of fluid removal from the patient which is to be maintained during treatment. In the case of the apparatus ofFIG.3, the control unit10would be only receive the set value for the patient fluid removal rate Qpfr_setand would be configured to control the ultrafiltration actuator based on said set value Qpfr_set. Then, the control unit may calculate the value Qeff_set(step101):
Qeff_set=Qdial_set+Qrep_set+Qpfr_set(1)

Note that in case there is a pre-blood pump infusion line either the user shall enter a set value Qpbp_setfor the flow rate Qpbpof the respective pump22, or the control unit is configured to calculate the set value Qpbp_setas a function of the set blood flow rate QB_set. In any case, if a pre-blood pump infusion line is present, the set flow rate is considered in equation (1) above and added at second member as follows:
Qeff_set=Qdial_set+Qrep_set+Qpbp_set+Qpfr_set(2).

Of course, in case there is no infusion line and no dialysis line then equation (2) becomes:
Qeff_set=Qpfr_set(3).

Then, the control unit uses the calculated Qeff_setas value of the effluent flow rate Qeff(step101a) which is used to control the flow of fluid through the effluent line. In detail, the control unit may control (step102) each of the infusion pumps and the dialysis pump such that the actual flow rate matches the respective set flow rate and may control the effluent pump17(or ultrafiltration actuator) such that the actual flow rate through the effluent line matches the calculated value Qeff_set. In other words, once the Qeff_sethas been calculated as a function of Qpfr_set, then Qeff_setmay be used as Qeffto control the ultrafiltration actuator, e.g. the effluent pump17in the examples ofFIGS.1-3.

The control unit10is also configured to execute at check points Ti(step103) during patient treatment a control procedure comprising the steps104,105and106as schematically shown in the flow chart ofFIG.4.

The control unit10may be configured for re-executing the control procedure at a plurality of check points Tiduring patient treatment: various criteria may be adopted to identify the check points Ti. For instance the control procedure may be repeated at periodic check points or at check points separated by time intervals following a prescribed rule (i.e. the time intervals between consecutive check points may not be all equal but nevertheless follow a prescribed rule). According to a further alternative the control procedure may be activated at check points triggered by specific events, such as a downtime of the machine due to a bag change or other reason, setting of a new set value Qpfr_setfor patient fluid removal rate, or setting of a new set value for any one of the flow rates Qrep_set, Qpbp_setthrough the infusion lines (when present), the set value Qdial_setto be imposed through the dialysis liquid line (when present).

Going now into the details of the exemplifying embodiment ofFIG.4, the control procedure comprises the following steps.

Step104: receiving one check information selected in the group of:a. a value of fluid removed from the patient over a time period preceding a check point Ti; this value may be calculated or measured by the scale or scales.b. an effective time portion, of said time period preceding a check point, during which said ultrafiltration actuator is operated; this value may be measured by the apparatus taking detecting all intervals when the machine or the treatment is stopped, e.g. due to an alarm or due to a bag change or due to a change of the disposable set or due to other reasons.c. a down time portion, of said time period preceding a check point Ti, during which said ultrafiltration actuator is not operated; this value may be measured by the apparatus taking detecting all intervals when the machine or the treatment is stopped, e.g. due to an alarm or due to a bag change or due to a change of the disposable set or due to other reasons.

Step105: calculating an updated value Qpfr_newfor said fluid removal rate Qpfras a function of said set value for a fluid removal rate Qpfr_setand of said check information. In most cases where the machine or the treatment has been interrupted in the period preceding a, the new value Qpfr_newis higher than the set value Qpfr_set. Note, however, that there may be cases (e.g. if there is a flow delivery problem on dialysate or replacement) where too much fluid could have been extracted in the period preceding a check point: in such a situation the new value Qpfr_newis smaller than the set value Qpfr_set.

Steps106: after calculation of said updated value Qpfr new, the control unit is configured for calculating a new Qefffor then returning to step102.

At step102the control unit controls the ultrafiltration actuator (and the other pumps if present as above described in connection with step102) as a function of said new Qeffand therefore as a function of the updated value Qpfr_newof the fluid removal rate. The control may use one of algorithms (1) or (2) or (3) depending upon the apparatus configuration, adopting Qpfr_newin place of Qpfr_set

The control with the updated value may start immediately after the check point and last until a subsequent check point.

Here below some implementing examples are provided in order to exemplify the operation of apparatuses according to the invention. In below examples it is assumed that the set patient fluid flow rate Qpfr_setis not changed in the time period preceding a check point.

Example 1

FIG.5shows a first example of implementation of the control procedure which has been described herein above.

