Non-invasive capnodynamic mixed venous oxygen saturation during major changes in oxygen delivery

Mixed venous oxygen saturation (SvO(2)) is an important variable in anesthesia and intensive care but currently requires pulmonary artery catheterization. Recently, non-invasive determination of SvO(2) (Capno-SvO(2)) using capnodynamics has shown good agreement against CO-oximetry in an animal model of modest hemodynamic changes. The purpose of the current study was to validate Capno-SvO(2) against CO-oximetry during major alterations in oxygen delivery. Furthermore, evaluating fiberoptic SvO(2) for its response to the same challenges. Eleven mechanically ventilated pigs were exposed to oxygen delivery changes: increased inhaled oxygen concentration, hemorrhage, crystalloid and blood transfusion, preload reduction and dobutamine infusion. Capno-SvO(2) and fiberoptic SvO(2) recordings were made in parallel with CO-oximetry. Respiratory quotient, needed for capnodynamic SvO(2), was measured by analysis of mixed expired gases. Agreement of absolute values between CO-oximetry and Capno-SvO(2) and fiberoptic SvO(2) respectively, was assessed using Bland–Altman plots. Ability of Capno- SvO(2) and fiberoptic SvO(2) to detect change compared to CO-oximetry was assessed using concordance analysis. The interventions caused significant hemodynamic variations. Bias between Capno-SvO(2) and CO-oximetry was + 3% points (95% limits of agreements – 7 to + 13). Bias between fiberoptic SvO(2) and CO-oximetry was + 1% point, (95% limits of agreements − 7 to + 9). Concordance rate for Capno-SvO(2) and fiberoptic SvO(2) vs. CO-oximetry was 98% and 93%, respectively. Capno-SvO(2) generates absolute values close to CO-oximetry. The performance of Capno-SvO(2) vs. CO-oximetry was comparable to the performance of fiberoptic SvO(2) vs. CO-oximetry. Capno-SvO(2) appears to be a promising tool for non-invasive SvO(2) monitoring. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10877-021-00762-5.