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Arterial Blood Gas
Aka: Arterial Blood Gas, Blood Gas, ABG, PaCO2, PCO2, PaO2, pO2, Arterial Oxygen Partial Pressure
- See Also
- ABG Interpretation
- A-a Gradient
- Labs
- See Venous Blood Gas
- Arterial Blood source
- Arterial Puncture
- Arterial Line
- Interpretation: Conditions invalidating or modifying ABG Results
- Delayed analysis
- Iced Sample maintains values for 1-2 hours
- Un-iced sample quickly becomes invalid
- PaCO2 rises 3-10 mmHg/hour
- PaO2 falls at a rate related to initial value
- pH falls modestly
- Excessive Heparin
- Dilutional effect on results
- Decreases bicarbonate and PaCO2
- Large Air bubbles not expelled from sample
- PaO2 rises 0-30 mmHg
- PaCO2 may fall slightly
- Fever or Hypothermia
- Machine Temperature approaches 37 C
- Patient Temperature shifts oxyhemoglobin curve
- Hyperventilation or breath holding (due to anxiety)
- May lead to erroneous lab results
- Causes: Primary and Secondary Acid Base Disorders
- Respiratory Acidosis (pCO2 increases)
- Compensated by Metabolic Alkalosis (HCO3 increases)
- Respiratory Alkalosis (pCO2 decreases)
- Compensated by Metabolic Acidosis (HCO3 decreases)
- Metabolic Acidosis (HCO3 decreases)
- Compensated by Respiratory Alkalosis (PCO2 decreases)
- Metabolic Alkalosis (HCO3 increases)
- Compensated by Respiratory Acidosis (PCO2 increases)
- Interpretation: pH
- See Calculated PaCO2
- Normal arterial pH = 7.36 to 7.44
- Metabolic Conditions are suggested if
- pH changes in the same direction as pCO2
- pH is abnormal but pCO2 remains unchanged
- Metabolic Conditions related changes in Bicarbonate
- Increase pH by 0.01 (with PaCO2 unchanged)
- Bicarbonate increases 0.67 meq/L
- Decrease pH by 0.01 (with paCO2 unchanged)
- Bicarbonate decreases 0.67 meq/L
- Interpretation: PaO2 (partial pressure of arterial oxygen)
- See A-a Gradient
- See Arterial Blood Oxygen Content (CaO2)
- Normal PaO2
- Room air at sea level: 80-100 mmHg
- Age Adjusted PaO2 = 100 mmHg – 0.3 * AgeY
- Where AgeY is age in years
- Adjusted for FIO2
- Approximate Normal PaO2 = FIO2 * 5
- Normal PaO2/FiO2 >400 mmHg
- Hypoxemia
- PaO2 < 50 mmHg
- Resources
- ABG Interpretation
- https://anesth.unboundmedicine.com/anesthesia/view/Pocket-ICU-Management/534207/all/Interpretation_of_Arterial_Blood_Gases
- References
- Arieff (1993) J Crit Illn 8(2): 224-46 [PubMed]
- Narins (1982) Am J Med 72:496 [PubMed]
- Narins (1980) Medicine 59:161-95 [PubMed]
- Ghosh (2000) Fed Pract p. 23-33
- Rutecki (Dec 1997) Consultant, p. 3067-74
- Rutecki (Jan 1998) Consultant, p. 131-42