Arterial Blood Gas Interpretation
Normal Values
pH: 7.35 - 7.45
PaCO2: 35-45mmHg (more = acidosis)
PaO2: 75-100mmHg
Hco3-: 22-28mmol/L (more = alkalosis)
Base Excess: +/- 2
Steps
Advanced
A-a gradient = PAO2 (alveolar O2) - PaO2 (arterial O2)
= [FiO2(Patm - Ph20) - 0.8PaCO2)] - Pa02
= (150 - 0.8PaCO2) - PaO2 @ sea level: FiO2 21% and 100% alveoli humidity
Normal A-a gradient = Age/4 + 4 (average 5-10mmHg for young adult, + 1 for every decade)
Low A-a gradient = hypoventilation (not moving CO2 out, thus A is low)
High A-a gradient = low V/Q or shunting
Source
Fletcher Ng 2015
pH: 7.35 - 7.45
PaCO2: 35-45mmHg (more = acidosis)
PaO2: 75-100mmHg
Hco3-: 22-28mmol/L (more = alkalosis)
Base Excess: +/- 2
Steps
- Assess pH
- Determine primary mechanism (PaCO2 or HCO3)
- Is it compensated (pH normal)
- Base excess? Out of range = metabolic
- Hypoxemic? (PaO2)
Advanced
A-a gradient = PAO2 (alveolar O2) - PaO2 (arterial O2)
= [FiO2(Patm - Ph20) - 0.8PaCO2)] - Pa02
= (150 - 0.8PaCO2) - PaO2 @ sea level: FiO2 21% and 100% alveoli humidity
Normal A-a gradient = Age/4 + 4 (average 5-10mmHg for young adult, + 1 for every decade)
Low A-a gradient = hypoventilation (not moving CO2 out, thus A is low)
High A-a gradient = low V/Q or shunting
Source
Fletcher Ng 2015