Arterial Blood Gas

• Conditions invalidating or modifying ABG Results
  1. Delayed analysis
     1. Iced Sample maintains values for 1-2 hours
     2. Un-iced sample quickly becomes invalid
        1. PaCO2 rises 3-10 mmHg/hour
        2. PaO2 falls at a rate related to initial value
        3. pH falls modestly
  2. Excessive Heparin
     1. Dilutional effect on results
     2. Decreases bicarbonate and PaCO2
  3. Large Air bubbles not expelled from sample
     1. PaO2 rises 0-30 mmHg
     2. PaCO2 may fall slightly
  4. Fever or Hypothermia
     1. Machine temperature approaches 37 C
     2. Patient temperature shifts oxyhemoglobin curve
  5. Hyperventilation or breath holding (due to anxiety)
     1. May lead to erroneous lab results

   

   

• Primary and Secondary Acid Base Disorders
  1. Respiratory Acidosis (pCO2 increases)
     1. Compensated by Metabolic Alkalosis (HCO3 increases)
  2. Respiratory Alkalosis (pCO2 decreases)
     1. Compensated by Metabolic Acidosis (HCO3 decreases)
  3. Metabolic Acidosis (HCO3 decreases)
     1. Compensated by Respiratory Alkalosis (PCO2 decreases)
  4. Metabolic Alkalosis (HCO3 increases)
     1. Compensated by Respiratory Acidosis (PCO2 increases)

   

   

• Interpretation: pH
  1. Normal arterial pH = 7.36 to 7.44
  2. Metabolic Conditions are suggested if
     1. pH changes in the same direction as pCO2
     2. pH is abnormal but pCO2 remains unchanged
  3. Metabolic Conditions related changes in Bicarbonate
     1. Increase pH by 0.01 (with PaCO2 unchanged)
        1. Bicarbonate increases 0.67 meq/L
     2. Decrease pH by 0.01 (with paCO2 unchanged)
        1. Bicarbonate decreases 0.67 meq/L