What is the recommended calculation and composition for priming fluid in a cardiopulmonary bypass (CPB) circuit?

Cardiopulmonary Bypass Circuit Priming: Calculation and Composition

Crystalloid solutions are recommended as the primary priming solution for cardiopulmonary bypass (CPB) circuits, with autologous priming techniques used when possible to reduce hemodilution and transfusion requirements. 1

Priming Volume Considerations

The optimal priming volume depends on several factors:

• Patient-specific variables (body surface area, preoperative hematocrit)
• Circuit-related variables (tubing length, oxygenator type, reservoir size)

Volume Calculation Approach

1. Determine the minimum volume required to safely operate the CPB circuit
2. Consider using minimized CPB systems when available
3. Aim to reduce priming volume through autologous priming techniques

Recommended Priming Solution Composition

Primary Components

• Base solution: Buffered crystalloid solutions (e.g., Ringer's lactate, Ringer's acetate) 1
• Avoid routine use of colloids: Evidence shows no benefit to routinely adding albumin or synthetic colloids to the priming solution 1

Additives to Consider

• Mannitol: Often added (typically 0.5-1.0 g/kg) though evidence supporting its role in reducing AKI is limited 1
• Heparin: Added to maintain anticoagulation in the circuit
• Avoid hydroxyethyl starch (HES): Associated with increased risk of acute kidney injury 1

Autologous Priming Technique

Autologous priming is strongly recommended, particularly for patients with small body surface area, as it:

• Preserves hematocrit
• Reduces homologous blood transfusion requirements
• Decreases fluid overload 1

Implementation Method

1. Allow patient's blood to displace priming fluid in the circuit
2. Direct displaced fluid into an external reservoir
3. Exclude this external reservoir from the circuit before initiating bypass

Fluid Management During CPB

• Monitor colloid osmotic pressure during bypass
• Avoid excessive hemodilution (maintain hematocrit >20% when possible)
• Limit ultrafiltration to <30 ml/kg to avoid excessive fluid removal 1
• Target ACT values between 300-600 seconds during CPB 1

Potential Pitfalls and Caveats

• Excessive hemodilution: Can lead to coagulopathy, increased transfusion requirements, and organ dysfunction
• Fluid overload: Associated with tissue edema, impaired gas exchange, and prolonged recovery
• Inadequate anticoagulation: May result in thrombus formation in the circuit
• Colloid use: Despite theoretical benefits for maintaining oncotic pressure, evidence does not support routine use of albumin or synthetic colloids in priming solutions 1
• CO2 flush: Remember to perform CO2 flush of the CPB circuit before priming to reduce gaseous microemboli 1, 2

By following these evidence-based recommendations for CPB circuit priming, clinicians can optimize patient outcomes by minimizing hemodilution, reducing transfusion requirements, and avoiding complications associated with fluid overload.