ABCP Perfusion Basic Science (PBSE) Practice Exam

The main idea is that the venous reservoir vent is there to remove trapped air from the venous side so air doesn’t get into the arterial circuit. In cardiopulmonary bypass, blood returns to a venous reservoir and is then pumped toward the oxygenator and arterial line. If air accumulates in the reservoir, it can be drawn into the pump head and travel downstream, risking air embolism and circuit arrest. The vent at the top of the reservoir provides an open pathway to atmosphere (often with a one-way control) so any bubbles rise to the vent and are expelled while the blood remains in the reservoir.

This is not primarily for removing CO2, which happens at the gas exchanger/oxygenator, nor for regulating venous return pressure (that depends on reservoir height and suction settings). It’s also not about de-airing the arterial line after the pump stops—that uses separate de-airing methods. The vent’s purpose is specifically to vent air and prevent air entrainment into the arterial circuit.