Abstract:
The invention relates to a method for monitoring the supply of substitution liquid during an extracorporeal blood treatment and to an extracorporeal blood treatment unit equipped with a device for monitoring the supply of substitution liquid. The monitoring of the supply of substitution liquid is based on the measurement of pressure waves, which are generated by the substitution liquid pump, in the extracorporeal blood circulation system. A disturbance in the supply of substitution liquid is inferred when the amplitude of the pressure waves exceeds a predetermined limit value. The amplitude of the pressure waves is preferably monitored in the venous blood line.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a method for monitoring the supply of substitution fluid during an extracorporeal blood treatment. Furthermore, the invention relates to equipment for extracorporeal blood treatment with a device for monitoring the supply of substitution fluid.  
       BACKGROUND OF THE INVENTION  
       [0002]     In order to remove substances usually eliminated with urine and for fluid withdrawal, various methods for extracorporeal blood treatment or cleaning are used in chronic kidney failure. In haemodialysis, the patient&#39;s blood is cleaned outside the body in a dialyser. The dialyser has a blood chamber and a dialysis fluid chamber, which are separated by a semipermeable membrane. During the treatment, the patient&#39;s blood flows through the blood chamber. In order to clean the blood effectively from substances usually eliminated with urine, fresh dialysis fluid flows continuously through the dialysis fluid chamber.  
         [0003]     Whereas the transport of the low-molecular substances through the membrane is essentially determined by the concentration differences (diffusion) between the dialysis fluid and the blood in haemodialysis (HD), substances dissolved in the plasma water, in particular higher-molecular substances, are effectively removed in haemofiltration (HF) by a high fluid flow (convection) through the membrane of the dialyser. In haemofiltration, the dialyser functions as a filter. Haemodiafiltration (HDF) is a combination of the two processes.  
         [0004]     In haemo(dia)filtration, part of the serum drawn off through the membrane is replaced by a sterile substitution fluid, which is fed to the extracorporeal blood circuit upstream of the dialyser (pre-dilution) or downstream of the dialyser (post-dilution).  
         [0005]     Devices for haemo(dia)filtration are known in which the dialysis fluid is produced online from fresh water and concentrates and the substitution fluid is produced online from the dialysis fluid.  
         [0006]     In known haemo(dia)filtration devices, the substitution fluid is fed to the extracorporeal blood circuit from the fluid system of the machine via a substitution fluid line. In pre-dilution, the substitution fluid line leads to a connection point on the arterial blood line upstream of the dialyser, whilst in post-dilution the substitution fluid line leads to a connection point on the venous blood line downstream of the dialyser. The substitution fluid line has a connector, with which it can be connected either to the venous or arterial blood line. In order to interrupt the fluid supply, a clamp or suchlike is provided on the substitution fluid line.  
         [0007]     The correct connection of the substitution fluid line is routinely checked before the commencement of the blood treatment with known haemo(dia)filtration equipment. For this purpose, the line leading to the dialysis fluid chamber and leading away from the dialysis fluid chamber of the dialyser and the venous blood line downstream of the connection point for the substitution fluid line are clamped by means of tube clamps. The arterial blood line is already interrupted by the stationary blood pump upstream of the connection point for the substitution fluid line. The substituate pump for conveying the substitution fluid is then started, and the pressure in the venous blood line is measured by means of a venous pressure sensor.  
         [0008]     In the event that a pressure in the venous blood line cannot be built up with the substituate pump that is greater than a preset limiting value, the conclusion is drawn that the connection of the substitution fluid line is not correct, i.e. the supply of fluid is interrupted. During the blood treatment, it can happen in dialysis practice that the treatment procedure is switched between post- and predilution. For this purpose, the clamp is closed on the substitution fluid line, and the substitution fluid line is separated from the venous or arterial blood line and connected to the arterial or venous blood line respectively. It cannot be ruled out in practice that the opening of the tube clamp may be forgotten. If the substituate pump is not stopped and the pressure test described above is not carried out, this state is not detected. It is a drawback that, with the known haemo(dia)filtration equipment, the supply of substitution fluid is not monitored during the treatment. An interruption of the substituate supply, therefore, remains undetected. In this case, haemodialysis can be carried out with only little effect during HDF treatment. During HF treatment, the patient is then not treated at all in the extreme case. This can have more or less serious consequences for the patient, although he/she is not directly endangered.  
