Nursing Acceleration Challenge Exam (NACE) PN-RN Practice Test

What acid-base imbalance is suggested by a patient with the following arterial blood gases: pH 7.28, PaCO2 48 mm Hg, HCO3 325 mEq/L?

1. Respiratory acidosis

2. Respiratory alkalosis

3. Metabolic acidosis

4. Metabolic alkalosis

The correct answer is: Respiratory acidosis

The arterial blood gas results indicate a pH of 7.28, which is below the normal range of 7.35 to 7.45, suggesting acidemia. The PaCO2 is elevated at 48 mm Hg, while the HCO3 is well above the normal range of 22 to 28 mEq/L at 325 mEq/L. In this case, the respiratory component (PaCO2) is the primary contributor to the acid-base disturbance. An elevated PaCO2 indicates that there is an excess of carbon dioxide in the blood, which typically results from respiratory depression or decreased ventilation. This leads to retention of carbonic acid, and consequently, a decrease in blood pH, resulting in respiratory acidosis. The high HCO3 level suggests that the body may be attempting to compensate for this respiratory acidosis. However, since the pH is still abnormal, it confirms that the primary imbalance is ongoing respiratory acidosis rather than a compensatory metabolic alkalosis. In summary, the combination of decreased pH alongside elevated PaCO2 clearly points towards respiratory acidosis as the correct identification of the acid-base imbalance.