In metabolic alkalosis on ABG interpretation, which pattern defines the disorder?

• A. pH < 7.35 with low HCO3-
• B. pH > 7.45 with elevated HCO3- (>26 mEq/L)
• C. pH > 7.45 with elevated PaCO2
• D. pH 7.35-7.45 with elevated PaCO2

Answer: (B)

In metabolic alkalosis, the body has an excess of base (bicarbonate), which shifts the blood toward alkalinity. The clue on an ABG is an alkalemic pH (greater than 7.45) with a high bicarbonate level (HCO3- above about 26 mEq/L). The elevated HCO3- is the primary abnormality, and the respiratory system may compensate by retaining CO2, so the PaCO2 can be higher than normal, but the defining feature is the high bicarbonate with an alkalemic pH.

The other patterns don’t fit because they either show acidosis (low pH with low HCO3-), or describe a situation that isn’t a pure metabolic alkalosis (such as a high pH with high PaCO2, which would imply a mixed disorder), or a normal pH with elevated PaCO2 (which points to a respiratory issue with compensation rather than metabolic alkalosis).