mixed venous oxygen saturation (SvO2 ) The balance between oxygen delivery and extraction, and a measure of the adequacy of oxygen delivery to the tissues. Tissue hypoxia may occur even when heart rate, blood pressure and central venous pressure are normal. Knowledge of the SvO2 has been shown to be valuable in any condition or state in which tissue hypoxia is possible. The normal range is 65 to 75 per cent. Unfortunately, its measurement requires a pulmonary artery catheter, the safety of which has been questioned.