CONICET | Buscador de Institutos y Recursos Humanos

Objectives: To evaluate arterial oxygenation during the first four postoperative hours in dogs administered different fractions of inspired oxygen (FIO2) during general anesthesia with mechanical ventilation.Study design: Prospective, randomized clinical trial. Animals A total of 20 healthy female dogs, weighing >15 kg and body condition scores 3?7/9, admitted for ovariohysterectomy.Methods: Dogs were randomized to breathe an FIO2 >0.9 or 0.4 during isoflurane anesthesia with intermittent positive pressure ventilation. The intraoperative PaO2:FIO2 ratio was recorded during closure of the linea alba. Arterial blood was obtained 5, 60 and 240 minutes after extubation for measurement of PaO2 and PaCO2 (FIO2 0.21). Demographic characteristics, duration of anesthesia, anesthetic agents and the PaO2:FIO2 ratio were compared between groups with Wilcoxon tests. The postoperative PaO2, PaCO2, rectal temperature, a visual sedation score and events of hypoxemia (PaO2 < 80 mmHg) were compared between groups with mixed effect models or generalized linear mixed models.Results: Groups were indistinguishable by demographic characteristics, duration of anesthesia, anesthetic agents administered and intraoperative PaO2:FIO2 (all p > 0.08). Postoperative PaO2, PaCO2, rectal temperature or sedation score were not different between groups (all p > 0.07). During the first four postoperative hours, hypoxemia occurred in three and seven dogs that breathed FIO2 >0.9 or 0.4 during anesthesia, respectively (p = 0.04).Conclusions and clinical relevance: The results identified no advantage to decreasing FIO2 to 0.4 during anesthesia with mechanical ventilation with respect to postoperative oxygenation. Moreover, the incidence of hypoxemia in the first four hours after anesthesia was higher in these dogs than for dogs breathing FIO2 >0.9.