Ultrafiltration and Hemoconcentration in Medical Applications Quiz

Ultrafiltration and Hemoconcentration in Medical Applications

• Ultrafiltration involves blood passing through a bundle of hollow fibers with a microporous membrane
• The process creates a positive pressure within the hollow fibers, driving water across the membrane
• The pressure gradient between the blood path and the ultrafiltrate compartment is called the transmembrane pressure (TMP)
• TMP can be expressed by the formula: TMP = (Pin + Pout)/2 + V
• The rate of fluid removal depends on membrane permeability, blood flow, TMP, and hematocrit
• An increase in TMP increases the rate of effluent removal, similar to the effect of increased blood pressure on the glomerular filtration rate
• Ultrafiltration removes plasma water and diffusible solutes in equal concentration to the plasma water, without affecting the overall concentration of diffusible solutes
• Solutes greater than 65,000 Da are typically not removed by ultrafiltration, and cellular elements, plasma proteins, and protein-bound solutes are not removed
• The sieving coefficient measures the ability of a solute to be filtered through the ultrafiltrator membrane
• Ultrafiltration during cardiopulmonary bypass (CPB) can remove excess fluid, concentrate blood without removing plasma proteins, and improve patient care
• Studies have shown that ultrafiltration during CPB leads to increased protein and red blood cell concentrations, reduced fluid balance, and improved perioperative hemostasis
• The ultrafiltrator is configured in parallel to the extracorporeal circuit, generally as a passive shunt from a point of higher pressure to lower pressure, and may use a flowmeter for precise measurements, especially in pediatric patients

Ultrafiltration and Hemoconcentration in Cardiopulmonary Bypass (CPB)

• Ultrafiltration during CPB is primarily used to remove excess water, concentrate cellular elements and proteins in the blood, and maintain the patient's plasma concentration of diffusible solutes.
• Continuous ultrafiltration during rewarming on CPB has been hypothesized to attenuate the inflammatory response, particularly during the peak of cytokine and complement levels.
• A balanced electrolyte solution can replace ultrafiltrate during rewarming to enable continuous ultrafiltration, potentially reducing the inflammatory response.
• Z-Buf, a form of ultrafiltration, has been used to correct hyperkalemia, particularly during cardiopulmonary bypass.
• Potassium loads during CPB, originating from potassium-based cardioplegia and red blood cells, can be effectively managed through ultrafiltration and replacement with a low-potassium solution.
• Z-Buf has also been used to correct severe electrolyte and acid-base disturbances in adults undergoing cardiac surgery, offering rapid corrections and the ability to select the concentration of diffusible solutes in the replacement fluid.
• Modified Ultrafiltration (MUF) has been described for pediatric patients, concentrating residual circuit blood for transfusion without the risk of hypervolemia, but requiring the patient to remain cannulated post-CPB.
• MUF can transfer nearly all circuit contents to the patient while the circuit remains primed with crystalloid solution, but protamine administration is contraindicated during MUF.
• Ultrafiltration can effectively remove direct thrombin inhibitors like bivalirudin, especially in patients with heparin-induced thrombocytopenia (HIT), a complication of heparin administration.
• Ultrafiltration can address challenges in managing hemodilution, electrolyte levels, and fluid shifts associated with the systemic inflammatory response during CPB.
• Z-Buf, when combined with MUF, has shown improved post-CPB outcomes and reduced levels of inflammatory mediators, demonstrating its potential clinical benefits.
• Ultrafiltration and dialysis, while serving similar functions in managing patient volume and electrolyte imbalances, have differences in efficiency in removing middle-molecule uremic solutes.