In respiratory alkalosis, the carbon dioxide ions will be:

• A. Increase initially, and then decrease
• B. Decrease initially, and then increase
• C. Increase continuously
• D. Decrease continuously

Answer: (B)

In this scenario, the main idea is that breathing rate drives carbon dioxide levels. When you hyperventilate, you blow off CO2 faster than your body produces it, so the partial pressure of CO2 in the blood falls, raising the pH and causing respiratory alkalosis. Over time, the body tries to compensate to bring the pH back toward normal. The kidneys do this by decreasing bicarbonate reabsorption and increasing bicarbonate excretion, which helps lower the buffering basis of the blood and move the system toward neutrality. Because of this sequence, carbon dioxide levels drop initially due to the rapid ventilation, and then, as the underlying cause is addressed or ventilation slows, CO2 can rise again toward normal levels. So the pattern is: an initial decrease in CO2, followed by a later increase as balance is restored.