EC Pulmonology and Respiratory Medicine

Pulse oximetry is a widely used, non-invasive method for monitoring oxygen saturation (SpO₂) in clinical and specialized settings, including maritime and high-altitude medicine. However, several pitfalls and misconceptions can lead to false readings, particularly in cases of severe hypoxemia. This mini-review explores the limitations of pulse oximetry, the role of perfusion index (PI) in assessing peripheral circulation, and common sources of measurement errors, such as low perfusion states, motion artifacts, and skin pigmentation. The clinical interpretation of SpO₂ levels is discussed, emphasizing the need for caution when readings fall below 65%, where peripheral cyanosis is evident, rendering further saturation assessment redundant. Additionally, a nomogram illustrating the relationship between SpO₂, partial pressure of oxygen (PaO₂), pH, and PaCO₂ is presented, aiding in the understanding of respiratory acidosis and alkalosis. The review also highlights the importance of SpO₂ monitoring in critical conditions, including cytokine storm syndromes, and discusses the integration of Bluetooth-enabled pulse oximeters for real-time data transmission. Understanding the limitations and proper interpretation of SpO₂ readings is crucial for avoiding misdiagnosis and ensuring accurate clinical decision-making.

 Keywords: Oxygen Saturation (SpO₂); Pulse Oximetry; Hypoxemia; Perfusion Index (PI)

1. Mehdipour A., et al. “The performance of digital monitoring devices for oxygen saturation and respiratory rate in COPD: A systematic review”. COPD: Journal of Chronic Obstructive Pulmonary Disease4 (2021): 469-475.
2. Chan C., et al. “A smartphone oximeter with a fingertip probe for use during exercise training: usability, validity and reliability in individuals with chronic lung disease and healthy controls”. Physiotherapy (United Kingdom) 3 (2019): 297-306.
3. Sheikh M., et al. “Pulse oximetry: why oxygen saturation is still not a part of standard pediatric guidelines in low-and-middle-income countries (LMICs)”. Pneumonia (Nathan)1 (2023): 3.
4. Sjoding MW., et al. “Racial bias in pulse oximetry measurement”. New England Journal of Medicine 25 (2020): 2477-2478.
5. Buckley RG., et al. “The pulse oximetry gap in carbon monoxide intoxication”. Annals of Emergency Medicine 2 (1994): 252-255.
6. Silverston P., et al. “Pulse oximetry in primary care: factors affecting accuracy and interpretation”. British Journal of General Practice 716 (2022): 132-133.
7. Milner QJ and Mathews GR. “An assessment of the accuracy of pulse oximeters”. Anaesthesia4 (2012): 396-401.
8. Yamazaki H., et al. “Use of perfusion index from pulse oximetry to determine efficacy of stellate ganglion block”. Local and Regional Anesthesia 5 (2012): 9-14.
9. Toyama S., et al. “Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery”. British Journal of Anaesthesia 2 (2013): 235-241.
10. Gudelunas MK., et al. “Low perfusion and missed diagnosis of hypoxemia by pulse oximetry in darkly pigmented skin: A prospective study”. Anesthesia and Analgesia 3 (2024): 552-561.
11. Lal J., et al. “A study to evaluate the change in perfusion index as an indicator of successful ultrasound-guided supraclavicular block”. Indian Journal of Anaesthesia 10 (2021): 738-743.
12. De Felice C., et al. “Maternal pulse oximetry perfusion index as a predictor of early adverse respiratory neonatal outcome after elective cesarean delivery”. Pediatric Critical Care Medicine 2 (2008): 203-208.
13. He H., et al. “Clinical classification of tissue perfusion based on the central venous oxygen saturation and the peripheral perfusion index”. Critical Care 1 (2015): 330.
14. Abraham EA., et al. “Comparative analysis of oxygen saturation by pulse oximetry and arterial blood gas in hypoxemic patients in a tertiary care hospital”. Cureus 7 (2023): e42447.
15. Donaldson MA., et al. “Characteristics of pulse oximetry and arterial blood gas in patients with fibrotic interstitial lung disease”. BMJ Open Respiratory Research 1 (2024): e002250.
16. Zeserson E., et al. “Correlation of venous blood gas and pulse oximetry with arterial blood gas in the undifferentiated critically Ill patient”. Journal of Intensive Care Medicine 3 (2018): 176-181.
17. Rauniyar N., et al. “Study of oxygen saturation by pulse oximetry and arterial blood gas in ICU patients: A descriptive cross-sectional study”. Journal of Nepal Medical Association 230 (2020): 789-793.
18. Avramovski P. “Cytokine storm: A threatening challenge for COVID-19 infected patients”. EC Pulmonology and Respiratory Medicine5 (2021): 11-14.
19. Käsinger W., et al. “In vivo oxygen dissociation curve for whole fetal blood: fitting the Adair equation and blood gas nomogram”. Scandinavian Journal of Clinical and Laboratory Investigation 7 (1981): 701-707.