FiO2 and PEEP both use to improve oxygenation, in ARDS, in the beginning you give high FiO2 and PEEP to improve oxygenation, once PaO2 is normal
then you first decrease FiO2 and keep it below 60 and then decrease PEEP, to wean off your target FiO2 should be less then 40
- Increasing FiO2 depresses respiratory drive
- PEEP keeps alveoli open at the end of expiration and it improves ventilation and gas exchange
- FiO2 should not be more than 60 for more than 48hrs it will cause oxygen toxicity, which will further destroy the lung.