Which interpretation best fits the blood gas with pH 7.01, PCO2 39, PO2 180, HCO3 16, BE -19 in a term infant?

• A. Metabolic Acidosis
• B. Respiratory Acidosis
• C. Metabolic Alkalosis
• D. Respiratory Alkalosis

Answer: (A)

Primary disturbance: metabolic acidosis. The acidemia (pH 7.01) with a low bicarbonate concentration (HCO3- = 16) and a markedly negative base excess (-19) points to a loss of base and accumulation of acids from a metabolic process. In metabolic acidosis, you expect the pH to be low and the HCO3- to be low, which is exactly what is seen here.

The PCO2 is 39, close to normal. In metabolic acidosis, the body usually compensates by blowing off CO2 to lower the acidity (respiratory compensation), which would bring the PCO2 down toward the mid-30s or lower depending on severity. Here the PCO2 is not reduced as much as expected, indicating incomplete compensation and potentially a mixed picture, but the dominant abnormality remains metabolic acidosis given the clear bicarbonate deficit and negative base excess. The high PO2 simply reflects oxygenation status and doesn’t drive the acid-base interpretation.

So the best fit is metabolic acidosis due to the low HCO3- and negative base excess with acidemia.