ABG pattern with pH 7.49, PCO2 59, HCO3- 25 indicates:

ABG pattern with pH 7.49, PCO2 59, HCO3- 25 indicates:

• A. Metabolic alkalosis, partially compensated
• B. Respiratory acidosis, uncompensated
• C. A dual problem of acidosis
• D. An error in measurement

Answer: (A)

The key idea is to identify the direction of the pH change and then see what the other values say about a primary disorder and its compensation. Here the pH is 7.49, which is alkaline. The high PCO2 of 59 mmHg would normally push the pH toward acidity, so the alkalemia means there must be a metabolic process driving the pH up. In metabolic alkalosis, the body compensates by hypoventilating to raise the PCO2. The PCO2 value of 59 mmHg shows this respiratory compensation. The bicarbonate value, 25 mEq/L, is essentially in the normal range. In metabolic alkalosis, you’d typically expect the bicarbonate to be elevated as the primary problem; however, compensation can sometimes be partial and bicarbonate may not be markedly raised yet, especially if the metabolic alkalosis is mild or mixed with other factors. The important takeaway is that the elevated CO2 indicates the body is trying to compensate for a metabolic alkalosis, and the overall pH remains alkalemic, consistent with partial compensation. So the best-fit interpretation is metabolic alkalosis with partial respiratory compensation. The other possibilities don’t fit as well: a purely respiratory acidosis would have an acidemic pH; a dual acidosis would not produce an alkalemic pH; while measurement error is possible, the pattern most supporting a metabolic alkalosis with incomplete compensation is the elevated CO2 alongside an alkalemic pH.

The key idea is to identify the direction of the pH change and then see what the other values say about a primary disorder and its compensation.

Here the pH is 7.49, which is alkaline. The high PCO2 of 59 mmHg would normally push the pH toward acidity, so the alkalemia means there must be a metabolic process driving the pH up. In metabolic alkalosis, the body compensates by hypoventilating to raise the PCO2. The PCO2 value of 59 mmHg shows this respiratory compensation.

The bicarbonate value, 25 mEq/L, is essentially in the normal range. In metabolic alkalosis, you’d typically expect the bicarbonate to be elevated as the primary problem; however, compensation can sometimes be partial and bicarbonate may not be markedly raised yet, especially if the metabolic alkalosis is mild or mixed with other factors. The important takeaway is that the elevated CO2 indicates the body is trying to compensate for a metabolic alkalosis, and the overall pH remains alkalemic, consistent with partial compensation.

So the best-fit interpretation is metabolic alkalosis with partial respiratory compensation. The other possibilities don’t fit as well: a purely respiratory acidosis would have an acidemic pH; a dual acidosis would not produce an alkalemic pH; while measurement error is possible, the pattern most supporting a metabolic alkalosis with incomplete compensation is the elevated CO2 alongside an alkalemic pH.