A side-by-side comparison of the decarboxylation efficacy of two pump-driven venovenous extracorporeal lung assist devices, i.e., a first prototype of the new miniaturized ambulatory extracorporeal membrane ventilator, I-lung versus the commercial system iLA-activve for more than a period of 72 hours in a large animal model. Fifteen German Landrace pigs were anesthetized and underwent mechanical hypoventilation to induce severe hypercapnia. Decarboxylation was accomplished by either the I-lung or the iLA-activve via a double lumen catheter in the jugular vein. Sham-operated pigs were not connected to extracorporeal devices. Cardiovascular, respiratory, and metabolic parameters were continuously monitored, combined with periodic arterial blood sampling for subsequent clinical blood diagnostics, such as gas exchange, hemolysis, coagulation parameters, and cytokine profiles. At the termination of the studies, lung tissue was harvested and examined histologically for pulmonary morphology and leukocyte tissue infiltration. Both extracorporeal devices showed high and comparable efficacy with respect to carbon dioxide elimination for more than 72 hours and were not associated with either bleeding events or clotting disorders. Pigs of both groups showed cardiovascular and hemodynamic stability without marked differences to sham-operated animals. Groups also did not differ in terms of inflammatory and metabolic parameters. We established a preclinical in vivo porcine model for comparative long-term testing of I-lung and iLA-activve. The I-lung prototype proved to be safe and feasible, providing adequate decarboxylation without any adverse events. Once translated into the clinical treatment, the new miniaturized and transportable I-lung device might represent a promising tool for treating awake and mobilized patients with decompensated pulmonary disorders.