Central venous oxygen saturation calculated by gasometry (Gaso-Scvo₂) is more available than central venous oxygen saturation measured by co-oximetry (Co-oxy-Scvo₂) in environments with less resources and underdeveloped countries. Therefore, we aimed to determine the agreement between Co-oxy-Scvo₂ and Gaso-Scvo₂ and between central venous oxygen tension measured by gasometry (Gaso-Pcvo₂) and Co-oxy-Scvo₂, respectively.

This is a prospective study in a university hospital’s intensive care unit.

Sixteen patients were studied during the first 48 hours after diagnosis of septic shock. All patients were intubated, connected to mechanical ventilation, and resuscitated according to the standards of care.

One hundred eleven pairs of central venous blood measurements were analyzed both by conventional gasometry and co-oximetry. Bland and Altman analysis between Co-oxy-Scvo₂ and Gaso-Scvo₂ showed lack of agreement (1.7 [−10.7, +14.2]). A Gaso-Scvo₂ less than 70% had a positive predictive value of 63% in relation to Co-oxy-Scvo₂, and its negative predictive value was 90% with 20% false-positives and 5% false-negatives. The area under the receiver operator characteristic curve of Gaso-Pcvo₂ to discriminate a Co-oxy-Scvo₂ greater than or equal to 70% was 0.87 (confidence interval, 0.80-0.93), and the best cut-off point was a Gaso-Pcvo₂ more than 40 mm Hg, (sensitivity, 75%; specificity, 93%).

The reliability of Gaso-Scvo₂ determination during the resuscitation phase of septic shock is not acceptable. There is a good agreement between a Gaso-Pcvo₂ more than 40 mm Hg and a Co-oxy-Scvo₂ greater than or equal to 70%. Our results suggest that given these limitations, Gaso-Scvo₂ results should be interpreted with caution, helped by Gaso-Pcvo₂ measurements and in context with other perfusion parameters.