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Copyright EMAP Publishing 2016 This article is not for distribution

Keywords: oximetry/ Nursing Practice saturation//Assessment Practice educator ●This article has been double-blind Respiratory peer reviewed is a vital tool in patient assessment. Nurses must use the correct procedure and be aware of situations where accuracy of reading may be compromised Using pulse oximetry to assess oxygen levels

In this article... 5 key What pulse oximetry measures and the most useful reading points Pulse oximetry is Indications for using pulse oximetry 1a non-invasive Understanding the limitations of pulse oximetry procedure that is used to assess patients’ oxygen Authors Sandra Olive is a respiratory nurse accurate devices were developed, which levels specialist at the Norfolk and Norwich led to pulse oximeters being introduced It should be University Hospital, Norwich. into clinical practice. 2 available in all Abstract Olive S (2016) Using pulse clinical settings oximetry to assess oxygen levels. Indications for use where hypoxaemia Nursing Times; 112: 16, 12-13. Cyanosis was traditionally the primary may occur Detecting low oxygen levels in patients is clinical sign of hypoxaemia but early Pulse oximetry important but not always easy; central studies found that even skilled observers 3 enables early cyanosis – when a patient’s lips, tongue are not consistently able to detect central identification and mucus membranes acquire a blue cyanosis (a blue tinge to the lips, tongue of hypoxia tinge – can be missed, even by skilled and mucus membranes) until oxyhaemo- It requires observers, until significant hypoxaemia is globin saturation is <80% (Hanning and 4 good pulsatile present. Pulse oximetry can be undertaken Alexander-Williams, 1995). At this level, flow to measure a patient’s oxygen levels and organ function, including brain, heart and Nurses should help identify earlier when action must be kidneys, may be compromised. Factors 5record whether taken. This article outlines the procedure such as ambient light, skin pigmentation the patient is and its limitations, as well as the and peripheral all affect the room circumstances in which it should be used. ability to identify cyanosis but pulse oxi- air or oxygen when metry enables clinically important low- the reading is ulse oximetry is a simple, non- tissue oxygenation to be identified earlier. taken, along with invasive method of measuring Pulse oximetry should be available for other factors oxygen levels and can be useful use in all clinical settings where hypox- that may affect Pin a variety of clinical settings aemia may occur and is used to: accuracy to continuously or intermittently monitor » Assess breathless patients or those who oxygenation. are acutely ill, including those who An oximeter is a device that emits red have acute confusion; and light, shone through a capil- » Provide an objective indication of the lary bed (usually in a fingertip or earlobe) severity of an acute respiratory episode onto a sensor (Fig 1). Multiple measure- and need for hospital admission – for ments are made every second and the ratio example, exacerbation of chronic of red to infrared light is calculated to obstructive pulmonary disease, FIG 1. Oximeter determine the peripheral oxygen satura- (British Thoracic Society and Scottish tion (SpO2). Deoxygenated haemoglobin Intercollegiate Guidelines Network, absorbs more red light and oxygenated 2014; National Institute for Health and haemoglobin absorbs more infrared light. Care Excellence, 2010) or In the 1970s it was discovered that red/ (NICE, 2014); infrared wavelength absorption could be » Determine the need for emergency calculated from pulsatile blood flow and in acute illness the term “pulse oximeter” was coined. (O’Driscoll et al, 2008); However, early devices were cumbersome, » Provide a continuous inaccurate and prohibitively expensive recording, for example, during

Alamy (Tremper 1989). By the early 1980s, more anaesthesia or sedation, or in the

12 Nursing Times 20.04.16 / Vol 112 No 16 / www.nursingtimes.net Copyright EMAP Publishing 2016 This article is not for distribution

