Abstract:
Fluid processing systems and methods make use of a replenishable source containing a volume of a processing fluid that is dispensed during a processing period. A processor serves to sequentially pause and resume the processing period. The processor records weight values of the source at commencement of the processing period; upon pauses in the processing period; and upon resumptions of the processing period. At termination of the processing period, the processor generates a total volume value of processing fluid dispensed from the source during the processing period, which takes into account replenishment of the processing fluid when the processing period is paused. The systems and methods can be integrated into blood processing circuits to monitor the introduction of anticoagulant.

Description:
FIELD OF THE INVENTION 
     The invention generally relates to fluid processing systems and methods. More particularly, the invention relates to blood processing systems and methods. 
     BACKGROUND OF THE INVENTION 
     Certain on-line blood collection procedures entail the processing of relatively large volumes of whole blood. This, in turn, requires the introduction of relatively large volumes of anticoagulant to the whole blood during processing period. It is important to accurately monitor the total volume of anticoagulant used during the procedure. This task becomes complicated when the operator is called upon to periodically pause the procedure to replenish the anticoagulant supply. 
     SUMMARY OF THE INVENTION 
     The invention provides systems and methods for keeping accurate track of a total fluid volume administered from a fluid source that can be periodically replenished during a fluid processing procedure. 
     One aspect of the invention provides fluid processing systems and methods that make use of a replenishable source containing a volume of a processing fluid. The systems and methods include a circuit to dispense the processing fluid from the source during a processing period. A weigh sensor is coupled to the source and operates to sense weight of the source. Knowing the density of the processing fluid, the weight translates to volume of processing fluid present in the source. 
     The systems and methods further include a processor coupled to the weigh sensor. The processor operates in response to commands to sequentially pause and resume the processing period. The processor includes a counting function that operates in a series of processing steps. The processing steps (i) record a current weight value of the source at commencement of the processing period; (ii) register a first subsequent weight value (Wt 1 ) of the source upon pause in the processing period; (iii) register a second subsequent weight value (Wt 2 ) of the source upon resumption of the processing period following the pause; (iv) generate an updated current weight value upon resumption of the processing period by adding to the current weight value the difference between Wt 2  and Wt 1 ; (v) register a final weight value of the source at termination of the processing period; and (vi) generate a total volume value of processing fluid dispensed from the source during the processing period, by subtracting the final weight value from the updated weight value. Due to the processing steps followed, the total volume value will take into account replenishment of the processing fluid when the processing period is paused. 
     Another aspect of the invention integrates the fluid processing systems and methods just described into blood processing systems and methods. According to this aspect of the invention, the processing fluid is introduced into a blood processing circuit. In one embodiment, the blood processing circuit separates blood into component parts. In this embodiment, the processing fluid comprises an anticoagulant solution that is added to the blood during processing. 
    
