Introduction of gaseous microemboli (GME) into the arterial line of a pediatric cardiopulmonary bypass (CPB) circuit may lead to cognitive decline and adverse outcomes of the pediatric patient.Arterial filters are incorporated into CPB circuits as a safeguard for gross air and to reduce GME. Recently, arterial filters were integrated in two neonatal oxygenators to reduce volume and foreign surface area. In this study a clinical CPB scenario was simulated. The oxygenators, the corresponding venous reservoirs and the complete CPB circuits were compared regarding air removal and bubble size distribution after the introduction of an air bolus or GME. During a GME challenge, the Capiox FX05 oxygenator removed a significantly higher volume of GME than the QUADROX-i Neonatal oxygenator (97% vs. 86%). Detailed air removal characteristics showed that more GME in the range of 20-50 µm were leaving the devices than were entering. This phenomenon seems to be more present in the Capiox FX05. The circuits were also challenged with an air bolus. Each individual component tested removed 99.9%, which resulted in an air volume reduction of 99.99% by either complete CBP circuit. Overall, we conclude that both CPB systems were very adequate in removing GME and gross air. The air removal properties of both systems are considered safe and reliable. Detailed GME distribution data show that the Capiox FX05 showed more small GME (<50 µm) due to fractionation of larger GME when compared to the QUADROX-i Neonatal. We may conclude that filtration may lead to fractionation.