Near-infrared spectroscopy for estimating mixed venous oxygen saturation and cardiac output during off-pump coronary artery bypass grafting: a prospective observational study

Abstract To evaluate whether jugular venous NIRS (rSjvO₂) and baseline-calibrated cerebral NIRS (cal-rScO₂) can serve as surrogates for mixed venous oxygen saturation (SvO₂), and whether these inputs can support continuous cardiac output (CO) estimation during off-pump coronary artery bypass grafting (OPCAB). In this prospective observational study, 25 adults undergoing elective OPCAB were enrolled at a single tertiary center. NIRS sensors were placed over the left internal jugular vein (IJV) under ultrasound guidance and over the bilateral forehead. Pulmonary artery catheter measurements served as the reference for SvO₂ and thermodilution CO (CO TD ). Agreement was assessed using Bland–Altman analysis with linear mixed-effects modeling, and trending ability by error grid analysis. CO was estimated using a previously derived modified Fick equation. rSjvO₂ showed modest bias versus SvO₂ (2.0%) but wide limits of agreement (LoA, − 14.9 to 18.9%). Accuracy varied with jugular anatomy, with the lowest error at an IJV depth of 1.38 cm. Cal-rScO₂ showed better agreement (bias 0.8%; LoA, − 7.8 to 9.4%), excellent discrimination for SvO₂ <65% (AUC, 0.970), and good trending ability. In contrast, NIRS-based CO estimation showed significant proportional bias, 33.0% percentage error (95% CI, 27.4 to 41.5%), and poor trending ability. Cal-rScO₂ appears to be a useful surrogate for SvO₂ trending during OPCAB after simple one-point calibration. Jugular NIRS may be useful in selected patients, whereas NIRS-based CO estimation remained clinically insufficient. Trial registration: Clinical Research Information Service (CRIS), Republic of Korea (KCT0007918 November 18, 2022).