Extracorporeal blood processing methods with return-flow alarm

1. A method for controlling flow rate of return of fluid to a fluid source in a fluid separation process wherein components have been separated from said fluid, said method comprising:

specifying a system return-flow alarm-triggering pressure, and when pressure of said return flow in the system is higher than or equal to said specified pressure, triggering a return-flow alarm wherein said specified system return flow alarm-triggering pressure is used to calculate a specified sensor pressure which triggers said return-flow alarm by modifying the specified sensor pressure in the system using the specified system return-flow alarm-triggering pressure and selected system parameters and wherein said system is a single-needle blood apheresis system, and said selected system parameters include the flow rate in the inlet tubing line, the hematocrit in the inlet tubing line, the flow rate in the needle, and the hematocrit in the needle.

2. The method of claim 1 wherein said return-flow alarm comprises stopping of said return fluid.

3. The method of claim 2 wherein said return-flow alarm comprises sounding an audible alarm and/or displaying a visible alarm.

4. The method of claim 2 wherein said specified system return-flow alarm-triggering pressure is between about 100 and about 310 mmHg.

5. The method of claim 1 wherein the specified sensor pressure that triggers the return-flow alarm condition is calculated using the formula:

Specified Sensor Pressure=Config−50−0.3309 *Q IN /(1 −H IN )−0.3026 *Q N /(1 −H N )

wherein Config is a configuration-specified system pressure (mmHg), Q IN is the flow rate in the inlet tubing line (ml/min), H IN is the hematocrit in the inlet tubing line, Q N is the flow rate in the needle (ml/min), and H N is the hematocrit in the needle.