Accuracy of central venous oxygen saturation with a fiberoptic catheter

Introduction

Central venous oxygen saturation (ScvO₂) can reflect the overall balance between the systemic oxygen delivery and supply. Several recent studies reported the importance of ScvO₂ monitoring in critically ill patients. Recently, ScvO₂ monitoring with fiberoptic catheters has been made available. The aim of this study was to evaluate the correlation between the ScvO₂ values obtained by a fiberoptic catheter (CeVOX; Seda, Milan, Italy) and those measured with a CO-oximeter (GEM 4000; Instrumentation Laboratory Milan, Italy).

Methods

After in vivo calibration of the fiberoptic catheter, blood samples were collected at intervals of no more than 12 hours. Twenty-nine critically ill patients from different aetiologies (septic shock, acute lung injury/acute respiratory distress syndrome pneumonia, pancreatitis, trauma), 21 male, with a mean age of 59.8 ± 17.7 years, mean weight 78.6 ± 10.0 kg and mean Simplified Acute Physiology Score of 39 ± 14 were enrolled.

Results

One hundred and nineteen samples were collected. The measured with the fiberoptic catheter showed a weak ScvO₂ correlation (r² = 0.46) with the CO-oximeter. The mean bias (average difference between catheter readings and CO-oximeter values), precision (standard deviation of the bias) and limits of agreement (bias ± 2 SD of bias) were -0.17, 4.7 and -0.17 ± 9.4 respectively (Figure 1).

Figure 1

Plot of the mean ScvO ₂ values versus their difference by the Bland–Altman method.

Conclusion

Considering the absolute value, the fiberoptic catheter, after 12 hours of usage without any further calibration, presented a weak accuracy. To improve the clinical management we suggest performing in vivo calibration more frequently.