ABG: pH / PaCO2 / PaO2 / HCO3– / Oxygen Sat / Base Excess
Normal ABG values
- pH: 7.35-7.45
- PaCO2: 35-45 mm Hg (Partial pressure of carbon dioxide in arterial blood)
- PaO2: 80-100 mm Hg (Partial pressure of oxygen in arterial blood)
- HCO3: 21-27 mEq/L (Bicarbonate)
- Oxygen saturation: 95%-98%
- Base excess: –2mEq/L to 2mEq/L (.ie. from minus 2 to positive 2 mEq/L)
Note: the venous blood gas (VBG) values are usually a little different from the ABG values.
In the VBG, the
– pH is about 0.03 to 0.04 pH units lower than in the ABG,
– [HCO3–] is about 1 to 2 mEq/L higher,
– PCO2 is about 3 to 8 mmHg (0.4 to 1.1 kPa) higher
Why is that so?
Oxygenated blood goes from arteries through the capillaries to the tissues where it picks up CO2 and other tissue wastes (organic acids produced by the tissues). All these are drained into the veins. Within the veins there is buffering of the increased CO2 and organic acids with the result that the pCO2 is higher, the bicarb concentration is a little higher, and the pH is slightly lower.