Catheter-Type sensor for potentiometric monitoring of oxygen, pH and carbon dioxide

The fabrication and analytical performance of a catheter-type electrode suitable for potentiometric monitoring of P-o2, pH and P-co2 in flowing blood is described. The catheter electrode is based on impregnating a single segment of dual-lumen gas permeable silicone rubber tubing with the proton ionophore tridodecylamine to impart H+ permselectivity to both inner and outer walls of the tubing. One lumen is filled with an unbuffered bicarbonate solution and the other lumen is filled with a strong buffer. By inserting Ag/AgCl reference electrode wires in each lumen and a cobalt electrode in the buffered lumen, simultaneous potentiometric detection of P-o2, pH and P-co2 is achieved. The response of cobalt electrode to P-o2 arises from a steady-state mixed potential owing to slow oxidation of cobalt and simultaneous reduction of oxygen on the surface of the cobalt electrode. The response towards P-co2 is completely analogous to the response mechanism of a conventional Severinghaus P-co2 sensor (i.e., change in pH of the bicarbonate solution). Continuous measurements of P-o2, pH and P-co2 during 4-5 h blood pump studies using the catheter electrodes correlate well with conventional bench-top blood gas analyzer (P-o2: r(2) = 0.992; pH: r(2) = 0.940; P-co2: r(2) = 0.993). (C) 1998 Elsevier Science S.A. All rights reserved.