How do PEEP and FiO2 interact to achieve target oxygenation?

• A. PEEP increases mean airway pressure and recruits alveoli to improve oxygenation; FiO2 provides the oxygen fraction.
• B. PEEP has no effect on oxygenation.
• C. FiO2 alone determines oxygen delivery and PEEP is only used to prevent barotrauma.
• D. PEEP only influences CO2 elimination.

Answer: (A)

The main idea here is that achieving target oxygenation relies on two adjustable factors: how much oxygen you’re delivering to the lungs and how well the lungs can exchange that oxygen into the blood. PEEP raises the mean airway pressure and helps keep alveoli open, which recruits collapsed units and improves ventilation–perfusion matching. When more alveoli participate in gas exchange, oxygen transfer to the blood improves, even before changing the oxygen content of the inhaled gas.

FiO2 tells you what fraction of inspired oxygen is available to the alveoli. Increasing FiO2 raises the oxygen content of the alveolar gas, pushing more oxygen into the blood, up to other limiting factors in the lung. So, together, PEEP makes the lung’s surface area and gas exchange more effective, while FiO2 increases the amount of oxygen available to that exchange. That combination is how you reach target oxygenation.

The other statements miss important points: PEEP does affect oxygenation, not just barotrauma prevention; FiO2 alone can’t ensure adequate oxygen delivery if alveoli aren’t recruited or if shunt is high; and while PEEP can influence CO2, its primary role in this context is improving oxygenation through recruitment and higher mean airway pressure.