1215 Calculation of recirculation during haemodialysis

  • Haemodialysis clearance depends on membrane type, the dialyser surface area, the blood flow rate and the dialysate flow rate

    A 50-60% reduction in serum urea and creatinine concentration is desirable during a single haemodialysis treatment.  If not, recirculation of blood may be occurring.  It can occur in the presence of good blood flow and normal venous pressure

    The amount of access recirculation is usually measured by comparing the blood urea entering the dialyser and blood urea leaving the dialyser.  The method of calculation of percentage recirculation is

    % Recirculation = 100 x Usystemic - Uarterial /  Usystemic - Uvenous

    Usystemic = systemic urea from peripheral vein taken from vein in opposite arm

    Uarterial = urea from blood entering dialyser (ie. from arterial line)

    Uvenous = urea from blood leaving the dialyser (ie. from venous line)

    No recirculation is present U arterial = U systemic.  If the blood entering the dialyser is being contaminated with blood leaving the dialyser (ie. from the venous line) then Uarterial < U peripheral

    If more than 20% of blood is recirculated then corrective access surgery should be strongly considered.  Recirculation is a well recognised risk of single needle dialysis