Controller for ultrafiltration blood circuit which prevents hypotension by monitoring osmotic pressure in blood

A method of controlling an extracorporeal blood circuit comprising:

• withdrawing blood from a withdrawal blood vessel in a patient into the extracorporeal circuit;
• filtering fluids from blood flowing through the circuit at a controlled filtration rate;
• measuring an osmotic pressure difference between blood and filtrate wherein the filtrate flows through a permeable membrane in the circuit;
• and
• reducing a flow rate of the filtrate if the measured osmotic pressure exceeds a threshold osmotic pressure level.

A system for treating blood from a patient comprising:

• an extracorporeal circuit having a blood passage including a blood withdrawal tube, a filter and an infusion tube,
• said filter having filter blood passage in fluid communication with the withdrawal tube, a blood outlet in fluid communication with the infusion tube, a filter membrane in fluid communication with the blood passage, a filter output section on a side of the membrane opposite to the blood passage, and a filtrate output line in fluid communication with the filter output section;
• a pressure sensor coupled to said extracorporeal circuit and generating a pressure signal indicative of an osmotic pressure difference across the filter membrane and between blood in the blood passage and filtrate in the filter output section;
• a filtrate pump coupled to the filtrate output line and adapted to draw filtrate fluid from the filter at a controlled filtration rate, and
• a filtrate pump controller regulating the controlled filtration rate based on the pressure signal indicative of the osmotic pressure across the membrane