Certified Post Anesthesia Nurse (CPAN) Practice Exam

What does an ABG showing pH = 7.50, pCO2 = 45 mmHg, and HCO3 = 30 mEq/L indicate?

1. Respiratory alkalosis

2. Respiratory acidosis

3. Metabolic acidosis

4. Metabolic alkalosis

The correct answer is: Metabolic alkalosis

The interpretation of an arterial blood gas (ABG) involves analyzing the pH, partial pressure of carbon dioxide (pCO2), and bicarbonate (HCO3) levels. In this case, a pH of 7.50 indicates alkalinity, as it is above the normal range of approximately 7.35 to 7.45. The pCO2 level of 45 mmHg is within the normal range (35-45 mmHg), indicating that it is not significantly affecting the pH in terms of respiratory contribution. The HCO3 level of 30 mEq/L is higher than the normal range (22-26 mEq/L), which further supports the presence of alkalosis. When evaluating the combination of a high pH with elevated bicarbonate, this is characteristic of metabolic alkalosis, as the elevated bicarbonate contributes to the increased pH. Metabolic alkalosis can result from factors such as excessive loss of hydrogen ions or an increase in bicarbonate levels through various mechanisms. This analysis reinforces why the indication of metabolic alkalosis is the correct conclusion based on the ABG values provided.