| EFFECT OF BIOFEEDBACK SYSTEMS FOR MONITORING HAEMODIALYSIS TREATMENTS |
| T. Petitclerc, Paris, France |
Chair: J.P. Kooman, Maastricht, the Netherlands |
F. N. Ozdemir, Ankara, Turkey |
|
Prof T. Petitclerc
Department of Nephrology Pitié-Salpétrière Hospital Paris, France
|
Slide 1
Prof Petitclerc: Thank you. Ladies and Gentlemen, Dear colleagues. Several devices based on a feedback loop and called biofeedback systems have been recently developed for monitoring hemodialysis treatments.
Slide 2
But what does monitoring hemodialysis treatment mean? Several dialysis parameters are of evident interest for example, the ultrafiltration rate, the dialysate sodium, the ionic dialysant, a surrogate for urea clearance. The online record of these parameters allows a real time analysis and permits a rapid intervention if the value of the parameter is not satisfactory. For example, if the value of unique dialysants calculated from the online record of dialysate conductivity at the dialyser inlet and outlet is lower than the expected value, it’s necessary to check the dialyser blood flow, concurrent dialysate and access the re-circulation etc.
Slide 3
Several parameters can be routinely monitored during the dialysis session. For example, the urea concentration in order to assess the nutritional status and the dialysis dose or the dialysate conductivity in order to assess the dialysis dose or the sodium balance.
Slide 4
A feedback system is a device using a feedback loop for monitoring a parameter called monitored parameter by an immediate, an automatic intervention on a parameter called command-controlled parameter. If the monitored parameter is a patient’s parameter, the feedback technique is often called biofeedback.
Slide 5
The aim of a biofeedback system is to maintain the monitored parameter at a constant value called target value or more generally to maintain the monitored parameter along a predefined trajectory towards a target value. Note that monitoring a parameter by a feedback loop needs the value of this parameter to be measurable or evaluated, calculated from the online record of dialysis parameters.
Slide 6
An example and probably the first example of a biofeedback system is the ultrafiltration controller. The aim of the ultrafiltration controller is to maintain the weight loss rate, which is the monitored parameter at a constant value. This target value is equal to the ratio of the desired weight loss and the dialysis time. Or to maintain the weight loss rate along a predefined trajectory called ultrafiltration profile.
Slide 7
The ultrafiltration controller is a biofeedback system routinely used in all dialysis monitors in order to accurately control the fluid balance by monitoring the weight loss rate. The weight loss rate is calculated from the measurement of the ultrafiltration rate. Using the value of the weight loss rate, which is the monitored parameter, the ultrafiltration controller sets the transmembrane pressure, which is the controlled parameter at the value required to reach the desired weight loss, which is the target.
Slide 8
Before the availability of ultrafiltration controllers in the 60s and 70s the statician should adjust the transmembrane pressure. The ultrafiltration controller gives the physician the possibility to prescribe the desired weight loss, which is a patient parameter instead of a transmembrane pressure, which is a technical parameter.
Slide 9
By prescribing weight loss equal to the interdialytic weight load, the physician allows the patient to come back to his or her physiological weight. Thus the ultrafiltration controller makes intelligent the dialysis monitor by enabling it to be adapted to the individual fluid load.
Slide 10
At the present time three other parameters can be routinely monitored by a biofeedback system. First the plasma conductivity, second the body temperature, third the blood volume change. We will successively study the specific biofeedback systems developed by manufacturers for monitoring these parameters.
Slide 11
Firstly what about the monitoring of plasma conductivity? The problem of determining the optimal value of dialysate sodium concentration is still debated because most standard dialysate sodium concentrations seem ideal for everyone.
Slide 12
For an individual patient too low a dialysate sodium concentration may generate interdialytic discomfort such as hypotension, itching, nausea, vomiting, cramps. Whereas too high a concentration is also responsible for interdialytic discomfort such as thirst and long term complications such as hypertension, cardiac failure.
