Wednesday November 18, 2009


Q: Which patient is more hypoxemic?

Patient A: PaO2 85 mm Hg, SaO2 95%, Hb 7 gm%
Patient B: PaO2 55 mm Hg, SaO2 85%, Hb 15 gm%


Answer:

Calculate arterial oxygen content (CaO2) (SaO2 x Hb x 1.34) assuming PaO2 is constant

Patient A
CaO2 = .95 x 7 x 1.34 = 8.9 ml O2/dl

Patient B
CaO2 = .85 x 15 x 1.34 = 17.1 ml O2/dl

Patient A, with the higher PaO2, is more hypoxemic.


Full formula: Ca02 = (Hgb)(1.34)(Sa02) + (0.0031)(Pa02)