Critical Assessment of Use of Central Venous Oxygen Saturation as a Mirror of Mixed Venous Oxygen in Severely Ill Cardiac Patients

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Abstract
Bedside catheterization of the right heart with a percutaneously introduced flowdirected catheter was carried out in 24 critically ill patients; 71 determinations of mixed venous oxygen saturation (MVo2) were obtained. A second catheter was inserted either into a central intrathoracic vein or the right atrium for simultaneous sampling of central venous (CVo2) or right atrial (RAo2) oxygen saturation. For the group as a whole, mean CVo2 (57.9% ± 15.25) was significantly greater than mean MVo2 (53.3% ± 14.84) (P2 and MVo2 (r=+0.95). Patients with heart failure or shock showed poor correlation between CVo2 and simultaneously determined MVo2. Furthermore, subjects with shock showed a mean CVo2 (58.0%±13.05) that was significantly greater than mean MVo2 (47.5% ± 15.11). In contrast, there was no significant difference between mean RAo2 and mean MVo2 and excellent correlation of individual values in patients with either heart failure or shock. Although CVo2 is a poor reflection of MVo2 in subjects with severe heart failure or shock, there was a better correlation between changes in CVo2 with corresponding changes in MVo2. In addition, RAo2 correlated closely with corresponding values of MVo2. The reversal of the normal relationship between CVo2 and MVo2 under these circumstances is compatible with the thesis that low output states are attended by redistribution of blood flow away from femoral, splanchnic, and renal circulation with preferential preservation of cerebral blood flow.