What are the fluid shifts associated with Cardiopulmonary Bypass (CPB)?

From the Guidelines

Fluid shifts during cardiopulmonary bypass (CPB) involve significant movement of fluid from the intravascular space to the interstitial space, resulting in edema and potential organ dysfunction, with approximately 1.5-2 liters of fluid shifting from the vascular compartment to the interstitial space within the first 24 hours, as reported in recent guidelines 1. The mechanisms behind these fluid shifts include hemodilution from the CPB circuit prime, activation of inflammatory mediators, increased capillary permeability, and changes in oncotic pressure.

• The inflammatory response to CPB causes endothelial damage, allowing albumin and fluid to leak into tissues.
• Hypothermia during CPB causes vasoconstriction, further promoting fluid shifts. To manage these shifts,
• maintain adequate perfusion pressure (50-70 mmHg)
• use balanced crystalloid solutions for volume replacement, as recommended by recent evidence-based consensus recommendations 1
• consider avoiding excessive use of colloids like albumin, as it may increase the risk of major bleeding, re-sternotomy, and infection, as shown in a recent RCT 1
• administer diuretics like furosemide (10-20 mg IV) post-CPB to mobilize excess fluid
• avoid excessive ultrafiltration (>30 ml kg−1) during CPB, as it may increase the risk of postoperative acute kidney injury (AKI), as reported in a recent meta-analysis 1 Vasopressors such as norepinephrine (0.01-0.1 mcg/kg/min) may be needed to maintain blood pressure despite fluid shifts. Monitoring parameters including central venous pressure, urine output, and laboratory values helps guide fluid management. Understanding these fluid dynamics is essential for preventing complications like pulmonary edema, prolonged ventilation, and renal dysfunction following cardiac surgery, and recent guidelines emphasize the importance of evidence-based fluid management strategies to improve patient outcomes 1.

From the Research

Fluid Shifts Associated with Cardiopulmonary Bypass (CPB)

The fluid shifts associated with CPB can be significant, leading to fluid overload and its associated complications. Some key points to consider include:

• Fluid overload is common before, during, and after cardiac surgery, with CPB and cardioplegia being important sources of such fluid overload 2
• The use of diuretics can help prevent fluid overload, but may not be sufficient in all patients, with hemofiltration (HF) during and after CPB being an effective and safe approach to maintaining fluid homeostasis 2
• The type of priming solution used in CPB can affect fluid balance, with hydroxyethyl starch 130/0.4 resulting in a lower fluid overbalance compared to crystalloid solution 3
• Albumin in the prime may attenuate the extravasation of fluid out of the vascular space, but may be associated with an increased transfusion rate 4
• CPB is associated with massive fluid shifts, as well as the activation of blood components and a whole body inflammatory response 5

Factors Influencing Fluid Shifts

Several factors can influence the fluid shifts associated with CPB, including:

• The type of priming solution used, with colloid solutions such as hydroxyethyl starch 130/0.4 and albumin potentially reducing fluid overload 3, 4
• The use of diuretics and hemofiltration to manage fluid balance 2
• The patient's underlying renal function, with renal dysfunction contributing to fluid overload 2
• The duration and complexity of the CPB procedure, with longer and more complex procedures potentially resulting in greater fluid shifts 6, 5