SIMPLIFIED DUAL-LUMEN CATHETER DESIGN FOR SIMULTANEOUS POTENTIOMETRIC MONITORING OF CARBON-DIOXIDE AND PH

A novel dual-lumen catheter electrode design suitable for the simultaneous measurement of P-CO2 (partial pressure of carbon dioxide) and pH in flowing blood is described. The probe is fabricated from a single segment of dual-lumen silicone rubber or polyurethane tubing that is impregnated with the proton ionophore tridodecylamine. The impregnation step imparts H+ permselectivity to both inner and outer walls of the tubing. By filling each lumen with a suitable buffer/electrolyte solution and Ag/AgCl reference electrode wire, simultaneous potentiometric detection of both P-CO2 and pH is achieved. Careful optimization of incorporated proton carrier (tridodecylamine), plasticizer (o-nitrophenyl octyl ether), and lipophilic counteranion sites (tetrakis[3,5-bis(trifluoromethyl)phenyl] berate) within the tubing walls yields catheter electrodes with resistance values of 10-20 M Omega and relatively high stability in flowing blood. Results from continuous measurements of P-CO2 and pH during long-term 30-65-h blood loop experiments demonstrate that, after an initial conditioning period, the catheter exhibits low drift rates (P-CO2, 4.7 +/- 1.7 mV/30 h; pH, 1.4 +/- 0.5 mV/30 h) and yields continuously measured values in good agreement with those obtained on discrete samples with a commercial blood gas analyzer (P-CO2, r(2) = 0.997; pH, r(2) = 0.915). In vivo evaluation of the catheter sensors, performed by implanting silicone rubber dual-lumen probes in the arteries of anesthetized dogs, indicates that the proposed catheter design can closely follow P-CO2/pH changes induced in the animals during 6-13 h of continuous monitoring.