Caval collapse during cardiopulmonary bypass: a reproducible bench model

Area of Science:

• Cardiovascular Surgery
• Biomedical Engineering
• Fluid Dynamics

Background:

• Atrial chatter, a consequence of right atrial or caval collapse, is common during open heart surgery.
• Caval axis collapse during cardiopulmonary bypass (CPB) impedes venous return, potentially reducing pump flow and end-organ perfusion.
• Understanding and mitigating venous collapse is crucial for optimizing CPB procedures.

Purpose of the Study:

• To replicate venous collapse in a controlled flow bench environment.
• To investigate the mechanisms and conditions leading to caval collapse during simulated CPB.
• To evaluate the impact of venous cannula insertion and pump augmentation on venous drainage.

Main Methods:

• A polyethylene caval tree model with afferent veins was designed to simulate venous anatomy.
• Scenario A: Gravity drainage with a preload of 4.4 mmHg and outflow of 4500 ml/min.
• Scenario B: Venous drainage augmented by a centrifugal pump with a 23-Fr percutaneous venous cannula.

Main Results:

• Spontaneously reversible atrial chatter was reproducible under gravity drainage.
• Irreversible caval collapse occurred reproducibly with pump augmentation at specific pressures and speeds.
• Cavitation, indicated by bubble formation, was observed at the cannula tip, posing risks of tissue damage and embolization.

Conclusions:

• The caval model accurately depicts flow limitations caused by reversible atrial chatter and irreversible venous collapse during CPB.
• Temporary cessation of negative pressure in the venous line can restore venous drainage.
• Findings can inform the design of venous cannulas and optimize CPB perfusion strategies.