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 PO2, pH and PCO2 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 PO2, pH and PCO2 is achieved. The response of cobalt electrode to PO2 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 PCO2 is completely analogous to the response mechanism of a conventional Severinghaus PCO2 sensor (i.e., change in pH of the bicarbonate solution). Continuous measurements of PO2, pH and PCO2 during 4-5 h blood pump studies using the catheter electrodes correlate well with conventional bench-top blood gas analyzer (PO2: r2 = 0.992; pH: r2 = 0.940; PCO2: r2 = 0.993.