Which ABG pattern defines metabolic alkalosis?

Which ABG pattern defines metabolic alkalosis?

• A. Low pH with low HCO3-
• B. Low pH with high PaCO2
• C. High pH with low PaCO2
• D. High pH with high HCO3-

Answer: (D)

Metabolic alkalosis shows an alkaline pH with elevated bicarbonate. When bicarbonate rises, the blood becomes more alkaline, raising the pH. The body tries to compensate by retaining CO2 through hypoventilation, so the PaCO2 is higher than normal, though this is a secondary, compensatory change rather than a primary problem. That combination—high pH with high HCO3−—defines metabolic alkalosis. The other patterns involve either acidosis (low pH) or a primary respiratory imbalance (high pH with low PaCO2 indicates respiratory alkalosis; low pH with high PaCO2 indicates respiratory acidosis).

Metabolic alkalosis shows an alkaline pH with elevated bicarbonate. When bicarbonate rises, the blood becomes more alkaline, raising the pH. The body tries to compensate by retaining CO2 through hypoventilation, so the PaCO2 is higher than normal, though this is a secondary, compensatory change rather than a primary problem. That combination—high pH with high HCO3−—defines metabolic alkalosis. The other patterns involve either acidosis (low pH) or a primary respiratory imbalance (high pH with low PaCO2 indicates respiratory alkalosis; low pH with high PaCO2 indicates respiratory acidosis).