What is the normal reference range for arterial pCO2 in healthy adults?

• A. 35-45 mmHg
• B. 25-35 mmHg
• C. 50-60 mmHg
• D. 10-20 mmHg

Answer: (A)

Arterial pCO2 is kept within a narrow range by the balance between CO2 production in the body's metabolism and its removal by the lungs. In healthy adults, this balance normally yields a pCO2 around 35 to 45 mmHg. Values within this window indicate normal alveolar ventilation and effective CO2 elimination. If pCO2 rises above this range, ventilation is insufficient or CO2 elimination is impaired, leading to hypercapnia. If pCO2 falls below this range, ventilation is excessive, causing hypocapnia. The other options lie far outside the normal range and would reflect abnormal breathing patterns or pathology.