Characterizing the Racial Discrepancy in Hypoxemia Detection in VV-ECMO: An ELSO Registry Analysis

Abstract

Importance: Skin pigmentation influences peripheral oxygen saturation (SpO₂) measured by pulse oximetry compared to the arterial saturation of oxygen (SaO₂) measured via arterial blood gas analysis. However, data on SpO₂-SaO₂ discrepancy are limited in venovenous-extracorporeal membrane oxygenation (VV-ECMO) patients.

Objective: To determine whether there is racial/ethnical discrepancy between SpO₂ and SaO₂ in patients receiving VV-ECMO. We hypothesized VV-ECMO cannulation, in addition to race/ethnicity, accentuates the SpO₂-SaO₂ discrepancy due to significant hemolysis.

Design: Retrospective cohort study of the Extracorporeal Life Support Organization Registry from 1/2018-5/2023.

Setting: International, multicenter registry study including over 500 ECMO centers.

Participants: Adults (≥ 18 years) supported with VV-ECMO with concurrently measured SpO₂ and SaO₂ measurements.

Exposure: Race/ethnicity and ECMO cannulation.

Main outcomes and measures: Occult hypoxemia (SaO₂ ≤ 88% with SpO₂ ≥ 92%) was our primary outcome. Multivariable logistic regressions were performed to examine whether race/ethnicity was associated with occult hypoxemia in pre-ECMO and on-ECMO SpO₂-SaO₂ calculations. Covariates included age, sex, temporary mechanical circulatory support, pre-vasopressors, and pre-inotropes for pre-ECMO analysis, plus single-lumen versus double-lumen cannulation, hemolysis, hyperbilirubinemia, ECMO pump flow rate, and on-ECMO 24h lactate for on-ECMO analysis.

Results: Of 13,171 VV-ECMO patients (median age = 48.6 years, 66% male), there were 7,772 (59%) White, 2,114 (16%) Hispanic, 1,777 (14%) Black, and 1,508 (11%) Asian patients. The frequency of on-ECMO occult hypoxemia was 2.0% (N = 233). Occult hypoxemia was more common in Black and Hispanic versus White patients (3.1% versus 1.7%, P < 0.001 and 2.5% versus 1.7%, P = 0.025, respectively).In multivariable logistic regression, Black patients were at higher risk of pre-ECMO occult hypoxemia versus White patients (adjusted odds ratio [aOR] = 1.55, 95% confidence interval [CI] = 1.18-2.02, P = 0.001). For on-ECMO occult hypoxemia, Black patients (aOR = 1.79, 95%CI = 1.16-2.75, P = 0.008) and Hispanic patients (aOR = 1.71, 95%CI = 1.15-2.55, P = 0.008) had higher risk versus White patients. Furthermore, higher pump flow rate (aOR = 1.29, 95%CI = 1.08-1.55, P = 0.005) and higher on-ECMO 24h lactate (aOR = 1.06, 95%CI = 1.03-1.10, P < 0.001) significantly increased the risk of on-ECMO occult hypoxemia.

Conclusions and relevance: Hispanic and Black VV-ECMO patients experienced occult hypoxemia more than White patients. SaO₂ should be carefully monitored during ECMO support for Black and Hispanic patients especially for those with high pump flow and lactate values at risk for occult hypoxemia.

Keywords: arterial blood gas; hypoxemia; pulse oximetry; racial/ethnical disparities; venovenous extracorporeal membrane oxygenation.

Figure 1

Creation of study cohort from the ELSO Registry.

Figure 2

Forest plots of odds ratios and 95% confidence intervals from the multivariable logistic regression for occult hypoxemia in A) pre-ECMO SpO₂-SaO₂ and B) on-ECMO SpO₂-SaO₂ pairs. Pre-ECMO and on-ECMO SpO₂-SaO₂ measurements were extracted from the same patient.

Figure 3

Boxplots showing pulse oximetry (SpO₂) overestimates arterial blood gas (SaO₂) in Black, Asian, and Hispanic venovenous (VV)-extracorporeal membrane oxygenation (ECMO) patients, compared to White VV-ECMO patients. Purple color = White patients. Green color = Black patients. Red color = Asian patients. Turquoise color = Hispanic patients. Solid black line represents the median value while the upper and lower limits of the boxes represent the 75% and 25% quartiles, respectively. White patients were used as the reference comparator. **** and *** represent P values <0.0001 and <0.001, respectively.