In hypoxemic respiratory failure, which ABG value defines hypoxemia on room air?

• A. PaO2 > 80 mmHg on room air
• B. PaO2 60-70 mmHg on room air
• C. PaO2 40-50 mmHg on room air
• D. PaO2 < 60 mmHg on room air

Answer: (D)

Hypoxemia means there isn’t enough oxygen in the arterial blood, and on room air the normal PaO2 is about 80–100 mmHg. When PaO2 falls to 60 mmHg or lower, oxygen delivery to tissues becomes markedly inadequate for many patients (SaO2 is roughly 90% at that point), which is the threshold used to define hypoxemic respiratory failure. So the defining ABG finding on room air is a PaO2 below 60. Values above that range indicate milder hypoxemia or normal oxygenation, and a PaO2 well below 60 indicates more severe hypoxemia but the formal definition centers on crossing that 60 threshold.