Chapter 7: Vital Signs
Oxygen Saturation Levels
Normal oxygen saturation ranges from 97–100% (OER #1) in a healthy individual. However, there are reasons why a lower range occurs and in some cases, why it is sometimes acceptable.
Older adults typically have lower oxygen saturation levels than younger adults. For example, someone older than 70 years of age may have an oxygen saturation level of about 95%, which is an acceptable level.
It is important to note that the oxygen saturation level varies considerably based on a person’s state of health. Thus, it is important to understand both baseline readings and underlying physiology associated with certain conditions to interpret oxygen saturation levels and changes in these levels.
- People who are obese and/or have conditions such as lung and cardiovascular diseases, emphysema, chronic obstructive pulmonary disease, congenital heart disease and sleep apnea tend to have lower oxygen saturation levels.
- Smoking can influence the accuracy of pulse oximetry in which the the SpO2 is low or falsely high depending on whether hypercapnia is present. With hypercapnia, it is difficult for the pulse oximeter to differentiate oxygen in the blood from carbon monoxide (caused by smoking).
- Oxygen saturation levels may decrease slightly when a person is talking.
- Oxygen saturation may remain normal (e.g., 97% and higher) for people with anemia. However, this may not indicate adequate oxygenation because there are less hemoglobin to carry an adequate supply of oxygen for people who have anemia. The inadequate supply of oxygen may be more prominent during activity for people with anemia.
- Falsely low oxygen saturation levels may be associated with hypothermia, decreased peripheral perfusion, and cold extremities. In these cases, an ear lobe pulse oximeter device or arterial blood gases would provide a more accurate oxygen saturation level. However, arterial blood gases are usually only taken in critical care or emergency settings.
Points to Consider
In practice, such as a hospital setting, the SpO2 range of 92–100% is generally acceptable for most clients. Some experts have suggested that a SpO2 level of at least 90% will prevent hypoxic tissue injury and ensure client safety (Beasley, et al., 2016). However, with children, a saturation that drops below the normal of 97%-100% is always something that you should investigate further.
Contextualizing Inclusivity – Pulse Oximetry Biases
There are biases ingrained in the technology of pulse oximetry, which results in racial disparities in care. Despite decades of research showing the inherent and systematic racism that is part of pulse oximetry (Hidalgo et al., 2021), practices have been slow to change. This is a serious issue considering that treatment decisions are influenced by pulse oximetry, and hypoxemia can lead to complications including higher mortality rates and organ dysfunction (Wong et al., 2021)
In the context of hypoxemia, pulse oximeters have been found to generally overestimate oxygen saturations (Feiner et al., 2007) particularly as the SpO2 lowers to 88%. This overestimation is sometimes described as hidden hypoxemia (Wong et al., 2021) in which the oxygen saturation on a pulse oximeter is higher than an oxygen saturation measured via arterial blood draw. For several years, this overestimation has been particularly greatest in people with darker skin tones (Bickler et al., 2005; Feiner et al., 2007). For example, it has been noted that hypoxemia is detected (via pulse oximetry) less in Black patients than white patients (Sjoding et al., 2020). In a large, multi-site study with over 79,000 patients, it was found that hidden hypoxemia was found more in Black patients followed by Hispanic and then similar rates for Asian and white patients (Wong et al., 2021). In another study in the context of COVID-19, hidden hypoxemia was found more in Asian, Black and Hispanic patients than white patients and significantly affected treatment in Black and Hispanic patients (Fawzy et al., 2022).
As you go into practice, keep in mind that you should critically reflect on your pulse oximetry findings. For example, if the client’s SpO2 finding is normal, but they are presenting with difficulty breathing or signs of respiratory distress (e.g., shortness of breath, audible breathing, , ), consider your priorities of care. First, always believe the patient and then, consider the findings in the context of your subjective assessment and other physical findings. It may be appropriate to advocate for arterial blood gases to be drawn to verify oxygen saturation levels if the patient is having breathing problems and their pulse oximetry findings are normal.
Please answer the four questions in the following question set.
References
Bickler, P., Feiner, J., & Severinghaus, J. (2005). Effects of skin pigmentation on pulse oximeter accuracy at low saturation. Anesthesiology, 102(4), 715-719.
Fawzy, A., Wu, T., Wang, K., Robinson, M., Farha, J., Bradke, A., Golden, S., Xu, Y. & Garibaldi, B. (2022). Racial and ethnic discrepancy in pulse oximetry and delayed identification of treatment eligibility among patients with COVID-19. JAMA Internal Medicine, 182(7), 730-738.
Feiner, J., Severinghaus, J., & Bickler, P. (2007). Dark skin decreases the accuracy of pulse oximeters at low oxygen saturation: the effects of oximeter probe type and gender. Anesth Analg, 105(6)(suppl):S18-S23.
Hidalgo, D., Olusanya, O., & Harlan, (2021). Critical care trainees call for pulse oximetry reform. The Lancet: Respiratory Medicine, 9(4), e37.
Sjoding, M., Dickson, R., Iwashyna, T., Gay, S., & Valley, T. (2020). Racial bias in pulse oximetry measurement. New England Journal of Medicine, 383, 2477-2478.
Wong, A., Charpignon, M., Kim, H., Josef, C., de Hond, A., Fojas, J., Tabaie, A., Liu, X., Mireles-Cabodevila, E., Carvalho, L., Kamaleswaran, R., Madushani, R., Adhikari, L., Holder, A., Steyerberg, E., Buchman, T., Lough, M., & Celi, L. (2021). Analysis of discrepancies between pulse oximetry and arterial oxygen saturation measurements by race and ethnicity and association with organ dysfunction and mortality. JAMA Network Open, 4(11).
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Part of this content was adapted from OER #1 (as noted in brackets above):
© 2015 British Columbia Institute of Technology (BCIT). Clinical Procedures for Safer Patient Care by Glynda Rees Doyle and Jodie Anita McCutcheon, British Columbia Institute of Technology. Licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Download this book for free at http://open.bccampus.ca
is leaning forward with hands and/or forearms resting on their legs or another surface such as a table.
are when the muscles in between the ribs are sucked inward when breathing.
