Sodium flux during hemodialysis and hemodiafiltration treatment of acute kidney injury: Effects of dialysate and infusate sodium concentration at 140 and 145 mmol/L.

BACKGROUND: A higher sodium (Na) dialysate concentration is recommended during renal replacement therapy (RRT) of acute kidney injury (AKI) to improve intradialytic hemodynamic tolerance, but it may lead to Na loading to the patient. We aimed to evaluate Na flux according to Na dialysate and infusate concentrations at 140 and 145 mmol/L during hemodialysis (HD) and hemodiafiltration (HDF). METHODS: Fourteen AKI patients that underwent consecutive HD or HDF sessions with Na dialysate/infusate at 140 and 145 mmol/L were included. Per-dialytic flux of Na was estimated using mean sodium logarithmic concentration including diffusive and convective influx. We compared the flux of sodium between HD140 and 145, and between HDF140 and 145. RESULTS: Nine HD140, ten HDF140, nine HD145, and 11 HDF145 sessions were analyzed. A Na gradient from the dialysate/replacement fluid to the patient was observed with dialysate/infusate Na at 145 mmol/L in both HD and HDF (p = 0.01). The comparison of HD145 to HD140 showed that higher Na dialysate induced a diffusive Na gradient to the patient (163 mmol vs. -25 mmol, p = 0.004) and that of HDF145 to -140 (211 vs. 36 mmol, p = 0.03) as well. Intradialytic hemodynamic tolerance was similar across all RRT sessions. CONCLUSIONS: During both HD and HDF, a substantial Na loading occurred with a Na dialysate and infusate at 145 mmol/L. This Na loading is smaller in HDF with Na dialysate and infusate concentration at 140 mmol/L and inversed with HD140. Clinical and intradialytic hemodynamic tolerance was fair regardless of Na dialysate and infusate.

Routine online assessment of dialysis dose: Ionic dialysance or UV-absorbance monitoring?

For three-weekly hemodialysis, a single-pool Kt/V target of at least 1.4 together with a minimal dialysis dose Kt at 45 L for men and 40 L for women per each session is currently recommended. Fully automatic online calculation of Kt and Kt/V from conductivity or UV-absorbance measurements in the dialysate is standardly implemented on some hemodialysis monitors and makes it possible to estimate the dialysis dose without the need for blood or dialysate samples. Monitoring the UV-absorbance of the spent dialysate is the most direct method for estimating Kt/V as it does not require an estimate of V. Calculation of ionic dialysance from conductivity measurements is the most direct method for estimating Kt and BSA-scaled dialysis dose. Both ionic dialysance monitoring and UV-absorbance monitoring may help detect a change in urea clearance occurring during the session, but this change must be interpreted differently depending on the monitoring being considered. An abrupt decrease in urea clearance results in a decrease in ionic dialysance but, paradoxically, a sudden increase in estimated urea clearance provided by dialysate UV-absorbance monitoring. Healthcare teams who monitor both ionic dialysance and UV-absorbance in their hemodialysis units must be clearly informed of this difficulty.

Hemodialysis patients receiving a greater Kt dose than recommended have reduced mortality and hospitalization risk.

Achieving an adequate dialysis dose is one of the key goals for dialysis treatments. Here we assessed whether patients receiving the current cleared plasma volume (Kt), individualized for body surface area per recommendations, had improved survival and reduced hospitalizations at 2 years of follow-up. Additionally, we assessed whether patients receiving a greater dose gained more benefit. This prospective, observational, multicenter study included 6129 patients in 65 Fresenius Medical Care Spanish facilities. Patients were classified monthly into 1 of 10 risk groups based on the difference between achieved and target Kt. Patient groups with a more negative relationship were significantly older with a higher percentage of diabetes mellitus and catheter access. Treatment dialysis time, effective blood flow, and percentage of on-line hemodiafiltration were significantly higher in groups with a higher dose. The mortality risk profile showed a progressive increase when achieved minus target Kt became more negative but was significantly lower in the group with 1 to 3 L clearance above target Kt and in groups with greater increases above target Kt. Additionally, hospitalization risk appeared significantly reduced in groups receiving 9 L or more above the minimum target. Thus, prescribing an additional 3 L or more above the minimum Kt dose could potentially reduce mortality risk, and 9 L or more reduce hospitalization risk. As such, future prospective studies are required to confirm these dose effect findings.

