Continuous analysis in extracorporeally circulating blood - A rat model applying flow-through ion-selective electrodes for the measurement of Ca2+, K+, Na+ and pH

A rat model is introduced which enables investigations in anticoagulated bl ood with continuous measurements by a flow-through electrode system. In the present study, a potentiometric ion-selective electrode (ISE)-system was u sed for measuring Ca2+, K+, Na+ and pH in rats. The setup was adjusted to a n extracorporeal blood-volume of 0.750 mi. This permits indirect measuremen ts of the analytes via a dialysis membrane, with electrical separation of t he ISE's and the animal. The flow-rates of blood and dialysis-solution were adjusted in such a way that water diffusing from the aqueous dialysis solu tion into the blood, across the dialysis membrane, does not alter the haema tocrit. Polyethyleneglycol-hirudin was used for anticoagulation, since it w as superior to heparin. The assembly enables continuous measurements in the living anaesthetized rat over a time period of at least 3 hours.