Monitoring changes in mixed venous oxygen saturation using photoplethysmography on the sternum – a proof of concept study

Mixed venous oxygen saturation (SvO 2 ) is a valuable indicator of the balance between oxygen delivery and consumption in the body. However, the invasiveness and risk of complications limit its use. This study aimed to test the feasibility of continuously monitoring variations in SvO 2 from photoplethysmography (PPG) measurements of sternal intramedullary oxygen saturation. In an animal model, including anesthetized pigs ( n = 15, mean 33.1 (SD 2.0) kg), alterations in SvO 2 were instituted by separate sessions: incremental decrease in arterial oxygen saturation using hypoxic gas mixtures (N 2 /air), and hemorrhage of 20% plus 20% of estimated blood volume. Estimations of non-invasive sternal oxygen saturation (nSsO 2 ) were derived from calibrating PPG measurements against SvO 2 sampled from the pulmonary artery. Individual linear correlations were found between SvO 2 and PPG measurements. nSsO 2 and SvO 2 co-varied, except in severe hypovolemia. A concordance rate between nSsO 2 and SvO 2 was determined to 87% (95% CI 79.1–95.0). In this study, we demonstrated linear correlations between SvO 2 and PPG-measurements on the sternum, enabling estimation of nSsO 2 , which trends with changes in SvO 2 . The results support further technical development of non-invasive monitoring of SvO 2 from sternal measurements. Graphical abstract Non-invasive sternal oxygen saturation (nSsO 2 ) is derived from photoplethysmographic measurements of sternal intramedullary blood flow (SQV), correlated against mixed venous oxygen saturation (SvO 2 ). The performance of nSsO 2 to detect changes in SvO 2 is subsequent analyzed with a concordance analysis.