The Effect of Catheter Size on the Efficacy of Ultralow-flow Extracorporeal Carbon Dioxide Removal System in Acute Respiratory Distress Syndrome

This pilot randomized controlled trial will evaluate whether catheter size affects the efficacy and performance of ultra-low-flow extracorporeal carbon dioxide removal (ECCO₂R) in mechanically ventilated adults with acute respiratory distress syndrome (ARDS) and hypercapnic respiratory acidosis. Participants will be randomly assigned to receive ECCO₂R using a 12F, 13F, or 15F catheter. The primary outcome is the percentage change in PaCO₂ from baseline during ECCO₂R. Secondary outcomes include achievement and time to correction of hypercapnic respiratory acidosis, changes in PaO₂, circuit lifespan, maximum blood flow, and device- and patient-related complications.

Inclusion Criteria: Participants must meet all of the following criteria: 1. Age ≥18 years. 2. Acute respiratory distress syndrome (ARDS), mild to moderate severity, with a PaO₂/FiO₂ ratio of 100-300 while receiving PEEP ≥5 cmH₂O, after initiation of mechanical ventilation within the preceding 72 hours. 3. Hypercapnic respiratory acidosis, defined by PaCO₂ \>60 mmHg and/or arterial blood gas pH \15 cmH₂O; * Plateau pressure \>27 cmH₂O; * Tidal volume \>6 mL/kg predicted body weight; or * Mechanical power \>17 J/min associated with respiratory rate \>25 breaths/min. Exclusion Criteria: * Severe shock that is preload non-responsive and requires norepinephrine \>1 µg/kg/min. * Acute brain injury or cerebral edema, increased intracranial pressure, status epilepticus, intracerebral hemorrhage, or acute ischemic stroke. * Pregnancy. * Morbid obesity with BMI \>40 kg/m². * Chronic respiratory acidosis. * End-stage cancer patients. * Coagulation disorders, defined as a platelet count of less than 10,000 cells/mm3 or an INR greater than 3. * Patients undergoing targeted temperature management for 24 hours after return of spontaneous circulation. * End-stage renal disease (ESRD) patients with a blood urea nitrogen (BUN) level greater than 60 mg/dL. * Patients or legal representatives who do not consent to participation. * Patients with an indication for ECMO according to the EOLIA trial criteria, specifically a PF ratio \< 50 mmHg more than 3 hours or a PF ratio \< 80 mmHg more than 6 hours.