Combining transcutaneous blood gas measurement and pulse oximetry.

We are describing the preliminary results of tests performed in adult volunteers and in adult patients during and after general anesthesia with a miniaturized single sensor combining the continuous and non-invasive measurement of oxygen saturaiton by pulse oximetry (SpO2) and transcutaneous PCO2 (OxiCarbo sensor). The sensor is heated to 42 degrees C to arterialize the cutaneous tissue and is applied at the ear lobe with a special low-pressure clip. The results indicate a good agreement between ear lobe PCO2 and arterial PCO2 in the range 35 to 70 mmHg (10 patients, number of measurements 104, regression line TcPCO2 = 1.01 PaCO2 + 0.59 mmHg, bias 1.22 mmHg, SD 3.69 mmHg) and between ear lobe SpO2 and SaO2 (bias 0.44% with SD 0.77% in the range 80% to 100%, bias 1.39% with SD 1.43% in the range 60% to 80%). The ear lobe OxiCarbog sensor detects the SpO2 change 5 to 37 sec faster than a finger sensor and the PCO2 change 9 to 48 sec faster than a transcutaneous sensor fixed at the upper arm. Further improvements versus single sensors are a higher stability of the SpO2 signal and the possibility of performing long term SpO2 and PCO2 measurement at the ear lobe.