Which acid-base disturbance is characterized by a high pH and a low PaCO2?

Which acid-base disturbance is characterized by a high pH and a low PaCO2?

• A. Respiratory alkalosis
• B. Metabolic alkalosis
• C. Respiratory acidosis
• D. Metabolic acidosis

Answer: (A)

High pH with a low PaCO2 points to a respiratory process causing alkalemia. CO2 is the respiratory acid in the blood, so blowing off CO2 lowers acid load and raises the pH. When the pH is elevated and PaCO2 is decreased, the disorder is respiratory alkalosis, typically from hyperventilation. The body may compensate over time by reducing bicarbonate, more noticeable in chronic cases, but the primary driver here is the reduced CO2 from rapid breathing. In contrast, respiratory acidosis would show a high PaCO2 with a low pH, metabolic alkalosis would usually have a high pH with normal or elevated PaCO2 (compensation would raise CO2), and metabolic acidosis would present with a low pH and low bicarbonate.

High pH with a low PaCO2 points to a respiratory process causing alkalemia. CO2 is the respiratory acid in the blood, so blowing off CO2 lowers acid load and raises the pH. When the pH is elevated and PaCO2 is decreased, the disorder is respiratory alkalosis, typically from hyperventilation. The body may compensate over time by reducing bicarbonate, more noticeable in chronic cases, but the primary driver here is the reduced CO2 from rapid breathing. In contrast, respiratory acidosis would show a high PaCO2 with a low pH, metabolic alkalosis would usually have a high pH with normal or elevated PaCO2 (compensation would raise CO2), and metabolic acidosis would present with a low pH and low bicarbonate.