Paschold B-S, Braeuer BLP, Santer P, et al. Impact of high versus low fraction of inspired oxygen for anaesthetic washout and extubation on postoperative pulmonary atelectasis formation and oxygenation: a randomised controlled trial.
Giving 100% oxygen right before extubation feels like the safe move — maximize the margin against desaturation. This trial tests whether that habit is actually working against you.
Clinicians commonly deliver FiO2=1.0 during anaesthetic washout and extubation specifically to optimize oxygen delivery and buy safety margin. But absorption atelectasis is a well-described phenomenon: pure oxygen in poorly-ventilated alveoli gets absorbed into the bloodstream faster than nitrogen would, causing those alveoli to collapse. This trial directly tests whether that theoretical risk translates into measurable lung volume loss and worse post-extubation oxygenation — and whether there's a "sweet spot" FiO2 that avoids both hyperoxia-driven atelectasis and hypoxia risk.
| Design | Single-center RCT, three-arm (100% vs. 70% vs. 40% FiO2) |
| Population | 48 adults, elective surgery under general anesthesia with tracheal intubation, 1–5 hour anticipated duration |
| Groups | 24 received 100% FiO2 during washout/extubation; 24 received lower FiO2 (12 at 70%, 12 at 40%) |
| Primary outcome | Atelectasis formation, measured 1 min after extubation via electrical impedance tomography (EIT): center-of-ventilation shift and change in end-expiratory lung volume (EELV) |
| Secondary outcomes | SpO2 trajectory around extubation, lowest SpO2, hypoxemia (SpO2<90%) incidence, PACU clinical outcomes |
| Outcome | 100% FiO2 | Lower FiO2 (70%/40%) | P value |
|---|---|---|---|
| Center of ventilation shift (ventral = worse) | −0.3% (median) | +1.3% (median) | 0.041 |
| Reduction in end-expiratory lung volume | −1067 mL | −423 mL | 0.006 |
| EELV, 70% vs. 40% FiO2 specifically | No significant difference | 0.39 | |
| SpO2 at 10 min post-extubation | Higher with 70% FiO2 than either 100% or 40% | 0.028 (interaction) | |
The atelectasis-prevention benefit of avoiding pure oxygen held whether patients got 70% or 40% — there was no significant difference between those two lower-FiO2 groups on lung volume. But 70% specifically produced the best oxygenation trajectory in the 10 minutes after extubation. Put together: 40% avoids atelectasis just as well as 70%, but 70% is the concentration that also keeps SpO2 highest and most stable — which is why the trial's own conclusion lands on 70% as the practical target, not the lowest FiO2 that still avoids atelectasis.
This isn't a new mechanism — it's a well-established one getting its first dedicated washout/extubation-specific RCT.
Absorption atelectasis from high FiO2 is established physiology, and prior trials have tested FiO2 during other phases of anesthesia (recruitment maneuvers, intraoperative maintenance, TAVI procedures) with generally consistent findings that lower FiO2 reduces atelectasis risk. What's genuinely new here is the specific focus on the washout-to-extubation window — the exact moment many clinicians default to 100% oxygen for a safety margin — and using EIT (bedside, continuous, radiation-free) rather than CT to quantify the atelectasis directly at the bedside.
The trial supports its own conclusion: avoiding pure oxygen during washout preserved end-expiratory lung volume, and post-extubation SpO₂ was steadiest with 70%. Those are EIT surrogates measured in the first minutes after extubation, in 48 low-risk elective patients, and the reported differences faded within an hour without a difference in clinical outcomes. Reasonable to adopt 70% for routine low-risk extubations; not a reason to withhold 100% oxygen from the obese, the difficult airway, or anyone with little apnea reserve.