Diagnostic accuracy of central venous saturation in estimating mixed venous saturation is proportional to cardiac performance among cardiac surgical patients

Purpose: Advanced hemodynamic monitoring in cardiac surgery translates into improvement in outcomes. We evaluated the relationship between central venous (ScvO(2)) and mixed venous (SvO(2)) saturations over the early postoperative period. The adequacy of their interchangeability was tested in patients with varying degrees of cardiac performance. Methods: In this prospective observational study, we evaluated 156 consecutive cardiac surgical patients in an academic center. The ScvO(2) and SvO2 data were harvested from 468 paired samples taken preoperatively (T0), after weaning from cardiopulmonary bypass (T1) and on postoperative day 1 (T2). Results: The relationship between ScvO(2) and SvO(2) was inconsistent, with inferior correlations in patients with lower cardiac indices (CI) (Pearson r(2) = 0.37 if CI <= 2.0 L/min per square meter vs r(2) = 0.73 if CI >2.0 L/min per square meter, both P < .01). Patients with lower CI also had wider 95% limits of agreement between SvO(2) and ScvO(2). The proportion of patients with a negative SvO(2)-ScvO(2) gradient increased over time (48/156 [31%] at T0 to 73/156 [47%] at T2; P < .01). This subgroup more frequently required inotropes at T2 than patients with a positive SvO(2)-ScvO(2) gradient (odds ratio, 6.46 [95% confidence interval, 0.81-51.87], P = .06) and also had higher serum lactate levels (1.5 +/- 0.8 vs 1.0 +/- 0.4; P < .01). Conclusions: The diagnostic accuracy of ScvO(2) for estimating SvO(2) is proportional to cardiac performance. A negative SvO(2)-ScvO(2) gradient at T2 correlated with inotropic support requirement, higher operative risk score, age, lactate level, and duration of cardiopulmonary bypass. (C) 2014 Elsevier Inc. All rights reserved.