In this embodiment, the control procedure comprises:determining a value of the fluid removed from the patient Vpfr_removedover a time period Tretropreceding a check point Ti;determining a value of fluid to be removed from the patient Vpfr_needover a time period Tprospfollowing the check point Tiin order to achieve the set value Qpfr_setfor fluid removal rate Qpfrover the sum of the time period Tretropreceding check point Tiand of the time period Tprospfollowing the check point (Ti); inFIG.5, Tretrois equal to Tprosp: although this may be a preferred option, it should be noted that Tretromay also be different from Tprosp.calculating the updated value Qpfr_newfor said fluid removal rate Qpfrbased on the set value for a fluid removal rate Qpfr_set, on the value of fluid to be removed from the patient Vpfr_needover the time period Tprospfollowing the check point (Ti) and on the duration the time period Tprospfollowing the check point Ti.

For example the following formula may be adopted for the calculation of Qpfr_new:
Qpfr_new=[(Tretro+Tprosp)·Qpfr_set−Vpfr_removed)/Tprosp(4)
where:Qpfr_setis the set value for fluid removal rate;Vpfr_removedis the value of the fluid removed from the patient over time period Tretropreceding a check point Ti;Tretrois a time period preceding check point Ti;Tprospis a time period following the check point Ti;(Tretro+Tprosp) is the reference time interval which is the sum of the time period Tretropreceding check point Tiand of the time period Tprospfollowing the check point Ti.

The ‘check point’ Tiwhen instantaneous Qpfr_newis computed may be done:after each treatment interruption (down time),on a periodic basis,each time the a flow rate setting is changed,by time Ti+Tprosp.

In the context of patient fluid removal management, relevant values for Tretroand Tprospmay be in the range of 1 to 6-8 hours.

Applying the above algorithm to the apparatus ofFIG.3assuming that:the operator initially sets a Qpfr_set=100 ml/h,Tretroand Tprospboth equal to 4 h,the fluid actually removed Vpfr_removedfrom the patient as measured by scale33(in case the apparatuses ofFIGS.1and2would be used then information from all scales would be received by the control unit) over time period Tretro=4 h preceding check point T1is Vpfr_removed=390 ml,
then applying formula (4) above:
Qpfr_new=(ΔT·Qpfr_set−Vpfr_removed)/Tprosp=[(4+4)·100−390]/4=102.5 ml/h

Thus, the control unit10will control the pump17based on the new calculated value of 102.5 ml/h during the 4 h following the first check point.

Example 2

FIG.6shows a second example of implementation of the control procedure which has been described herein above.

In this case, the procedure aims at achieving the most accurate Patient Fluid Removal over predefined time periods. In this example, periods of constant duration ΔT are prefixed, beginning at a prefixed time T00:
T00;T00+ΔT; . . . ;T00+k·ΔTand ending at prefixed ending times
T00+ΔT;T00+2ΔT; . . . ;T00+(k+1)·ΔT.

In this variant, the control unit10aims at delivering the exact patient fluid removal prescription over predefined time windows, such as matching with staff shifts or simply ‘round hours’ (13:00, 14:00, 15:00 . . . ).

The ‘check point’ Tiwhen instantaneous Qpfr_newis computed may be done:at each treatment interruption (down time),at each time a flow rate setting is changed,at each predefined time window limit (T00+k·T),

According to this variant, the control procedure comprises calculating the updated value Qpfr_newfor said fluid removal rate Qpfrat check point Ticomprised between a start time T00+k·ΔT and an end time T00+(k+1)·ΔT according to the formula:
Qpfr_new=(ΔT·Qpfr_set−Vpfr(0))/[(T00+(k+1)·ΔT)−Ti]  (5)or according to the formula (which takes into account the volume of fluid removed in a further time window):
Qpfr_new=(2·ΔT·Qpfr_set−Vpfr(0)−Vpfr(k−1))/[(T00+(k+1)·ΔT)−Ti]  (6)where:Qpfr setis the set value for fluid removal rate;Vpfr(0)is the value of fluid removed from patient over time window running from (T00+k·ΔT) to check point (Ti);Vpfr(k−1)is the value of fluid removed from patient over time window running from (T00+(k−1)·ΔT) to (T00+k·ΔT);[(T00+(k+1)·ΔT)− Ti] is the duration of time period following the check point (Ti);ΔT is the duration of the reference time interval.
Note:

Formula 5 is equivalent to formula 4 with:
Tretro+Tprosp=ΔT
Tprosp=(T00+(k+1)·ΔT)−Ti

