Background: Assessment of access recirculation (AR) is crucial to dialysis
efficiency and there is thus a need for a method yielding a highly accurate
, fast, easy and economical measurement that can be applied in any busy dia
lysis clinic. Non-urea based dilutional methods are more accurate than urea
based methods and avoid problems with cardiopulmonary recirculation, but t
hey require expensive specialized devices, which limit their applicability.
Methods: We developed a simple dilutional method of AR which does not requi
re any specific device, based on the determination of serum potassium [K+]
in two samples. Briefly, a basal sample is drawn at the time of needle inse
rtion (basal (K+)); needles are connected to blood lines and blood flow rat
e is quickly increased to 300 ml/mm; a second sample (arterial (K+)) is dra
wn from the arterial line port within 5 to 10 seconds, to avoid errors due
to cardiopulmonary recirculation of the normal saline entering the blood st
ream. At this time, if recirculation is present, part of the normal saline
will enter the arterial line and dilute the serum [K+]. The AR formula is:
AR (%) - 100 x [1 - arterial K+/basal K+]
We compared our method with the two-needle urea and ultrasound velocity dil
ution methods.
Results: AR values by the ultrasound method > 10% were hypothesized as gold
standard for AR, against which values obtained with the potassium method w
ere compared. The potassium based method showed: sensitivity (100%,); speci
ficity (95%); predictive value, positive (91%); predictive value, negative
(100%). In addition, the potassium based method appears to be more reliable
than the two-needle urea based method.
Conclusion: Our method, similar to other dilutional methods, is not influen
ced by cardiopulmonary recirculation or veno-venous disequilibrium and is f
ast and accurate. Moreover it is very simple, economical, and can easily be
performed in any dialysis unit.