Pulse Oximetry | VetGirl Veterinary

Pulse oximetry is a non-invasive method of measuring the oxygen saturation of hemoglobin (SpO2) in arterial blood. It it perfect?  Is it the gold standard?  No: an arterial blood gas (ABG) is considered the gold standard.  Due to the complexity of arterial blood gas sampling, it is often reserved for critically ill canine patients, leaving pulse oximetry the common bedside test for evaluating oxygenation. That said, in VetGirl’s opinion: pulse oximeter + venous blood gas (VBG) = ABG.

So, how exactly does the pulse oximeter work?

The pulse oximeter calculates the percent of oxygen saturation of hemoglobin in arterial blood using spectrophotometry. The probe passes light through the tissues at two different wavelengths: a red and infrared light absorption.  Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated (or reduced) hemoglobin absorbs more red light and allows more infrared light to pass through. The difference in light absorption is calculated and the final figure is displayed as a percentage (SpO2%).

So, why should you care? Because with the non-invasive pulse oximeter, you can correlate your  SpO2% to the partial pressure of oxygen in the blood (PaO2) based off the oxyhemoglobin dissociation curve. Bare with us and think back to third-year veterinary school… VetGirl