Which ABG result demonstrates metabolic acidosis?

Which ABG result demonstrates metabolic acidosis?

• A. pH 7.30, PaCO2 40, HCO3 18
• B. pH 7.49, PaCO2 30, HCO3 25
• C. pH 7.54, PaCO2 41, HCO3 36
• D. pH 7.12, PaCO2 28, HCO3 10

Answer: (A)

In ABG interpretation, metabolic acidosis shows acidemia with a low bicarbonate level. The key clue is low HCO3- along with a reduced pH, reflecting an excess of acid or a loss of base from the body. Here, the pH is 7.30 (acidic) and the bicarbonate is 18 mEq/L (low), which directly indicates metabolic acidosis. The PaCO2 is 40 mmHg, which is within the normal range; in pure metabolic acidosis we’d often see the CO2 fall as compensation, but a normal CO2 doesn’t negate the diagnosis—the primary deficit is the low bicarbonate with a酸emic pH. For context, if you apply the usual compensatory rule (Winter’s formula), with HCO3- at 18, the expected PaCO2 would be about 1.5×18 + 8 ≈ 35 mmHg. The observed 40 mmHg is higher than that expectation, suggesting possible concurrent respiratory involvement, but the defining feature here is the low bicarbonate paired with acidemia, which signals metabolic acidosis. The other values either show alkalemia or do not have a low bicarbonate with acid pH, so they do not demonstrate metabolic acidosis.

In ABG interpretation, metabolic acidosis shows acidemia with a low bicarbonate level. The key clue is low HCO3- along with a reduced pH, reflecting an excess of acid or a loss of base from the body. Here, the pH is 7.30 (acidic) and the bicarbonate is 18 mEq/L (low), which directly indicates metabolic acidosis. The PaCO2 is 40 mmHg, which is within the normal range; in pure metabolic acidosis we’d often see the CO2 fall as compensation, but a normal CO2 doesn’t negate the diagnosis—the primary deficit is the low bicarbonate with a酸emic pH.

For context, if you apply the usual compensatory rule (Winter’s formula), with HCO3- at 18, the expected PaCO2 would be about 1.5×18 + 8 ≈ 35 mmHg. The observed 40 mmHg is higher than that expectation, suggesting possible concurrent respiratory involvement, but the defining feature here is the low bicarbonate paired with acidemia, which signals metabolic acidosis. The other values either show alkalemia or do not have a low bicarbonate with acid pH, so they do not demonstrate metabolic acidosis.