“…Explanations by study authors were grouped into individual-level, hospital-level, and systemic/structural factors (21). Individual-level primary themes were: 1) differential access to care (28, 30, 33, 106, 114, 122, 168, 170), 2) varying clinical presentations (26, 27, 30, 31, 80, 92, 128, 161, 168), 3) different religious/cultural preferences (26, 27, 80, 89, 93, 168), or other unmeasured individual SDoH as confounders (30, 84, 96). Hospital-level mechanisms included: 1) provider-level treatment variation (26, 31, 80, 93, 167, 169) and 2) between-hospital variability in offering ECMO, timing of initiation, organizational structure, experience, and standardized care practices/processes (27, 30, 31, 80, 90, 106, 122, 123, 129–131, 154, 157, 161, 168–173).…”