Which condition is characterized by decreased CO2 levels in the blood?

• A. Renal failure
• B. Metabolic acidosis
• C. Respiratory failure
• D. Hypoventilation

Answer: (B)

Metabolic acidosis is characterized by decreased CO2 levels in the blood due to an increase in acid production or a loss of bicarbonate. In this condition, the body often compensates by increasing respiratory rate, which leads to greater exhalation of CO2. As a result, the arterial blood gas analysis typically shows a decrease in CO2 levels, reflecting the body's attempt to correct the acid-base imbalance.

In metabolic acidosis, the primary issue may stem from conditions such as diabetic ketoacidosis, lactic acidosis, or chronic diarrhea, which can either add acid to the system or deplete bicarbonate reserves. The respiratory compensation effectively lowers carbon dioxide levels by promoting increased breathing, thus helping to regulate the pH toward normal ranges.

Other conditions mentioned, such as renal failure, respiratory failure, and hypoventilation, usually lead to increased CO2 levels rather than decreased. In renal failure, the kidneys are unable to excrete acids effectively, leading to a build-up. Respiratory failure can cause retention of CO2 due to inadequate ventilation, while hypoventilation also results in CO2 accumulation. Therefore, only metabolic acidosis directly correlates with decreased CO2 levels in the bloodstream.