Pulse oximeter: checking oxygen levels

A pulse oximeter is a small sensor that estimates oxygen saturation and pulse rate without a needle.

The clip uses light passing through a body part, often a fingertip, to produce a reading. Oxygen saturation describes the proportion of haemoglobin carrying oxygen in the blood. Pulse rate is the number of heartbeats detected over a minute. The display is a useful snapshot, not a complete assessment of breathing or circulation.

The sensor is placed on a warm, still finger, toe or earlobe and left in place until the display settles. Remove nail polish or artificial nails if they cover the measurement site. Cold hands, movement and poor contact can interfere with the signal, so the clinician may repeat the reading or choose another site.

It can be used when someone has breathlessness, cough, fever, chest symptoms or a condition that affects breathing. Clinicians also observe how a person looks, listens to the chest when appropriate, and consider the pattern of symptoms rather than relying on one screen value.

The device estimates a value and may be less dependable when circulation to the measurement site is reduced, the person is moving, or the sensor does not fit well. Nail products, strong external light and some differences in skin pigmentation can also affect performance. A reading does not identify the cause of a breathing problem.

Do not use a home reading to dismiss severe symptoms. A person can need urgent assessment because of worsening breathlessness, chest pain, blue or grey lips, confusion, fainting, or difficulty staying awake even if a device produces a number.

A clinical examination can assess breathing effort, chest sounds, colour and circulation. When more detail is needed, a clinician may arrange tests that measure gases in a blood sample or investigate the heart and lungs. Each approach provides different information from the clip sensor.

A clinician interprets the reading against your usual health, altitude, symptoms and examination. If you monitor at home, record the value, the time and what you were doing, then note any breathlessness or change from your usual state. A GP Consultation can review repeated readings and decide whether further assessment is needed.

The sensor is non-invasive, but it is not an emergency decision-maker. Seek urgent medical help for severe or rapidly worsening breathing difficulty, chest pain, blue or grey colouring of the lips or face, collapse, confusion, or a person who is difficult to wake. Do not delay care while repeating measurements.