Oxygen Extraction Ratio (O2ER) is the amount of oxygen extracted by the peripheral tissues (CaO2-CvO2) divided by the amount of oxygen delivered (CaO2) to the peripheral tissues.

Normal O2ER is around 0.25 or 25%

O2ER: Oxygen Extraction Ratio
CaO2: Arterial oxygen content (mmHg)
CvO2: Venous oxygen content (mmHg)

CaO2: Arterial oxygen content: mmHg
CvO2: Venous oxygen content mmHg
O2ER: Oxygen Extraction Ratio