Arterial Blood Gases (ABGs): 1  Arterial PO2: to confirm central cyanosis : SaO2 not as good an indicator due to Increase fetal Hb affinity for O2 (left-shift) 2  Increase PaCO2: may indicate pulmonary or CNS disorders, heart failure. 3  Decrease pH: sepsis, circulatory shock, severe hypoxemia.