Pulse oximetry at the bedside: placement and pitfalls

What it is

Pulse oximetry is easy to use and easy to misread. The sensor needs a warm, well-perfused site; poor circulation, cold, nail polish or artificial nails, severe anaemia, tobacco use and skin pigmentation can distort the reading, and carbon monoxide gives a falsely high one. Nurses read the number together with breathing, colour and consciousness, record whether the patient is on room air or oxygen (and how much), and remember that early hypoxia shows as anxiety, confusion and restlessness before the saturation falls.

Reference values

• Adult target: 94 to 98 %.
• Below 94 % in an adult without a lung condition is investigated: hypoxaemia or measurement error.
• Prescribed target in chronic hypercapnia: 88 to 92 %.
• Always recorded with the oxygen supply: room air, or L/min and device.

What you need

• Oximeter with the right sensor: finger, ear or forehead; finger clips are too large for newborns and young children, so the sensor is taped on.
• A warm, well-perfused site without polish or an artificial nail.
• Knowing whether the patient is on oxygen and what the saturation target is.

How to measure it (and why)

1. Choose a warm, well-perfused finger; remove polish or artificial nails or change site — they reduce accuracy.
2. If hands are cold or perfusion is poor, use the earlobe or a forehead sensor — poor perfusion gives a falsely low reading.
3. In newborns and young children, tape the sensor instead of using a clip — clips are too large.
4. Ask about tobacco use and look at the skin — tobacco, skin pigmentation, thickness and temperature affect accuracy.
5. Read the value together with breathing, colour and consciousness — the oximeter gives an estimate, not a certainty.
6. Record saturation, site, room air or oxygen in L/min with the device — without the oxygen supply the value cannot be interpreted.

How to read it

• Severe anaemia leaves less haemoglobin to carry oxygen and affects the reading.
• Carbon monoxide binds haemoglobin and gives a falsely high saturation.
• An arterial blood gas is more accurate than oximetry because the PaO2 is not affected by haemoglobin.
• On NEWS2, needing supplemental oxygen to keep the prescribed saturation adds 2 points.

Next step: when to call for help

• Call if saturation falls below the prescribed target range.
• Call if the patient needs supplemental oxygen, or more of it, to keep the target.
• Call at once if low saturation comes with breathing difficulty, confusion or cyanosis.
• Per protocol, nurses may start emergency oxygen and obtain the order afterwards.

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Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.

Sources: Nursing Skills (Open RN), 1.3 Vital Signs (Open RN, Wisconsin Technical College System (LibreTexts), 2021); Nursing Fundamentals (Open RN), 8.2 Oxygenation Basic Concepts (Open RN, Wisconsin Technical College System (LibreTexts), 2021); Pulse Oximeters (U.S. Food and Drug Administration, 2025); National Early Warning Score (NEWS) 2: executive summary and recommendations (Royal College of Physicians, 2017).

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