What is the critical range for pCO2 in arterial blood gas values?

• A. 20-60 mmHg
• B. 30-70 mmHg
• C. 10-50 mmHg
• D. 40-80 mmHg

Answer: (A)

pCO2 in arterial blood gas analysis mainly reflects how well ventilation is matching CO2 production. Normal arterial pCO2 is about 35-45 mmHg, but many labs use 20-60 mmHg as the practical threshold distinguishing non-urgent from urgent abnormalities. Values outside this window signal dangerous ventilation problems: pCO2 below 20 mmHg indicates marked hyperventilation (risk of respiratory alkalosis and cerebral effects), while pCO2 above 60 mmHg indicates hypoventilation or respiratory failure (risk of respiratory acidosis and CO2 retention). So the range 20-60 mmHg is the cut-off used to flag critical pCO2 abnormalities, making it the best choice.