A blood processing system comprising: a blood separation device for separating whole blood into a red blood cell component and a plasma component; an inlet flowpath indirectly communicating with a patient, including a pump operable at a prescribed rate Q WB to convey whole blood from the patient having a whole blood volume V, a whole blood hematocrit value H T into the separation device; a return flowpath indirectly communicating with the patient, to convey fluid to the patient; a first outlet flowpath including a pump operable at a prescribed flow rate Q P to convey separated plasma from the separation device; a second outlet flowpath to convey separated red blood cells from the separation device; a source of replacement red blood cells having a hematocrit H T1 in fluid communication with the return flowpath; a third flowpath indirectly communicating with the patient, including a pump operable at a prescribed flow rate Q RF to convey replacement red blood cells to the patient; and a controller (24, 36) including a first stage operable to accept or derive input values relating to the patient condition and clinical objectives; a second stage operable to derive operating values for the for Q WB, Q P, and Q RF such that the clinical objectives are achieved simultaneously at the end of the procedure; and a third stage operable to maintain and or adjust these values in accordance with changing procedural conditions, characterized in that the second stage is operable to determine the parameters M and F as follows: M = 1 − ln FCR ln 1 + Δ V / V 0 Δ V ≠ 0 and F = H T 8 H T 0 FCR M M − 1 − 1 FCR M M − 1 − H TF H T 0 Δ V ≠ 0 F = H T 8 H T 0 Δ V = 0 and is then further operable to determine the operating flow rates as follows: Q RF = M F M − 1 Q WB, MAX Q P = F − 1 Q RF wherein FCR is the target post-procedure fraction of patient cells remaining, H TF is the target post-procedure hematocrit, H T8 is the hematocrit of the replacement fluid; ΔV is the target post-procedure patient fluid volume change; V 0 is the initial patient fluid volume; H T0 is the initial patient hematocrit; and Q WB, MAX is the maximum blood draw rate. a blood separation device for separating whole blood into a red blood cell component and a plasma component; an inlet flowpath indirectly communicating with a patient, including a pump operable at a prescribed rate Q WB to convey whole blood from the patient having a whole blood volume V, a whole blood hematocrit value H T into the separation device; a return flowpath indirectly communicating with the patient, to convey fluid to the patient; a first outlet flowpath including a pump operable at a prescribed flow rate Q P to convey separated plasma from the separation device; a second outlet flowpath to convey separated red blood cells from the separation device; a source of replacement red blood cells having a hematocrit H T1 in fluid communication with the return flowpath; a third flowpath indirectly communicating with the patient, including a pump operable at a prescribed flow rate Q RF to convey replacement red blood cells to the patient; and a controller (24, 36) including a first stage operable to accept or derive input values relating to the patient condition and clinical objectives; a second stage operable to derive operating values for the for Q WB, Q P, and Q RF such that the clinical objectives are achieved simultaneously at the end of the procedure; and a third stage operable to maintain and or adjust these values in accordance with changing procedural conditions, characterized in that the second stage is operable to determine the parameters M and F as follows: M = 1 − ln FCR ln 1 + Δ V / V 0 Δ V ≠ 0 and F = H T 8 H T 0 FCR M M − 1 − 1 FCR M M − 1 − H TF H T 0 Δ V ≠ 0 F = H T 8 H T 0 Δ V = 0 and is then further operable to determine the operating flow rates as follows: Q RF = M F M − 1 Q WB, MAX Q P = F − 1 Q RF wherein FCR is the target post-procedure fraction of patient cells remaining, H TF is the target post-procedure hematocrit, H T8 is the hematocrit of the replacement fluid; ΔV is the target post-procedure patient fluid volume change; V 0 is the initial patient fluid volume; H T0 is the initial patient hematocrit; and Q WB, MAX is the maximum blood draw rate.