[Comparison of a reflectance sensor and a transmittance sensor for pulse oximetry]

We have investigated a new optical reflectance sensor for pulse oximetry in 70 patients under general anesthesia. The reflectance sensor was applied to the forehead, the dorsal manus, the inguinal region, and the anterior crus of the patients. We could obtain a reliable SpO2 value when the reflectance sensor was applied on both forehead and anterior crus. It was difficult to obtain a reliable SpO2 value with the reflectance sensor without using an additional attachment especially for children. We compared the SpO2 value using the reflectance sensor attached to the forehead, with the SpO2 value obtained by the transmittance sensor attached to a finger or an ear lobe, in 7 volunteers who held the breath as long as possible. When we attached the probes on both ear lobe and forehead, the response time was faster, but and the maximum changing value was much larger, compared with those on the finger. We could obtain a reliable and stable SpO2 value using the reflectance sensor, when it was placed on the appropriate site as the forehead or the anterior crus.