Evaluation of pulse oximetry as a surrogate for PaO 2 in awake dogs breathing room air and anesthetized dogs on mechanical ventilation.

Objective To evaluate the ability of arterial hemoglobin oxygen saturation measurement via pulse oximetry (SpO(2)) to serve as a surrogate for PaO2 in dogs. Design Two-part study: prospective observational and retrospective components. Setting University teaching hospital. Animals Ninety-two dogs breathing room air prospectively enrolled on a convenience basis. Retrospective evaluation of 1,033 paired SpO(2) and PaO2 measurements from 62 dogs on mechanical ventilation. Interventions Dogs with concurrent SpO(2) and PaO2 measured on room air had a data sheet completed with blood gas analysis. SpO(2), PaO2, and FiO(2) values were collected from medical records of dogs on mechanical ventilation. Measurements and Main Results Predicted PaO2 was calculated from SpO(2) using the dog oxyhemoglobin dissociation curve. The correlation coefficient between measured and predicted PaO2 was 0.49 (P < 0.0001) in room air dogs and 0.74 (P < 0.0001) in ventilated dogs. In room air dogs, Bland-Altman analysis between measured minus predicted PaO2 versus the average showed a mean bias of -6.0 mm Hg (95% limit of agreement, -35 to 23 mm Hg). The correlation coefficient between PaO2/FiO(2) and SpO(2)/FiO(2) ratios was 0.76 (P < 0.0001). After combining data sets, receiver operating characteristic curve analysis showed the optimal cutoff value for detecting hypoxemia (PaO2 < 80 mm Hg) was an SpO(2) of 95%, with sensitivity and specificity of 77.8% and 89.5%, respectively. Using this cutoff, 6.9% of SpO(2) readings failed to detect hypoxemia, whereas 7.2% predicted hypoxemia that was not present. Conclusions The SpO(2) was not clinically suitable as a surrogate for PaO2, though it performed better in mechanically ventilated dogs. As sensitivity for the detection of hypoxemia was poor, pulse oximetry does not appear to be an acceptable screening test. The SpO(2)/FiO(2) ratio may have value for evaluation of anesthetized dogs on supplemental oxygen. Arterial blood gas analysis remains ideal for assessment of oxygenation.