Comparison of central venous saturation by standard ABG machine versus co-oximeter: Is 18 carat as good as the 24 carat gold standard?

AIMS: Aggressive therapy aimed at desired end-points of Early Goal Directed Therapy (EGDT) is the cornerstone of septic shock management. A key endpoint that improves outcomes is achieving central venous saturation (ScvO(2)) >70%. The gold standard to measure ScvO(2) is by a co-oximeter (co-ox). SETTINGS AND DESIGN: This prospective, observational study from a multidisciplinary pediatric intensive care unit (PICU) was conducted to assess the validity of ScvO(2) levels by standard ABG (stand ABG) machine in comparison with co-ox in conditions that shifted the oxygen dissociation curve (ODC) to the right or left in sick children and controls. MATERIALS AND METHODS: Data from paired samples was tested for correlation coefficient for pH, paCO(2), paO(2), and ScvO(2). Tests for correlation (Pearson's coefficient) and agreement (Bland–Altman analysis) were performed on ScvO(2) values obtained in various subgroups. Sensitivity and specificity for ScvO(2) values determined by standard ABG machine versus co-ox were calculated in reference to EGDT endpoints. RESULTS: A total of 141 paired samples were collected from 82 children. Despite a statistically significant difference in the pH and ScvO(2), there was good linear correlation between these parameters. Limits of agreement between ScvO(2) measured by standard ABG machine and co-ox by Bland–Altman gave 2.3% bias with 95% CI of -24.2% to 19.5%. Sensitivity and specificity of standard ABG machine in detecting low ScvO(2) in shock was 84.21% and 93.18% respectively, while it was false positive in 4 samples. CONCLUSIONS: The less expensive standard ABG machine showed satisfactory correlation with gold standard co-ox over a range of patient conditions; however, the wide range for agreement was of concern and it performed particularly poorly in anemic patients.