Which statement defines 'adequate' oxygenation in respiratory failure?

• A. SpO2 >92% and ETCO2 30-40 with clinical improvement
• B. SpO2 >90%, ETCO2 between 35-45, and clinical improvement
• C. SpO2 >95% only
• D. ETCO2 between 25-35 with stable vitals

Answer: (B)

Adequate oxygenation in respiratory failure means not only having enough oxygen in the blood but also ensuring ventilation is appropriate and the patient is improving. A practical target combines a safe oxygen saturation with a normal ventilation surrogate and signs of clinical progress. An SpO2 above 90% indicates the patient isn’t severely hypoxemic, and an etCO2 in the normal range (about 35–45) shows that CO2 is being eliminated without hypoventilation or excessive ventilation. When these are paired with clear clinical improvement, you have a reliable indication that both oxygenation and ventilation are adequate.

Why this set is better than the others: setting SpO2 a bit higher than 90% is acceptable but not strictly necessary, and using a normal ventilation range reinforces that ventilation is adequate. Relying on SpO2 alone ignores ventilation status, and a CO2 range that’s too low or too high suggests either hyperventilation or hypoventilation, which would not reflect true adequacy. Lacking the clinical improvement aspect leaves uncertainty about how the patient is actually responding.