Abstract:
A method of testing the integrity of a membrane of at least one filter located along a dialysis solution circuit. The method includes the steps of wetting the test membrane with an aqueous solution, expelling the aqueous solution from the filter, filling a fill chamber of the filter with a given quantity of gas after closing the gas flow lines from the fill chamber, and detecting gas flow through the membrane, which bounds the fill chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority under 35 U.S.C. § 119 to Italian Patent Application No. BO2006A 000625 filed Sep. 5, 2006, which is incorporated herein by reference in its entirety.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to a method of testing the integrity of dialysis circuit filters.  
       BACKGROUND  
       [0003]     Haemodialysis is a blood-purifying method for restoring hydrosaline balance and eliminating surplus water and toxic substances accumulating in the body as a result of kidney failure, by releasing them to an electrolytic fluid similar to that of normal plasma not containing them. Here and hereinafter, this fluid is referred to as “dialysis solution.” In dialysis, blood drawn from the patient&#39;s arm flows along the so-called artery line into the dialyzer, out of the dialyzer along the so-called vein line, and is restored, purified, to the patient.  
         [0004]     In haemodiafiltration, to which the following description refers purely by way of example, blood is purified by both diffusion and convection. Purification by diffusion is based on the presence of a concentration gradient between the two solutions on either side of the membrane, which causes solutes to pass to the lower-concentration side; while purification by convection is based on generating in the dialysis fluid a negative hydraulic pressure with respect to the blood. Because the dialysis membrane is partly permeable by solutes, plasma water flow is accompanied by a stream of plasma solutes compatible in size with the porosity of the membrane.  
         [0005]     Part of the plasma flow through the membrane is replaced with a sterile substitution fluid, which is added to the extracorporeal blood flow either upstream (pre-dilution) or downstream (post-dilution) from the dialyzer.  
         [0006]     The substitution fluid may be formed “on-line” from the dialysis fluid, and, since the dialysis fluid is not always sterile and devoid of pyrogenous substances, is formed by filtering the dialysis fluid using one or two filters located along the dialysis circuit, upstream from the dialyzer, and comprising two chambers separated by a hydrophilic membrane.  
       SUMMARY  
       [0007]     In one embodiment, the present invention is a method of testing the integrity of a filter in a dialysis solution circuit. The method comprises introducing a gas into a fill chamber of the filter, the fill chamber bound by a membrane, and detecting gas flow from the fill chamber through the membrane.  
         [0008]     In another embodiment, the present invention is a method of testing the integrity of a membrane of at least one filter located along a dialysis solution circuit. The filter includes a fill chamber which is bounded by the membrane and is in fluid communication with at least one fluid flow line. The method comprises wetting the membrane with an aqueous solution, expelling the aqueous solution from the filter, blocking the fluid flow line to substantially prevent fluid flow therethrough, introducing a gas into the fill chamber, and detecting gas flow through the membrane.  
         [0009]     In yet another embodiment, the present invention is a system for testing a dialysis solution circuit. The system comprises a dialysis filter having a fill chamber bounded by a membrane, means for introducing a gas into the fill chamber, and means for detecting gas flow through the membrane. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     A number of non-limiting embodiments of the invention will be described by way of example with reference to the accompanying drawings, in which:  
         [0011]      FIG. 1  is a schematic view of a portion of a dialysis machine in accordance with a first embodiment of the present invention;  
         [0012]      FIG. 2  is a schematic view of a portion of a dialysis machine in accordance with a second embodiment of the present invention; and  
         [0013]      FIG. 3  is a schematic view of a portion of a dialysis machine in accordance with a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  is a schematic view of portions of a dialysis machine  1  in accordance with one embodiment of the present invention. As shown in  FIG. 1 , the dialysis machine  1  comprises a known haemodialysis filter  2  (not described in detail), an artery line  3  for feeding blood from a patient P to filter  2 , a pump  3   a  fitted to artery line  3  to ensure blood flow, a vein line  4  for feeding blood from filter  2  to patient P, a drip chamber  5  located along vein line  4 , and a dialysis solution circuit  6 .  
