Tissues begin to remove or extract a higher percentage of oxygen from the arterial blood.
Prolonged anaerobic metabolism leads to energy depletion and metabolic acidosis. If SvO2 decreases, it indicates that the tissues are extracting a higher percentage of oxygen from the blood than normal. In otherwords, a decreased SvO2 indicates that the cardiac output is not high enough to meet tissue oxygen needs. Thus, SvO2 can indicate whether an individual's cardiac output is high enough to meet their needs. A rise in SvO2 demonstrates a decrease in oxygen extraction, and usually indiates that the cardiac output is meeting the tissue oxygen need.