Post‐operative atelectasis – a randomised trial investigating a ventilatory strategy and low oxygen fraction during recovery

Background Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy with a combination of 1) continuous positive airway pressure ( CPAP ) or positive end‐expiratory pressure ( PEEP ) and 2) a reduced end‐expiratory oxygen concentration during recovery would reduce post‐operative atelectasis. Methods Sixty patients were randomized into two groups. During anaesthesia induction, inspiratory oxygen fraction ( F I O 2 ) was 1.0, and depending on weight, CPAP 6, 7 or 8  cmH 2 O was applied in both groups via facemask. During maintenance of anaesthesia, a laryngeal mask airway ( LMA ) was used, and PEEP was 6–8  cmH 2 O in both groups. Before removal of the LMA , F I O 2 was set to 0.3 in the intervention group and 1.0 in the control group. Atelectasis was studied by computed tomography ( CT ) approximately 14 min post‐operatively. Results In one patient in the group given an F I O 2 of 0.3 before removal of the LMA a CT scan could not be performed so the patient was excluded. The area of atelectasis was 5.5, 0–16.9 cm 2 (median and range), and 6.8, 0–27.5 cm 2 in the groups given F I O 2 0.3 or F I O 2 1.0 before removal of the LMA , a difference that was not statistically significant ( P  = 0.48). Post‐hoc analysis showed dependence of atelectasis on smoking (despite all were clinically lung healthy) and American Society of Anesthesiologists class ( P  = 0.038 and 0.015, respectively). Conclusion Inducing anaesthesia with CPAP / PEEP and F I O 2 1.0 and deliberately reducing F I O 2 during recovery before removal of the LMA did not reduce post‐operative atelectasis compared with F I O 2 1.0 before removal of the LMA .