You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Pulse oximetry is the indirect measurement of the saturation of arterial hemoglobin with oxygen using a non-invasive device called a pulse oximeter.

Low blood oxygen concentration is a major cause of anesthetic death - so monitoring oxygen concentrations is important, particularly in high risk patients (eg post-trauma, geriatrics, patients with cardiovascular, pulmonary or chest disease). Hypoxemia exists when the arterial oxygen falls to less than 80mmHg, and this most frequently occurs when there is inadequate oxygen in a closed breathing system, when the patient is not breathing frequently or deeply enough (hypoventilation) or if there is lung disease present which is preventing normal gas exchange across the alveoli.

The pulse oximeter measures the pulsatile absorbance of infrared light (wavelengths 940nm - absorbed by oxyhemoglobin; and 660nm - absorbed by deoxygenated hemoglobin) when it is transmitted through a tissue. Common sites at which to use the device are :

• Ear
• Lip
• Tongue
• Toe

There is an extremely narrow range of oxygen tension which is safe and this needs to be calculated from the readings given by a pulse oximeter - which is a measurement of the  % saturation with oxygen. A reading of 95% saturation on a pulse oximeter is equivalent to 80mmHg PaO₂ . At a saturation reading of 90% the patient only has a PaO₂  of 60mmHg which indicates serious hypoxemia. In addition it should be remembered that for technical reasons pulse oximeter readings are artificially high if the saturated oxygen is less than 85%, and artificially low if the saturated oxygen is more than 85%.

Common errors in interpretation of oximeter readings are caused by :

• Patients with a weak pulse
• Patients treated with vasoconstricting agents
• Patients with an irregular heart rhythm
• Patients with a low PCV (<10%)
• Oximeter probe too large for patient
• Patients with high methemoglobin or carboxyhemoglobin concentrations in their blood

Last updated : January 2016