INTRODUCTION
At each hemodialysis process several factors take place that may have an influence on the dialytic efficacy, so that it seems reasonable that control systems have been created in order to quantify at real time and at each session the dose the patient is receiving. In this sense, different monitoring devices have currently incorporated biosensors that measure in a non-invasive way, and using the conductivity probes of the devices, the effective ionic dialysance, which is equivalent to urea clearance (K), and thus it allows calculating the dialysis dose without additional workload, analytical determinations, or cost.1-3
Systematic determination of K by the time on dialysis allows obtaining the Kt, a real way of measuring the dialysis dose, expressed in liters. Working with the Kt has advantages since K and t are real and measured by the monitoring device. If we prescribe a Kt/V we have to introduce V, and thus an almost always wrong value that may be manipulated during the session.
Since 1999, Lowrie et al.4 proposed the Kt as a marker of the dialysis dose and mortality, recommending a minimum Kt of 40-45 liters for women and 45-50 for men. In a study on 3,009 patients,5 the authors observed a J-shaped survival curve when the categorized the patients by PUR quintiles, whereas the curve was descendent when the Kt was used, that is to say, a higher Kt value was accompanied by higher survival. In the year 2005, the Kt prescription was adjusted to the body surface area,6 which was validated in a further study.7 The aim of the present study was to undertake a follow-up of the dialysis dose with the Kt at each session for 3 months, and to assess the adherence to prescriptions and usual recommendations, for both those based on the monthly laboratory workup and those referred to the Kt.
PATIENTS AND METHODS
This is a prospective study including 51 patients, 58% from the Hemodialysis Unit, 32 males and 19 women, aged 60.7 ± 14 years (range 28-82 years), on hemodialysis program for 37.7 ± 52 months, and dialyzed with ionic dialysance-equipped monitor. The only inclusion criteria were the availability of ionic dialysance-equipped monitors. The etiology of chronic renal failure was tubulointerstitial nephropathy,3 chronic glomerulopathy,9 nephroangiosclerosis,12 polycystic renal disease, 7 diabetes mellitus,7 and of unknown origin.13 Every patient received a usual hemodialysis regimen with dialyzers of 2.1-m2 diacetate cellulose (33.3%), 1.9-m2 polysulphone (33.3%), and 1.8-m2 helixone, with a mean duration of 263 ± 32 minutes (range 180-300), and blood flow of 405 ± 66 mL/min (range 300-500), and bath flow at 712 ± 138 mL/min, dry weight 66.7 ± 14 kg. The vascular access was as follows: 40 arterial-venous fistulas (38 endogenous and 2 PTFAprostheses), and 11 central funneled catheters. The residual renal function was considered negligible.
The patients were dialyzed with monitors 4008 S (Fresenius) or Integra (Hospal) equipped with OCM (On-line clearance monitoring) or Diascan biosensors, respectively, which non-invasively measure the effective ionic dialysance equivalent to urea clearance by using conductivity probes. By taking two measurements of the fluid conductivity and the dialyzer inlet and outlet, a mathematic model is applied of two equations for two unknown values, which allows knowing the effective ionic dialysance corrected for ultrafiltration and recirculation through the vascular access.
At each dialysis session, initial ionic dialysance, final ionic dialysance, and Kt were recorded. On a monthly basis, the second generation Daurgidas Kt/V was calculated from routine laboratory work-up and the percentage of urea reduction (PUR). A follow-up of the dialysis dose administered was done, as well as of adherence to the recommendations on dialysis dosing:
¿ Recommendations from the main Clinical Guidelines, the most widely used to date: Kt/V > 1.3 and/or PUR > 70%.8-10
¿ Gender-adjusted recommendations: Kt/V > 1.3 in men and 1.6 in women.11-12
¿ Recommendation of Kt > 45 liters according to the SEN Guidelines.10
¿ Recommendation of Kt 40-45 L in women and Kt 45-50 L in men, within the recommended upper limit, Kt > 45 L in women and Kt > 50 L in men.4
¿ Recommendation of Kt adjusted by body surface area.6
These recommendations individualized for each patient and body surface area (BSA) are shown in table 1.
The results are expressed as arithmetic mean + standard deviation. The Student¿s t test has been used for the analysis of statistical significance of quantitative parameters. A p value < 0.05 has been considered to be statistically significant.
RESULTS
One thousand six hundred and six sessions with ionic dialysance from the 51 patients included during a follow-up period of 3 moths were recorded, whereas analytical samples were obtained at 153 sessions (one per month per patient). Due to logistic problems dealing with changes to spare monitors or technical problems, ionic dialysance could not be recorded at every dialysis session.
About the follow-up at each dialysis session, mean initial ID was 232 ± 41 mL/min (range: 145-313 mL/min), and mean final ID was 197 ± 44 mL/min (range: 122-254 mL/min). The mean Kt dose was 56.6 ± 14 L (range: 34.8-88.3 L).
