A pulse oximeter gives you a non-invasive estimate of hemoglobin saturation (SpO2) and a pulse rate, which makes it a continuous read on your patient’s oxygenation. It’s one of the simplest and least expensive monitoring tools in the practice, and one of the easiest to misread. This guide covers what SpO2 does and doesn’t tell you, where to put the probe in dogs and cats, why readings go wrong, and what to look for when you buy a veterinary pulse oximeter.
What SpO2 measures, and what it doesn’t
SpO2 estimates how much of the hemoglobin in arterial blood is carrying oxygen. That makes it a measure of oxygenation, not ventilation. The ACVA’s monitoring guidelines list pulse oximetry for oxygenation and capnography (end-expired CO2) for ventilation, and you need both questions answered. A patient can hold a reassuring SpO2 while ventilation is failing, so don’t let a good number on the oximeter talk you out of watching the capnograph.
There’s a second catch with anesthetized patients on 100% oxygen. In a healthy anesthetized dog or cat breathing 100% oxygen, PaO2 can sit well above 200 mm Hg and reach as high as 650 mm Hg, according to Today’s Veterinary Practice. SpO2 can’t distinguish between those values, because hemoglobin is already nearly fully saturated. So a normal SpO2 on 100% oxygen doesn’t prove the lungs are working well.
Reading the number
Remember the oxyhemoglobin dissociation curve? Its S-shape is why SpO2 is a blunt tool at the high end and a sharp one at the low end. Most references treat 95% or higher as normal, and a reading below that deserves a look. At the low end, an SpO2 of 90% corresponds to a PaO2 of about 60 mm Hg, which is hypoxemia. That’s the figure Today’s Veterinary Practice gives, and it’s a reading that calls for action, not a “close enough.”
| SpO2 | Approximate meaning | What to do |
|---|---|---|
| 95% or higher | Normal range | Keep monitoring |
| Below 95% | Worth investigating | Check the probe, the circuit, and the patient |
| 90% or lower | PaO2 around 60 mm Hg or below, hypoxemia | Act now: confirm oxygen delivery, airway, and ventilation |
Always follow your own protocols, and confirm a low reading by checking the patient, not just the screen.
Where to put the probe
Any hairless, thin, minimally pigmented area with a pulsing arteriolar bed can work. Common veterinary sites include:
- The tongue. The standard site in anesthetized dogs and cats.
- The lip or buccal fold.
- The ear pinna.
- The toe web (interdigital space).
- The vulva or prepuce.
For awake patients, non-oral sites like the ear or toe web are usually more practical. On a long procedure, move the probe periodically so the tissue doesn’t suffer from pressure.
Why readings go wrong
Most bad readings are technical, not clinical. The usual culprits:
- Motion, including shivering.
- Hypothermia and peripheral vasoconstriction. Alpha-2 agonists are a common cause of vasoconstriction.
- Poor perfusion, such as hypotension or shock.
- Dark pigmentation of the skin or tongue, or a thick hair coat.
- Ambient light, including strong surgical lights.
- Probe pressure or poor placement.
When the number looks wrong, work through it: try another site, warm the patient, reduce movement, shade the probe from bright light, and check that the plethysmograph waveform looks clean. Compare the oximeter’s pulse rate with a palpated pulse or the ECG. If they disagree, trust the patient, not the number.
Where a pulse oximeter fits in your monitoring
AAHA’s 2020 anesthesia guidelines recommend monitoring respiratory function, cardiovascular function, cardiac rhythm, and body temperature, with an anesthesia record. A pulse oximeter covers oxygenation and pulse. For the rest, you need capnography, blood pressure, ECG, and a thermometer. Our patient monitoring buyer’s guide covers the full picture.
Many multiparameter monitors include SpO2 already. Bionet lists the Brio XVet series with Suntech SpO2 measurement that tolerates motion up to 450 bpm, which matters for cats and other patients with fast heart rates.
Handheld or built in?
Most practices end up wanting both.
- Built in to a multiparameter monitor is the right choice for the surgical suite, where you want SpO2 alongside ECG, blood pressure, and capnography on one screen.
- A handheld or portable pulse oximeter is the right choice for dentals, recovery, exam rooms, and triage, where a full monitor is more than you need.
Recovery deserves special attention. In a UK study of more than 177,000 dogs and cats (CEPSAF, Brodbelt et al., 2008), 47% of anesthetic-related deaths in dogs and 61% in cats happened after the procedure. If your only oximeter is attached to the surgical monitor, recovery goes unwatched.