Correlation of plasmatic sodium determined by the laboratory and that determined by the dialysis machine.

INTRODUCTION: Changes in plasma sodium concentration (pNa, expressed in mEq/L) are common in hemodialysis (HD) patients. Hemodialysis monitors can estimate pNa by using an internal algorithm based on ion dialysance measurements. The present study studies the accuracy of the correlation between the pNa estimated by the dialysis monitor and that measured by the biochemistry laboratory at our center. MATERIAL AND METHODS: A single-centre prospective observational study in patients on a chronic HD program with the 6008 CAREsystem monitor and standard sodium (138mmol/L) and bicarbonate (32mmol/L) prescriptions. Venous blood samples were drawn from each patient before and after each HD session to ensure inter- and intra-individual validity. The pNa was measured in the biochemistry laboratory using indirect potentiometry and simultaneously the estimated pNa by the HD monitor was recorded at the beginning and at the end of the HD session. For statistical analysis, a scatterplot was made, and Spearman's correlation quotient was calculated. In addition, the differences between both methods were represented as Bland-Altman diagrams. RESULTS: The pre-dialysis pNa measured in the laboratory was 137.49±3.3, and that of the monitor, 137.96±2.91, with a correlation with R2 value of 0.683 (p<0.001). The post-dialysis pNa measured in the laboratory was 137.08±2.23, and that of the monitor was 138.87±1.88, with an R2 of 0.442 (p<0.001). On the Bland-Altman plots, the pre-dialysis pNa has a systematic error of 0.49, in favor of the monitor-estimated pNa, with a 95% confidence interval (CI) of (-3.24 to a 4.22). In the post-dialysis pNa, a systematic error of 1.79 with a 95% CI of (-1.64 to 5.22) was obtained. CONCLUSION: The correlation between the pNa estimated by Fresnius 6008 CAREsystem HD monitor and that measured by the laboratory is good, especially pre-dialysis measurements. Further studies should verify the external validity of these results.

Impact of targeting Kt instead of Kt/V.

BACKGROUND: Patients must receive an adequate dialysis dose in each hemodialysis (HD) session. Ionic dialysance (ID) enables the dialysis dose to be monitored in each session. The aim of this study was to compare the achievement of Kt versus eKt/V values and to analyse the main impediments to reaching the dialysis dose. METHODS: Of 5316 patients from 54 Fresenius Medical Care centers in Spain undergoing their usual HD regime, 3275 received ID and were included in the study. RESULTS: The minimum prescribed dose of eKt/V was reached in 91.2% of the patients, while the minimum recommended dose of Kt was reached in only 66.8%. Patients not receiving the minimum Kt dose were older, had spent 7 months less on dialysis, had a dialysis duration of 6 min less, had 5.7 kg more of body weight and Qb was 47 mL/min lower. The target Kt was not reached by 62% of patients with catheters and by 37% of women. With each quintile increase of body weight, eKt/V decreased and Kt increased. Of patients with a body weight >80 kg, 1.4%, mostly men, reached the target Kt but not prescribed eKt/V. CONCLUSIONS: The impact of monitoring the dose with Kt instead of Kt/V is that identifies 25.8% of patients who did not reach the minimum Kt while achieving Kt/V. The main impediments to achieving an adequate dialysis dose were catheter use, female sex, advanced age, greater body weight, shorter dialysis time and lower Qb.

