Assessment of early postoperative oxygenation after the application of a stepwise alveolar recruitment manoeuvre before anaesthesia recovery in healthy sheep

This study evaluated the effect of a stepwise alveolar recruitment manoeuvre (ARM) at the end of anaesthesia on arterial oxygenation and shunt fraction (F-shunt) during the early postoperative period in sheep. Twenty-four healthy, non-pregnant female Merino sheep underwent either laparoscopic or orthopaedic surgery under isoflurane anaesthesia. At the conclusion of surgery, and under isoflurane anaesthesia, oxygenation parameters and F-shunt values were analysed (Baseline). Animals were then randomly allocated to either the ARM group (ARMstepwise: laparoscopic n = 6, orthopaedic n = 6) or Control group (laparoscopic n = 6; orthopaedic n = 6). In the ARMstepwise group, animals received a stepwise, pressure-controlled ARM in sternal recumbency, with parameters re-evaluated 10 min post-application (PostARM). The control animals remained in sternal recumbency for 10 min following the completion of surgery without undergoing a stepwise ARM. Subsequently, isoflurane was discontinued in both groups. Oxygenation parameters and F-shunt values were recorded 10, 30, and 60 min after extubation. A linear mixed model was used for the statistical analysis. The implementation of a stepwise ARM at the end of isoflurane anaesthesia in healthy sheep enhanced oxygenation across both types of surgical procedures and significantly reduced F-shunt during orthopaedic surgery (Baseline: 26.31 ± 7.93 % vs PostARM: 6.47 ± 4.01 %; p = 0.001). These benefits were not sustained throughout the first postoperative hour, most likely because no PEEP was applied and oxygen was delivered with a high FiO₂ via facemask after extubation. Further research should clarify whether repeated intraoperative ARMs with PEEP and ∼ 60 % FiO₂ reduce atelectasis during anaesthetic recovery in sheep.