Arterial blood gas
Background
- Direct measurement of arterial pH, pCO2, pO2, and calculated HCO3
- Gold standard for acid-base assessment and oxygenation status
Normal Values
- pH: 7.35-7.45
- pCO2: 35-45 mmHg
- pO2: 80-100 mmHg
- HCO3: 22-26 mEq/L
Interpretation
- Step 1: Identify primary disorder (acidemia vs alkalemia)
- Step 2: Determine if primary process is respiratory (pCO2) or metabolic (HCO3)
- Step 3: Assess for appropriate compensation
- Step 4: Calculate anion gap if metabolic acidosis is present
- Step 5: If anion gap is elevated, calculate delta-delta to assess for concurrent non-gap acidosis or metabolic alkalosis
- A venous blood gas can be used as a screening tool; venous pH is ~0.03 lower and pCO2 is ~5-8 mmHg higher than arterial
- ABG is specifically needed when precise pO2 or A-a gradient is required (e.g., CO poisoning, methemoglobinemia)