Preliminary evaluation of the utility of comparing SpO2/FiO2 and PaO2/FiO2 ratios in dogs


  • Dr. Calabro's present address: The Friendship Hospital for Animals, Washington, District of Columbia, 20016.

  • Dr. Prittie is an Assistant Editor for the journal and did not participate in the peer review process of this manuscript other than as an author.

  • The authors declare no other conflicts of interest.

Address correspondence and reprint requests to

Dr. Janine Calabro, Friendship Hospital for Animals, Washington, DC 20016, USA.




To determine whether the ratio of pulse oximetry saturation/fraction of inspired oxygen (SpO2/FiO2, [SF]) correlates with the ratio of partial pressure of oxygen in arterial blood/FiO2 (PaO2/FiO2, [PF]) in dogs.


Prospective, observational pilot study.


Urban tertiary veterinary referral center.


Thirty-eight client-owned dogs requiring assessment of oxygenation.



Measurements and Main Results

Arterial blood gas analysis with co-oximetry was performed on samples obtained from the dorsal pedal artery. Median SpO2 was 91.5% (range 80–97%) and median PaO2 was 70.1 mmHg (range 44.5–103.8 mmHg). Hypoventilation was uncommon and venous admixture was the predominant cause of hypoxemia in this population. Median SF was 435.7 (range 381.0–461.9) and median PF was 334.0 (range 211.9–494.3). Nine dogs (23.6%) had PF <300; no dogs had PF below 200. SF and PF were correlated (ρ = 0.618, P < 0.01).


SF and PF in dogs spontaneously breathing room air have good correlation, suggesting that SF may be a useful, noninvasive surrogate for PF when assessing oxygenation in canine patients. Further studies are warranted to confirm and validate this relationship in spontaneously breathing and mechanically ventilated dogs on varying levels of FiO2 and to assess the ability of SF to predict outcome.