In respiratory alkalosis, which statement about pH is true?

In respiratory alkalosis, which statement about pH is true?

• A. pH decreases due to CO2 retention.
• B. pH increases due to excessive CO2 exhalation.
• C. pH remains unaffected.
• D. pH decreases due to bicarbonate loss.

Answer: (B)

When you hyperventilate, you blow off more CO2 than your body produces. CO2 combines with water to form carbonic acid, which dissociates into hydrogen ions and bicarbonate. If CO2 levels drop, less hydrogen ion is produced, so the hydrogen ion concentration falls and the pH rises, leading to alkalemia. That’s why excessive CO2 exhalation increases pH. The other statements don’t fit: retaining CO2 would raise hydrogen ions and lower pH (respiratory acidosis); pH is not unchanged during a disturbance; and while bicarbonate can be affected by compensation, the immediate driver of respiratory alkalosis’s elevated pH is CO2 loss, not bicarbonate loss.

When you hyperventilate, you blow off more CO2 than your body produces. CO2 combines with water to form carbonic acid, which dissociates into hydrogen ions and bicarbonate. If CO2 levels drop, less hydrogen ion is produced, so the hydrogen ion concentration falls and the pH rises, leading to alkalemia. That’s why excessive CO2 exhalation increases pH.

The other statements don’t fit: retaining CO2 would raise hydrogen ions and lower pH (respiratory acidosis); pH is not unchanged during a disturbance; and while bicarbonate can be affected by compensation, the immediate driver of respiratory alkalosis’s elevated pH is CO2 loss, not bicarbonate loss.