Slide 13
The aim of the diacontrol is to monitor the patients’ plasma conductivity, to have a predefined target for avoiding chronic sodium overload by answering at the end of each dialysis session, a stable sodium level allowing a predefined trajectory for avoiding disequilibrium syndrome by minimising the abrupt decrease in plasma osmolarity. The diacontrol software is based on a feedback loop. The monitored parameter is the patient’s plasma conductivity measured by the Diascan module, standard on the dialysis monitors of Hospal-Gambro from the measurement of dialysate conductivity at the dialyser inlet and outlet. The controlled parameter is the conductivity of the dialysate delivered by the dialysis monitor.
Slide 14
On this slide you can see the diacontrol software acting on the dialysate conductivity for monitoring the patient’s plasma conductivity toward a predefined target. This target is set here at 14 mM/cm along a predefined trajectory with a maximum at 14.1 mM/cm at 2 and a half hours.
Slide 15
On this slide you can see the principle of the feedback loop for monitoring the patient’s plasma conductivity. Each 15 minutes the values of unique dialysants and patients’ plasma conductivity are calculated by the diascan module from the measurements of dialysate conductivity at the dialyser inlet and outlet. From these values of unique dialysants and patient plasma conductivity, the diacontrol software adjusts each 15 minutes the value of dialysate conductivity required for reaching the target value of plasma conductivity set by the physician with the remaining time of the dialysis session. Note that the diascan module actually measures the effective dialysants, it has the value of the dialysants taking into account the re-circulation and the actual value of plasma conductivity, which is the plasma conductivity at the dialyser inlet corrected for re-circulation.
Slide 16
What are the benefits of diacontrol for monitoring hemodialysis treatment? Firstly the feedback loop allows the physician to prescribe a patient parameter it does the patient plasma conductivity instead of a technical parameter, that’s the dialysate sodium activity. The diacontrol should be logically associated with the ultrafiltration controller.
Slide 17
By setting the value of dry weight and plasma conductivity at the end of the session the physician allows the patient to come back to his or her physiological sodium water status. The diacontrol software associated with the ultrafiltration controller makes the dialysis monitor intelligent by enabling it to restore a stable sodium level at the end of each session and it’s a way for answering that sodium removal is equal to the sodium load.
Slide 18
Some studies in the 90s have shown that the use of diacontrol software is associated with an improvement of hemodynamic stability assessed by an important decrease in occurrence of hypertensive episodes. By prescribing the target value of patient plasma conductivity at the end of the session, the physician can set the value of patient sodium pool. On this slide you can see the results of a study presented as a poster in this congress. In 10 hypertensive patients, the progressive decrease of the prescribed target value of patient plasma conductivity at the end of the session is associated with an improvement of arterial pressure and a decrease in the required number of hypertensive drugs. The decrease in prescribed post dialytic plasma conductivity is responsible for an intelligent decrease in dialysate conductivity, which seems better tolerated than a blindfold decrease of dialysate conductivity prescribed by the physician. However, further studies are required in order to confirm these results.
Slide 19
A second feedback system routinely available is the blood temperature control developed by Fresenius.
Slide 20
A decrease in temperature of the dialysate delivered by the dialysis monitor improves cardio-muscular stability because the induced decrease in body temperature provokes vasoconstriction. However, this improvement is observed only for a dialysate temperature lower than 36°C and an important drawback of cooler dialysis is its poor tolerance with frequent sharing.
Slide 21
In addition, conventional dialysis is associated with an increase in body temperature, which prevents the vasoconstriction induced by ultrafiltration. This increase in body temperature is due to firstly an increase in the production of heat related to inflammatory reactions induced by a dialysate not ultra pure and by the bio incompatibility of the dialysis procedure. Secondly by a decrease in the removed quantity of heat related to the ultrafiltration induced vasoconstriction.
Slide 22
The aim of the blood temperature control is to monitor the body temperature in order to prevent its increase during the dialysis session.
