Which change is most characteristic of respiratory acidosis?

Which change is most characteristic of respiratory acidosis?

• A. Decreased PaCO2
• B. Decreased HCO3-
• C. Increased PaCO2
• D. Increased pH

Answer: (C)

In respiratory acidosis, the main issue is that ventilation is inadequate, causing CO2 to accumulate in the blood. That rising CO2 pushes the carbonic acid–bicarbonate buffering system toward more hydrogen ions, which lowers the pH. So the most characteristic change you’d expect is an increased PaCO2. Over time, the kidneys compensate by increasing HCO3-, but that is a secondary adjustment. This is why a decreased PaCO2 or an increased pH would point toward different problems, and a decreased bicarbonate isn’t the defining feature of this condition.

In respiratory acidosis, the main issue is that ventilation is inadequate, causing CO2 to accumulate in the blood. That rising CO2 pushes the carbonic acid–bicarbonate buffering system toward more hydrogen ions, which lowers the pH. So the most characteristic change you’d expect is an increased PaCO2. Over time, the kidneys compensate by increasing HCO3-, but that is a secondary adjustment. This is why a decreased PaCO2 or an increased pH would point toward different problems, and a decreased bicarbonate isn’t the defining feature of this condition.