ABSTRACT
A b n o rm a l D e sa tu ra tio n o f S y s te m ic V en o u s B lo o d Admixture of abnormally desaturated venous blood is an important mechanism acting to lower Pa02 in patients with impaired pulmonary gas exchange and reduced cardiac output. Svq2 (the oxygen of mixed venous blood), is influenced by cardiac output (Q), arterial 0 2 saturation (Sa02), and 0 2 consumption (Vo2)·
This equation illustrates that Sv02 is directly influenced by any imbalance between V02 and oxygen delivery. Thus, anemia uncompensated by an increase in cardiac output or a cardiac output too low for metabolic needs can cause both Sv02 and PaÛ2 to fall unless the lung is normal. In the normal lung, well-ventilated alveoli have adequate oxygenation reserve to compensate for a low Sv02. A marked decline in SvŨ2 without arterial hypoxemia occurs routinely during heavy exercise in healthy subjects.
