CVVHD / Dialysis

last updated: December 6, 2016

Orlando Debesa

Figure shows the relation between the clearance (solutes removal performance) and the molecular weight of solutes in each CRRT modality condition that the total volume of replacement fluid and dialysate in constant (1L/hr). CVVH has superior removal performance for high molecular weight solutes 

Terminology

Dialysate

  • the electrolyte solution

  • runs countercurrent to blood flow

Ultrafiltration (Uf)

  • the movement of fluid through semipermeable membrane

Convection

  • movement of molecules through semipermeable membrane

Slow Continuous Ultrafiltration (SCUF)

  • removes fluid but does not allow for significant solute clearance

  • usually used for volume overloaded patients with or without renal failure

  • rate = 2000 mL/hr (maximum patient fluid removal)

  • small amount of ultrafiltration, therefore, you do not have significant solute clearance, just only volume removal

  • no replacement fluid

Continuous Veno Venous Hemofiltration (CVVH)

  • solutes are removed by convection, no dialysate is used

  • usually UF rate of 1-2 L/hr is used 

  • much higher ultrafiltration rate, therefore you will have more convection (plasma water moves along concentration gradient) and receive clearance of solute

  • rate = 1000 mL/hr (maximum patient fluid removal)

  • electrolytes and acid-base are corrected by replacement fluid (R)

  • highly permeable membrane which removes low and high molecular weight molecules

Continuous VenoVenous Hemodialysis (CVVHD)

  • rate = 1000 mL/hr (maximum patient fluid removal)

  • no fluid removed because there is no ultrafiltration

Continuous VenoVenous Hemodiafiltration (CVVHDF)

  • CVVH + CVVHD

  • rate = 1000 mL/hr (maximum patient fluid removal)

  • hypercatabolic

  • effluent = Uf + dialysate

... but I would more especially commend the clinician who, in acute diseases, by which the bulk of mankind are cutoff, conducts the treatment better than others.
 
Hippocrates, 400 BC