In ABG interpretation, which pattern defines metabolic alkalosis?

• A. pH < 7.35 with elevated HCO3-
• B. pH > 7.45 with elevated HCO3-
• C. pH > 7.45 with low HCO3-
• D. pH < 7.35 with low HCO3-

Answer: (B)

Metabolic alkalosis is identified when the blood is alkaline (pH above 7.45) and the bicarbonate level is elevated. The excess HCO3- raises the pH, creating the alkalemic state. The body may try to compensate by reducing ventilation to raise CO2, but the defining clue remains the simultaneous alkalemia and high bicarbonate. This distinguishes it from patterns where the pH is alkalemic but bicarbonate is not elevated (which points to a respiratory cause or a mixed disorder), or patterns with acidemia or a low bicarbonate (which indicate metabolic acidosis).