       SUMMARY OF THE INVENTION  
       [0009]     The problem underlying the invention is to provide a method such that the monitoring of the supply of substitution fluid during an extracorporeal blood treatment is also permitted when the treatment procedure is changed. A further problem underlying the invention is to provide a device that also enables the monitoring of the substitution fluid supply when the treatment procedure is changed. The solution to these problems takes place according to the present invention.  
         [0010]     The monitoring of the supply of substitution fluid is based on the fact that the amplitude of the pressure waves of the substituate pump is monitored in the fluid system or extracorporeal blood circuit. It has been shown that a malfunction of the substitution fluid supply is present when the amplitude of the pressure waves exceeds a preset limiting value.  
         [0011]     The method according to the invention and the device according to the invention require that the substituate pump for conveying the substitution fluid is a pump generating pressure waves, in particular a volumetric occlusion pump (roller pump).  
         [0012]     The pressure waves emerging from the substituate pump are able to propagate via the fluid system of the extracorporeal blood treatment equipment through the dialyser into the extracorporeal blood circuit. This path is open even when the substitution fluid supply is interrupted. The substituate pump then operates against the closure. The amplitude of the pressure waves, which can be detected in the extracorporeal blood circuit, thus increases.  
         [0013]     In an embodiment of the invention, the amplitude of the pressure waves is measured in the extracorporeal blood circuit downstream of the dialyser. This has the advantage that a pressure sensor can be used that is in any case provided in the venous blood line in the known blood treatment equipment.  
         [0014]     In another embodiment of the invention, the amplitude of the pressure waves is measured in the fluid system upstream of the dialyser or filter. This has the advantage that monitoring is also possible during operation of the blood treatment equipment as haemofiltration equipment, in which the pressure waves cannot reach the extracorporeal circuit since the inlet of the dialyser or filter is cut off from the dialysis fluid supply.  
         [0015]     The pressure signal is preferably filtered with a bandpass in order to eliminate disturbing pulses, whereby the amplitude of the filtered pressure signal is then compared with the preset limiting value.  
         [0016]     It has been shown that the enlargement of the amplitude of the pressure waves is dependent on the pumping rate (speed) of the substituate pump. A false alarm can be eliminated by the fact that, when the preset limiting value is exceeded, the conclusion is drawn that there is a malfunction only if the pumping rate lies between preset limiting values. These limiting values should be rated in such a way that the change in amplitude traceable to the changes in the pumping rate is smaller than the change in amplitude due to an interruption of the substitution fluid supply.  
         [0017]     An acoustic and/or optical alarm is expediently emitted when the preset limiting value is exceeded. Action by the operator in the control of the blood treatment equipment can however also be taken.  
         [0018]     The monitoring device of the extracorporeal blood treatment equipment has means for monitoring the amplitude of the pressure waves of the substituate pump in the fluid system, preferably upstream of the dialyser or filter, or in the extracorporeal blood circuit, preferably downstream of the dialyser or filter, and means for evaluating the pressure-wave amplitude. The substituate pump generating pressure waves is arranged in the substitution fluid line, which leads from the fluid system to the blood circuit upstream or downstream of the dialyser or filter. The substitution fluid line can be a single tube line or also a tube-line system with several branches.  
         [0019]     The only decisive factor is that a flow connection is created between the fluid system and the blood circuit of the blood treatment equipment.  
         [0020]     The substitution fluid line can be connected directly to the venous or arterial blood line. It is however also possible for the line to be connected to drip chambers or suchlike, which are provided in the venous or arterial blood line.  
