Abstract:
A colloidal silver solution is introduced as a disinfectant to the blood and dialysate sides of a hemodialysis system at the conclusion of a dialysis session and is not flushed from the system until another dialysis is to be performed.

Description:
TECHNICAL FIELD 
     The present invention relates to the reuse of components in a hemodialysis system, and particularly, the manner of disinfecting them. 
     BACKGROUND OF THE INVENTION 
     The reuse of disposable artificial kidneys has grown greatly in the United States to the extent that reuse is reported to be practiced by more than 75% of all hemodialysis facilities. Reuse requires a cleaning and disinfecting program between uses for the dialyzer, blood and dialysate tubing sets, and related apparatus that guarantees bacteriological safety, the avoidance of contamination by the chemicals used in the cleaning and disinfecting process, and maintenance of the transfer efficiency of the dialyzer membrane. Economic concerns dictate that the reuse cycle be expedited and involve as little expense as possible. 
     In the past, various reuse procedures and apparatus have been developed to substantially automate cleaning, rinsing and sterilization cycles. U.S. Pat. No. 4,695,385 discloses a reuse system which has enjoyed some success. In this system as normally practiced, sterilization is accomplished by use of a formaldehyde solution, and it is essential that the blood, tubing and blood side of the dialyzer be absolutely free of formaldehyde before reuse since formaldehyde is extremely toxic if permitted to enter a patient&#39;s blood stream. 
     In U.S. Pat. No. 4,695,385, the blood tubing is isolated during the disinfecting cycle with the blood side of the dialyzer in a closed loop filled with the formaldehyde solution. This status is maintained during idle periods of the dialysis machine. To remove the formaldehyde from the system in preparation for another patient, the blood pump is started to circulate the formaldehyde solution in the closed loop, and the dialysate pump is started to circulate dialysate through the dialysate side of the dialyzer. As a result, molecular transfer of the formaldehyde across the dialyzer membrane occurs and the transferred formaldehyde is disposed of with the circulating dialysate. The formaldehyde solution in the blood tubing can be provided with a colored dye indicator so that there can be visual confirmation that the formaldehyde has been substantially removed. Then a chemical test is performed to verify that no disinfectant residue remains in the dialysis system. 
     A survey in 1996 indicated that about 90% of dialyzer centers used formaldehyde or Renalin as a dialyzer disinfectant. Renalin (Renal Systems, Minneapolis, Minn.) is a hydrogen peroxide-paracetic acid based product. At least one major manufacturer of hemodialysis machines advises that such peracetic acid products should be rinsed out after acting for 20 minutes and warns that they should not be left in the machine overnight because damage to internal components may occur. Also, some studies have indicated increased health risk concerns when peracetic acid is used in reprocessing dialyzers. Thus, heretofore, formaldehyde has been considered preferable for use as a dialyzer disinfectant for the blood circuit components, particularly when the dialysis machine may be idle for several hours, and therefore, preferably should have its blood circuit components exposed to disinfectant while idle to avoid the possibility of bacterial growth. 
     From the foregoing discussion it is seen that although it has been recognized that ideally the disinfecting agent for disinfecting a hemodyalisis system for reuse should be a chemically pure, non-toxic substance that can be easily removed from the dialyzer so as to minimize the risk to the patient from exposure to trace amounts, heretofore, not only was a suitable non-toxic disinfecting substance never found, but it has been considered that disinfectant removal from the blood side of the system requires that the disinfecting solution be dialyzed for removal of the disinfectant. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is apparent that there has been a significant need for an improved method for sterilization of the dialyzer and associated blood and dialysate exposed tubing and components in a hemodialysis machine when they are to be reused. I have found that this need can be filled by properly using colloidal silver as a disinfectant, preferably at a concentration of about 3 ppm. This disinfectant is circulated to fill the dialyzer and associated sets of dialysate and blood tubing and related apparatus after they have been rinsed following a dialysis treatment. The disinfectant is preferably left in place until shortly before another treatment is scheduled. Then the disinfectant may be flushed from the dialysis system with sterile water; no dialysis of the disinfectant is required for removal. However, even this water flushing is not essential because colloidal silver is not toxic. Hence, at the start of dialysis, when the blood is initially being pumped from the patient through the blood tubing and blood side of the dialyzer, the blood will flush the colloidal silver solution out of the tubing and dialyzer through the venous end of the tubing before the venous end is connected for the patient following appearance of the patient&#39;s blood at the venous end. The colloidal silver solution in the dialysate circuit will be flushed to drain by the circulating dialysate. It is of no concern if colloidal silver residue remains in the blood circuit and is gathered up by the patient&#39;s circulating blood because colloidal silver is not toxic, particularly in the concentration used. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a typical hemodialysis system to which the present invention may be applied. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, there is illustrated a hemodyalisis system having a dialyzer 9 containing a suitable membrane separating a blood side from a dialysate side. The latter is connected to a dialysate tubing set including an input line 10 connected to a supply line 11 from the dialysis machine 12 via a valve block 13, and a discharge line 14 leading to a drain line 15 via the valve block 13. The blood side of the dialyzer 9 has an inlet connected by a blood tube 18 to an arterial drip chamber 20 feeding from an arterial blood tube 22, and has an outlet feeding by a blood tube 24 to a venous drip chamber 26. This chamber discharges to a venous line 28. During dialysis the ends 22a and 28a of the blood tubes 22, 28 of the blood tube set are connected to the patient. A blood pump 30 operates to move blood from the patient to the blood side of the dialyzer where the toxins in the blood are transferred via the dialyzer membrane to the circulating dialysate on the other side of the membrane. The dialysate is mixed and pumped by a suitable pump 19 from the dialysis machine 12 to the dialyzer through supply line 11, valve block 13, and input line 10. After circulating through the dialyzer the then used dialysate is dumped through the discharge tubing 14, valve block 13, and a drain line 15. 
     After dialysis is completed, the arterial blood tube 22 is disconnected from the patient and it and the remaining blood side of the system are emptied of blood, preferably by pumping a disinfecting colloidal silver solution through the blood tube 22 until substantially all of the blood in the blood side is returned to the patient through the venous line 28. Then the venous line 28 is disconnected from the patient and circulation of the colloidal silver solution may be continued to purge the blood side of the system from remaining blood. The colloidal silver solution may be stored in a vessel 35 connected by a suction tube 36 to the suction side of the pump 19 so that the colloidal silver solution may be pumped through the line 11 to the valve block 13 where a suitable valve directs the flow to a branch 31 or input line 11 to the dialyzer 9. The arterial tubing 22 is connected to the branch 31 when the colloidal silver solution is to be circulated through the blood side of the system as at the end of a dialysis session to return as much of the patient&#39;s blood as feasible to the patient. When the blood side is full of the colloidal silver solution, the pumping may be stopped and the valving in the valve block 13 is set so that the arterial and venous lines 27, 28 are interconnected to make the blood side of the system a closed loop filled with the colloidal silver solution to maintain the blood side of the dialysis system in a disinfected condition until the start of the next dialysis session. 
     In the meantime, the dialysate side of the system can be flushed with water and then filled with colloidal silver solution in like manner as the blood side. When dialysis is to be again performed, dialysate is circulated through the dialysate side of the system and this adequately flushes out the colloidal silver solution. Likewise, the colloidal silver solution filling the blood side of the system can be removed by water flushing the blood lines and blood side of the dialyzer. However, since colloidal silver solution is not toxic, it can be adequately removed from the blood side by connecting the arterial tubing 22 to the patient, starting the blood pump 30, and commencing dialysis without the venous line 28 being connected to the patient. As the pumped blood travels through the blood side of the system it flushes out the colloidal silver solution through the outer end 28a of the venous line. When blood appears at this end 28a, the venous line is connected to the patient. 
     The preferred concentration of colloidal silver in sterile water for use according to the present invention is 3 ppm±10%. Greater concentrations can be used but there is no significant increase in disinfecting effectiveness, and there is the disadvantage of being more costly. In fact, concentrations above about 5 ppm do not give as good results for the practice of the present invention as concentrations of about 3 ppm. 
     A suitable colloidal silver solution can be produced in a batch procedure by suspending two substantially pure silver electrodes, as anode and cathode, about six inches apart in a large non-metallic container of pure water (preferably distilled) and subjecting the electrodes to a relatively high alternating current voltage, as for example, 440 volts. This procedure is continued until sufficient silver particles have sloughed into the water to achieve the desired concentration, and namely, about 3 ppm in the present instance. These silver particles are very minute, typically in the range of about 0.005 to 0.015 microns, and normally have the same polarity. Hence, the particles remain suspended in the water in a colloidal state. 
     From the foregoing it will be appreciated that, although the blood side of the system may include more or less components than discussed, the described sterilization procedure is equally applicable. Accordingly, the invention is not limited except as by the appended claims.