Formula 6 is equivalent to formula 4 with:
Tretro+Tprosp=2·ΔT
Tprosp=(T00+(k+1)·ΔT)−Ti

Applying the above algorithm to the apparatus ofFIG.3assuming that:the operator initially sets a Qpfr_set=100 ml/h;Predefined time windows: 0:00; 4:00; 8:00; 12:00; 16:00; 20:00;Check time Ti: 10:30,the fluid actually removed over [4:00; 8:00] as measured by scale33(of course in case the apparatuses ofFIGS.1and2would be used then information from all scales would be received by the control unit) is Vpfr(k−1)=396 ml;the fluid actually removed over [4:00; 10:30] as measured by scale33(of course in case the apparatuses ofFIGS.1and2would be used then information from all scales would be received by the control unit) is Vpfr(0)=245 ml, then applying formula (6) above:
Qpfr_new=(2·4·100−245−396)/(12−10.5)=106.0 ml/h

Thus, the control unit10will control the pump17based on the new calculated value of 106.0 ml/h during the 1.5 h following the check point at 10.30 in order to achieve the desired patient fluid removal by 12.00.

Anticipation of Down Times

Performance of the previous algorithms may be further enhanced when anticipating ‘future’ down times.

Several types of down-times may be estimated:related to bag management: flow rate and bag volume data available to the system allow anticipating the number of bag changes which will occur over the period of interest; corresponding down time of the ultrafiltration actuator may then be derived using an assumption of the time used for changing a bag; such an estimate may derive from general statistical data or statistics more specific to the system in use and the local handling processes;related to alarms: a simple alarm down time coefficient may be applied to estimate for the down times related to alarms interrupting the ultrafiltration actuator. Again such a coefficient may be built in the system or derived from statistics specific on the system in use.

By calculating the impact of the above down times it is possible to account for the effective portion Teffof the time period after check time Tiduring which it is forecasted that the ultrafiltration actuator will be actually pulling fluid from the primary into the secondary chamber4. This allows further correcting the value of the new calculated patient fluid removal rate.

In practice, the control procedure described above may comprises a step of determining an effective portion Teffof said the time period Tprospor (T00+(k+1)·ΔT)− Tifollowing the check point Ti. Then, the updated value Qpfr_newfor the fluid removal rate Qpfris calculated by the control unit using Teffin place of the duration the time period following the check point Ti, i.e. in place of Tprosp or (T00+(k+1)·ΔT)−Ti.

Example 3

The following example is similar to Example 2 (reference is made toFIGS.3and6) and shows calculation and use of the effective portion Teffwhich is determined in this case by reducing the duration of the time period following check point Tiby a first quantity linked to a bag change average time expected to be spent in the next time period and by a second quantity linked to down times caused by alarm conditions.

Applying algorithm (6) to the apparatus ofFIG.3assuming that:the operator initially sets a Qpfr_set=100 ml/h;Predefined time windows: 0:00; 4:00; 8:00; 12:00; 16:00; 20:00;Check time Ti: 10:30,the fluid actually removed over [4:00; 8:00] as measured by scale33is Vpfr(k−1)=396 ml;the fluid actually removed over [4:00; 10:30] as measured by scale33is Vpfr(0)=245 ml;Number of bag changes planned over [10:30; 12:00]: Nchange_bag=2;Mean time for changing a bag: Tchange_bag=100 s;Alarm down time coefficient: Kalarm=1.7%,

Thus, the effective run time of ‘prospective’ time window [10:30; 12:00] is:
Teff=1.5−0.017·1.5−2·(100/3600)=1.42 h

It should be noted that in calculating Teff, where Tprospbecomes small (e.g. <30 minutes) the predictive term due to alarms may be ignored.

Then applying formula (6) using the calculated Teff:
Qpfr_new=(2·4·100−245−396)/(1.42)=112.1 ml/h

Thus, the control unit10will control the pump17based on the new calculated value of 112.1 ml/h during the 1.5 h following the check point at 10.30 in order achieve the most accurate delivery of the desired patient fluid removal over the time periods [4:00; 8:00] and [8:00; 12:00]. According to the criteria used for deciding on check points, this flow rate will be further adjusted at least twice before the current time period [8:00; 12:00] is elapsed (2 planned bag changes).

Example 4

FIG.7shows another example of implementation of the control procedure which has been described herein above.

In this case, and as in example 2, the procedure aims at achieving the most accurate Patient Fluid Removal over predefined time periods. However, in this example, the time periods are defined around the clock and may be of different durations.

N clock times between 0:00 and 24:00 (T1, T2, . . . Tk, . . . TN) define N time periods [Tk, Tk+1] (for k=1 to N and TN+1=T1).

