IBSC Certified Critical Care Paramedic (CCP-C) Practice Test

When PaO2 is low, the arterial side isn’t getting enough oxygen from the lungs. The most effective and direct ways to fix this on a ventilator are to increase the oxygen content in the inspired gas and to keep the lungs open to improve oxygen exchange. Increasing FiO2 raises the fraction of oxygen in the air you’re delivering, boosting how much oxygen diffuses into the blood. Adding PEEP keeps alveoli open at the end of expiration, improves ventilation-perfusion matching, reduces shunt, and increases the surface area for gas exchange. Together, these options raise PaO2 efficiently.

Why not increasing tidal volume? It mainly targets ventilation and CO2 removal and can risk lung injury without reliably correcting hypoxemia. Decreasing FiO2 would worsen oxygenation, and turning off PEEP reduces alveolar recruitment, also decreasing PaO2. So the best approach to low PaO2 is to increase FiO2 or adjust PEEP.