What is the normal range for PaCO2?

• A. 10-20 mmHg
• B. 60-80 mmHg
• C. 35-45 mmHg
• D. 20-30 mmHg

Answer: (C)

PaCO2 reflects how effectively the lungs are removing carbon dioxide and is a key part of ventilation and acid-base balance. The normal arterial PaCO2 is about 35–45 mmHg, which shows matched CO2 production and exhalation. When PaCO2 rises above this range, ventilation is inadequate (hypoventilation), leading toward respiratory acidosis. When PaCO2 falls below this range, ventilation is excessive (hyperventilation), leading toward respiratory alkalosis. The other ranges listed are outside normal and would indicate abnormal ventilation rather than normal gas exchange.