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

Objective: To compare the effects of fraction of inspired oxygen (FiO) 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 FiO ≥ 0.95 and no PEEP (ZEEP), the use of intraoperative PEEP would improve postoperative oxygenation, and that the use of PEEP combined with an FiO of 0.4 would further improve it.

Study Design: Prospective, randomized study.

Animals: A total of 30 dogs undergoing unilateral stifle surgery.

Methods: Using a standardized anesthetic protocol, dogs were assigned to either FiO ≥ 0.95 and ZEEP, FiO ≥ 0.95 and 5 cmHO PEEP or FiO 0.4 and 5 cmHO PEEP. All dogs were mechanically ventilated with a tidal volume of 12 mL kg. 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 PaO, PaCO, PaO:FiO and shunt fraction (F-shunt) were assessed with mixed-effect models.

Results: The PaO and F-shunt were lower during anesthesia for dogs breathing FiO 0.4. No differences among groups were measured after extubation for any variable.

Conclusions And Clinical Relevance: Compared with dogs ventilated with FiO ≥ 0.95 and ZEEP, application of 5 cmHO PEEP did not improve intraoperative gas exchange. The combination of 5 cmHO PEEP and FiO 0.4 resulted in lower intraoperative F-shunt values. However, no benefits from those maneuvers on postoperative PaO and F-shunt were recorded after extubation, suggesting that alterations in pulmonary function imposed by anesthesia were reversed soon after extubation.