A Comparison of Mixed and Central Venous Oxygen Saturation in Patients during and after Cardiac Surgery

Monitoring of mixed venous oxygen saturation (Sv̄O 2 ) allows assessment of the global balance between oxygen supply and demand. Sv̄O 2 measurement requires the insertion of a pulmonary artery catheter (PAC) whereas central venous oxygen saturation (ScvO 2 ) monitoring only requires a central venous catheter. The aim of this study was to assess how continuous measurements of ScvO 2 relate to simultaneous measurements of Sv̄O 2 during and after cardiac surgery. Continuous Sv̄O 2 and ScvO 2 measurements in 15 patients undergoing elective cardiac surgery were recorded each minute for 24 hours. Bland-Altman analysis of 9,382 paired data points for Sv̄O 2 and ScvO 2 revealed a mean bias of 4.4% (95% Cl +22.3, −13.6%). Considerable inter- and intra-individual variability was noted. Based on these data and previous studies, ScvO 2 and Sv̄O 2 are not interchangeable variables.