Arterial Blood Gases (ABGs)

Definition:
Measurement of PaCO2 and PaO2 and H+ Conc. in arterial blood is valuable in assessment of hypoxemia or acid-base balance in respiratory failure and asthama.

Procedure:
Heparinize syringe with 0.1 ml heparin to prevent clot formation.
Draw blood from radial or brachial or femoral artery.
The sample should be immersed in ice bag immediately to prevent metabolism that can reduce PaO2 and increase PaCO2.

Normal values:
PH: 7.35 - 7.45
PaO2: 75 - 100 mm Hg
PaCO2: 35 - 45 mm Hg
HCO3: 24 - 28 mmol/L
O2 saturation: 95 - 100%

Types:
Respiratory Acidosis.
Respiratory Alkalosis.
Metabolic Acidosis.
Metabolic Alkalosis.

1- Respiratory Acidosis:
PH  < 7.35
PaCO2 increases > 45 mm Hg
HCO3 < 24 mmol/L

* If PH is normal, HCO3 is > 28 mmol/L, then it will be compensatory Respiratory Acidosis.

2- Respiratory Alkalosis:
PH > 7.45
PaCO2 < 35 mm Hg
HCO3 is normal or > 28 mmol/L

3- Metabolic Acidosis:
PH  < 7.35
PaCO2  is normal or < 35 mm Hg
HCO3 < 22 mmol/L

*  If PH is normal, PaCO2 is < 35 mm Hg, then it will be compensatory Metabolic Acidosis.

4- Metabolic Alkalosis:

PH > 7.45
PaCO2  35 - 45 mm Hg
HCO3 is > 28 mmol/L