Extracorporeal Membrane Oxygenation Physiological Factors Influence Pulse Oximetry and Arterial Oxygen Saturation Discrepancies

Background: Cannulation strategy, vasopressors, and hemolysis are important physiological factors that influence hemodynamics in extracorporeal membrane oxygenation (ECMO). We hypothesized these factors influence the discrepancy between oxygen saturation measured by pulse oximetry (SpO₂) and arterial blood gas (SaO₂) in patients on ECMO. Methods: We retrospectively analyzed adults (aged ≥18 years) on venoarterial or venovenous ECMO at a tertiary academic ECMO center. SpO₂−SaO₂ pairs with oxygen saturation ≥70% and measured within 10 minutes were included. Occult hypoxemia was defined as SaO₂ ≤88% with a time-matched SpO₂ ≥92%. Adjusted linear mixed-effects modeling was used to assess the SpO₂−SaO₂ discrepancy with preselected demographics and time-matched laboratory variables. Vasopressor use was quantified by vasopressor dose equivalences. Results: Of 139 venoarterial-ECMO and 88 venovenous-ECMO patients, we examined 20,053 SpO₂−SaO₂ pairs. The SpO₂−SaO₂ discrepancy was greater in venovenous-ECMO (1.15%) vs venoarterial-ECMO (−0.35%, P < .001). Overall, 81 patients (35%) experienced occult hypoxemia during ECMO. Occult hypoxemia was more common in venovenous-ECMO (65%) than in venoarterial-ECMO (17%, P < .001). In linear mixed-effects modeling, SpO₂ underestimated SaO₂ by 9.48% in central vs peripheral venoarterial-ECMO (95% CI, −17.1% to −1.79%; P = .02). Higher vasopressor dose equivalences significantly worsened the SpO₂−SaO₂ discrepancy (P < .001). In linear mixed-effects modeling, SpO₂ overestimated SaO₂ by 25.43% in single lumen–cannulated vs double lumen–cannulated venovenous-ECMO (95% CI, 5.27%-45.6%; P = .03). Higher vasopressor dose equivalences and lactate dehydrogenase levels significantly worsened the SpO₂−SaO₂ discrepancy (P < .001). Conclusions: Venovenous-ECMO patients are at higher risk for occult hypoxemia compared with venoarterial-ECMO. A higher vasopressor requirement and different cannulation strategies (central venoarterial-ECMO; single-lumen venovenous-ECMO) were significant factors for clinically significant SpO₂−SaO₂ discrepancy in both ECMO modes.