Written by Clay Smith
Occult hypoxemia occurred more often in Black than White inpatients. Is 92% SpO2 actually 87% SaO2?
Why does this matter?
We covered a previous study demonstrating the inaccuracy of pulse oximetry in critically ill Black patients. But would that hold among general medical and surgical inpatients?
Skin color matters in SpO2
This was a multicenter retrospective study from the Veterans Health Administration, with 30,039 paired SaO2 and SpO2 readings within 10 minutes of each other. They found occult hypoxemia (SaO2 <88% when SpO2 was ≥92%) in 15.6% of White patients and 19.6% of Black patients (statistically significant) but did not find a significant difference between White and Hispanic patients. Findings remained significant when SpO2-SaO2 pairings were even tighter, within 5 or 2 minutes.
The Masimo founder and CEO made some fair critiques about the NEJM study linked above: Did they control for sickle cell anemia, methemoglobinemia, and type of pulse oximeter used? A Masimo pulse oximeter is going to perform better than a cheap clip-on (used by RTs throughout the hospital – with results documented in the chart). That said, yet another study in August found that Black, Asian, and Hispanic patients in the ICU received supplemental oxygen less often than White patients, and this was associated with the SpO2-SaO2 discrepancy.
My take: I think the SpO2-SaO2 discrepancy in darkly pigmented patients is probably real. This is important in darkly pigmented patients with marginal SpO2 readings. Consider pulse ox confounders: sickle cell anemia, methemoglobinemia, and cheapo equipment. Use high quality equipment, especially in patients with dark skin pigmentation.
Racial bias and reproducibility in pulse oximetry among medical and surgical inpatients in general care in the Veterans Health Administration 2013-19: multicenter, retrospective cohort study. BMJ. 2022 Jul 6;378:e069775. doi: 10.1136/bmj-2021-069775.