Preterm birth requires technologies for supporting immature organ systems on one hand while minimizing technology-induced injury on the other that may contribute to long-term adverse outcomes. Specific problems of this kind are extremes in arterial partial pressure of oxygen and carbon dioxide. A variety of pathological conditions are known to result from both hypoxemia and hyperoxia. However, current understanding is that the range for acceptable paO2 is quite narrow. Similarly, hypocarbia or hypercarbia can result in brain or ocular pathology. The optimal range of paCO2 has not been established, but avoiding extremes is critical for survival. Thus, arterial blood gas (ABG) measurements are indispensable for respiratory management in the neonatal intensive care unit (NICU). But because these require the withdrawal of blood, they can lead to complications such as infection, thrombus formation, bleeding, and pain. Furthermore, ABGs provide only intermittent information concerning dynamic changes in blood gases. To address some of these concerns, transcutaneous monitors for O2 (tcpO2) and CO2 (tcpCO2) using electrochemical sensors have been used. However, these electrodes have many disadvantages: (1) They suffer from calibration drift due to depletion of the electrolyte; (2) lack of sensitivity at low O2 due to consumption of O2 by the Clark electrode; (3) potential membrane failure; (4) use of adhesives to maintain direct skin contact; (5) possible burns from raising skin temperature to 43C; (6) time-consuming due to large transcutaneous mass transfer resistance and equilibrium-based measurements. The goal of this project is to develop a combined tcpO2/tcpCO2 monitor for the neonate based on the optical sensing of O2 and CO2 that is free from the drawbacks mentioned above. We propose to use highly sensitive noninvasive optical sensors in a unique design to achieve our objective. A collaborative team of scientists, engineers and clinicians has been assembled. Phase II will address the further clinical testing of the device.