Cardiac vent
Mechanism
- Roller pump at low RPM with gravity/siphoning principle
- Without roller-pump gravity-only circuit.
Indications
- Reduce distension: blood leakage into heart during CPB causes distension àincreases O2 demand + impairs subendocardial perfusion
- Bloodless field
- Reduce myocardial rewarming
- Prevent ejection of air
Usually only left heart is vented as right is vented by venous cannulae.
Causes of distension during CPB
- Blood may leak into heart (assuming CPB circuit is normally working) by the following ways:
- LA/LV receives bronchial art & Thebesian veins
- RA/RV receives coronary sinus & venous cannulae leakage
- Aortic regurgitation
- Left-right communications: PDA, ASD, VSD, other systemic-pulmonary shunts
- Anomalous venous drainage: left-sided SVC, P-/T-APVC
How much to vent
Based on amount of distension by:
- inspection/palpation of LV,
- LA pressure monitor,
- PA catheter – subtle/moderate distension
Check especially when:
- On commencement of CPB
- On aortic cross-clamp
- On administration of cardioplegia
Placement of vents
- Aortic root cardioplegia cannula – cannot vent during antegrade cardioplegia administration or off cross-clamp. However, can vent air when cross-clamp released
- Right Superior Pulm Vein – into LV through LA/mitral valve
- LA – into LA through appendage/RSPV (not into LV) to avoid going through mitral valve
- LV apex
- PA – vents blood from LV through pulmonary vasculature. Not enough for LV if AR + competent MV.
When to vent right heart
Venous cannulae ‘vent’ RA/RV normally, and doesn’t need additional venting except in these situations:
- Leakage around venous cannula – use bicaval cannulation, caval snares.
- Leaking antegrade cardioplegia from coronary sinus – release caval snare and allow venting into venous cannula
- Left SVC (90% pts drain into CS, otherwise into LA) – additional drainage of coronary sinus
Complications of venting
- Steal of systemic perfusion – AR + excessive venting
- Air embolism – when vent is inserted or removed
- Bleeding from vent site – e.g. LV apex
- Stenosis of vent site – e.g. PA, PV stenosis
- LV aneurysm if LV apex used as vent site