Use a pulse oximeter according to its instructions and your treating team’s monitoring plan. The aim is to make a useful observation under known conditions, not to keep repeating the test until a preferred number appears.
If the person has severe breathing difficulty, chest pain, confusion or unusual drowsiness, seek urgent medical help. Do not delay care while trying to obtain a perfect reading.
Prepare before measuring
Choose a device and sensor intended for the person’s age and measurement site. An adult fingertip clip may not fit a small child, and a fingertip sensor should not be moved to an ear unless its instructions allow that use.
Check the battery and that the sensor is clean and undamaged. Follow the cleaning instructions; do not spray liquid into it. Let the person settle in the position recommended for their monitoring. If they use prescribed oxygen, leave it at the prescribed setting unless the treating team has given different instructions for a supervised assessment.
Use a warm, relaxed hand. Remove nail polish from the chosen finger where practical, and tell the clinician about artificial nails or other barriers if a suitable site is difficult to find. Do not compensate by inventing a different sensor position.
Place the sensor and wait
Insert the finger as shown in the manual. Support the hand so the person can remain still, and avoid strong light falling directly on the sensor. Check that the clip fits comfortably and is not partly off the fingertip.
Wait for the reading to settle according to the device instructions. Note the SpO₂ percentage and pulse rate. If the device shows a signal indicator, use its own instructions to interpret it; there is no single perfusion-index cutoff that validates every oximeter.
An unstable number or implausible pulse rate may indicate a poor signal, but does not prove that the person’s oxygen level is normal. Report persistent difficulty obtaining a reading rather than guessing what the number should have been.
Record the circumstances
Write down the date, time, SpO₂ and pulse rate, together with symptoms and whether the person was resting or had recently been active. Include the oxygen device and prescribed setting where relevant. Use the frequency of checks requested by the treating team rather than adding an exhausting monitoring routine yourself.
If a reading is unexpected and the person is not acutely unwell, check placement and obvious measurement problems and repeat as instructed. Do not average away a low result, discard it merely because another finger reads higher, or delay the action required by the clinical plan.
Bring problems to review
Take the home device and log to a clinical appointment if readings are repeatedly difficult to interpret. A comparison can identify a concern, but one agreement with a clinic instrument is not a calibration certificate.
Skin pigmentation, circulation and other factors can affect accuracy even when technique looks correct. Read the companion guide to what the numbers mean, and ask for an individual plan if you have not been told when to seek help.