A nurse is reviewing the laboratory results of a client who has DKA. The client’s ABG results are pH 7.30, PaCO₂ 34 mm Hg and HCO₃ 21 mEq/L. The nurse should identify that these values indicate which of the following acid-base imbalances?
A.
Respiratory alkalosis
B.
Metabolic alkalosis
C.
Metabolic acidosis
D.
Respiratory acidosis
The Correct Answer and Explanation is:
The correct answer is C. Metabolic acidosis.
Here’s a detailed explanation:
1. Understanding the Components of ABG:
- pH measures the hydrogen ion concentration in the blood, indicating the acidity or alkalinity. A normal pH range is 7.35 to 7.45. A pH below 7.35 suggests acidosis, while a pH above 7.45 indicates alkalosis.
- PaCO₂ (Partial Pressure of Carbon Dioxide) reflects the respiratory component of acid-base balance. The normal range is 35 to 45 mm Hg. Elevated PaCO₂ indicates respiratory acidosis, while decreased PaCO₂ indicates respiratory alkalosis.
- HCO₃ (Bicarbonate) represents the metabolic component. The normal range is 22 to 28 mEq/L. Decreased HCO₃ suggests metabolic acidosis, while increased HCO₃ indicates metabolic alkalosis.
2. Analyzing the Given Values:
- pH 7.30: This is below the normal range, indicating acidosis.
- PaCO₂ 34 mm Hg: This is slightly below the normal range of 35 to 45 mm Hg. A lower PaCO₂ typically suggests that the respiratory system is compensating for metabolic acidosis by “blowing off” CO₂ to decrease acidity.
- HCO₃ 21 mEq/L: This is slightly below the normal range of 22 to 28 mEq/L. A lower HCO₃ indicates a reduction in the buffering capacity of the blood, which is consistent with metabolic acidosis.
3. Determining the Type of Acid-Base Imbalance:
- In metabolic acidosis, the primary defect is a decrease in HCO₃. The pH is low due to this decrease, and the PaCO₂ might be normal or slightly decreased as a compensatory mechanism.
- In respiratory acidosis, the primary defect is an increase in PaCO₂, causing a decrease in pH. However, in this scenario, PaCO₂ is not elevated.
- In metabolic alkalosis, the HCO₃ is elevated, which would increase the pH, contrary to the findings.
- In respiratory alkalosis, PaCO₂ would be decreased significantly, but HCO₃ levels would be normal or slightly decreased as a compensatory response.
4. Conclusion: The combination of a low pH, normal PaCO₂, and low HCO₃ points towards metabolic acidosis as the primary diagnosis. This aligns with the clinical scenario of diabetic ketoacidosis (DKA), which is characterized by a significant decrease in bicarbonate levels due to the accumulation of ketoacids.