Lab
Arterial Blood Gas
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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
Images
AcidBaseNomogram
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)
Uncompensated pH decreased = (Normal HCO3)/(Increased pCO2)
Compensated by
Metabolic Alkalosis
(HCO3 increases)
Compensated pH normalizes = (Increased HCO3)/(Increased pCO2)
Respiratory Alkalosis
(pCO2 decreases)
Uncompensated pH increased = (Normal HCO3)/(Decreased pCO2)
Compensated by
Metabolic Acidosis
(HCO3 decreases)
Compensated pH normalizes = (Decreased HCO3)/(Decreased pCO2)
Metabolic Acidosis
(HCO3 decreases)
Uncompensated pH decreased = (Decreased HCO3)/(Normal pCO2)
Compensated by
Respiratory Alkalosis
(PCO2 decreases)
Compensated pH normalizes = (Decreased HCO3)/(Decreased pCO2)
Metabolic Alkalosis
(HCO3 increases)
Uncompensated pH increased = (Increased HCO3)/(Normal pCO2)
Compensated by
Respiratory Acidosis
(PCO2 increases)
Compensated pH normalizes = (Increased HCO3)/(Increased pCO2)
Mixed
Respiratory Acidosis
and
Metabolic Acidosis
(pCO2 increases and HCO3 decreases)
pH decreased = (Decreased HCO3)/(Increased pCO2)
Mixed
Respiratory Alkalosis
and
Metabolic Alkalosis
(pCO2 decreases and HCO3 increases)
pH increased = (Increased HCO3)/(Decreased pCO2)
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
Acid-Base
Interpreter
(fpnotebook)
https://fpnotebook.com/_media/acidbaseapp.html
ABG Interpretation
(unbound medicine)
https://anesth.unboundmedicine.com/anesthesia/view/Pocket-ICU-Management/534207/all/Interpretation_of_Arterial_Blood_Gases
ABG Nomogram
Code for the ABG nomogram is included in Jupyter Notebook
AcidBaseNomogram.html
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
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