Mixed venous oxygen saturation remains constant during 0 through 45 degrees of backrest elevation.
[67.] Tidwell S, Ryan W, Osguthorpe S et al: Effects of position changes on mixed venous oxygen saturation in patients after coronary revascularization.
[72.] Winslow E, Clark A, White K et al: Effects of a lateral turn on mixed venous oxygen saturation and heart rate in critically ill adults.
Measuring central venous oxygen saturation and central venous-arterial carbon dioxide (CVA-C[O.sub.2]) tension gradient represents an attractive alternative to mixed venous oxygen saturation and SVA-C[O.sub.2] tension gradient because central venous catheterisation is a less invasive procedure than pulmonary artery catheterisation (10).
Although central venous oxygen saturation has been shown to correlate well with mixed venous oxygen saturation during different phases of haemorrhagic shock, hypoxia and hyperoxia in an experimental model of circulatory failure (18), recent clinical studies showed that the agreement between the two oxygen saturation measurements can be very unpredictable in patients with septic and cardiogenic shock (19,20).
Continuous monitoring of mixed venous oxygen saturation
(Sv|O.sub.2~), which provides an estimate of that ratio, can be accomplished with a fiberoptic pulmonary artery catheter.|21~ When the oxygen needs of tissue exceed its delivery, tissue p|O.sub.2~ falls, increasing p|O.sub.2~ diffusion from capillaries into the tissue.