Pulse oximetry

Pulse oximetry is an non-invasive procedure that enables monitoring of the blood oxygen levels of patients in various stages of their care. Oximetry gives an objective indication of the oxygenation status of an individual which supplements visual assessment.

Among other indications, pulse oximetry is used to:

• assess the status of acutely ill patients including the degree of breathlessness
• assess the needs of patients in the community and the potential need for hospital admission
• monitor patients state of oxygenation during clinical procedures
• monitor the status of patients with known respiratory disease
• enable staff to titrate oxygen therapy (Olive, 2016)

Nurses should be aware that pulse oximetry is useful for measuring the state of an individual’s perfusion, which is essentially oxygenation plus circulation. This means its use is limited in people who have circulatory disorders. Depending on the reasons for monitoring, pulse oximetry can be undertaken either continuously or intermittently.

Nurses must know the various areas of the body where pulse oximetry can be undertaken, which are generally a finger, usually an index finger, or an earlobe. In extreme circumstances, toes and the nose can be used for readings (Carvalho et al, 2021), although nurses need experience in order to be able to place a probe for this.

A normal oxygen saturation is in excess of 95%, although nurses should be alert to the fact that some individuals, such as people with chronic obstructive pulmonary disease and emphysema, may have a lower than average oxygen saturation (Carvalho et al, 2021).

The equipment required in order to undertake pulse oximetry will depend on the type of pulse oximeter being used, but will always involve an oximeter probe. Sometimes devices use a lead connecting the probe to a separate reading device or monitor, although integrated oximeters with inbuilt monitors are increasingly common and are becoming more accurate.

An oximeter probe is a device which uses both red and infrared light to shine through the patient’s capillary bed in their finger (or other site) to gain an estimation of the oxygen saturation of the individual's blood. Oxygen-rich, saturated haemoglobin absorbs more infrared light, while deoxygenated haemoglobin absorbs more red light. The oximeter reads the ratios of the two lights to work out the oxygen saturation of the patient multiple times every second by measuring the absorption of both forms of light (Jubran, 2015).

The nurse must ensure they gain consent before undertaking pulse oximetry by explaining to the patient the nature of the procedure as well as why it is being undertaken. Nurses must observe hand hygiene procedures prior to undertaking pulse oximetry to prevent the transmission of infection.

The patient should be rested and comfortable and the nurse should attend to any privacy and dignity issues associated with the procedure. The nurse should observe the patient for any signs that they may be breathless or otherwise unwell. Key visual indicators of breathlessness include:

• laboured breathing and inability to speak
• a blue or grey colouring to the skin and/or around the lips (depending on the patient's skin tone)
• noisy breathing
• audible wheezing

The nurses should take note of these additional signs and symptoms which may validate or call into question the reading from the oximeter.

1. Ensure device is clean and in working

The biggest risk related to recording of a person’s pulse oximetry is that it is done incorrectly, and the results are then used to inform practice. If the patient is particularly cold at the time of the saturation reading, it may be difficult to obtain a true reading as their peripheral circulation may have shut down (Foley, 2015). Other sources of potential errors include:

• high levels of ambient light
• patients who are unable to keep still or who keep removing the finger probe
• patients with anaemia
• patients with nails which are
  
  • false
  • dirty
  • varnished
• patients with jaundice (Olive, 2016)

People with darker skin tones may get false high readings when pulse oximetry is used (Medicines and Healthcare products Regulatory Agency, 2021). It is important to combine the reading with other clinical observations to ensure evidence-based care.

Nurses should be aware of the ways in which oximetry is undertaken. They should be alert to any emerging guidance about the use of oximetry in different disease states and interpretation of the readings in people with a variety of diseases and skin tones.

While pulse oximetry is a valuable tool, it does not provide a complete picture of a person's respiratory health. Pulse oximetry cannot diagnose the cause of low oxygen levels or assess other important factors such as carbon dioxide levels in the blood, so it is often used in conjunction with other clinical assessments and tests to make a comprehensive evaluation of a patient's respiratory status.

Nursing and Midwifery Council: standards of proficiency for registered nurses

Part 1: Procedures for assessing people’s needs for person-centred care

2.7 undertake a whole body systems assessment including respiratory, circulatory, neurological, musculoskeletal, cardiovascular and skin status

Part 2: Procedures for the planning, provision and management of person-centred nursing care

8. Use evidence-based, best practice approaches for meeting needs for respiratory care and support, accurately assessing the person’s capacity for independence and self-care and initiating appropriate interventions

8.3 take and interpret peak flow and oximetry measurements

Carvalho F, Breen EC, Bullock Z et al. Observations. In: Lister S, Hofland J, Grafton H and Wilson C (eds). The Royal Marsden Manual of clinical nursing procedures. 10^th edn. Chichester: Wiley Blackwell; 2021:719-800

Dobson C, Simpson T. Clinical measurement. In Delves-Yates C (ed). Essentials of nursing practice. London: Sage; 2022

Jubran A. Pulse oximetry. Crit Care. 2015;19(1):272 https://doi.org/10.1186/s13054-015-0984-8

Medicines and Healthcare products Regulatory Agency. The use and regulation of pulse oximeters (information for healthcare professionals). 2021. https://www.gov.uk/guidance/the-use-and-regulation-of-pulse-oximeters-information-for-healthcare-professionals (accessed 5 February 2024)

Olive S. Using pulse oximetry to assess oxygen levels. Nursing Times. 2016;112(16):12-13