Haemodialysing infants: theoretical limitations, and single versus double lumen lines

Abstract

Haemodialysing small infants is difficult because of vascular access limitations. We show that Poiseuille's law (that flow through a tube varies with its radius4) makes it inevitable that the blood flow that can be achieved in smaller patients will fall disproportionately compared to their need for dialysis. Poiseuille's law also predicts that for single and multiple lumen cannulae of the same outside gauge, blood flow through the single lumen will be several times greater. Measurements confirmed this. It is argued that haemodialysis efficiency will therefore be improved by using a single lumen cannula to alternately withdraw and return blood, compared to sampling and returning continuously through a multiple lumen cannula, despite only withdrawing for half the time.

Outcome of reaching end stage renal failure in children under 2 years of age

“…Further, adequate clearances are seldom produced in small children, 17 probably because of the widespread use of double lumen vascular access lines which limit the blood flow that can be achieved. 18 Managing end stage renal failure in young children involves much more than just dialysis. As well as dietary modifications, fluid restrictions, and oral medications, other treatments are increasingly used, including overnight gastrostomy feeding, and subcutaneously administered erythropoietin and growth hormone.…”

Comparison of alteplase and heparin in maintaining the patency of paediatric central venous haemodialysis lines: a randomised controlled trial

“…We routinely use single lumen central lines because of their greater efficiency, 3 and ones with multiple distal side holes to minimise obstruction against the vessel walls. We use 8FG lines for children under 10 kg, and 10FG lines for larger children.…”

A machine for haemodialysing very small infants

“…This factor alone makes it about four times harder to dialyse a term baby than an adult, and around seven times harder to dialyse a 1 kg neonate [4]. Resultant poor flows may prevent effective dialysis, and lead to clotting within the dialyser.…”

“…Single lumen access was used to improve access efficiency [4], and the circuit consisted merely of two syringes, a small dialyser, and a series of three-way taps. The first syringe had a reservoir function which allowed blood to be sampled slowly from the child's line, but to be passed quickly across the dialysis membrane.…”