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

Abstract

Monitoring of mixed venous oxygen saturation (Sv̄O2) allows assessment of the global balance between oxygen supply and demand. Sv̄O2 measurement requires the insertion of a pulmonary artery catheter (PAC) whereas central venous oxygen saturation (ScvO2) monitoring only requires a central venous catheter. The aim of this study was to assess how continuous measurements of ScvO2 relate to simultaneous measurements of Sv̄O2 during and after cardiac surgery. Continuous Sv̄O2 and ScvO2 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 Sv̄O2 and ScvO2 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, ScvO2 and Sv̄O2 are not interchangeable variables.

Role of Central and Mixed Venous Oxygen Saturation Measurement in Perioperative Care

“…73 This lack of numerical equivalence has been demonstrated in various groups of critically ill patients, including those with cardiogenic, septic and hemorrhagic shock. 31,68 -70,76 -78 This has also been demonstrated in patients undergoing general anesthesia for cardiac 71,72,79 and noncardiac surgery. 69,80 Although trends in ScvO 2 may closely reflect those of SvO 2 , absolute values differ and the variables cannot be used interchangeably.…”

“…As the use of the pulmonary artery catheter declines, measurement of ScvO 2 is usually more convenient than SvO 2 , although ScvO 2 measurements cannot be cannot be used to calculate VO 2 or shunt fraction. 72…”