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

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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.


Retrospective study.


University veterinary teaching hospital.


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).


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.

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