Guide to Pulse Oximetry

Pulse oximeters have revolutionized anesthesia monitoring because of their ease of use, rapidity of application,

reliability as continuous, peripheral pulse monitors and their ability to non-invasively measure hemoglobin

(Hb) saturation with O2 (SpO2). Pulse oximeters can detect problems in two main areas. First is hypoxia (lack

of oxygen delivery to tissue), which is the most common cause of anesthetic mortality; second is changes in

pulse strength and regularity - commonly caused by lack of blood flow, bradycardia, and dysrhythmias.

Basic Understanding

1. Physiology

2. Methodology

SpO2 Interpretation and Trouble Shooting

Sensors application sites

The most useful sites for application of clip-type sensors in dogs & cats are the tongue, the lip, and the ear in non-pigmented skin. Other

useful sites include the paw of cats, across the individual toes of dogs, and the thin skin fold above the hock caudal to the tibia. Clipping a

small area of hair at the application site (e.g. ear, hock) will improve sensor performance.

Handle tissue (tongue, ear, etc) gently when positioning sensors to avoid vasoconstriction which alters SpO2 readings. In cats and other

small patients, folding a surgical swab over the tongue underneath the probe improves performance because this eliminates some

light, “damping the signal.” Motion artifacts (sensor movement or shivering) and extraneous light reduce pulse oximeter performance.

Dark, pigmented skin absorbs most of the infrared light so pulse oximetry won’t work.

Interpretation of SpO2 readings

SpO2 and pulse rate normal ranges measured with pulse oximeters

Alarm Settings

SpO2 measured by a pulse oximeter is generally 2-3% lower than SaO2 because it reads capillary blood through skin/mucosa. We aim to maintain arterial Hb O2 over 90% so alarms are typically set at 85% to 87%.

Troubleshooting low SpO2 readings