Diagram of the flow model. Pump C, representing the cardiac output, was set to draw 3 l/min from the 50 litre bucket of saline (bottom right). Some of this flow passed via the ECMO pump (E) through the membrane oxygenator (M) and then either recirculated through the ECMO circuit via the shunt pump (S) or returned to the bucket. There are two lithium sensors: A is in the ECMO circuit and B is in the patient circuit (in a real patient this would be equivalent to measuring the curve in the arterial blood).