1.
Principle functions
of venous reservoir:
a) Acts as a high capacitance (low pressure) receiving chamber for venous return; facilitates gravity drainage of venous blood
b) Acts as a buffer for fluctuation & imbalances between venous return & arterial flow
c) Remove both air & microaggregates present in venous blood
2.
Types
a)
Hardshell reservoir
i) Rigid (hard) transparent plastic canister
ii) Contains a defoaming layer and a filtering screen (100-200 mm)
iii) Capacity: 1 — 4.5 litres
iv) Advantages:
a) easier to measure volume
b) handles venous air more effectively
c) easier to prime
d) less expensive
b)
Softshell reservoir
i) ‘Bag’ consists of soft PVC
ii) Filtering screen (100-200 mm)
iii) Capacity: 200 — 3000 ml
iv) Venous resistance is dependent on height of cardiotomy of venous overflow
v)
Advantages:
a) eliminates blood-gas interface
b)
reduce risks of massive air embolism because they
collapse when empty
c)
No anti foam (is in cardiotomy reservoir)
d)
3.
Operating
response time with flow
a) Reaction time is the period of time before the venous reservoir (or arterial reservoir in the bubble oxygenator) completely empties if the venous flow is abruptly stopped.
b) At a given flow rate, a higher venous reservoir is associated with a longer reaction time.
c) Reaction time is prolonged if the venous return is only partially restricted
Reaction
time = (Reservoir volume [ml] ´ 60) ¸ Blood flow rate (ml/min)
4.
Minimum operating
levels
a) A high operating reservoir level is desirable not only because it will increase reaction time, but also because bubbles that make their way into the reservoir will have a chance to be absorbed or float away if a high level is maintained (increased dwell & transit times)
b) Low reservoir levels are associated with a higher bubble count leaving the reservoir (vortex effect)