• Alexander Larsson, Erland Östberg, and Lennart Edmark.
• From the Department of Anaesthesia and Intensive Care (AL, EÖ, LE) and Region Vastmanland - Uppsala University, Centre for Clinical Research, Vastmanland Hospital Vasteras, Sweden (AL, EÖ, LE).
• Eur J Anaesthesiol. 2023 Sep 1; 40 (9): 699706699-706.

BackgroundThe prerequisites for the early formation of anaesthesia-related atelectasis are pre-oxygenation with its resulting high alveolar oxygen content, and airway closure. Airway closure increases with age, so it seems counterintuitive that atelectasis formation during anaesthesia does not. One proposed explanation is that pre-oxygenation is impaired in the elderly by airway closure present in the waking state. The extent of airway closure cannot be assessed at the bedside, but arterial partial pressure of oxygen ( Pa O 2 ) as a surrogate variable of the resulting ventilation to perfusion mismatch can.ObjectiveThe primary aim was to test the hypothesis that a decreased efficacy of pre-oxygenation, measured as the fraction of end-tidal oxygen (F E' O 2 ) after 3 min of pre-oxygenation, correlates with decreased Pa O 2 on room air. We also re-investigated the influence on F E' O 2 by age.DesignProspective observational study.SettingTwo regional hospitals, Västerås and Köping County Hospitals, Västmanland, Sweden, between 30 October 2018 and 17 September 2021.ParticipantsWe included 120 adults aged 40 to 79 years presenting for elective noncardiac surgery.InterventionAn arterial blood gas was sampled before commencing pre-oxygenation.ResultsNo linear correlation was found between F E' O 2 at 3 min and Pa O 2 or age (Pearson's r  = -0.038, P  = 0.684; and Pearson's r  = -0.113, P  = 0.223, respectively). The mean ± SD F E' O 2 at 3 min for the population studied was 0.87 ± 0.05.ConclusionThe lack of correlation between F E' O 2 at 3 min and Pa O 2 or age during pre-oxygenation has implications for further studies concerning the interaction between airway closure and atelectasis. After 3 min of pre-oxygenation, F E' O 2 , even in the elderly, indicated a high enough alveolar oxygen concentration to promote atelectasis after induction, therefore, it is still unclear why atelectasis formation diminishes after middle age.Trial RegistrationClinicalTrials.gov NCT03395782.Copyright © 2023 European Society of Anaesthesiology and Intensive Care. Unauthorized reproduction of this article is prohibited.

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