         [0021]     The fluid system of the blood treatment equipment can include a dialysis fluid supply line leading to the dialysis fluid chamber of the dialyser and a dialysis fluid discharge line leading away from the dialysis fluid chamber of the dialyser. One or more filters can be arranged in the fluid system in order to increase safety. Further lines, for example bypass lines etc., can also be provided. The only decisive factor is the fact that the fluid system permits a propagation of pressure waves, i.e. is a system completely filled with a medium. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  shows equipment for extracorporeal blood treatment with a device for monitoring the supply of substitution fluid in a greatly simplify diagrammatic representation.  
         [0023]      FIG. 2  shows the filtered venous pressure signal as a function of time in post-dilution ( FIG. 2A ), disconnection ( FIG. 2B ) and pre-dilution ( FIG. 2C ), when the pumping rate of the substituate pump amounts to 20 ml/min.  
         [0024]      FIG. 3  shows the filtered venous pressure signal as a function of time in post-dilution ( FIG. 3A ), disconnection ( FIG. 3B ) and pre-dilution ( FIG. 3C ), with a substituate pumping rate of 60 ml/min.  
         [0025]      FIG. 4  shows the filtered venous pressure signal as a function of time in post-dilution ( FIG. 4A ), disconnection ( FIG. 4B ) and pre-dilution ( FIG. 4C ), with a substituate pumping rate of 100 ml/min. 
     
    
     DETAILED DESCRIPTION  
       [0026]     An exemplary embodiment of the invention will be explained in greater detail below by reference to the drawings.  
         [0027]      FIG. 1  shows a simplified diagrammatic representation of the essential components of haemo(dia)filtration equipment together with a device for monitoring the supply of substitution fluid from the fluid system of the haemo(dia) filtration equipment in the extracorporeal blood circuit.  
         [0028]     The haemo(dia) filtration equipment has a dialyser or filter  1 , which is separated by a membrane  2  into a first chamber  3  through which blood flows and a second chamber  4  through which dialysis fluid flows. First chamber  3  is connected into an extracorporeal blood circuit  5 A, whilst second chamber  4  is connected into fluid system  5 B of the haemo(dia)filtration equipment.  
         [0029]     Extracorporeal blood circuit  5 A includes an arterial blood line  6 , which leads to inlet  3   a  of blood chamber  3 , and a venous blood line  7 , which leads away from outlet  3   b  of blood chamber  3  of dialyser  1 . In order to eliminate air bubbles, an arterial drip chamber  8  is connected into arterial blood line  6  and a venous drip chamber  9  is connected into venous blood line  7 . The patient&#39;s blood is conveyed through the blood chamber of the dialyser by means of an arterial blood pump  10 , in particular a roller pump, which is arranged on arterial blood line  6 .  
         [0030]     Fluid system  5 B includes a dialysis fluid supply line  11 , which leads to inlet  4   a  of dialysis fluid chamber  4 , and a dialysis fluid discharge line  12 , which leads away from outlet  4   b  of dialysis fluid chamber  4  of dialyser  1 . Fresh dialysis fluid flows from a dialysis fluid source (not shown) into the dialysis fluid chamber via dialysis fluid supply line  11 , whilst the used dialysis fluid is discharged from the dialysis fluid chamber via dialysis fluid discharge line  12  to a discharge (not shown). The balancing device for balancing fresh against used dialysis fluid, as generally provided in haemo(dia)filtration equipment, has not been represented for the sake of better clarity. Additional equipment for cleaning and rinsing the system are likewise not represented.  
         [0031]     Dialysis fluid supply line  11  includes a first section  11   a,  which leads to inlet  13   a  of a first chamber  13  of a sterile filter  16 , subdivided by a membrane  14  into the first chamber and a second chamber  15 , and a second section  11   b,  which runs away from outlet  13   b  of first chamber  13  of filter  16  and leads to inlet  4   a  of dialysis fluid chamber  4 .  
