In-line optical monitoring of oxygen saturation and hematocrit for cardiopulmonary bypass: Adjustment-free and bloodless calibration

Abstract Background and objective: This article describes a new sensor for monitoring oxygen saturation (sO2) and hematocrit (Hct) of blood during cardiopulmonary bypass. The sensor is calibrated without blood and does not need to be adjusted by laboratory blood parameter analysis when in operation. Materials and methods: The optical sensor presented here uses near-infrared spatially resolved reflectance spectroscopy. The primary calibration model for a master sensor is derived from the measurement of circulating human blood from a number of different patients with references taken from standard laboratory analysis of blood parameters. Transfer of the calibration model from the master sensor to new sensors is performed by measurement of an optical standard made of artificial material with defined and controlled optical properties. Results: The predicted values of sO2 and Hct exhibit an accuracy of 1.2% for sO2 and 1.1% for Hct compared to the reference values. The optical standard yields optical signals similar to the measurement of blood. After calibration transfer, the mean accuracy of the measurement of 10 sensors is 1.3% for sO2 and 1.2% for Hct. Conclusion: A new sensor with high degree of accuracy for sO2 and Hct compared to commercially available sensor systems is presented. The calibration transfer using optical standards gives a comparable degree of accuracy. The method could be adapted for use with existing sensors. No animal blood needs to be used in calibration process anymore.