Arterial Blood Gas Analysis: Example Set 1
Case A
A patient is brought back to the floor from the operating room on a patient controlled analgesia (PCA) pump with hydromorphone. The patient hits his PCA button several times in the first hour. Shortly thereafter, the nurse walks in the room and finds him somnolent and difficult to arouse.
His SpO2 is only 88% so the nurse obtains a blood gas that reveals:
- pH 7.25
- PCO2 55
- PO2 60
- HCO3- 25
Step 1: pH is low (acidemia)
Step 2: The PCO2 is high (respiratory acidosis) and the bicarbonate is normal. A low pH with a high PCO2 indicates that the primary process is a respiratory acidosis.
Summary
In this case, the patient started hypoventilating because he had likely given himself too much narcotic pain medications.
Case B
A patient presents with a one-day history of productive cough, fevers and increasing dyspnea. In the ER, the chest x-ray shows a right middle lobe opacity. His oxygen saturation is 90% on room air.
An arterial blood gas is obtained and it reveals a
- pH 7.55
- PCO2 30
- PO2 63
- HCO3- 22
Step 1: The pH is high (alkalemia)
Step 2: The PCO2 is low (respiratory alkalosis) and the bicarbonate is on the low side of normal. A high pH with a low PCO2 indicates that the primary process is a respiratory alkalosis.
Summary
In this case, the patient is likely hyperventilating because he is hypoxemic. This is a good example of the hypoxemic ventilatory response.
Case C
A patient with Type I diabetes presents to the ER complaining of feeling poorly two days after running out of his insulin.
An arterial blood gas is obtained and shows
- pH 7.25
- PCO2 28
- PO2 95
- HCO3- 15.
Step 1: The pH is low (acidemia)
Step 2: The PCO2 is low (respiratory alkalosis) and the bicarbonate is low (metabolic acidosis). A low pH and low bicarbonate signifies that the metabolic acidosis is the primary process.
Summary
In this case, the patient is likely in diabetic ketoacidosis because he was not taking insulin.
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