Influential factors on dose by ionic dialysance in daily practice in chronic hemodialysis.

BACKGROUND: The determination of Kt/V by ionic dialysance is a technique that has extended its use in hemodialysis clinics. The clinical guidelines have reflected the need to validate this method as a determinant of the dose of dialysis. OBJECTIVES: Determine in daily practice, the influence of hemodialysis characteristics and medication on Kt/V results by ionic dialysance (Kt/V OCM) and compare them with Kt/V measures by serum urea (Kt/V Daugirdas). DESIGN: Cross-sectional and observational study. PARTICIPANTS: 127 patients on chronic hemodialysis. MEASUREMENTS: Descriptive variables, study variables (Kt/VOCM, Kt/VDaugidas), and the variables that modified the effect (patient temperature, serum sodium, vascular access, recirculation, blood flow, hemodialysis technique, dialyzer, acid concentrate, conductivity, dialyzate flow). RESULTS: The mean of Kt/V Daugirdas was 1.84 and the Kt/VOCM mean 1.65; Pearson's was CC r=0.54; P<0.001 and Lin CCC=0.48. In the linear regression, the variables related to hemodialysis technique showed no statistical association with the measurement obtained by Kt/VOCM. Monosodium phosphate and 20% sodium chloride dispensing were associated with a higher Kt/VOCM. CONCLUSIONS: The different technical aspects noted during HD sessions do not influence Kt/V OCM outcomes. Kt/V determined by ionic dialysance isn't similar to that determined by serum urea. When assessing dialysis doses measured by dialysance, consider that it is not the same as determined with serum urea, but it provides an approximation to estimate dialysis doses in real time. It is necessary to consider if drugs or supplements have been administered that can modify it when interpreting the results.

Impact of the intensity of intermittent renal replacement therapy in critically ill patients.

BACKGROUND: Intermittent renal replacement therapy (IRRT) is prescribed across intensive care units (ICU) worldwide. While research regarding the prescribed dialysis dose has not yielded results concerning mortality, it is still unknown whether the same applies to the actual delivered dose. METHODS: We retrospectively analyzed two different cohorts of patients (562 IRRT sessions) who were admitted to the intensive care units at Hospital Clínic of Barcelona and required renal replacement therapy with IRRT. The first cohort included patients with acute kidney injury (AKI) (n = 42) and the second included patients already on chronic hemodialysis (CKD 5D) (n = 47). Only patients who had at least 3 recorded hemodialysis sessions in the ICU and with no previous continuous renal replacement therapy (CRRT) were included. The achieved dose was measured as Kt (L) by ionic dialysance and the primary endpoint was 90-day mortality. RESULTS: Ninety-day mortality was 40.5% (n = 17) in the AKI cohort and 23.9% (n = 11) in the CKD 5D cohort with mean Kt of 43 ± 8.27 L and 47 ± 9.65 L respectively. Kt dose of IRRT was associated with 90-day mortality in the AKI cohort in a multivariate surveillance analysis adjusted for confounding factors (HR 0.935 [0.88-0.99], p = 0.02). Only the Kt dose and age remained statistically associated with the outcome in the AKI cohort. CONCLUSIONS: Delivered dialysis dose as measured by ionic-dialysance Kt may be associated with survival in critically-ill patients with AKI, while it does not seem to affect outcomes in critically-ill CKD 5D patients. This exploratory analysis will need confirmation in larger prospective studies.

What volume to choose to assess online Kt/V?

