Central Venous Oxygen Saturation Cannot Replace Mixed Venous Saturation in Patients Undergoing Cardiac Surgery

Objective

It has been argued that venous oxygen saturation from a central venous catheter (ScvO₂) could be an inexpensive alternative to mixed venous oxygen saturation (SvO₂). The aim was to evaluate whether ScvO₂ measurements could replace SvO₂ readings after cardiac surgery and to analyze factors influencing any differences found.

Design

A prospective observational study.

Setting

A university hospital.

Participants

Twenty patients scheduled for elective cardiac surgery.

Interventions

Patients were followed postoperatively with corresponding ScvO₂/SvO₂ measurements.

Measurements and Main Results

The overall bias between ScvO₂ and SvO₂ was 1.9. In coronary artery bypass graft (CABG) patients, the bias was 0.6 compared with 6.4 in procedures involving aortic valve replacement. In situations with peripheral saturation (SAT) <92%, the bias was 10.7 compared with 0.8 when SAT was ≥99%. In 25.5% of measurements, the ScvO₂ was more than 10% different from SvO₂, and in only 50% the difference was less than 5%.

Conclusions

The ScvO₂ and SvO₂ measurements are not interchangeable, and, especially in patients undergoing aortic valve surgery, this lack of agreement is crucial. However, the present data indicate that ScvO₂ may be used in CABG patients, although it is not completely accurate in terms of absolute venous saturations. A low SAT, low hemoglobin, or low cardiac index increased the venous gap.

Key Words: mixed venous oxygenation, venous oxygenation, cardiac surgery, cardiac output