Slide 23
For a better understanding of these benefits it is necessary to give some definitions. In conventional hemodialysis the temperature of the dialysate delivered by the dialysis monitor is set at a constant value during the session. Thermoneutral dialysis is a procedure aimed at preventing any transfer of thermal energy between dialysate and extra corporal blood. Because the dialysis session is associated with a production of heat this procedure requires a progressive increase in the temperature of the dialysate delivered by the dialysis monitor. Isothermic dialysis is a procedure aimed at keeping body temperature unchanged during the dialysis session because the dialysis session is associated with a production of heat, this procedure requires a progressive decrease in temperature of the dialysate delivered by the dialysis monitor.
Slide 24
On this slide you can see the feedback loop used by the Fresenius software. The monitored parameter is the body temperature calculated by the blood temperature monitor from the temperature of the blood in the arteriole and venous lines. The controlled parameter is the dialysate temperature not that the body temperature is a better temperature in the arteriole line corrected for re-circulation. The re-circulation is calculated by the blood temperature monitor from the values of blood temperature measured by this module in the arteriole and venous lines.
Slide 25
What are the benefits of Fresenius software for monitoring hemodialysis treatment? Firstly the feedback loop allows the physician to decide a physiologic prescription, it has body temperature kept constant instead of a technical prescription it has the value of temperature of dialysate delivered by the dialysis monitor. Thus the Fresenius software makes the dialysis monitor intelligent by enabling it to adapt the thermal balance to the individual patient.
Slide 26
By prescribing a body temperature kept constant during the dialysis session, the physician allows the patient to improve his or her hemodynamic stability.
Slide 27
As you can see on this slide we show the results of a European randomised clinical trial. The Fresenius software prevents the dialysis-induced change in body temperature. By progressively decreasing the dialysate temperature by about 1 °C between the beginning and the end of the dialysis session. You can see that the percentage of sessions with symptomatic hypotension is reduced by half. A drawback of this study is the absence of comparison with conventional hemodialysis. Isothermic dialysis is only compared with thermo neutral dialysis, a procedure which requires an increase in dialysate temperature by about 0.5°C. However, a study presented as a poster in this congress suggests that isothermic dialysis requiring a decrease in dialysate temperature from 36.8 to 35.7°C has the same beneficial effects on the hemodynamic stability that a cool dialysis with a dialysate temperature set at 35.5 during the entire session. The benefit of isothermic dialysis is the absence of sharing because the body temperature is unchanged during the session.
Slide 28
I terminate with two biofeedback systems for monitoring the change in blood volume, the blood volume control developed by Fresenius and the hemocontrol developed by Hospal.
Slide 29
The hemodialysis session is associated with a decrease in blood volume related to the ultrafiltration. The aim of the Fresenius device is to control the change in blood volume by acting on the ultrafiltration profile for avoiding a relative blood volume lower than a critical relative blood volume.
Slide 30
From the continuous measurement of the relative blood volume by the volume monitor module, the blood volume control set the ultrafiltration rate at the value which makes it possible to obtain the expected fluid balance without reaching the critical value fixed by the physician.
Slide 31
What is the benefit of the Fresenius device? In a study presented as a poster in this congress the blood volume control software allows a dramatic decrease in the incidence of interdialytic hypertension.
Slide 32
However, the accurate determination of the critical relative blood volume is complex and time consuming because this critical value depends on several parameters which vary from one session to another.
Slide 33
Because the change in relative blood volume is often irregular over time and because this irregularity is a poor predictor of interdialytic hypertension.
Slide 34
The aim of the biofeedback loop developed by Hospal is to control the relative blood volume for avoiding its irregularity. There are two controlled parameters the ultrafiltration profile and the dialysate conductivity profile making this device particularly complex.
Slide 35
Ronco has shown a 60% reduction is a number of sessions with hypotensive episodes in 12 patients treated with acetate-free hemodialysis. Santoro has shown a 30% reduction in interdialytic hypotension in 36 patients treated by hemodialysis.
Slide 36
In conclusion by using biofeedback loops the dialysis mission becomes an intelligent artificial kidney making the dialysis treatment more physiologic. However, biofeedback systems need still simplification of instructions for use and an improvement in reliability.
Thank you very much.
Chairman: Thank you very much Doctor Petitclerc.
