Continuous blood gas and pH monitoring devices developed over the past 20 years have failed primarily due to lack of stability and the associated dependency on the clinical laboratory for calibration. Continuous electrolyte monitor developments, of particular importance for neonatal and infant monitoring applications, have not been attempted. The goal of this project is to develop a commercially viable continuous blood gas, pH, and electrolyte monitor which utilizes a self-calibration mechanism and existing sensor technology and can maintain levels of accuracy and reliability equal or superior to and independent of the clinical laboratory and is cost effective. Concept feasibility for monitoring by this principle as well as the supporting sensor technology for gases and ions has been established. What remains to be demonstrated is that a suitable membrane can be developed so that pH and electrolytes can also be monitored - simultaneously with blood gases. Therefore, this proposal is directed toward establishing that a gas and ion permeable membrane can be developed, having ion (and gas) diffusivities and resistance to protein fowling and clotting which meet the specification for the blood gas, pH and electrolyte monitor.