Pulse Ox/Blood Gas Discrepancies Tied to Poor Outcomes in Racial, Ethnic Subgroups

By Marilynn Larkin

November 12, 2021

NEW YORK (Reuters Health) - Discrepancies between pulse oximetry (SPO2) and arterial oxygen saturation (SAO2) among Blacks, Hispanics, and Asians were associated with higher rates of hidden hypoxemia, organ dysfunction and mortality in an electronic health records analysis.

"This work doesn't ask us to throw out pulse oximetry entirely," Dr. An-Kwok Ian Wong of Duke University in Durham, North Carolina told Reuters Health by email. "But it does suggest that we may need to be more cautious in interpreting its values to guide care."

"Until more equitable pulse oximetry is in widespread use, we make one potential recommendation," he said. "We may need to consider higher pulse oximetry targets to achieve equal risk of hidden hypoxemia across all race and ethnicity subgroups. This is a very nuanced question and needs further research."

As reported in JAMA Network Open, Dr. Wong and colleagues studied data from close to 90,000 patients with first arterial blood gas (ABG) measurements and an SPO2 of at least 88% within five minutes before the ABG test. The mean age was 62; 65.5% were White; 29.6%, Black; 2.7%, Hispanic; and 2.3%, Asian.

Hidden hypoxia - defined as an SPO2 of at least 88% but an SAO2 of less than 88% - was seen in all subgroups, although the incidence varied: Blacks, 6.8%; Hispanics, 6.0%; Asians, 4.8%; and Whites, 4.9%.

Hidden hypoxia was associated with greater organ dysfunction 24 hours after the ABG measurement, as shown by higher mean Sequential Organ Failure Assessment (SOFA) scores (7.2 vs. 6.29) and higher in-hospital mortality, with a significant difference in the latter between Blacks and Whites (21.1% vs. 15.0%).

Patients with hidden hypoxemia also had higher mean lactate levels before the ABG test (3.15 mg/dL vs. 2.66mg/dL) and 24 hours afterward (2.83 mg/dL vs. 2.27 mg/dL), with less lactate clearance (−0.54 mg/dL vs. −0.79 mg/dL).

The authors note, "Patients with and without hidden hypoxemia were demographically and clinically similar at baseline ABG measurement by SOFA scores, but those with hidden hypoxemia subsequently experienced higher organ dysfunction scores and higher in-hospital mortality."

"To ensure a risk of hidden hypoxemia of less than 10%, SPO2 should be greater than 93% among Asian patients (mean risk, 11.0%), 96% among Blacks (mean risk, 8.2%); 92% among Hispanic patients (mean risk, 18.4%), and 93% among White patients (mean risk, 10.6%)."

Dr. Megan Conroy, a pulmonologist at The Ohio State University Wexner Medical Center in Columbus, told Reuters Health by email, "We have known for some time that there is risk for falsely reassuring oxygen readings from the finger pulse oximetry probe for patients with darker skin colors, but the frequency, magnitude and consequences of this possible risk have not been well understood."

"I would venture few physicians are aware of this risk, or are actively considering this risk when making clinical decisions for patients with respiratory problems in the hospital - including those who are critically ill," she said.

"This study finds these devices are surprisingly inaccurate even at normal numbers," she noted. "Another concerning finding is that patients of color are less likely to have invasive testing performed to measure oxygen levels when compared with White patients, showing yet another way in which physicians, even unconsciously, make different diagnostic and treatment decisions for patients of different races."

"We see evidence of bias not only in human actions in healthcare, but as shown here, racial bias is even baked into the very tools that we use to diagnose and monitor patients," she added. "Openness to exploring the ways in which implicit biases may affect your diagnostic approach to a patient is necessary. The study finds we are less likely to obtain arterial blood gases from non-White patients, and such behavioral bias only improves when we start to realize where this stems from and work to be better, do better."

SOURCE: https://bit.ly/30fBO67 JAMA Network Open, online November 3, 2021.