         [0015]     In the illustrated embodiment, the dialysis solution circuit  6  comprises a preparation device  7 , an inflow branch  8  for feeding dialysis solution to filter  2 , a first sterile filter  9  along inflow branch  8 , a substitution-fluid line  10  for feeding substitution fluid from first sterile filter  9  to drip chamber  5 , a second sterile filter  11  along substitution-fluid line  10 , a pump  12  located along substitution-fluid line  10 , downstream from second sterile filter  11 , a dialysis solution outflow branch  13  from filter  2 , and a flow gauge  14  through which inflow branch  8  and outflow branch  13  extend. Inflow branch  8  and outflow branch  13  are fitted with respective pumps  15  and  16 .  
         [0016]     As shown, the first and second sterile filters  9 ,  11  each comprise a pair of chambers  9   a ,  9   b  and  11   a ,  11   b , with each pair separated by a hydrophilic membrane  9   c ,  11   c , respectively. In various embodiments, the membranes  9   c ,  11   c  are configured to prevent bacteria or endotoxins in the dialysis solution from passing from the chambers  9   a ,  11   a  to the chambers  9   b ,  11   b , respectively, of the filters  9 ,  11 .  
         [0017]     Inflow branch  8  comprises a first bypass solenoid valve  17  for bypassing the chamber  9   a  of first sterile filter  9  and connecting inflow branch  8 , by means of a connecting line  10   a , to chamber  9   b  of the first sterile filter and, hence, to substitution-fluid line  10 , which, in the example shown, extends from chamber  9   b  of filter  9 . Inflow branch  8  also comprises a second bypass solenoid valve  18  for bypassing haemodialysis filter  2  and connecting inflow branch  8  directly to outflow branch  13 , either upstream or downstream from a solenoid valve  18   a , depending on the operating mode employed.  
         [0018]     Dialysis machine  1  comprises a first drain line  19  connecting chamber  9   a  of first sterile filter  9  to outflow branch  13 , and a second drain line  20  connecting chamber  11   a  of second sterile filter  11  to outlet branch  13 . Drain lines  19 ,  20  are fitted with respective solenoid spill valves  19   a ,  20   a , which are opened periodically to wash the membranes of filters  9  and  11  and prevent accumulated bacteria and endotoxins from impairing operation of the filters.  
         [0019]     Dialysis machine  1  also comprises a test line  21  connecting substitution-fluid line  10 , downstream from second sterile filter  11 , to outflow branch  13 .  
         [0020]     Finally, in the illustrated embodiment, the dialysis machine  1  comprises an antibacterial filter  22  for filtering outside air, a solenoid valve  23  for switching the fluid source of inflow branch  8  from preparation device  7  to antibacterial filter  22 , and an air sensor  24  located along outflow branch  13 , downstream from the connections to drain lines  19 ,  20  and test line  21 . The sensor  24  can be of any type suitable for detecting fluid flow through the outflow branch  13 . In one embodiment, the sensor  24  may be an ultrasound sensor. In one embodiment, the sensor  24  may be an optical sensor. In various embodiments, the sensor  24  may be a continuous-reading type sensor. In other embodiments, other types of sensors may be utilized.  
         [0021]     In actual use, once dialysis treatment is completed, the dialysis machine  1  is switched from dialysis mode to wash/test mode. After dialysis solution circuit  6  has been flushed with an aqueous solution, e.g. the dialysis solution itself, solenoid valve  23  is switched to antibacterial filter  22  to feed circuit  6  with air from antibacterial filter  22  as opposed to the dialysis solution from preparation device  7 . At the same time, the outlet of chamber  9   b  of first filter  9  is closed by closing solenoid valve  18   a  and switching bypass solenoid valve  18  to the circuit portion upstream from solenoid valve  18   a , the outlet of chamber  11   a  of second filter  11  is closed by closing solenoid valve  20   a . In addition, the solenoid valve  17  is set to connect inflow branch  8  directly to substitution-fluid line  10 , so that the air pumped by pump  15  is fed into chamber  9   b  of first sterile filter  9  and into chamber  11   a  of second sterile filter  11  to expel the liquid from the filters. In the event of damage to either one of membranes  9   c ,  11   c  separating chambers  9   a  and  9   b  and chambers  11   a  and  11   b  respectively, air flows along drain line  19  or test line  21 , and is detected by sensor  24 . More specifically, comparison of the information from sensor  24  with a reference threshold determines the integrity or not of membranes  9   c  and  11   c  and, hence, of filters  9  and  11 .  
