Fig. 1.

Pathway analysis: stepwise mediation analysis assessing whether the association between age and mortality is mediated by age-dependent differences in biomarker levels. *Adjusted for ethnic background, gender, admission type, readmission, direct hit for ARDS, Charlson Comorbidity Index, APACHE-IV score adjusted for age, immunodeficiency, tidal volume per predicted body weight, positive end-expiratory pressure. C = average direct effect (ADE); A*B = average causal mediation effect (ACME). A’, B’, and C’—adjusted for confounders