INTRODUCTION: Urea distribution volume (V) can be assessed in different ways, among them the anthropometric Watson Volume (VW). However, many studies have shown that VW does not coincide with V and that the latter can be more accurately estimated with other methods. The present multicentre study was designed to answer the question: what V to choose to assess online Kt/V? MATERIALS AND METHODS: Pre- and postdialysis blood urea nitrogen concentrations and the usual input data set for urea kinetic modelling were obtained for a single dialysis session in 201 Caucasian patients treated in 9 Italian dialysis units. Only dialysis machines measuring ionic dialysance (ID) were utilized. ID reflects very accurately the mean effective dialyser urea clearance (Kd). Six different V values were obtained: the first one was VW; the second one was computed from the equation established by the HEMO Study to predict the single pool-adjusted modelled V from VW (VH) (Daugirdas JT et al. KI 64: 1108, 2003); the others were estimated kinetically as: 1. V_ID, in which ID is direct input in the in the double pool variable volume (dpVV) calculation by means of the Solute-solver software; 2. V_Kd, in which the estimated Kd is direct input in the dpVV calculation by means of the Solute-solver software; 3. V_KTV, in which V is calculated by means of the second generation Daugirdas equation; 4. V_SPEEDY, in which ID is direct input in the dpVV calculation by means of the SPEEDY software able to provide results quite similar to those provided by Solute-solver. RESULTS: Mean± SD of the main data are reported: measured ID was 190.6 ± 29.6 mL/min, estimated Kd was 211.6 ± 29.0 mL/min. The relationship between paired data was poor (R2 = 0.34) and their difference at the Bland-Altman plot was large (21 ± 27 mL/min). VW was 35.3 ± 6.3 L, VH 29.5 ± 5.5, V_ID 28.99 ± 7.6 L, V_SPEEDY 29.4 ± 7.6 L, V_KTV 29.7 ± 7.0 L. The mean ratio VW/V_ID was 1.22, (i.e. VW overestimated V_ID by about 22%). The mean ratio VH/V_ID was 1.02 (i.e. VH overestimated V_ID by only 2%). The relationship between paired data of V_ID and VW was poor (R2 = 0.48) and their mean difference at the Bland-Altman plot was very large (- 6.39 ± 5.59 L). The relationship between paired data of V_ID and VH was poor (R2 = 47) and their mean difference was small but with a large SD (- 0.59 ± 5.53 L). The relationship between paired data of V_ID and V_SPEEDY was excellent (R2 = 0.993) and their mean difference at the Bland-Altman plot was very small (- 0.54 ± 0.64 L). The relationship between paired data of V_ID and V_KTV was excellent (R2 = 0.985) and their mean difference at the Bland-Altman plot was small (- 0.85 ± 1.06 L). CONCLUSIONS: V_ID can be considered the reference method to estimate the modelled V and then the first choice to assess Kt/V. V_SPEEDY is a valuable alternative to V_ID. V_KTV can be utilized in the daily practice, taking also into account its simple way of calculation. VW is not advisable because it leads to underestimation of Kt/V by about 20%.

Continuing education: online monitoring of haemodialysis dose.

BACKGROUND: Kt/Vurea reflects the efficacy of haemodialysis scaled to patient size (urea distribution volume). The guidelines recommend monthly Kt/V measurements based on blood samples. Modern haemodialysis machines are equipped with accessories monitoring the dose online at every session without extra costs, blood samples and computers. OBJECTIVE: To describe the principles, devices, benefits and shortcomings of online monitoring of haemodialysis dose. DESIGN: A critical literature overview and discussion. RESULTS: UV absorbance methods measure Kt/V, ionic dialysance Kt (product of clearance and treatment time; cleared volume without scaling). Both are easy and useful methods, but comparison is difficult due to problems in scaling of the dialysis dose to the patient's size. CONCLUSIONS: The best dose estimation method is the one which predicts the quality of life and survival most accurately. There is some evidence on the predictive value of ionic dialysance Kt, but more documentation is required on the UV method. Online monitoring is a useful tool in everyday quality assurance, but blood samples are still required for more accurate kinetic modelling. LEARNING OUTCOMES: After reading this article the reader should be able to: Understand the elements of the Kt/V equation for dialysis dose. Compare and contrast different methods of measurement of dialysis dose. Reflect on the importance of adequate dialysis dose for patient survival and life quality.

