Dialysis
Figure 1: Example of a Within-centre Distribution of Delivered Ionic Kt/V over Six Months in 66 Haemodialysis Patients, Showing Inter- as well as Intra-patient Variation
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4
Patient Data from 16 October 2006 to 12 April 2007, sampled by Qcontrol software and kindly provided to Gambro. Kt/v defined using v equal to 55 % of dry body weight. Ionic Clearance Measurement
Control of dialysis delivery at each treatment cannot be based on blood urea sampling but requires an automated monitoring device that is accurate, precise and easily applied at no or minimal extra cost. The technology of ionic clearance monitoring (also referred to as ionic dialysance or conductivity clearance) delivers to that need, being fully integrated into the dialysis machine and requiring no extra disposables to run. Here, the instantaneous clearance (K) by dialysis is assessed repeatedly during the dialysis session by generating well-defined conductivity pulses in the dialysis fluid and analysing the appearance of those pulses in the dialysate after passing the dialyser. No blood samplings are required. Diascan is the name of one such monitoring system (Gambro, Medolla) that measures K values that closely reflect urea clearances when the effects of access and cardiopulmonary recirculation are taken into account.28,29
The conductivity pulses are set up in such a way that their contribution to the overall sodium mass transfer is negligible.30
The ionic clearance measurement device is an effective quality control tool in dialysis. Contemporary dialysis machines provide applications that automatically warn if K drops below a certain level. This helps to detect dialysis inefficiency at an early stage, whether caused by access recirculation or by human errors in the setup of the treatment, like wrongly placed access needles.31
Having a
measured K value within the first 30 minutes of treatment is to get confirmation that the dialysis session proceeds as planned, or indication that corrective actions are needed to reach the target Kt/V at treatment end.
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Having an ionic clearance device to repeatedly measure the effectiveness of dialysis also means that the delivered dose is available for every treatment. The effectively cleared Kt is derived by multiplying K, integrated over the full session length, with the effective treatment time. Alternatively, by entering the patient’s V, the ionic clearance device presents the delivered dose as Kt/V.32
By displaying ionic Kt/V
data over a range of treatments you may get a clear overview of the variability in delivered dose between and within patients (see Figure 1).
Early Warnings on Access Failure
Access patency is vital to achieving the prescribed blood flow rate. Having ionic K data, treatment by treatment, also provides means to detect access problems at an early stage. Compared to access flow measurement that, for practical reasons, is rarely applied at a high enough frequency to be useful for a general screening of patients, ionic K measurement is a practical chairside tool. The ratio of ionic K over the actual blood flow rate, or Kt over the volume of blood processed, makes a particularly useful parameter to unveil access recirculation.33
A clinical IT tool designed to automatically score the risk of developing access failure based on trends in ionic K, actual blood flow rate and arterial and venous line pressures, has shown promising initial results.34,35
Opportunity to Reduce Variability
The immediate control of treatment efficiency provided by the ionic clearance device offers an unparalleled opportunity to address the issue of variable dose delivery. Built into the dialysis machine for automatic operation and requiring no extra disposables, the device is
EUROPEAN NEPHROLOGY
Kt/v
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