Non-invasive, Continuous Venous Oxygen Saturation and Oxygen Extraction Estimation from the Internal Jugular Vein.

Venous blood oxygen saturation (SvO2) measurements are critical for monitoring oxygen use. Currently, accurate SvO2 measurement requires invasive blood sampling. Conventional peripheral pulse oximetry techniques cannot measure SvO2 because peripheral veins are not pulsatile. This study explores the potential for non-invasive SvO2 estimation using internal jugular vein (IJV) pulsations detected by a flexible sensor array, to thus exploit standard pulse oximetry. A prototype sensor was developed to detect pulsatile signals from the carotid artery and IJV on the right-hand side of the neck. The sensor's performance was evaluated in 6 healthy adult subjects with arterial oxygen saturation (SaO2) measured using a commercial pulse oximeter and SvO2 estimated using the detected IJV pulse and breathing modulations. These estimates were combined to determine the subjects' cerebral oxygen extraction ratio (O₂ER). The sensor reliably detected pulsations in both upright and supine positions, with an average SvO2 of 65.70-80.91% with standard deviations of 1.67% and 4.26% for the IJV pulse and breathing modulations respectively, corresponding to an O2ER of 0.18-0.33 (±0.03). Differences in IJV pulse and breathing modulation estimations, as well as between upright and supine positions, are likely due to the influence of crosstalk between the carotid artery and IJV. The proof-of-concept sensor demonstrated the ability to continuously and non-invasively monitor SvO2 and O₂ER, producing estimates within expected literature ranges. Further validation with a larger cohort and comparison to blood gas analysis is necessary to confirm the sensor's accuracy, along with methods to mitigate crosstalk between arteries and veins.Clinical Relevance- This paper demonstrates the feasibility of a non-invasive sensor for simultaneously measuring arterial and venous oxygen saturations, enabling reliable and continuous estimation of oxygen extraction ratio to support clinical diagnosis and monitoring of critically ill patients.