Fluid Management of the Cardiac Patient Undergoing Cardiopulmonary Bypass

Fluid Management of the Cardiac Patient Undergoing Cardiopulmonary Bypass

When it comes to fluid management in cardiac patients undergoing cardiopulmonary bypass (CPB), perfusionists face a multitude of challenges. This comprehensive webinar transcript, “Fluid Management of the Cardiac Patient Undergoing Cardiopulmonary Bypass,” delves into the complexities of fluid therapy, providing insights into the physiology, principles, and practical considerations of managing fluids effectively during CPB. Presented in a detailed manner, it aims to educate perfusionists on making better decisions that positively impact patient outcomes.

Part One: Understanding the Basics

The first part introduces the principles of fluid therapy, focusing on maintaining tissue perfusion. It outlines the common crystalloids used in clinical practice, including:

• Normal Plasma: The most prevalent fluid in the body.
• 0.9% Sodium Chloride (Normal Saline): Available in half or quarter normal saline concentrations.
• Plasma-Lyte: Popular for perfusion priming due to its acetate-based composition.
• Hartmann Solution and Lactated Ringer’s: Utilize lactate as a buffer.

The webinar stresses the importance of acetate-based solutions for pH adjustment and briefly touches on bicarb-based fluids. Bicarbonate solutions like Duosol are effective due to their lack of lactate and their ability to stabilize the pH with bicarbonate.

Bicarb-Based Fluids

• Duosol by B. Braun
• Baxter Solutions
• NextStage Solutions

These fluids have variations in potassium, calcium, and magnesium concentrations, allowing for tailored therapy based on individual patient needs.

Fluid Distribution in the Body

Normal fluid distribution is a crucial aspect of fluid management:

• Total Body Water: 42 liters (~60% of body weight).
• Intracellular Fluid (ICF): ~28 liters.
• Extracellular Fluid (ECF): ~14 liters, including:
  • Intravascular Space: ~3 liters.
  • Interstitial Space: ~11 liters.

Understanding this distribution is vital to avoid overhydration or underhydration during and after CPB.

Daily Fluid and Electrolyte Requirements

• Fluids: 2.5 liters/day.
• Sodium: 0.5-1 mmol/kg/day.
• Potassium: Similar to sodium.

Colloids vs. Crystalloids

This section provides an in-depth comparison between colloids and crystalloids:

• Intravascular Persistence: Colloids > Crystalloids.
• Hemodynamic Stabilization: Colloids provide prolonged stabilization.
• Infusion Volume Requirement: Crystalloids require larger volumes.
• Tissue Edema Risk: High with crystalloids, low with colloids.
• Anaphylaxis Risk: Low to moderate for colloids.

Practical Crystalloid Therapy

The infusion of 0.9% sodium chloride expands only the extracellular fluid compartment. However, intravascular volume increases by only 250 mL due to third spacing.

Colloids and Their Role in Fluid Management

• Gelatins: Not widely used in the U.S. but still prevalent in Europe.
• Albumin: Effective volume expander with a molecular weight of 62 kDa.

Part Two: Fluid Balance and Why We Pee

This section explores the physiology of fluid balance and the importance of urine output. It highlights the role of the glomerular filtration rate (GFR) and discusses the diameters of afferent and efferent arterioles.

GFR Regulation:

• Increased GFR: Dilated afferent arterioles, constricted efferent arterioles.
• Decreased GFR: Constricted afferent arterioles, dilated efferent arterioles.

Glomerular Filtration Mechanisms:

• Natriuretic Peptides: Regulate sodium and water balance.
• Nitrous Oxide and Dopamine: Influence afferent arteriole dilation.
• Vasopressin (ADH): Constricts afferent arterioles, reducing urine output.

Fluid Management Strategies

• Resuscitative Fluids: Salt-rich solutions.
• Maintenance Therapy: Water with sodium and potassium.
• Blood Transfusion: For active bleeding or anemia.

Ultra-Filtration and Plasma Water Removal

Ultrafiltration is emphasized for plasma water removal. The presentation introduces animations to explain this process visually, demonstrating how excess fluid can be filtered out while maintaining electrolyte balance.

Part Three: Colloid vs. Crystalloid Controversy

This final segment discusses the long-standing debate between colloids and crystalloids. Albumin, a natural colloid, is argued to be a superior plasma volume expander compared to synthetic colloids like gelatins and starches. The meta-analyses presented demonstrate that albumin:

• Reduces platelet drop during CPB.
• Decreases weight gain post-operatively.
• Prevents erythrocyte crenation.
• Protects against acute kidney injury (AKI).
• Lowers mortality rates post-cardiac surgery.

Conclusion

The webinar concludes by emphasizing the need for meticulous fluid management strategies. Perfusionists are encouraged to consider the choice of fluids based on individual patient needs, intraoperative conditions, and the physiological impact of each fluid type. By understanding these principles, perfusionists can make informed decisions that reduce complications, enhance patient outcomes, and contribute to the overall success of cardiac surgeries involving CPB.

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