What is the recommended cannulation approach for cardiopulmonary bypass (CPB) in a patient with severe aortic regurgitation undergoing cardiac surgery?

Cannulation for Cardiopulmonary Bypass in Severe Aortic Regurgitation

In patients with severe aortic regurgitation undergoing cardiac surgery, standard ascending aortic cannulation with immediate left ventricular venting is the recommended approach to prevent catastrophic ventricular distension once cardiopulmonary bypass is initiated. 1

Critical Pathophysiology Requiring Modified Approach

Severe aortic regurgitation creates a unique and dangerous situation during CPB initiation because the incompetent aortic valve allows retrograde flow from the arterial cannula directly into the left ventricle, causing rapid and potentially fatal ventricular distension. This occurs the moment CPB flow begins and can lead to:

• Subendocardial ischemia from elevated wall tension 1
• Ventricular rupture in extreme cases
• Inability to achieve adequate systemic perfusion despite high pump flows
• Myocardial damage that compromises postoperative recovery

Mandatory Cannulation Strategy

Arterial Cannulation Site Selection

The ascending aorta remains the preferred arterial cannulation site unless contraindicated by aortic pathology, atherosclerosis, or dissection. 1

• Lower systolic blood pressure below 100 mmHg before cannulation to reduce dissection risk (0.06-0.23% incidence) 1
• Perform epiaortic ultrasonography before cannulation in patients >50-60 years or those with stroke history, peripheral arterial disease, or visible calcifications to detect atherosclerotic plaque and reduce stroke risk 1
• If ascending aorta is unsuitable, use axillary-subclavian artery as first alternative (provides antegrade flow, usually atherosclerosis-free, rich collaterals) 1, 2
• Femoral artery serves as rapid access for emergency situations but provides retrograde flow 1, 3

Venous Cannulation Approach

Use bicaval cannulation rather than single atrial cannulation to provide complete venous drainage and facilitate optimal surgical exposure for valve replacement. 1

• Bicaval approach involves separate cannulation of superior and inferior vena cava 1
• Select cannula size based on patient weight, anticipated flow rate (target >2.5 L/min/m²), and catheter resistance characteristics 1
• Consider assisted venous drainage with negative pressure (roller or centrifugal pump) if using smaller diameter cannulas, though this increases risk of air aspiration and hemolysis 1

Essential Venting Strategy - The Critical Difference

Immediate left ventricular venting must be established BEFORE or simultaneously with initiation of CPB flow in severe aortic regurgitation. 1

Venting Options (in order of preference):

1. Left ventricular vent through right superior pulmonary vein - most direct decompression
2. Aortic root vent - placed after aortic cannulation but before CPB initiation
3. Transapical left ventricular vent - direct apex cannulation if other routes unavailable 4

Venting Technique Considerations

• Avoid excessive negative pressure and air entrainment into vent lines (causes hemolysis and gaseous microemboli) 1
• Use passive venting or smart suction devices that only aspirate when contacting blood to minimize blood trauma 1
• Maintain continuous venting throughout CPB until aortic cross-clamp is applied and cardioplegia arrests the heart 1

Preoperative Team Coordination

The perfusionist and surgeon must reach preoperative agreement on cannula sizes, types, and venting strategy specific to the aortic regurgitation pathology (Class I recommendation, Level C evidence). 1

This discussion should address:

• Anticipated CPB flow requirements based on body surface area
• Backup cannulation sites if primary site fails
• Timing sequence for cannulation and vent placement
• Monitoring strategy for adequate decompression

Common Pitfalls to Avoid

Never initiate CPB flow in severe aortic regurgitation without functional left ventricular venting in place - this is the single most dangerous error and can cause immediate ventricular distension, myocardial ischemia, and inability to wean from bypass. 1

Do not rely on aortic root venting alone after cross-clamp application - the incompetent valve allows continued regurgitation until the heart is arrested with cardioplegia. 1

Avoid femoral cannulation as first choice unless emergency access needed - retrograde flow may worsen cerebral embolic risk in patients with aortic atherosclerosis (0.7-4.3% have porcelain aorta). 1

Do not use excessive suction pressure on cardiotomy or vent lines - this causes hemolysis and increases gaseous microemboli, particularly when air interfaces with blood. 1