Abstract
Background. Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy, without recruitment manoeuvres, using a combination of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and a reduced end-expiratory oxygen fraction (FETO2) before ending mask ventilation with CPAP after extubation would reduce the area of postoperative atelectasis.Methods. Thirty patients were randomized into three groups. During induction and emergence, inspiratory oxygen fractions (FIO2) were 1.0 in the control group and 1.0 or 0.8 in the intervention groups. No CPAP/PEEP was used in the control group, whereas CPAP/PEEP of 6 cmH2O was used in the intervention groups. After extubation, FIO2 was set to 0.30 in the intervention groups and CPAP was applied, aiming at FETO2 < 0.30. Atelectasis was studied by computed tomography 25 min postoperatively.Results. The median area of atelectasis was 5.2 cm2 (range 1.6–12.2 cm2) and 8.5 cm2 (3–23.1 cm2) in the groups given FIO2 1.0 with or without CPAP/PEEP, respectively. After correction for body mass index the difference between medians (2.9 cm2) was statistically significant (confidence interval 0.2–7.6 cm2, p = 0.04). In the group given FIO2 0.8, in which seven patients were ex- or current smokers, the median area of atelectasis was 8.2 cm2 (1.8–14.7 cm2).Conclusion. Compared with conventional ventilation, after correction for obesity, this ventilation strategy reduced the area of postoperative atelectasis in one of the intervention groups but not in the other group, which included a higher proportion of smokers.
Highlights
The combination of reduced functional residual capacity, airway closure, and a high inspiratory oxygen fraction (FIO2) are the main factors implicated in the development of atelectasis, shunt and shunt-like effects that account for the majority of the impaired oxygenation seen during general anaesthesia [1,2]
Previous studies have shown that formation of atelectasis during preoxygenation and induction of anaesthesia can be avoided by adding a continuous positive airway pressure (CPAP) followed by a positive end-expiratory pressure (PEEP) [3,4]
We studied 1) a control group with no CPAP/PEEP and an FIO2 of 1.0 while breathing spontaneously after extubation; and 2) two intervention groups that were on CPAP/ PEEP of 6 cmH2O from induction to extubation, one group receiving an FIO2 of 1.0 and the other FIO2 0.8 until extubation, and in both groups an FIO2 of 0.3 via a face-mask while on CPAP after extubation
Summary
The combination of reduced functional residual capacity, airway closure, and a high inspiratory oxygen fraction (FIO2) are the main factors implicated in the development of atelectasis, shunt and shunt-like effects that account for the majority of the impaired oxygenation seen during general anaesthesia [1,2].Previous studies have shown that formation of atelectasis during preoxygenation and induction of anaesthesia can be avoided by adding a continuous positive airway pressure (CPAP) followed by a positive end-expiratory pressure (PEEP) [3,4]. CPAP of 10 cmH2O until extubation, failed to improve postoperative oxygenation compared with that achieved with zero end-expiratory pressure (ZEEP) [6]. This failure may have been caused by the presence of lung regions with high oxygen concentrations, which are prone to collapse shortly after extubation and the discontinuation of CPAP. We hypothesized that a ventilation strategy, without recruitment manoeuvres, using a combination of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and a reduced end-expiratory oxygen fraction (FETO2) before ending mask ventilation with CPAP after extubation would reduce the area of postoperative atelectasis. After correction for obesity, this ventilation strategy reduced the area of postoperative atelectasis in one of the intervention groups but not in the other group, which included a higher proportion of smokers
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