Authors
- Elliott, Malcolm PhD, RN
Article Content
The use of pulse oximeters for remote monitoring has surged amid the COVID-19 pandemic, but their accuracy in people with darker skin remains concerning. In fact, the US FDA has issued a safety communication about these devices' limitations. What do I need to understand about the link between skin pigmentation and pulse oximeter results?
Malcolm Elliott, PhD, RN, replies-Pulse oximeters were introduced to clinical practice in the 1980s as a unique and innovative tool for measuring peripheral arterial oxygen saturation (SpO2) as a surrogate marker for tissue oxygenation.1 Prior to this, skin assessment was the most common method for monitoring oxygenation, which is difficult to differentiate from natural skin color.2,3 Pulse oximetry provides many benefits over clinical judgment, including guiding the delivery of oxygen therapy and enabling the early detection and treatment of hypoxemia and respiratory-related events.4,5 SpO2 is also important to the success of rapid response teams.6 A recent systematic review found that pulse oximetry can reduce mortality and length of ED stay while also changing healthcare providers' decisions on illness severity, diagnosis, and treatment.4
Today, pulse oximetry is the accepted clinical standard for measuring oxygenation outside of critical care areas.7 With the emergence of COVID-19, assessment and monitoring of at-risk patients using pulse oximetry are recommended.8 The World Health Organization also recommended pulse oximetry monitoring at home as part of a COVID-19 patient package of care.9 Other emerging trends in pulse oximetry include smartphone oximetry applications and oximeters with multiple wavelengths that can measure more than two forms of hemoglobin.10,11
Limitations
Despite the many clinical benefits of pulse oximetry, numerous factors have been shown to influence the accuracy or reliability of oximeter readings. False normal or elevated SpO2 readings can be caused by A1c levels greater than 7% in patients with type 2 diabetes and poor glucose control, as well as carboxyhemoglobin levels in patients with carbon monoxide poisoning.12 False low SpO2 readings can be caused by venous pulsations, severe anemia, methemoglobinemia, sulfhemoglobinemia, fingernail polish, or inadequate signals due to excessive patient movement.12,13 Hypoperfusion and hypothermia may also result in low readings.14 Clinicians must be aware of these factors when interpreting oximetry readings. However, research has found that clinicians' understanding of pulse oximetry is often poor.3 This includes incorrectly believing that pulse oximetry measures arterial oxygenation and reflects adequate ventilation or that it can be used to replace respiratory rate monitoring.15,16
Influence of skin color
Historically, dark skin pigmentation was also believed to influence the accuracy of SpO2 readings, but limited evidence was available to support this claim.17-19 A recent study explored this by comparing 48,097 paired pulse oximetry readings with oxygen saturations in arterial blood gas.20 The oxygenation readings were performed within 10 minutes of each other. The study cohorts included 10,091 patients, of which 8,765 identified their race as White and 1,326 identified their race as Black.20 Data analysis found that patients who identified as Black had three times the frequency of occult hypoxemia, which was not detected by pulse oximetry as White patients. Occult hypoxemia was defined as arterial oxygen saturation of less than 88% despite an SpO2 of 92% to 96%.20 The researchers concluded that reliance on pulse oximetry to triage patients and adjust supplemental oxygen levels may place Black patients at increased risk of hypoxemia.20 It has since been suggested that oximeters could be calibrated to dark skin, and bedside adjustments can be made for readings taken from light skin.21
Understanding the principles behind pulse oximetry and the significance of oximetry readings impacts the interpretation of measurements, which may affect the provision of quality care.14 Given the new evidence about the reliability of pulse oximetry in patients with dark skin pigmentation, clinicians should use oximetry readings cautiously in this patient cohort and interpret oximetry readings in the context of other relevant clinical data. If there is a concern that skin pigmentation is impacting SpO2 readings, an arterial blood gas should be obtained. Clinicians should also consider accuracy limitations when using an oximeter and make treatment decisions based on data trends rather than isolated readings.22
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