Is it possible for one of the motors to turn faster than it should and actulally pump more blood away from the patient than the machine is able to return back to that patient, what could cause this to happen?

veriturus,

The blood is pumped by a single pump in a closed circuit...what comes out has to go back in, unless there was a leak but you would know that because there would literally be a bloody mess.

Not sure if this is helpful but....The pump can be adjusted for different tubing sizes according to the diameter of the tubing. Make sure the correct setting is being used for the tubing you are using. For instance on the Fresenius 2008H, we normally use 8.0 and occasionally 6.5 for different procedures requiring different tubing size. The wrong setting can make the blood flow rate different then expected.

Thanks for the input, I'll check the tubes.