Which ABG pattern represents primary respiratory acidosis with no metabolic compensation?

• A. pH decreased; PaCO2 increased; HCO3- near normal
• B. pH increased; PaCO2 increased; HCO3- increased
• C. pH decreased; PaCO2 decreased; HCO3- near normal
• D. pH normal; PaCO2 increased; HCO3- decreased

Answer: (D)

The main idea here is recognizing a primary respiratory problem without metabolic compensation by looking at how acidemia/alkalemia, PaCO2, and bicarbonate relate. In primary respiratory acidosis, ventilation is inadequate, so PaCO2 rises and the pH drops. The kidneys haven’t had time to compensate yet, so bicarbonate (HCO3-) stays near its normal level. Therefore the pattern shows a decreased pH, increased PaCO2, and bicarbonate near normal.

If the pH is normal despite a high PaCO2, that would imply a mixed disorder or that metabolic compensation has already occurred, which isn’t the scenario described. A decreased bicarbonate with a normal pH wouldn’t fit primary respiratory acidosis without compensation either.

So the correct interpretation for primary respiratory acidosis with no metabolic compensation is: decreased pH, increased PaCO2, bicarbonate near normal.