Mortality in premature infant population suffering from severe lung or kidney failure is high. Current treatments are less adapted to neonatal physiology, invasive and have side-effects. The Artificial Placenta (ArtPlac) preclinical project aims to provide a miniaturized assist device providing simultaneous pulmonary and renal support. The model configuration of the lung and kidney assists device (LKAD) will be adopted for either microfluid or hollow-fiber approach. The in-development procedure promises a low invasive support and mortality rates as well as a reduced risk occurrence of lifelong disabilities. Moreover, the innovative umbilical cannulation will provide large bore access. One aspect of the device development lies in the oxygenation and filtration performance, achieving an efficient gas exchange while keeping resistance within the device low and minimizing device induced complications such as blood clot formation and hemolysis. To assess the computational framework to be applied on the device and associated sensitivity, a preliminary analysis was carried out on a generic geometry, evaluating the influence of methodology on species transport. A computational fluid dynamics (CFD) analysis is carried out to mathematically assess the mass transport through membranes between gas or dialysate and blood as well as overall in-device hemodynamic performance. The models are implemented with the commercial Comsol Multiphysics software. A parametric analysis is conducted to assess the sensitivity of physical quantities of interest (related to both hemodynamics and species transport rates) to the inputs, including the influence of blood structural/rheological model, flow unsteadiness (temporal and spatial gradients), fiber arrangement, membrane porosity and species diffusivity.