Evaluation of pulse oximetry as a surrogate for PaO2 in awake dogs breathing room air and anesthetized dogs on mechanical ventilation

Abstract

Objective: To evaluate the ability of arterial hemoglobin oxygen saturation measurement via pulse oximetry (SpO₂ ) 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 SpO₂ and PaO₂ measurements from 62 dogs on mechanical ventilation.

Interventions: Dogs with concurrent SpO₂ and PaO₂ measured on room air had a data sheet completed with blood gas analysis. SpO₂ , PaO₂ , and FiO₂ values were collected from medical records of dogs on mechanical ventilation.

Measurements and main results: Predicted PaO₂ was calculated from SpO₂ 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 /FiO₂ and SpO₂ /FiO₂ 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 SpO₂ of 95%, with sensitivity and specificity of 77.8% and 89.5%, respectively. Using this cutoff, 6.9% of SpO₂ readings failed to detect hypoxemia, whereas 7.2% predicted hypoxemia that was not present.

Conclusions: The SpO₂ 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 SpO₂ /FiO₂ ratio may have value for evaluation of anesthetized dogs on supplemental oxygen. Arterial blood gas analysis remains ideal for assessment of oxygenation.

Keywords: blood gas analysis; hemoglobin oxygen saturation; hypoxemia; monitoring.