Postoperative oxygenation in healthy dogs following mechanical ventilation with fractions of inspired oxygen of 0.4 or >0.9.

To evaluate arterial oxygenation during the first 4 postoperative hours in dogs administered different fractions of inspired oxygen (F i O 2) during general anesthesia with mechanical ventilation. Prospective, randomized clinical trial. A total of 20 healthy female dogs, weighing >15 kg and body condition scores 3–7/9, admitted for ovariohysterectomy. Dogs were randomized to breathe an F i O 2 >0.9 or 0.4 during isoflurane anesthesia with intermittent positive pressure ventilation. The intraoperative PaO 2 :F i O 2 ratio was recorded during closure of the linea alba. Arterial blood was obtained 5, 60 and 240 minutes after extubation for measurement of PaO 2 and PaCO 2 (F i O 2 = 0.21). Demographic characteristics, duration of anesthesia, PaO 2 :F i O 2 ratio and anesthetic agents were compared between groups with Wilcoxon tests. The postoperative PaO 2 , PaCO 2 , rectal temperature, a visual sedation score and events of hypoxemia (PaO 2 < 80 mmHg) were compared between groups with mixed-effects models or generalized linear mixed models. Groups were indistinguishable by demographic characteristics, duration of anesthesia, anesthetic agents administered and intraoperative PaO 2 :F i O 2 ratio (all p > 0.08). Postoperative PaO 2 , PaCO 2 , rectal temperature or sedation score were not different between groups (all p > 0.07). During the first 4 postoperative hours, hypoxemia occurred in three and seven dogs that breathed F i O 2 >0.9 or 0.4 during anesthesia, respectively (p = 0.04). The results identified no advantage to decreasing F i O 2 to 0.4 during anesthesia with mechanical ventilation with respect to postoperative oxygenation. Moreover, the incidence of hypoxemia in the first 4 hours after anesthesia was higher in these dogs than in dogs breathing F i O 2 >0.9. [ABSTRACT FROM AUTHOR]