In this variant, the control unit10aims at delivering the exact patient fluid removal prescription over each predefined time window, such as matching with staff shifts.

The ‘check point’ Ti when instantaneous Qpfr_newis computed may be done:at each treatment interruption (down time),at each time a flow rate setting is changed,at each predefined clock time Tk.

According to this variant, the control procedure comprises calculating the updated value Qpfr_newfor said fluid removal rate Qpfr at check point Ticomprised between a start time Tkand an end time Tk+1according to the formula:
Qpfr_new=[(Tk+1−Tk)·Qpfr_set−Vpfr(0)]/(Tk+1−Ti)  (7)where:Qpfr_setis the set value for fluid removal rate;Vpfr(0)is the value of fluid removed from patient over time window running from clock time Tkto check point (Ti);Tk+1-Tkmatches with Tretro+Tprosp;Tk+1−Ti matches with Tprosp;

Applying the above algorithm (again refer toFIG.7) and assuming that:the operator initially sets a Qpfr_set=100 ml/h;Predefined clock times: 6:00; 13:00; 20:00;Check time Ti: 11:12;The fluid actually removed over [6:00; 11:12] as measured by scale33(of course in case the apparatuses ofFIGS.1and2would be used then information from all scales would be received by the control unit) is Vpfr(k−1)=508 ml;No bag change expected before next predefined clock time T2=13:00;Mean time for changing a bag: Tchange_bag=100 s;Alarm down time coefficient: Kalarm=1.5%,the effective run time Teffof ‘prospective’ time window [11:12; 13:00] is:
Teff=(13.0−11.2)−0.015·(13.0−11.2)−0·(100/3600)=1.773 h

Then, applying formula (7) above:
Qpfr_new=[(13.0−6.0)·100−508]/1.773=108.3 ml/h

Thus, the control unit10will control the pump17based on the new calculated value of 108.3 ml/h from the 11:12 check point in order to achieve the desired patient fluid removal by 13.00.

Safety Features

The apparatus described above may include one or more of the following safety features.

For instance safety features below disclosed may play an important role after a therapy interruption of several tens of minutes, e.g. change of the disposable tubing or substitution of filter set associated with the apparatus, temporary patient disconnection due to any reason. These situations may lead to relatively high Qpfr_new values which if actuated with no safety checks might lead to problems for the treated patient.

The control procedure executed by the control unit10may include a step of requesting the user, for instance via the user interface12, to confirm that the calculated updated value Qpfr_newfor said fluid removal rate Qpfris acceptable before using it for controlling the ultrafiltration actuator. In practice the control unit would in this case wait for a user confirmation before actually using the calculated updated value Qpfr newfor controlling pump17.

The control procedure may also include comparing the calculated updated value Qpfr_newfor said fluid removal rate (Qpfr) against a maximum threshold value before using it for controlling the ultrafiltration actuator. In practice in case the calculate value would be too high either a lower value is used or an alarm condition is generated or a warning signal sent to the operator e.g. via user interface12.

The control procedure may comprise executing one or more of the following further safety checks:comparing the ratio between the calculated updated value and the set value for the patient fluid removal rate with a first boundary condition (typically to ±30%),comparing the absolute difference between the calculated updated value and the set value for the patient fluid removal rate with a second boundary condition (typically by ±100 ml/h),comparing the absolute difference between the calculated updated value and the set value for the patient fluid removal rate as a function of patient body weight with a third boundary condition (typically by 0.1 ml/min/kg).

If a prefixed number of said checks is positively passed, for instance if all checks are passed, the update value Qpfr_newis used for controlling the ultrafiltration actuator.

Note that the control unit is may also be configured for allowing setting of one or more boundary conditions in order to customize the apparatus to specific needs or patients.

Control Unit

As already indicated the apparatus according to the invention makes use of at least one control unit. This control unit may comprise a digital processor (CPU) with memory (or memories), an analogical type circuit, or a combination of one or more digital processing units with one or more analogical processing circuits. In the present description and in the claims it is indicated that the control unit is “configured” or “programmed” to execute certain steps: this may be achieved in practice by any means which allow configuring or programming the control unit. For instance, in case of a control unit comprising one or more CPUs, one or more programs are stored in an appropriate memory: the program or programs containing instructions which, when executed by the control unit, cause the control unit to execute the steps described or claimed in connection with the control unit. Alternatively, if the control unit is of an analogical type, then the circuitry of the control unit is designed to include circuitry configured, in use, to process electric signals such as to execute the control unit steps herein disclosed.