a) Venous return
As the hydrostatic pressure drop through a bubble oxygenator is
small, it can be placed before the CPB pump; the flow through the bubble
oxygenator is driven primarily by the hydrostatic pressure head generated
within the venous return tubing (therefore explaining why CPB machines are
designed to be near the ground)
b) Mixing chamber
i) Venous blood first enters
a mixing chamber, where fresh blood flows into the blood via a screen, which
causes small bubbles to form
ii) The blood & bubbles coalesce — sufficient time is allowed in this section for adequate gas exchange to occur prior to defoaming in the second section
iii) The mixing chamber is
designed so that the blood flows through it in an upwards direction, thereby
exploiting the tendency of the rising bubbles to facilitate blood flow and
reduce the pressure drop
c) Heat exchanger
i) The hydrostatic pressure
& drag from the bubbles carry the blood over the top of a separator &
into the heat exchanger, bubble remover & reservoir
ii) The advantage of having the heat exchanger down stream from the bubble chamber is that gas exchange continues while heat transfer occurs
d) Defoamer
i) Blood is defoamed by silicone antifoam-A and
particulate silica which destabilise the bubbles causing them to collapse
ii) Bubbles are also mechanically restrained by a mesh net through which the blood & bubble must pass
e) Reservoir section
i) Blood exits from the
reservoir through the bottom, away from
bubbles floating to the top thereby augmenting debubbling
ii) Compensates for flow
discrepancies between passively flowing venous return & pump driven
arterial output