         [0032]     During the dialysis treatment, dialysis fluid can be fed from fluid system  5 B as substitution fluid via tube line  17  to extracorporeal blood circuit  5 A. Substitution fluid line  17  has at both ends two line sections  17   a,    17   b,    17   c,    17   d  respectively. Line section  17   a  is connected with a first outlet  15   a  and line section  17   b  with a second outlet  15   b  of second chamber  15  of sterile filter  16 , whilst a connector  18   a,    18   b  is connected respectively to line sections  17   c  and  17   d.  With the two connectors  18   a,    18   b,  substitution fluid line  17  is connected to a connection line  19  leading to arterial drip chamber  8  and a connection line  20  leading to venous drip chamber  9 . Connection lines  19 ,  20  have corresponding connection pieces  19   a,    20   a  for this purpose. There are provided on line sections  17   c  and  17   d  tube clamps  35 ,  36 , with which a fluid connection can optionally be created with connection line  19  or  20  in order to undertake a pre- or post-dilution. A branch can however also be dispensed with if a tube clamp is provided downstream of substituate pump  22  for the purpose of clamping substitution fluid line  17 . It is then necessary, however, to exchange the line connections manually.  
         [0033]     The substitution fluid is conveyed by means of an occlusion pump, in particular roller pump  22 , into which substitution fluid line  17  is inserted. Such roller pumps belong to the prior art. They have several rollers  22   a,    22   b,  with which the cross-section of the tube line for conveying the fluid is reduced. As a result, pressure waves arise which can be propagated in both directions via the substitution fluid line. A Hall sensor  23 , which measures the pumping rate, is provided on substituate pump  22 .  
         [0034]     In order to measure the pressure in venous blood line  7 , a pressure sensor  24  is provided, which is connected via a pressure line  25  to venous drip chamber  9 . The pressure sensor delivers an electrical signal proportional to the pressure in the venous blood line.  
         [0035]     For the operation of the haemo(dia)filtration equipment as haemodialysis equipment, tube clamps  35 ,  36  are closed, so that dialysis fluid flows through dialysis fluid chamber  4  of the dialyser. For the operation of the haemo(dia)filtration equipment as haemodiafiltration equipment, tube clamp  35 ,  36  is opened, so that sterile dialysis fluid as substitution fluid flows from sterile filter  16  into venous drip chamber  8  (pre-dilution) or arterial drip chamber  9  (post-dilution). Operation of the haemo(dia)filtration equipment solely as haemofiltration equipment is however also possible if the supply of dialysis fluid into dialysis fluid chamber  4  of dialyser  1  is interrupted. In order to interrupt the fluid supply, a shut-off device  26  is provided upstream of dialyser  1 .  
         [0036]     Venous pressure sensor  24  is connected to a signal line  28  with a bandpass filter  29 . Bandpass filter  29  is in turn connected to a data line  30  with an evaluation unit  31 , which receives an electrical signal dependent on the pumping rate of substituate pump  22  via a further signal line  34  of Hall sensor  23 .  
         [0037]     Evaluation unit  31  determines the amplitude of the pressure signal filtered with bandpass filter  29  and compares the amplitude with a preset limiting value. 1.5 to 2.5 times, preferably 1.8 to 2.2 times, in particular 2.0 times the amplitude of the pressure waves measured during trouble-free operation is adopted as the preset limiting value.  
         [0038]     In the event that, following a change of the treatment, for example from pre- to post-dilution, the opening of tube clamps  35 ,  36  is forgotten, i.e. substitution fluid line  17  is clamped, the amplitude of the pressure signal increases sharply.  
         [0039]      FIGS. 2A, 2B  and  2 C show the filtered venous pressure signal together with the periodic signal of the Hall sensor as a function of time with a substituate pumping rate of 20 ml/min. for the cases of post-dilution (A), disconnection (B) and predilution (C). Blood and dialysate flow are set at  300  ml/min. The following values result: 
 Ampl post =1.5 V; Ampl discon =3.0 V; Ampl pre =1.5 V.  Ampl discon /Ampl post =2.0; Ampl discon /Ampl pre =2.0  
         [0040]     It emerges that the amplitude of the pressure waves is doubled when the substitution fluid flow is interrupted. Therefore, when the evaluation unit establishes that the pressure amplitude is greater than the preset limiting value, for example 2.0 times the normal value, the evaluation unit generates an alarm signal, which is received by an alarm unit  32  via an alarm line  33 . Alarm unit  32  then emits an acoustic and/or optical alarm.  
