Central venous versus mixed venous oxygen content.

Mixed venous oxygen content (commonly measured as oxygen saturation) is a highly relevant parameter in the monitoring of critically ill patients; unfortunately, its measurement requires catheterization of the pulmonary artery. Though less invasive, the central venous oxygen saturation is an unsatisfactory substitute, due to fluctuations in perfusion distribution and regional oxygen extraction in the course of illness. The present study examined the relation of oxygen contents in simultaneously withdrawn central venous and mixed venous blood samples from critically ill patients, in order to validate a hypothetical algorithm for the estimation of mixed venous oxygen content from a central venous sample: Although the proposed algorithm had a fairly high power of prediction, its merits in comparison to assuming simple proportionality between central venous and mixed venous oxygen content seemed marginal. However, as it is likely that the results so far are mathematically coupled, further prospective studies are necessary.