Pulse Oximetry and Arterial Blood Gas Oxygen Saturation Discrepancies and Mortality in Extracorporeal Cardiopulmonary Resuscitation Patients: An Extracorporeal Life Support Organization Registry Analysis

OBJECTIVES: Previous studies have shown that inaccurate peripheral oxygen saturation (Sp o2 ) readings compared with arterial oxygen saturation (Sa o2 ) may occur in extracorporeal membrane oxygenation (ECMO) patients. We hypothesized that a greater Sp o2 -Sa o2 discrepancy in extracorporeal cardiopulmonary resuscitation (ECPR) patients is associated with higher mortality due to unrecognized hypoxemia. DESIGN: Retrospective analysis. SETTING: Data within the Extracorporeal Life Support Organization Registry from 496 ECMO centers (2018-2024). PATIENTS: Patients 18 years old or older receiving ECPR (first-run only). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Laboratory measurements including Sp o2 -Sa o2 were measured at 24 hours of ECMO support. Acute brain injury (ABI) included hypoxic-ischemic brain injury, ischemic stroke, intracranial hemorrhage, and seizures. Based on an inflection point in cubic spline analysis, a Sp o2 -Sa o2 threshold greater than or equal to 4% was used as a binary variable to assess its association with in-hospital mortality. Three thousand nine hundred seventy ECPR patients (median age, 57 yr; 71% male) were included. The median ECMO duration was 4 days (interquartile range, 2-7 d). There were 634 patients (16%) with Sp o2 -Sa o2 greater than or equal to 4% and 3336 (84%) with Sp o2 -Sa o2 less than 4%. Overall mortality was 60% ( n = 2391). Patients with Sp o2 -Sa o2 greater than or equal to 4% had higher mortality compared with patients with Sp o2 -Sa o2 less than 4% (67%, n = 425 vs. 59%, n = 1966; p < 0.001). Patients with Sp o2 -Sa o2 greater than or equal to 4% had higher serum lactate values than those with Sp o2 -Sa o2 less than 4% (3.1 vs. 2.8 mmol/L; p = 0.0017). In multivariable logistic regression adjusted for preselected covariates, Sp o2 -Sa o2 greater than or equal to 4% was associated with increased risk of mortality (adjusted odds ratio [aOR], 1.39; 95% CI, 1.13-1.71). Additional risk factors associated with higher mortality included ABI (aOR, 5.81; 95% CI, 4.70-7.20), hyperoxemia greater than or equal to 300 mm Hg (aOR, 1.93; 95% CI, 1.53-2.43), hyperoxemia 200-299 mm Hg (aOR, 1.76; 95% CI, 1.37-2.25), gastrointestinal hemorrhage (aOR, 1.69; 95% CI, 1.42-2.00), renal replacement therapy (aOR, 1.48; 95% CI, 1.03-2.11), hypoxemia less than 60 mm Hg (aOR, 1.45; 95% CI, 1.00-2.10), older age (aOR, 1.19; 95% CI, 1.13-1.26), and higher lactate (aOR, 1.17; 95% CI, 1.13-1.20). Race/ethnicity was not associated with higher mortality. CONCLUSIONS: Sp o2 -Sa o2 greater than or equal to 4% in the first 24 hours after ECPR is associated with increased risk of mortality, potentially due to unrecognized hypoxemia, irrespective of race/ethnicity.