Comparison of Central Venous to Mixed Venous Oxygen Saturation in Patients With Low Cardiac Index and Filling Pressures After Coronary Artery Surgery

Objective: To evaluate the correlation and agreement between mixed venous oxygen saturation (SvO2) and central venous oxygen saturation (ScvO2) in patients with low cardiac index and filling pressures after coronary artery surgery.Design: Prospective observational study.Setting: Tertiary care academic hospital.Participants: Sixty consecutive patients with a cardiac index <2 L/min/m2 and a pulmonary artery occlusion pressure <12 mmHg after coronary artery surgery were included.Interventions: Patients were monitored by a pulmonary artery catheter and a central venous catheter positioned in the superior vena cava.Measurements and Results: SvO2 and ScvO2 were simultaneously measured before (T0) and after (T1) normalization of the cardiac index (>2.5 L/min/m2) by fluid therapy. Sixty pairs of measures were obtained at T0 and at T1. Bias between SvO2 and ScvO2 was −0.6% (T0) and −0.8% (T1). Limits of agreement were from −19.2% to 18% (T0) and from −15.6% to 14% (T1), and the correlation coefficient was 0.463 (T0) and 0.72 (T1). SvO2 and ScvO2 changes from T0 to T1 (ΔSvO2 and ΔScvO2) were calculated. The bias between ΔSvO2 and ΔScvO2 was −0.25. Limits of agreement were from −20% to 19.5%, and the correlation coefficient was 0.6.Conclusions: In patients with low cardiac index and filling pressures after coronary artery surgery, ScvO2 could not be used as a direct alternative for SvO2. After fluid therapy and normalization of the cardiac index, differences between individual values remained large, and the disagreement between ScvO2 and SvO2 changes was significant.