Evaluation of PaO2 /FiO2 and SaO2 /FiO2 ratios in postoperative dogs recovering on room air or nasal oxygen insufflation.

OBJECTIVE: To evaluate partial pressure of oxygen in arterial blood/fractional percentage of inspired oxygen (PaO2 /FiO2 ) and SaO2 /FiO2 ratios (where SaO2 is percentage of oxyhemoglobin saturation in arterial blood), and the correlation between PaO2 /FiO2 and SaO2 /FiO2 , in healthy dogs recovering postoperatively on room air versus nasal oxygen insufflation.

DESIGN: Retrospective study.

SETTING: University veterinary teaching hospital.

ANIMALS: Nineteen dogs.

MEASUREMENTS AND MAIN RESULTS: Medical records were retrospectively evaluated for data from a previous prospective study of dogs undergoing ovariohysterectomy, subsequently randomized to receive 100 mL/kg/min of nasal oxygen insufflation (estimated 37% FiO2 , n = 9) or room air (estimated 21% FiO2 , n = 10) for 2 hours postoperatively. Baseline information was obtained 1 hour intraoperatively, followed by three postoperative time points (10, 60, and 120 min). Data recorded for each time point included FiO2 , PaO2 , SaO2 , PaO2 /FiO2 , SaO2 /FiO2 , partial pressure of carbon dioxide in arterial blood (PaCO2 ), rectal temperature, and arterial blood pH. The PaO2 /FiO2 in dogs recovering on supplemental oxygen was significantly higher compared to dogs recovering on room air (516 ± 28 vs. 359 ± 10, P < 0.0001), whereas the SaO2 /FiO2 ratio in dogs recovering on supplemental oxygen was significantly lower compared to dogs recovering on room air (268 ± 0.5 versus 448 ± 1.4, P < 0.0001). The PaO2 /FiO2 and SaO2 /FiO2 ratios demonstrated excellent correlation for both groups at each postoperative time point. In dogs breathing room air, PaO2 /FiO2 and SaO2 /FiO2 correlation coefficients were 0.90, 0.95, and 0.93 (P < 0.001). In dogs receiving supplemental oxygen, PaO2 /FiO2 and SaO2 /FiO2 correlation coefficients were 0.94, 0.93, and 0.90 (P < 0.001).

CONCLUSIONS: In this population of postoperative dogs breathing either room air or with nasal oxygen insufflation, PaO2 /FiO2 and SaO2 /FiO2 had excellent correlation. Further evaluation into the correlation between SaO2 /FiO2 or pulse oximeter oxygen saturation (SpO2 )/FiO2 with PaO2 /FiO2 in both healthy dogs, and dogs with pulmonary dysfunction is warranted.