Positive end-expiratory pressure prevents atelectasis during general anaesthesia even in the presence of a high inspired oxygen concentration

Background: General anaesthesia impairs the gas exchange in the lungs, and moderate desaturation (SaO(2) 86-90%) occurred in 50% of anaesthetised patients in a blinded pulse oximetry study. A high FiO(2) might reduce the risk of hypoxaemia, but can also promote atelectasis. We hypothesised that a moderate positive end-expiratory pressure (PEEP) level of 10 cmH(2)O can prevent atelectasis during ventilation with an FiO(2)=1.0. Methods: Atelectasis was evaluated by computed tomography (CT) in 13 ASA I-II: patients undergoing elective surgery. CT scans were obtained before and 15 min after induction of anaesthesia. Then, recruitment of collapsed lung tissue was performed as a "vital capacity manoeuvre" (VCM, inspiration with Paw=40 cmH(2)O for 15 s), and a CT scan was obtained at the end of the VCM. Thereafter, PEEP=0 cmH(2)O was applied in group 1, and PEEP=10 cmH(2)O in group 2. Additional CT scans were obtained after the VCM. Oxygenation was measured before and after the VCM. Results: Atelectasis (>1 cm(2)) was present in 12 of the 13 patients after induction of anaesthesia. At 5 and 10 min after the VCM, atelectasis was significantly smaller in group 2 than group I. (P<0.005). A significant inverse correlation was found between PaO2 and atelectasis. Conclusions: PEEP=10 cmH(2)O reduced atelectasis formation after a VCM, when FiO(2)=1.0 was used. Thus, a VCM followed by PEEP=10 cmH(2)O should be considered when patients are ventilated with a high FiO(2) and gas exchange is impaired.