Objectives: 

Previous studies have shown that inaccurate peripheral oxygen saturation (SpO2) readings compared with arterial oxygen saturation (SaO2) may occur in extracorporeal membrane oxygenation (ECMO) patients. We hypothesized that a greater Spo₂–Sao₂ 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 Spo₂–Sao₂ 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 Spo₂–Sao₂ 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 Spo₂–Sao₂ greater than or equal to 4% and 3336 (84%) with Spo₂–Sao₂ less than 4%. Overall mortality was 60% (n = 2391). Patients with Spo₂–Sao₂ greater than or equal to 4% had higher mortality compared with patients with Spo₂–Sao₂ less than 4% (67%, n = 425 vs. 59%, n = 1966; p < 0.001). Patients with Spo₂–Sao₂ greater than or equal to 4% had higher serum lactate values than those with Spo₂–Sao₂ less than 4% (3.1 vs. 2.8 mmol/L; p = 0.0017). In multivariable logistic regression adjusted for preselected covariates, Spo₂–Sao₂ 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: 

Spo₂–Sao₂ 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.