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

OBJECTIVE

To evaluate arterial oxygenation during the first 4 postoperative hours in dogs administered different fractions of inspired oxygen (FiO) 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 FiO >0.9 or 0.4 during isoflurane anesthesia with intermittent positive pressure ventilation. The intraoperative PaO:FiO ratio was recorded during closure of the linea alba. Arterial blood was obtained 5, 60 and 240 minutes after extubation for measurement of PaO and PaCO (FiO = 0.21). Demographic characteristics, duration of anesthesia, PaO:FiO ratio and anesthetic agents were compared between groups with Wilcoxon tests. The postoperative PaO, PaCO, rectal temperature, a visual sedation score and events of hypoxemia (PaO < 80 mmHg) were compared between groups with mixed-effects models or generalized linear mixed models.

RESULTS

Groups were indistinguishable by demographic characteristics, duration of anesthesia, anesthetic agents administered and intraoperative PaO:FiO ratio (all p > 0.08). Postoperative PaO, PaCO, 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 FiO >0.9 or 0.4 during anesthesia, respectively (p = 0.04).

CONCLUSIONS AND CLINICAL RELEVANCE

The results identified no advantage to decreasing FiO 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 FiO >0.9.