In respiratory acidosis, the H+ ions will:

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

Answer: (A)

In respiratory acidosis, CO2 builds up in the blood because ventilation is reduced. CO2 combines with water to form carbonic acid, which dissociates into hydrogen ions (H+) and bicarbonate. That immediate effect is an increase in H+, so acidity rises (pH falls).

Over time, the body compensates by the kidneys reabsorbing more bicarbonate and excreting more hydrogen ions, which buffers the excess acid. This buffering lowers the H+ concentration toward normal levels, even though CO2 may remain high. The result is a rise in H+ initially, followed by a decrease as compensation kicks in. In acute cases the decrease may be modest, but in chronic cases the compensation is more pronounced.