Multiple fluid source isolation, metering and alarm system and method

An apparatus for monitoring the amount of fluid flow from replacement fluid containers into a disposable flow line for use in plasmapheresis, said apparatus comprising:

• at least one replacement fluid container of limited capacity;
• a replacement fluid weighing bag;
• an input fluid flow line connected at one end to the exit from the container and at the other end to a replacement fluid weighing bag;
• an output fluid flow line connected at one end to the exit from the weighing bag and at the other end to a disposable plasmapheresis fluid flow system for withdrawing whole blood from a subject, separating out and collecting a first blood fraction therefrom and for reinfusing into the subject a mixture of replacement fluid and the remaining blood fraction;
• weighing means disposed for weighing the fluid contents of the weighing bag;
• alarm means connected to the weighing means for initiating an alarm signal when the weight of fluid in the weighing bag drops below a preselected warning amount;
• and
• control means connected to the weighing means for controlling flow of replacement fluid into and out of the weighing bag.

A plasma exchange system for separating blood received from a subject into constituents and infusing the subject with a first blood constituent and a replacement fluid, comprising:

• a separator for separating first and second blood constituents from whole blood;
• an attachment means for continuously withdrawing whole blood from a subject and supplying the blood to the separator;
• means for introducing anticoagulant to the whole blood withdrawn from the subject;
• an attachment means for continuously reinfusing the subject with the first blood constituent and a replacement fluid;
• a fluid replacement supply source;
• flow means including the withdrawal attachment means for flowing the whole blood and the anticoagulant to the separator and means including the reinfusion attachment means for receiving the first blood constituent from the separator and the replacement fluid from the replacement fluid source and for flowing the first blood constituent and the replacement fluid to the subject;
• control means in communication with the fluid replacement supply source for monitoring the amount of replacement fluid flowed to the subject from the fluid replacement supply source and for initiating a warning alarm when the supply source approaches empty;
• and wherein the control means comprises a weighing bag and attached weighing means interposed between the fluid replacement supply source and the flow means for sequentially receiving and weighing isolated amounts of replacement fluid passing from the supply source to the flow means.

A method of monitoring fluid flow from one or more containers having a limited fluid source into a fluid flow system so as to prevent air from an empty container entering the flow system, said method comprising:

• (1) flowing a first isolated amount of fluid from at least one of said fluid sources into a weighing bag;
• (2) weighing the fluid in the weighing bag;
• (3) controlling the flow of fluid from the fluid source such that fluid is flowed into the weighing bag when the weight of fluid in the bag has dropped below a preselected lower working limit and fluid flow into the weighing bag is stopped when the weight of fluid in the weighing bag rises above a preselected upper working limit;
• and
• (4) initiating flow from the weighing bag into the flow system until the weight of fluid falls below the lower working limit.

A method of monitoring fluid flow from replacement fluid sources into a disposable non-invasive fluid path used for plasmapheresis so as to prevent air from an empty replacement fluid source entering the flow path, said method comprising:

• (1) flowing a first isolated amount of fluid from at least one of said replacement fluid sources into a weighing bag;
• (2) weighing the weighing bag;
• (3) isolating the weighing bag from flow disturbances during weighing;
• (4) continuously flowing fluid from the weighing bag into the flow path while maintaining the amount of fluid in the weighing bag between upper and lower working limits by replenishing the weighing bag from the fluid source fill.