Why Hemoconcentration Decreases After Blood Transfusion in Hemodialysis Patients
Direct Answer
Blood transfusion in hemodialysis patients decreases hemoconcentration because the transfused packed red blood cells increase intravascular volume and red cell mass, which improves hemodynamic stability and reduces the rate of ultrafiltration-induced volume contraction that normally occurs during dialysis. 1
Physiological Mechanism
Hemodynamic Stabilization
- Transfusion raises intradialytic blood pressure and slows the rate of mean arterial pressure decline during dialysis, preventing the compensatory hemoconcentration that occurs when patients become hypovolemic 1
- In a study of 25 ESRD patients with severe anemia (mean hemoglobin 5.9 g/dL), transfusion of 2 units of packed red cells reduced hypotensive episodes from 28 to 12 episodes (p=0.02) 1
- The improved hemodynamic stability means less need for compensatory fluid shifts from extravascular to intravascular compartments, which normally cause hemoconcentration 1
Volume Distribution Changes
- Hemoglobin concentration depends on both red cell mass AND plasma volume—transfusion increases red cell mass while simultaneously affecting plasma volume distribution 2
- The infusion of packed red blood cells (approximately 200-300 mL per unit) expands intravascular volume, which dilutes the blood and reduces hemoconcentration 2
- Mean postdialysis weight fell from 62.0 kg before transfusion to 61.5 kg following transfusion (p<0.001), indicating better volume control without excessive hemoconcentration 1
Reduced Ultrafiltration Stress
- Transfusion reduces the need for aggressive ultrafiltration by improving oxygen-carrying capacity, allowing more gradual fluid removal without triggering compensatory hemoconcentration 1
- Intravenous sodium chloride used to treat hypotension declined from 20.4 to 10.2 mEq per dialysis (p=0.01) after transfusion, indicating less hemodynamic instability and less need for volume expansion that would cause hemoconcentration 1
Clinical Context in Hemodialysis
Normal Hemoconcentration During Dialysis
- During standard hemodialysis, ultrafiltration removes plasma water faster than it can be mobilized from extravascular spaces, causing transient hemoconcentration 2
- This hemoconcentration is a normal compensatory response to volume removal but becomes problematic in severely anemic patients who cannot tolerate the hemodynamic stress 1
Post-Transfusion Changes
- After transfusion, the improved red cell mass and oxygen delivery capacity allows patients to tolerate ultrafiltration without excessive sympathetic activation and fluid shifts 1
- The reduction in hypotensive episodes (from 28 to 12) demonstrates that transfusion stabilizes the cardiovascular response to volume removal 1
Important Clinical Pitfalls
Avoid Confusing Hemodilution with Decreased Hemoconcentration
- The saline reinfused at the end of hemodialysis (150-500 mL) can dilute plasma and lower hemoglobin concentration, but this is a measurement artifact, not the primary mechanism of reduced hemoconcentration 2
- For small patients with diminished intravascular distribution volume, this saline dilution effect can be noteworthy and should not be confused with the physiologic changes from transfusion 2
Transfusion Timing Considerations
- In hemodialysis patients with hemoglobin <6 g/dL, transfusion should be immediate to prevent the severe hemodynamic instability that leads to excessive hemoconcentration during ultrafiltration 3
- Each unit of packed red blood cells increases hemoglobin by approximately 1-1.5 g/dL, but the hemodynamic benefits occur before the full hematocrit rise is apparent 3
Monitoring Requirements
- Blood losses in hemodialysis patients average 165 mL/year from the dialysis technique itself, but can reach 2,680 mL/year with double-lumen catheters, contributing to chronic anemia and abnormal hemoconcentration patterns 2
- Regular monitoring of hemoglobin is essential because hemoconcentration during dialysis may mask the true severity of anemia 2