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.

Abstract

Clinicians often administer 100% inspired oxygen (fraction of inspired oxygen [Fio₂] = 1) for washout of volatile anaesthetics before tracheal extubation, potentially aggravating atelectasis formation and compromising oxygenation. We evaluated whether lower Fio₂ during emergence from anaesthesia reduces atelectasis and improves oxygenation. We conducted a single-centre, randomised controlled trial (NCT06538740) in 48 adult participants undergoing elective surgery under general anaesthesia. Participants were randomised to receive either pure oxygen (100%) or lower (70% or 40%) Fio₂ for anaesthetic washout before extubation. The primary outcome was atelectasis, assessed as changes in centre of ventilation and end-expiratory lung volume using electrical impedance tomography. Twenty-four participants (mean age 57 [range: 19-82] yr; 42% female) were randomly allocated to receive pure oxygen and 24 received 40% or 70% Fio₂. Participants receiving pure oxygen had a more ventral shift in the centre of ventilation (median [IQR], -0.3% [-2.2 to 1.3]), compared with lower Fio₂ (1.3% [0.0-2.8]; P=0.041). Participants receiving pure oxygen also had a greater reduction in end-expiratory lung volume after extubation (-1067 [-1839 to -589] ml) compared with participants receiving lower Fio₂ (-423 ml [-873 to -53]; P=0.006). There was no difference in end-expiratory lung volume between patients receiving 70% or 40% Fio₂ (P=0.39). Spo₂ (oxygen saturation measured by pulse oximetry) 10 min after extubation was higher in participants receiving 70% Fio₂ (interaction P=0.028). Avoiding pure oxygen before extubation preserved end-expiratory lung volume with more dorsal distribution of ventilation. Postextubation oxygenation was optimal with 70% Fio₂.