    
     Features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a fluid processing system that incorporates feature of the invention. 
     FIG. 2 is a flow chart showing a fluid processing method that incorporates features of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an extra-corporeal blood processing system  10 . The system  10  includes a device  12  in which whole blood drawn from a donor  14  is separated into its principal component parts, i.e., red blood cells, platelets, and plasma. In certain, more specialized procedures, other less numerous component species, such as mononuclear cells, can be harvested using the device  12 . 
     The device  12  can take various forms. In the illustrated embodiment, the device  12  takes the form of a centrifuge. 
     An inlet line  16  draws whole blood from the donor  14  and conveys it (by operation of an inlet pump P 1 ) into the centrifuge  12  for processing. An outlet line  18  typically returns selected blood components, e.g., red blood cells and at least some of the plasma, to the donor  14  either continuously or in batches. One or more collection lines  20  convey the components targeted for collection to appropriate storage containers  22 . 
     Further details concerning systems and methods for processing blood on-line in this manner, either continuously or in a series of draw and return cycles, are well known and are not material to the invention. Representative systems are disclosed, e.g., in U.S. Pat. No. 5,370,802; U.S. Pat. No. 5,676,841; and U.S. Pat. No. 5,980,760, which are incorporated herein by reference. 
     Various processing fluids are introduced during a typical blood separation process. For example, saline is typically added to prime and flush the system. Saline can also be introduced as a replacement fluid. 
     As FIG. 1 show, an anticoagulant solution  24 , e.g., acid-citrate-dextrose (ACD), is also metered by a pump P 2  from a source  26  into the whole blood inlet line  16  throughout the procedure, to prevent blood coagulation. The source  26  containing the anticoagulant solution  24  is typically a flexible bag, which is typically suspended on a hook  28  near the centrifuge  12 . 
     It is important to account for the volume of anticoagulant solution  24  introduced during a given procedure. For this purpose, a weigh scale  30  monitors the weight of the source bag  26 . Knowing the density of the anticoagulant solution  24  (which, for ACD, is approximately 1 g/ml), the weight of the anticoagulant solution  24  can be translated to volume of anticoagulant solution  24 . Changes in the sensed weight can thereby be translated into volume of anticoagulant solution  24  delivered. 
     Relatively large volumes of whole blood are required to be processed during certain blood collection procedures; for example, in the collection of less numerous species of mononuclear cells. During these procedures, the overall volume of anticoagulant solution  24  required to be added can exceed the volume of anticoagulant solution  24  contained in a given source bag  26  (which is typically about 500 ml). In this circumstance, the operator needs to replenish the anticoagulant solution source  26 , by pausing the procedure and exchanging an empty or near empty bag  26  with a full bag  26 . In this way, the supply of anticoagulant solution  24  is sustained during the procedure. It is desirable to maintain an accurate account of the total volume of anticoagulant solution  24  introduced in this dynamic environment, regardless of how many source bags  26  are used or exchanged during a given procedure. 
     According to the invention, the system  10  includes a processor  32  coupled to the weigh scale  30 . The processor  32  includes a weight function  34  that monitors the weight of the anticoagulant solution source bag  26 . The weight function  34  compares the monitored weight to a set threshold weight, and generates an EMPTY source signal  36  when the monitored weight falls below the set threshold (e.g., 100 ml). The EMPTY source signal pauses the blood processing procedure to prompt the operator to replenish the anticoagulant solution bag  26 . The operator can also manually pause the procedure when desired for this or another reason, by using an appropriate input device  38  coupled to the processor  32 . The operator can manually resume the procedure using the device  38  or another suitable input. 
     The processor  32  also includes a counting function  40  that accumulates the changes in weight of the one or more anticoagulant solution source bags  26  used during a procedure, to derive the total volume of anticoagulant solution  24  used, designated ACD(Total Vol). 
     At the outset of a given blood processing procedure (see also FIG.  2 ), the weight function  34  registers the weight of the anticoagulant solution  24  source bag  26 . The counting function  40  records this value as ACD(Initial). The weight function  34  continues to monitor the weight of the anticoagulant solution source bag  26  and compare it to the EMPTY source threshold. 
     If the operator manually pauses the procedure (using the device  38 ), or if the weight function  34  generates an EMPTY source signal  36  to pause the procedure, the counting function  40  registers the current weight of the anticoagulant solution source bag  26  and records this value as ACD(in). When the procedure resumes, the counting function  40  again registers the current weight of the anticoagulant solution source bag  26  and records this value as ACD(out). 
     Upon resumption of a paused procedure, the a counting function  40  updates ACD(Initial) as follows: 
     
       
           ACD (Initial) New   =ACD (Initial)Old +ACD (Diff) 
       
     
     where: 
     
       
           ACD (Diff)= ACD (out)− ACD (in) 
       
     
     When the anticoagulant solution source bag  26  is not exchanged during a given pause in the procedure, ACD(Diff) is zero (this is because no anticoagulant solution  24  is introduced when the system  10  is paused, as no additional whole blood is being drawn). However, when the anticoagulant solution source bag  26  is exchanged during a given pause in the procedure, ACD(Diff) will reflect the difference in weight between the previous source bag  26  and the new source bag  26 . 
     The counting function  40  updates ACD(Initial) in this manner each time the procedure is paused, either manually or by generation of the EMPTY source signal  36 , and then resumed. 
     The processor  32  will generate a PROCEDURE WRAP-UP command when the criteria governing the particular blood collection procedure are met (e.g., a targeted volume of whole blood has been processed, or a targeted volume of blood component has been collected). The operator, too, can manually generate a PROCEDURE WRAP-UP command using an appropriate input device. In response to the PROCEDURE WRAP-UP command, the counting function  40  registers the current weight of the anticoagulant solution source bag  26  and records this value as ACD(Final). 
     The counting function  40  then derives the total volume of anticoagulant solution  24  used—ACD(Total Vol)—as follows: 
     