         [0041]      FIGS. 3A, 3B  and  3 C show the filtered venous pressure signal and the Hall signal as a function of time with a higher pumping rate of 60 ml/min. with post-dilution (A), disconnection (B) and pre-dilution (C). Blood and dialysate flow are again 300 ml/min. The following values result: 
 Ampl post =1.9 V; Ampl discon =3.6 V; Ampl pre =1.8 V.  Ampl discon /Ampl post =1.9; Ampl discon /Ampl pre =2.0  
         [0042]     The filtered venous pressure signal and the Hall signal with a still higher pumping rate of 100 ml/min. with post-dilution (A), disconnection (B) and pre-dilution (C) is shown in  FIGS. 4A, 4B  and  4 C. Blood and dialysate flow are again 300 ml/min. The following values result: 
 
Ampl post =1.7 V; Ampl discon =3.2 V; Ampl pre =1.7 V. 
 
Ampl discon /Ampl post =1.9 Ampl discon /Ampl pre =1.9 
 
         [0043]     Concerning the amplitude values of  FIGS. 2 and 3 , it should be noted that the measured values have been adapted in order to have comparable magnitudes. In practice, the increase in the pressure amplitude when the flow of substitution fluid is interrupted is not independent of the pumping rate.  
         [0044]     In order to increase safety, a false alarm can be eliminated by the fact that the pumping rate is also taken into account in the comparison of the measured pressure signal with the preset limiting value. For this purpose, evaluation unit  31  also receives the signal of Hall sensor  23 .  
         [0045]     As long as the pumping rate lies between preset limits, the evaluation unit assumes that an increase in the pressure amplitude is a consequence of an interruption of the substitution fluid supply. For example, Ampl after /Ampl before &gt;1.5 can be adopted as the limiting value. The threshold value needs to be correspondingly corrected for higher pumping rates. This can take place by the fact that different threshold values are adopted for different pumping rate ranges.  
         [0046]     The increase of the pressure amplitude can be traced back to the following. In the case of a blockage of the supply of substitution fluid, the spring forces of the rotor of roller pump  22  are no longer capable of compressing substitution fluid tube  17 , so that the maximum system pressure is reached. This pressure, which is also referred to as the occlusion pressure, is much higher than the normal system pressure. The rotor thus delivers against the higher occlusion pressure in the case of a substitution fluid blockage. On account of closed tube clamp  35  and  36  respectively, the transmission path of the pressure waves via substitution fluid tube  17  to venous pressure sensor  24  is completely blocked. The pressure waves generated by substituate pump  22  reach venous pressure sensor  24 , however, via sterile filter  16 , second section  11   b  of the dialysis fluid supply line, dialyser  1 , venous blood line  7 , venous drip chamber  9  and finally pressure line  25 . As FIGS.  2  to  4  show, the amplitude of the pressure signal is doubled at the time of disconnection on account of the raised occlusion pressure.  
         [0047]     In another embodiment of the invention, the pressure waves are monitored not in the extra corporeal blood circuit ( 5 A), but in the fluid system ( 5 B) of the blood treatment equipment upstream of dialyser  1  or of the filter. This form of embodiment differs from the example of the embodiment described above in that pressure sensor  24  is not provided in venous blood line  7 , but rather a pressure sensor  24 ′ is provided in second section  11   b  of the dialysis fluid supply line. This pressure sensor  24 ′ is indicated in  FIG. 1  with dashed lines as an alternative form of embodiment. It is connected with low-pass filter  29  via signal line  28 ′ also indicated with dashed lines. The pressure waves can however also be measured at another point of the fluid system.