Urea kinetic modelling (UKM) has been generally accepted as a method for quantifying hemodialysis (HD) treatment. During hemodialysis, reduction in the urea concentration in the intracellular fluid (ICF) compartment will lag behind that in the extra cellular fluid (ECF) compartment, and following the end of dialysis, a ”rebound” in the blood level of urea will occur where it continues to rise due to diffusion of urea from the ICF to ECF to establish an equilibrium state. Because of compartment effects, the dose of dialysis with regard to urea removal is significantly overestimated from immediate post-dialysis urea concentrations, because 30 to 60 min are required for concentration gradients to dissipate and for urea concentrations to equilibrate across body water spaces during the post-dialysis period. To avoid the delay of waiting for an equilibrated post-dialysis sample, it became necessary to describe and to quantitate effects causing the urea compartmentalization during dialysis; two-pool modeling approaches have been developed that more accurately reflect the amount of urea removed. This in turn gives more adequate measures not only of dialysis adequacy, but also of the protein catabolic rate, an important nutritional measure that is clinically monitored in dialysis patients. This chapter discusses the double pool urea kinetic models and regional blood flow models in order to understand the concept of urea rebound. |
