Recirculation and the post-dialysis rebound.

Abstract

Limitations to short haemodiaiysis It is now generally accepted that there is a significant risk of underdialysis if the treatment time is shortened towards 4 h or less. To avoid these risks, a return to longer dialysis times has been advocated, despite the increase in cost and inconvenience to the patient. An alternative strategy would be to understand the mechanism of reduced efficiency in short dialysis and specifically correct for it without resorting to long treatments. If it were possible to increase the rate of removal of fluid and solute mass in proportion to the reduction of dialysis time, without increasing the patient's fluid content, blood pressure or solute concentrations, then the short treatment would have equivalent efficacy to the long treatment. There are a number of factors which combine to reduce rate of fluid and solute removal in short dialysis. These include the relatively slow diffusion of middle and large molecular weight solutes, hypotension related to high ultrafiltration rates and the post-dialysis rebound. This paper will consider only the post-dialysis rebound, although it is accepted that other factors need to be considered when prescribing short dialysis. The rate at which solute can be removed from the patient is dependent on the dialyser clearance and on the rate at which solute can be conveyed from all parts of the body into the arterial needle. While the dialyser clearance rate is controllable and relatively easy to measure, the other factors are much more difficult to measure and are generally impossible to modify. For solute to travel from the intracellular compartment (which is the largest body water compartment) to the needle, it must cross the cell membrane, be carried into the central circulation by venous blood flow, be pumped into the aorta by the heart and carried to the needle by the fistula blood flow. Therefore the rate of transfer depends on the intra/extracellular mass transfer coefficient, regional blood flow rates, cardiac output