Effects of intraoperative positive end-expiratory pressure and fraction of inspired oxygen on postoperative oxygenation in dogs undergoing stifle surgery

ObjectiveTo compare the effects of fraction of inspired oxygen (FiO₂) with the addition of positive end-expiratory pressure (PEEP) during anesthesia on arterial oxygenation in the first 4 postoperative hours in dogs. We hypothesized that compared with dogs breathing FiO₂ ≥ 0.95 and no PEEP (ZEEP), the use of intraoperative PEEP would improve postoperative oxygenation, and that the use of PEEP combined with an FiO₂ of 0.4 would further improve it.Study designProspective, randomized study.AnimalsA total of 30 dogs undergoing unilateral stifle surgery.MethodsUsing a standardized anesthetic protocol, dogs were assigned to either FiO₂ ≥ 0.95 and ZEEP, FiO₂ ≥ 0.95 and 5 cmH₂O PEEP or FiO₂ 0.4 and 5 cmH₂O PEEP. All dogs were mechanically ventilated with a tidal volume of 12 mL kg^–1. Dogs breathed room air after recovery from anesthesia. Arterial blood gases were measured during surgical closure and 10, 120 and 240 minutes after extubation. Demographic characteristics were compared with Kruskal–Wallis tests. The effects of treatment and time on the PaO₂, PaCO₂, PaO₂:FiO₂ and shunt fraction (F-shunt) were assessed with mixed-effect models.ResultsThe PaO₂ and F-shunt were lower during anesthesia for dogs breathing FiO₂ 0.4. No differences among groups were measured after extubation for any variable.Conclusions and clinical relevanceCompared with dogs ventilated with FiO₂ ≥ 0.95 and ZEEP, application of 5 cmH₂O PEEP did not improve intraoperative gas exchange. The combination of 5 cmH₂O PEEP and FiO₂ 0.4 resulted in lower intraoperative F-shunt values. However, no benefits from those maneuvers on postoperative PaO₂ and F-shunt were recorded after extubation, suggesting that alterations in pulmonary function imposed by anesthesia were reversed soon after extubation.