       
           ACD (TotalVol)= ACD (Initial) New   −ACD (Final) 
       
     
     where ACD(Initial) New  is the most current updated value of ACD(Initial). 
     EXAMPLE 
     At the outset of a blood processing procedure, the operator hangs a full anticoagulant solution source bag  26  (e.g., 500 ml) on the hook  28 . The weight function  34  registers the weight of the source bag  26  as 500 g (i.e., 500 ml). The counting function  40  records ACD(Initial)=500. 
     The operator causes a first manual pause of the procedure. The weight function  34  now registers the weight of the source bag  26  as 400 g (i.e., 400 ml), which indicates that 100 ml of anticoagulant solution  24  have been introduced since the beginning of the procedure. The counting function  40  records ACD(in)=400. During this pause, the operator does not exchange the anticoagulant solution source bag  26 . When the procedure is resumed, the weight function  34  still registers the weight of the source bag  26  as 400 g (i.e., 400 ml). The counting function  40  records ACD(out)=400, and generates ACD(Diff)=0. The counting function  40  updates ACD(Initial) New =500 (i.e., 500 plus 0). 
     The operator causes a second manual pause of the procedure. The weight function  34  now registers the weight of the source bag  26  as 300 g (i.e., 300 ml), which indicates that an additional 100 ml of anticoagulant solution  24  have been introduced between the first and second pauses. The counting function  40  records ACD(in)=300. Again, during this pause, the operator does not exchange the anticoagulant solution  24  source bag  26 . When the procedure is resumed, the weight function  34  still registers the weight of the source bag  26  as 300 g (i.e., 300 ml). The counting function  40  records ACD(out)=300, and generates ACD(Diff)=0. The counting function  40  updates ACD(Initial) New =500 (i.e., 500 plus 0). 
     An EMPTY source signal  36  causes a third pause in the procedure, when the weight function  34  registers the contents of the source bag  26  as being 100 ml, i.e., at the 100 ml threshold. The counting function  40  records ACD(in)=100, which also indicates that 200 ml of anticoagulant have been introduced between the second and third pauses. In this pause, the operator is prompted to exchange the near empty anticoagulant solution source bag  26 , replacing it with a new source bag  26  (containing, e.g., 500 ml of anticoagulant solution  24 ). 
     The weight function  34  registers the weight of the new source bag  26  as 500 g (i.e., 500 ml). When the procedure is resumed, the counting function  40  records ACD(out)=500, and generates ACD(Diff)=400. The counting function  40  updates ACD(Initial) New =900 (i.e., 500 plus 400). 
     In time, the processor  32  will generate a PROCEDURE WRAP-UP command, or the command is otherwise generated by the operator. The weight function  34  registers the weight of the source bag  26  as 250 g (i.e., 250 ml). This indicates that 250 ml of additional anticoagulant solution  24  have been introduced between the third pause and the PROCEDURE WRAP-UP command. The counting function  40  registers the current weight of the anticoagulant solution  24  source bag  26  and records this value as ACD(Final)=250. The counting function  40  then derives ACD(Total Vol)=650 ml (i.e., 900-250). 
     As the Example demonstrates, the value of ACD(Total Vol) derived in this fashion by the counting function  40  in effect preserves and sums up the incremental volumes of anticoagulant solution  24  introduced between procedure start-up and the first pause (100 ml); between the first pause and the second pause (100 ml); between the second pause and the third pause (200 ml); and between the third pause and the PROCEDURE WRAP-UP command (250 ml). Despite the exchange of the anticoagulant source bag  26  once or several times while processing is paused, the counting function  40  continuously preserves and carries forward all incremental weight changes, which translate to incremental fluid volumes. 
     The invention has been described in the context of blood processing, because it is well suited for use in this environment. Still, it should be appreciated that use of the invention is not limited to blood processing. The features of the invention can be used in association with any system in which it is desired to track the volume of processing fluid used during a given processing procedure. 
     The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. 
     The features of the invention are set forth in the following claims.