Which of the following statement(s) is/are true concerning O2 venous saturation monitoring?

c. If arterial blood is fully saturated, the saturation of mixed venous blood is 80%

d. In less than fully saturated blood, the difference between arterial and venous saturation corresponds to oxygen extraction

The relationship between oxygen delivery and oxygen consumption is reflected in the amount of oxygen in venous blood. Under normal circumstances, oxygen delivery is 1000 cc/min and oxygen consumption is 200 cc/min. The amount of oxygen extracted is 20% of that delivered, and 80% of oxygen is still present in venous blood returning to the heart. Usually arterial blood is fully saturated, and under normal circumstances, the saturation of mixed venous blood (SVO2) will be 80%. This measurement must be made in mixed venous blood since the relative extraction of organs served by the superior and inferior vena cava and coronary sinus are quite different. As long as arterial blood is fully saturated, this observation holds true regardless of the absolute level of oxygen consumption or oxygen delivery. If the arterial blood is less than fully saturated, the difference between arterial and venous saturation corresponds to the oxygen extraction, hence the oxygen delivery/oxygen consumption ratio.