Central venous saturation is not an alternative to mixed venous saturation during cardiopulmonary bypass in coronary artery surgery patients

Abstract

Background:

To evaluate the correlation and agreement between central venous saturation (ScvO₂) and mixed venous saturation (SvO₂) during cardiopulmonary bypass.

Methods:

Twenty-two consecutive patients scheduled for coronary artery surgery were prospectively included. Paired measurements of ScvO₂ and SvO₂ were performed 5 minutes after aortic cross-clamping, after each cardioplegia dose and after de-clamping of the aortic cross-clamp. ScvO₂ and SvO₂ were measured, respectively, by a fibreoptic catheter in the superior vena cava and on blood samples from the venous return line of the extracorporeal circuit, using a blood gas analyser

Results:

Ninety-five paired measurements of venous saturation were obtained. Correlation between the measurements was associated with an r = 0.55. The mean bias was 2.2 [Limits of agreement: –13.6%, +18%]. Changes in oxygen saturation over time showed an r = 0.4 and a mean bias of 0.2 [Limits of agreement: –17.9%, +18.3%]. Multivariate analysis identified the oxygen consumption index as the only factor explaining this variability.

Conclusions:

Although mean biases between the measurements were low, limits of agreement were too large to provide a clinically acceptable estimation of SvO₂ by ScvO₂ in these conditions. Variations in regional oxygen consumption seem to be the main factor worsening the relationship.