What is an ABG?
 Arterial Blood Gas is a lab that shows us the status of a
patient’s chemical balance
 In general lab with be drawn from an artery by a RT
not a nurse
 However nurses are responsible for the analysis of the
lab and the reaction to the analysis
Main Components of ABG
 pH-Measures hydrogen ion (H+) concentration
 PCO2-Partial pressure of CO2 in arteries
 HCO3-Measures serum bicarbonate
Normal Values of ABG
 pH-7.35-7.45
 PCO2-35-45mmHg
 HCO3-22-26 mEq/l
Abnormal ABG Readings
 The body will work hard to balance any abnormal
values within the acid-base system
 How the body works to do this depends on the issue:
 CO2 is controlled by the lungs
 HCO3 is controlled by the kidneys
Compensated Vs Uncompensated
 If the body can work to balance the issue through the
lungs or kidneys it will result in a normal pH
 Other values in the ABG will be ABNL however do not
matter since there not an overall effect on the pH
 This is a compensated ABG
 Allow the body to continue the balance and monitor
patient closely
Step 1
 Look at the pH-if abnormal you have an
uncompensated disturbance
 Now figure out if the disturbance is acidosis or
alkalosis-this will determine the treatment
 Acidosis is pH below7.35 and results from adding H+
an acid
 Alkalosis is pH above 7.45 and results from decrease in
H+ an acid
Step 2
 When in ROME…
 Respiratory Opposite-the HCO3 is normal and the
arrows for the pH and PCO2 point in opposite
directions
 Metabolic Equal-the PCO2 is normal and the arrows
for pH and HCO3 point in the same direction
Step 3
 Put all your findings together to determine the overall
imbalance
 Example: pH 7.29
PCO2 50 HCO3 26
 What is this patient’s condition?
Answer
 pH 7.29
 PCO2 50
 HCO3 26
 Respiratory acidosis
More Practice
 pH 7.50, PCO2 30, HCO3 26
 pH 7.30, PCO2 42, HCO3 20
 pH 7.48, PCO2 42, HCO3 32
 pH 7.29, PCO2 55, HCO3 26
Primary Cause of Imbalances
 Respiratory acidosis-hypoventilation
 Metabolic acidosis-addition of large amounts of fixed
acids to body fluids-Ketoacidosis with diabetes
 Respiratory alkalosis-hypoventilation
 Metabolic alkalosis-retention of base or loss of acid
through body fluids
Other Important Values on ABG
 PaO2-The partial pressure of oxygen that is dissolved
in arterial blood.
 The normal range is 80 to 100 mm Hg.
 SaO2-The arterial oxygen saturation.
 The normal range is 95% to 100%.
Oxyhemoglobin Dissociation
Curve
Refers to the relationship between oxygen and
hemoglobin
Normal-oxygen has affinity for hemoglobin until it
reaches tissues in need of oxygen
Once it reaches the tissues the oxygen releases
itself from the hemoglobin and becomes available
for use (all of this is good)
Changes in Oxyhemoglobin
Dissociation Curve
 Certain conditions in the body can change the
relationship between oxygen and hemoglobin
 This change can lead to oxygen leaving hemoglobin
before reaching tissues in need (shift to right)
 Or cause the oxygen and hemoglobin to bond so
tightly it cannot be released in tissues (shift to left)
 Shift to left is worse for the patient-beware SPO2 will
be normal however patient will be hypoxic
Causes for Shifts
 Shift to the right: acidosis, fever, elevated CO2 levels,
and increased 2,3-diphosphoglycerate (2,3-DPG, a byproduct of glucose metabolism)
 Shift to the left: hypothermia, alkalosis, low PCO2,
and decrease in 2,3-DPG