What does a SvO2 measurement below 50% indicate?

A SvO2 measurement, or mixed venous oxygen saturation, reflects the balance between oxygen delivery (DO2) and oxygen consumption (VO2) in the body. When SvO2 levels fall below 50%, it typically indicates that the body is not receiving sufficient oxygen to meet its metabolic demands.

This low measurement suggests that the tissues are extracting a higher amount of oxygen from the blood, leading to reduced oxygen saturation in the venous blood returning to the heart. Such a situation often triggers anaerobic metabolism, as the body resorts to alternate methods of energy production when adequate aerobic pathways cannot function due to low oxygen availability. Anaerobic metabolism results in the production of lactic acid as a byproduct, which accumulates in the body and can lead to metabolic acidosis.

Understanding this concept is crucial in the context of ECMO, as monitoring SvO2 can help assess the adequacy of oxygen delivery and inform interventions to optimize patient care.