Atelectasis during general anaesthesia increases with age up to 50 years and BMI up to 30 kg/m^2, but appears curiously limited beyond this.

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• Göran Hedenstierna, Leif Tokics, Henrik Reinius, Hans U Rothen, Erland Östberg, and John Öhrvik.
• Department of Medical Sciences, Clinical Physiology, Uppsala University, Uppsala, Sweden. Electronic address: goran.heenstierna@medsci.uu.se.
• Br J Anaesth. 2020 Mar 1; 124 (3): 336-344.

BackgroundGeneral anaesthesia is increasingly common in elderly and obese patients. Greater age and body mass index (BMI) worsen gas exchange. We assessed whether this is related to increasing atelectasis during general anaesthesia.MethodsThis primary analysis included pooled data from previously published studies of 243 subjects aged 18-78 yr, with BMI of 18-52 kg m-2. The subjects had no clinical signs of cardiopulmonary disease, and they underwent computed tomography (CT) awake and during anaesthesia before surgery after preoxygenation with an inspired oxygen fraction (FIO2) of >0.8, followed by mechanical ventilation with FIO2 of 0.3 or higher with no PEEP. Atelectasis was assessed by CT.ResultsAtelectasis area of up to 39 cm2 in a transverse scan near the diaphragm was seen in 90% of the subjects during anaesthesia. The log of atelectasis area was related to a quadratic function of (age+age2) with the most atelectasis at ∼50 yr (r2=0.08; P<0.001). Log atelectasis area was also related to a broken-line function of the BMI with the knee at 30 kg m-2 (r2=0.06; P<0.001). Greater atelectasis was seen in the subjects receiving FIO2 of 1.0 than FIO2 of 0.3-0.5 (12.8 vs 8.1 cm2; P<0.001). A multiple regression analysis, including a quadratic function of age, a broken-line function of the BMI, and dichotomised FIO2 (0.3-0.5/1.0) adjusting for ventilatory frequency, strengthened the association (r2=0.23; P<0.001). PaO2 decreased with both age and BMI.ConclusionsAtelectasis during general anaesthesia increased with age up to 50 yr and decreased beyond that. Atelectasis increased with BMI in normal and overweight patients, but showed no further increase in obese subjects (BMI ≥30 kg m-2). Therefore, greater age and obesity appear to limit atelectasis formation during general anaesthesia.Copyright © 2019 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.

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