What to look for when you buy
- A clear display with a visible waveform, so you can judge signal quality, not just read a number.
- User-definable alarms for SpO2 and pulse rate.
- Low-perfusion performance, since your patients are often cold and vasoconstricted.
- Battery life, so it works in the dental room and in recovery without a cord.
- Probe options suited to the sites you use, and a way to replace probes.
- Ruggedness and easy cleaning.
- A device made for veterinary use. Human oximeters are built for human tissue, and veterinary probes are designed for animal sites.
The Bionet Oxy9Wave Vet is a portable color-display veterinary pulse oximeter. Audible alarms sound if SpO2 or pulse falls outside limits you set, and it’s intended for monitoring blood oxygen saturation in cats and dogs. Bionet lists a 3.5″ color display, low-perfusion SpO2 measurement, and up to 20 hours of cordless use on its rechargeable battery. It comes with an SpO2 sensor, a power adaptor, and a pole mount bracket.
Bionet year-end promotion, through December 31, 2026. Buy any Brio XVet monitor (X3Vet, X5Vet, or X7Vet) and get a free Oxy9Wave Vet pulse oximeter. Ask us about the offer.
A shortlist to start from
Based on the specs on each product page, here’s how I’d sort it. It’s a starting point, not a ranking:
- Dental station or recovery area: the Oxy9Wave Vet, so you can watch oxygenation without moving a full monitor. See also our guide to choosing dental X-ray equipment if you’re equipping a dental suite.
- Surgical suite: a Brio XVet monitor, with SpO2 built in. You can browse all of them on our Bionet patient monitors page, and read more in our post on Bionet’s latest advances in veterinary monitoring.
- Both: a monitor for surgery and an Oxy9Wave for everything else. That’s often the setup that covers induction, surgery, and recovery.
Questions to ask any vendor before you buy
- What does the warranty cover, and who services the unit?
- What probe types are included, and can I add a tongue clip or other sites later?
- How does it perform with cold, low-perfusion patients?
- Is a loaner available if the unit needs repair?
Our repair team provides phone support and repairs, our inspection service covers preventative maintenance, and financing is available. See also our anesthesia circuits guide, our clinic equipment list, and our guide to repair versus replace. For a quote, request one here.
Frequently asked questions
What is a normal SpO2 in dogs and cats? Most references treat 95% or higher as normal. A reading below that deserves investigation, and 90% or lower corresponds to a PaO2 of about 60 mm Hg, which is hypoxemia.
What does an SpO2 of 90% mean? It corresponds to a PaO2 of about 60 mm Hg, which indicates hypoxemia. Treat it as a reading that needs action, not a borderline result.
Where do you put a pulse oximeter on a dog or cat? On a hairless, thin, minimally pigmented area with a good pulse, such as the tongue (in anesthetized patients), lip, ear pinna, toe web, vulva, or prepuce.
Why is my pulse oximeter reading low or erratic? Usually a technical cause: motion, hypothermia, vasoconstriction, poor perfusion, dark pigmentation, a thick coat, ambient light, or probe placement. Try another site, warm the patient, and check the waveform and pulse rate.
Can a pulse oximeter replace capnography? No. Pulse oximetry reflects oxygenation, and capnography reflects ventilation. ACVA’s guidelines list both, and a patient can have a normal SpO2 while ventilation is falling.
Is a normal SpO2 on 100% oxygen reassuring? Only partly. On 100% oxygen a healthy patient’s PaO2 can reach several hundred mm Hg, and SpO2 can’t tell the difference, so a normal reading doesn’t prove the lungs are working well.
Do I need a handheld pulse oximeter if my monitor has SpO2? Often yes. The monitor in your surgical suite can’t also sit in the dental room or recovery area, and a lot of anesthetic deaths happen after the procedure.
Can I use a human pulse oximeter on animals? It’s better to use a device made for veterinary use. Human devices are designed for human tissue and fingertips, and veterinary probes are designed for animal sites.
Further reading:
- AAHA, 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats
- American College of Veterinary Anesthesia and Analgesia, Monitoring Guidelines Update, 2009
- Today’s Veterinary Practice, Oxygen and monitoring in anesthetized dogs and cats
- VetGirl, Using pulse oximetry in veterinary medicine
