This Study Collects Information on the Safety of Inhaled Pegylated Adrenomedullin (PEG-ADM), How the Drug is Tolerated and How it Affects Patients Suffering From a Type of Lung Failure That Cause Fluid to Build up in the Lungs Making Breathing Difficult (ARDS)

Inclusion Criteria: * ≥18 years of age at the time of inclusion into study. * Invasively mechanically ventilated acute respiratory distress syndrome \[ARDS\] patients (diagnosed according to Berlin definition of ARDS, including positive end-expiratory pressure \[PEEP\] of ≥5 cm H2O, X-ray (or CT scan) indicative of ARDS: bilateral opacities not fully explained by cardiac failure, fluid overload, lobar/lung collapse, effusions or nodules). * Initial diagnosis of mild, moderate or severe ARDS prior to study inclusion, with acute onset of ARDS within 1 week after suspected trigger factor of * Pneumonia * Aspiration * Sepsis * Pancreatitis * Prior to randomization, hypoxemia with PaO2:FiO2 ≤300 mmHg continuously observed for a period of ≥4 hours (with values of ≥2 arterial blood gas \[ABG\] analyses during that time, with the last value obtained timely (generally ≤3 hours) prior to randomization), under ventilation with minimum PEEP ≥8 cm H2O. * Time from first meeting the last diagnostic ARDS criterion (Berlin criteria) to randomization must be ≤48 hours. * For Study Part A: ARDS patients for whom measurements of extra-vascular lung water are regarded as medically indicated by the treating physician, and these measurements are planned as part of their clinical care, from Study Day 1 up to Study Day 7 (if then still intubated). Exclusion Criteria: * Any value of a PaO2:FiO2 ratio \>300 mmHg within a time interval of 4 hours before randomization * Rescue therapy (e.g. inhalation of nitric oxide gas and/or inhalation of prostacyclin analogues, or extra corporeal membrane oxygenation \[ECMO\] / extra corporeal CO2 removal \[ECCO2R\]) already initiated at screening and/or Study Day 1 (prior to first dose of the study intervention) * Moribund participants not expected to survive 24 hours (clinical decision) * Expected duration of invasive mechanical ventilation less than 48 hours (clinical decision) * History of co-morbidities requiring long-term/home oxygen use (e.g. severe chronic obstructive pulmonary disease \[COPD\], pulmonary fibrosis) or non-invasive ventilation (except for sleep apnea management), or making weaning per se improbable (e.g. ALS, muscular dystrophy) * Smoke inhalation injury, extensive burns or trauma/head injury as concomitant condition * History of pneumectomy, lung lobectomy or lung transplant * Diffuse alveolar hemorrhage from vasculitis * Current lung malignancy (incl. lung metastasis), or other malignancy requiring chemotherapy or radiation within the last month * Chronic kidney disease with a history of renal replacement therapy (e.g. dialysis) * Chronic liver disease Child-Pugh Class C * Chronic heart failure NYHA IV * Known hypersensitivity to polyethyleneglycol (PEG, Macrogol) * Participation in other interventional studies involving pharmacological interventions, or biological or cell therapy interventions * Diagnosis of COVID-19 pneumonia within 6 weeks prior to study inclusion. History of SARS-CoV-2 infection (positive test based on nucleic acid amplification technology or positive antigen test) without COVID-19 pneumonia does not exclude patients