         [0022]     Moreover, by acting on solenoid valve  19   a , the integrity first of membrane  11   c  and then of membrane  9   c  can be tested separately.  
         [0023]      FIG. 2  is a schematic view of portions of a dialysis machine  30  according to another embodiment of the present invention. Parts identical to those of dialysis machine  1  are indicated using the same reference numbers, with no further description. As can be seen in  FIG. 2 , the dialysis machine  30  differs from dialysis machine  1  by comprising one three-chamber filter  31  as opposed to two sterile filters  9  and  11  (see  FIG. 1 ), which means integrity testing of machine  30  applies to filter  31  and, more specifically, to the two membranes  32  and  33  dividing filter  31  into three chambers  31   a ,  31   b ,  31   c.    
         [0024]     As shown, dialysis machine  30  comprises a dialysis solution circuit  34  connected selectively to chamber  31   a  or chamber  31   b  of filter  31 , and a substitution-fluid line  36  connecting chamber  31   c  of filter  31  to drip chamber  5 .  
         [0025]     In the illustrated embodiment, the inflow branch  35  comprises a bypass solenoid valve  37  which, in test mode, bypasses chamber  31   a  of filter  31  to connect inflow branch  35  directly, along a connecting line  39 , to chamber  31   b . In normal operating mode, solenoid valve  37  connects inflow branch  35  to chamber  31   a  of filter  31 , spill valve  38   a.    
         [0026]     As further shown, the dialysis machine  30  also comprises a drain line  40  connecting chamber  31   a  directly to outflow branch  13 , and which is fitted with a solenoid spill valve  40   a.    
         [0027]     In actual use, once dialysis treatment is completed, dialysis machine  30  is switched from dialysis mode to wash/test mode. After dialysis solution circuit  34  has been flushed with an aqueous solution, e.g. the dialysis solution itself, solenoid valve  23  is switched to antibacterial filter  22  to feed circuit  34  with air from antibacterial filter  22  as opposed to the dialysis solution from preparation device  7 .  
         [0028]     At the same time, the outlet of chamber  31   b  of filter  31  is closed by closing solenoid valve  18   a  and switching bypass solenoid valve  18  to the circuit portion upstream from solenoid valve  18   a , and solenoid valve  37  is set to connect inflow branch  35  directly to chamber  31   b  of filter  31 , so that the air pumped by pump  15  is fed into chamber  31   b  of filter  31  to expel the liquid from the filter. In the event of damage to either one of membranes  32 ,  33 , air flows along drain line  40  or test line  21 , and is detected by sensor  24 . As in dialysis machine  1 , comparison of the information from sensor  24  with a reference threshold determines the integrity or not of membranes  32  and  33  and, hence, of filter  31 .  
         [0029]      FIG. 3  is a schematic view of portions of a dialysis machine  41  according to a third embodiment of the present invention. Parts identical to those of dialysis machine  1  are indicated using the same reference numbers, with no further description. As can be seen in  FIG. 3 , the dialysis machine  41  differs from dialysis machine  1  by having no sensor  24 , and by comprising a solenoid valve  42  located between preparation device  7  and solenoid valve  23  to completely cut off inflow branch  8  when solenoid valve  23  is switched to preparation device  7 .  
         [0030]     In actual use, once dialysis treatment is completed, dialysis machine  41  is switched from dialysis mode to wash/test mode. After dialysis solution circuit  6  has been flushed with an aqueous solution, e.g. the dialysis solution itself, solenoid valve  23  is switched to antibacterial filter  22  to feed air into respective chambers  9   b  and  11   a  of filters  9  and  11 , in the same way as described for machine  1 . Once chamber  9   b  of filter  9  and chamber  11   a  of filter  11  are filled with air, solenoid valve  23  is switched to preparation device  7 , and branch  8  is fed with a sufficient amount of fluid to further compress the air inside chambers  9   b  and  11   a.    
         [0031]     At this point, solenoid valve  42  is closed, and flow along branch  8  is measured by differential flow gauge  14 . In other words, any damage to either one of membranes  9   c ,  11   c  would result in air flow and, consequently, flow of the fluid compressing the air, thus giving a flow reading of other than zero along branch  8 .  
         [0032]     As will be apparent to anyone skilled in the art, the test method and relative unit according to the present invention are controlled by a known central control unit not described or illustrated.