Respiratory Acidosis is characterized by which finding?

• A. Regulation of pH
• B. Excess acid from poor perfusion
• C. Elevated CO2
• D. Measure of acidity or alkalinity

Answer: (C)

Elevated carbon dioxide in the blood is the defining feature of respiratory acidosis. When ventilation is insufficient, CO2 accumulates in the arterial blood. CO2 combines with water to form carbonic acid, which dissociates and lowers the pH. So the key finding you’d expect is high PCO2 with a low pH on an arterial blood gas. In acute cases the CO2 rise happens quickly and the kidneys haven’t had time to compensate; in chronic cases the kidneys raise bicarbonate to offset the acidity, so bicarbonate levels are higher as compensation progresses. The other options don’t pinpoint the cause: regulation of pH is a broad homeostatic process, excess acid from poor perfusion points to metabolic acidosis, and a measure of acidity or alkalinity refers to pH rather than the CO2-driven change that defines respiratory acidosis.