By means of monthly laboratory work-up, we obtained a mean Kt/V value of 1.98 ± 0.5 (range: 1.30-3.20) and a mean PUR value of 79.2 ± 7% (range: 65-92%). The graphical plotting of the dose obtained by monthly laboratory work-up (153 measurements) and that obtained by Kt at each session (1606 measurements) is shown in Figure 1. The Kt during the first month was 57.2 ± 14 L, during the second one 56.4 ± 13.7, and during the third one 55.9 ± 13.7. It is observed that the dose was kept constant during the three follow-up months with both ID determinations and laboratory work-up.
All patients received a minimal Kt/V dose of 1.3, although when analyzing by gender only two women did not reach a minimal Kt/V of 1.6. Ninety percent of the patients obtained a PUR ≥ 70%, and five patients did not reach that target. About the recommendations on Kt prescription, 78% of the patients reached a minimum of 45 L. However, if we use the genderadjusted Kt as the reference, 31% of the patients did not reach the minimal prescribed dose (48.1 ± 2.4 L), 34.4% of male patients and 26.3% of female patients. Finally, if we adjust the prescriptions to the Kt adjusted by body surface area, 49.1 ± 4 L, we observed that 43.1% of the patients did not reach the minimal prescribed dose, with 4.6 ± 3.4 L lower dose than prescribed, in 14 patients the difference was < 5 liters and in 8 patients > 5 liters (table II).
The vascular access had an influence on the dose reached. Patients dialyzed through an arterial-venous fistula (40 patients) had a mean Kt of 59.2 ± 14 L, whereas in those dialyzed through a central funneled catheter (11 patients) the mean Kt was 46.9 ± 5 L, of whom seven did not reach the prescribed dose. The differences by time, Qb, Qd, and dose between both groups are shown in table III.
DISCUSSION
The present work shows a different, more stringent, way of carrying out the control and follow-up of the dialysis dose. It is different both because of the way of determining the dose (Kt expressed in liters) and because of the close follow-up at every dialysis session. The higher demand placed comes from the fact that by comparing with the usual analytical recommendations, the adherence the minimal Kt dose was not reached in 30% and 40% of the study patients when adjusting by gender or body surface area, respectively.
The current recommendations on the dialysis dose are based on monthly analytical determinations, although many times they are done every 3 to 6 months. An American multicenter study recommends a Kt/V ≥ 1.3 and/or PUR of 70%.8 According to the hemodialysis practice guidelines (DOQI) of the National Kidney Foundation, a minimum Kt/V of 1.2 and/or PUR of 65% is recommended, although the ideal should be a Kt/V of 1.3 and PUR of 70% in order to assure these minimal requirements.9 These recommendations are also recommended by the European,13 Canadian,14 British,15 and Spanish Guidelines of the Spanish Society of Nephrology.10
Using the Kt offers some advantages: both K and t are realtime measurements from the monitor, which cannot be manipulated by the user and they may be used at every dialysis session with no additional cost. The J-shaped survival curve that occurs when the patients are categorized in quintiles by the PUR or Kt/V values5 is avoided, and we may identify a subgroup of patients that seem to be receiving a high dialysis dose if measured by the Kt/V or PUR, but which may be considered under-dialyzed if we use the Kt. In 1999, the initial recommendations were done according to gender, with a minimal Kt of 40-45 liters in women and 45-50 in men;4 in the year 2005, they were individualized by body surface area.6 Later on, these indications were valid7 observing that patients receiving 4-7 liters less than those prescribed increased their mortality by 10%, in those with 7-11 liters less the mortality was increased by 25%, and in those receiving ≥ 11 liters less than prescribed the mortality was increased by 30%. In the present study we observe that following the classical prescriptions of Kt/V or PUR, almost all patients received the recommended dose, whereas if we used the Kt only 60%-70% of the patients reached the target dose, these patients having lower dry weight and a catheter as their vascular access.
Different studies having used ionic dialysance in hemodialysis expressed it as the Kt/V, and they concluded that the Kt/measured by ionic dialysance is different from the Kt/V measured by laboratory work-up, although there exists a correlation,16-19 similarly to what happens with hemodiafiltration,20 showing that there exists an inter-method variability. In order to obtain the Kt/V it is necessary to introduce the V, a very inaccurate value that may be obtained by anthropometrical equations such as Watson¿s, by calculating the measured Kt divided by the analytical Kt/V,21 or by bioimpedanciometry.22 Other methods using total or partial collection of the dialysis fluid23-25 are more accurate although less practical to be used in routine clinical practice. The Kt/V determined by ionic dialysance usually yields an underestimation when compared with the Kt/V calculated by the second-generation Daurgidas¿ formula obtained from the laboratory data.
Another issue deserving our attention is that working with ionic dialysance increases the accuracy of the results since the measurements are done at each dialysis session. In the present study, using the Kt for dose follow-up was done in more than 1600 sessions as compared with 153 analytical measurements, which represent a monthly determination per patient according to the recommendations contained in the K-DOKI guidelines.9 Generalizing the use of the Kt will allow an accurate comparison of the different groups of hemodialysis patients.
We may conclude that the follow-up of the dialysis dose by using the Kt achieves an adequate control of the dialysis dose, allows for better discrimination of adequacy to dialysis, and identifies 30% to 40% of the patients not reaching their target dose by gender or body surface area, respectively. Its use is recommended in a routine way in all patients usually receiving dialysis with monitors measuring the ionic dialysance.
