Monitoring and Detecting Empty Fluid Containers in A Blood Processing System

Abstract

Systems and methods for determining when a fluid supply container of a blood processing apparatus becomes empty. The system uses a scale to monitor and detect when a fluid supply container is empty based on the rate of change of the container weight, and a controller receives a signal from the scale and controls the operation of a pump to stop pumping when the fluid supply container is empty.

1 . A system for determining when a fluid supply container of a blood processing apparatus becomes empty, the system comprising:
 a first fluid supply container;   a first scale for measuring the weight of the first fluid supply container and providing a first output signal indicative of the measured weight of the first fluid supply container;   a pump for pumping fluid from the first fluid supply container;   a controller for receiving the first output signal from the first scale, the controller determining the rate of change in weight of the first fluid supply container, the controller determining that the first fluid supply container is empty when the rate of change becomes substantially zero.   
   
   
       2 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 1  wherein the controller causes the pump to cease pumping when the controller determines that the first fluid supply container is empty. 
   
   
       3 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 1  further comprising:
 a first valve in fluid communication between the first fluid supply container and the pump, the first valve normally in an open condition;   a second fluid supply container;   a second scale for measuring the weight of the second fluid supply container and providing a second output signal indicative of the measured weight of the second fluid supply container;   a second valve in fluid communication between the second fluid supply container and the pump, the second valve normally in a closed condition;   the controller causing the pump to cease pumping upon determining that the first fluid supply container is empty, causing the second valve to move to an open condition and causing the first valve to move to a closed condition, the controller then activating the pump to begin pumping fluid from the second fluid supply container.   
   
   
       4 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 3  wherein the pump operates in a first direction when pumping fluid from the first fluid supply container and the pump operates in a second direction when pumping fluid from the second fluid supply container. 
   
   
       5 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 3  wherein the controller receives the second output signal from the second scale and determines the rate of change in weight of the second fluid supply container, the controller determining that the second fluid supply container is empty when the rate of change becomes substantially zero. 
   
   
       6 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 5  wherein the controller causes the pump to cease pumping when the controller determines that the second fluid supply container is empty. 
   
   
       7 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 1  wherein the first scale measures the weight of the first fluid supply container over pump-unit intervals and compares weight change measured by the first scale for each pump-unit interval to a volume pumped during the pump-unit intervals. 
   
   
       8 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 7  wherein if the ratio of the weight change to the volume pumped is less than about 0.5 for two consecutive pump-unit intervals then the controller indicates that the first fluid supply container is empty. 
   
   
       9 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 8  wherein if the controller indicates that the first fluid supply container is empty then the controller causes the pump to stop pumping. 
   
   
       10 . A system for determining when a fluid supply container of a blood processing apparatus becomes empty, the system comprising:
 a first fluid supply container;   a first scale for measuring the weight of the first fluid supply container and providing a first output signal indicative of the measured weight of the first fluid supply container;   a pump for pumping fluid from the first fluid supply container;   a controller for receiving the first output signal from the first scale, the controller determining the rate of change in weight of the first fluid supply container, means for determining the rate of fluid flow from the pump;   the controller determining that the first fluid supply container is empty when the ratio of the rate of change in weight of the first fluid supply container to the rate of fluid flow from the pump is less than about 0.5.   
   
   
       11 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 10  wherein the controller causes the pump to cease pumping when the controller determines that the first fluid supply container is empty. 
   
   
       12 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 10  further comprising:
 a first valve in fluid communication between the first fluid supply container and the pump, the first valve normally in an open condition;   a second fluid supply container;   a second scale for measuring the weight of the second fluid supply container and providing a second output signal indicative of the measured weight of the second fluid supply container;   a second valve in fluid communication between the second fluid supply container and the pump, the second valve normally in a closed condition;   the controller causing the pump to cease pumping upon determining that the first fluid supply container is empty, causing the second valve to move to an open condition and causing the first valve to move to a closed condition, the controller then activating the pump to begin pumping fluid from the second fluid supply container.   
   
   
       13 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 12  wherein the pump operates in a first direction when pumping fluid from the first fluid supply container and the pump operates in a second direction when pumping fluid from the second fluid supply container. 
   
   
       14 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 12  wherein the controller receives the second output signal from the second scale and determines the rate of change in weight of the second fluid supply container, the controller determining that the second fluid supply container is empty when the rate of change becomes substantially zero. 
   
   
       15 . The system for determining when a fluid supply container of a blood processing apparatus becomes empty in accordance with  claim 14  wherein the controller causes the pump to cease pumping when the controller determines that the second fluid supply container is empty. 
   
   
       16 . A method of determining when a fluid supply container of a blood processing system becomes empty, the method comprising:
 providing a first fluid supply container adapted to be in communication with a patient when a first valve is in an open condition;   measuring the weight of the first fluid supply container while it is being emptied by a pump that is pumping fluid from the first fluid supply container into the patient;   determining a rate of change of the weight of the first fluid supply container;   determining when the rate of change of the weight of the first fluid supply container becomes substantially zero; and   stopping the operation of the pump when the rate of change of the weight of the first fluid supply container is determined to be substantially zero.   
   
   
       17 . The method of  claim 16  wherein when upon determining that the rate of change of the weight of the first fluid supply container is substantially zero further moving the first valve to a closed condition. 
   
   
       18 . The method of  claim 17  further comprising:
 providing a second fluid supply container adapted to be in communication with a patient when a second valve is in an open condition; and   moving the second valve to an open condition upon determining that the rate of change of the weight of the first fluid supply container is substantially zero.   
   
   
       19 . The method of  claim 17  further comprising:
 measuring the weight of the second fluid supply container while it is being emptied by a pump that is pumping fluid from the second fluid supply container into the patient;   determining a rate of change of the weight of the second fluid supply container;   determining when the rate of change of the weight of the second fluid supply container becomes substantially zero; and   stopping the operation of the pump when the rate of change of the weight of the second fluid supply container is determined to be substantially zero.   
   
   
       20 . The method of  claim 19  wherein when upon determining that the rate of change of the weight of the second fluid supply container is substantially zero further moving the second valve to a closed condition.