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assessment of oxygenation during tissues. Inappropriately sized probes Box 1. The procedure sleep studies; or excessive ambient light may result » Undertake routine in in inaccuracies ● Ensure oximeter is in good condition chronic respiratory disease to screen » Interference with transmission/ and probe sensor is cleaned for suitability for assessment for detection of light signals: according to local infection control domiciliary oxygen therapy (BTS, 2015; » Dirty probe sensors policy/manufacturer’s guidance NICE, 2010); » Nail varnish/synthetic nails ● Explain procedure to the patient and » Guide titration of oxygen therapy » Anaemia/skin discolouration (very dark gain consent where possible during acute illness (O’Driscoll et al, skin/jaundice) may affect readings, but ● Select the most appropriate probe 2008) or for domiciliary use (BTS, 2015). is rarely clinically significant. for the site chosen; in adult patients, Additional monitoring with arterial Pulse oximetry supports rather than the most common sites are the blood gas sampling may be required replaces comprehensive assessment and fingertip and earlobe. Using the where patients are at risk of type 2 examination. Results should be inter- incorrect probe will lead to (hypercapnic) respiratory failure. preted with clinical judgement in the con- inaccuracies in the readings obtained Pulse oximetry does not give a measure text of the patient’s existing diagnoses, ● Consider choice of device: of oxygen content or ventila- presenting symptoms and other findings ● Fingertip devices with integrated tion; oxygen delivery to the tissues is (Holmes et al, 2013; Kelly, 2008). sensor and display may be dependent on adequate ventilation and cir- appropriate for spot checks of culation. However, oximetry can add to the Procedure SpO2 (Fig 1) clinical picture to aid diagnostic and treat- The correct procedure that should be fol- ● Handheld devices with detachable ment decisions. lowed when conducting pulse oximetry is sensor allow the most appropriate detailed in Box 1. probe to be selected Limitations ● Wrist-worn devices have a sensor Pulse oximetry requires a good pulsatile Competencies attached by a short cable and are blood flow and no interference with meas- A range of competencies relate to the safe useful for overnight oximetry and urement of light absorption and detection. undertaking of pulse oximetry: exercise testing Pulse strength can be checked by ensuring » Be aware of, and understand, local ● Desktop/bedside devices may be the recorded correlates with a infection control policy/guidelines in more appropriate in the acute manual pulse rate; some devices have a relation to monitoring equipment; setting for continuous monitoring pulse amplitude indicator in addition to a » Demonstrate a basic understanding of ● Ensure the chosen site is warm and pulse detector. Where a good signal is how oxygen saturations are derived; well perfused obtained, pulse oximetry readings are » Be able to discuss the indications for, ● Apply the probe to the site, ensuring accurate within saturation range of and limitations of, pulse oximetry; the sensor is correctly positioned 70-100% but cannot be relied on outside of » Demonstrate an ability to use a pulse ● Ask the patient to rest the hand with this range. oximeter safely and effectively, the sensor on it down gently to Common causes of inaccuracy include: selecting the appropriate probe and reduce interference of motion » Poor peripheral circulation: device for the clinical situation; ● Check the pulse strength signal and » Cold peripheries » Demonstrate accurate documentation ensure the pulse-rate reading » Constriction, for example, from of results. correlates with the manual pulse blood pressure cuff, tight clothing or Health professionals should be able to ● Allow the pulse oximeter to remain tight oximeter probe demonstrate competence before under- in situ for at least five minutes to » Poor perfusion due to hypovolaemia, taking and interpreting pulse oximetry. NT ensure it equilibrates marked or cardiac ● Document the reading, noting arrhythmias, peripheral References whether the patient is breathing British Thoracic Society (2015) BTS Guidelines for vascular disease Home Oxygen Use in Adults. Thorax; 70: Suppl 1. room air or oxygen, then record the » Raynaud’s syndrome British Thoracic Society and Scottish oxygen delivery device used and flow » Motion artefact: Intercollegiate Guidelines Network (2014) rate or percentage. Note any other British Guideline on the Management of Asthma. » Gross movement may cause loss Bit.ly/BTSSIGNAsthma factors that may influence accuracy, of signal Hanning CD, Alexander-Williams JM (1995) Pulse such as movement, cold hands etc » Fine vibration may interfere with oximetry: a practical review. BMJ; 311: 7001, 367-370. ● In acute illness, resting saturations are Holmes S et al (2013) Pulse oximetry in primary usually most useful, but in non-acute accuracy care. PCRS Opinion; 28. Bit.ly/PulseOxPC » /smoke Kelly C (2008) The use of pulse oximetry in settings, oximetry may be used inhalation/intravenous dyes (for primary care. British Journal of Primary Care during exercise testing to determine example, methylene blue) used in Nursing; 2: 2, 27-29. exertional desaturation. Record National Institute for Health and Care Excellence diagnostic tests: (2014) Pneumonia in Adults: diagnosis and whether the readings have been » Carboxyhaemoglobin (from carbon management. Nice.org.uk/guidance/cg191 taken at rest or during/after activity monoxide) is detected as National Institute for Health and Care Excellence in addition to inspired oxygen/air (2010) Chronic Obstructive Pulmonary Disease in oxyhaemoglobin and will Over 16s: diagnosis and management. Nice.org.uk/ overestimate true oxygen saturation cg101 For more on this topic go online... » Ambient light interference: O’Driscoll BR et al (2008) BTS guideline for Practical procedures: » Light emitters and detectors must be emergency oxygen use in adult patients. Thorax; 63: Suppl 6, vi1-vi68. oxygen therapy directly opposite each other and light Tremper K (1989) Pulse oximetry. Chest; 95: 4, Bit.ly/NTOxygenTherapy should only reach the detector via 713-715.

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