Respiratory Therapy – Formulas Practice Test

When estimating DO2, the key factor is arterial oxygen content, which comes mainly from hemoglobin carrying oxygen. The dissolved oxygen in plasma is small in comparison, so the Hb value you use shapes the result a lot.

In standard DO2 calculations, a normal adult hemoglobin concentration of 15 g/dL is assumed. This provides a representative baseline when patient-specific Hb isn’t given. Using Hb = 15 g/dL in CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2) typically yields about 19–20 mL O2/dL of blood under normal saturations and PaO2, since the Hb-bound portion dominates. If actual Hb differs, you would substitute that value to adjust CaO2 and thus DO2 accordingly.

So, the hemoglobin concentration used is 15 g/dL.