Transonic, thermodilution, or ionic dialysance to manage vascular access: which method is best?

Regularly monitoring blood flow through a vascular access (Qa) can predict a dysfunction and dramatically reduce the number of thromboses. The aim of our study was to compare two integrated access flow devices, thermodilution (Qa-BTM: BTM(®), Fresenius Medical Care, Bad Homburg, Germany) and ionic dialysance (Qa-ID: OCM(®), Fresenius Medical Care, Bad Homburg, Germany), with the "gold standard" saline dilution (Qa-T: Transonic(®), Systems Inc., Ithaca, NY, USA). Measurements were performed sequentially and were repeated in the first 90 minutes of a single dialysis session in 24 long-term hemodialysis patients with a vascular access. Bland-Altman, linear regression (r(2)), and intraclass correlation coefficients (ICC) assessed reproducibility, correlations, and concordance between the techniques. Average access flow for Qa-T was 1549 (± 844) mL/minute, Qa-BTM was 1530 (± 856) mL/minute (P = NS), and Qa-ID was 1619 (± 1085) mL/minute (P = NS). Respectively, ICC, (r(2)), and bias were 0.99, (0.98), and -19 mL/minute for Qa-BTM, and 0.75, (0.65), and +69 mL/minute for Qa-ID. The limits of agreement were -287 to +250 mL/minute for Qa-BTM and -1647 to +1785 mL/minute for Qa-ID. Reproducibility of thermodilution and ionic dialysance, expressed as relative differences, was not significantly different from saline dilution. Recirculation, measured by saline dilution, was 0% (0-4%), the same as the 0% measured by thermodilution, with correct placement of bloodlines and corrected for cardiopulmonary recirculation. The integrated access flow measurement devices, thermodilution and ionic dialysance, are reasonable alternatives to using saline dilution to measure Qa: Thermodilution showed better precision and correlation. They are reliable, make monitoring of vascular access easier, incur no extra costs, and use no additional consumables.

The Kt/V by ionic dialysance: Interpretation limits.

The availability of hemodialysis machines equipped with online clearance monitoring (OCM) allows frequent assessment of dialysis efficiency and adequacy without the need for blood samples. Accurate estimation of the urea distribution volume (V) is required for Kt/V calculated from OCM to be consistent with conventional blood sample-based methods. A total of 35 patients were studied. Ionic dialysance was measured by conductivity monitoring. The second-generation Daugirdas formula was used to calculate the Kt/V single-pool (Kt/VD). Values of V to allow comparison between OCM and blood-based Kt/V were determined using Watson formula (VWa), bioimpedance spectroscopy (Vimp), and blood-based kinetic data (Vukm). Comparison of Kt/Vw ocm calculated by the ionic dialysance and Vw (Kt/Vw ocm) with Kt/VD shows that using VW leads to significant systematic underestimation of dialysis dose by 24%. Better agreement between Kt/V ocm and Kt/VD was observed when using Vimp and Vukm. Bio-impedancemetry and the indirect method using the second-generation Daugirdas equation are two methods of clinical interest for estimating V to ensure greater agreement between OCM and blood-based Kt/V.

Is ionic dialysance useful for early detection of vascular access dysfunction? Six illustrative cases.

Continuous ionic dialysance monitoring is a useful clinical tool to determine the dialysis dose in real time in each hemodialysis session. We followed up 49 patients for 16 months. Six patients with a Kt reduction of ≥20% in >3 consecutive hemodialysis sessions were identified. Fistulography demonstrated significant stenosis in all 6 patients. Angioplasty was performed in 5 with an excellent angiographic result and optimal Kt levels were restored. Unexplained and persistent Kt reduction in patients with stable chronic kidney disease under hemodialysis could represent, together with an accurate vascular access examination, a practical and additional indirect method for the early detection of vascular access dysfunction.