Sodium and ultrafiltration profiling in hemodialysis: A long-forgotten issue revisited

Sodium and ultrafiltration profiling are method of dialysis in which dialysate sodium concentration and ultrafiltration rate are altered during the course of the dialysis session. Sodium and ultrafiltration profiling have been used, commonly simultaneously, to improve hemodynamic stability during hemodialysis. Sodium profiling is particularly effective in decreasing the incidence of intradialytic hypotension, while ultrafiltration profiling is suggested to decrease subclinical repeated end organ ischemia during dialysis. However, complications such as increased interdialytic weight gain and thirst due to sodium excess have prevented widespread use of sodium profiling. Evidence suggest that different sodium profiling techniques may lead to different clinical results, and preferring sodium balance neutral sodium profiling may mitigate adverse effects related to sodium overload. However, evidence is lacking on the long-term clinical outcomes of different sodium profiling methods. Optimal method of sodium profiling as well as the utility of sodium/ultrafiltration profiling in routine practice await further clinical investigation.

Mathematical Modeling of Solute Kinetics and Body Fluid Changes during Profiled Hemodialysis

A mathematical model of solute kinetics oriented to improve hemodialysis treatment is presented. It includes a two-compartment description of the main solutes (K+, Na+, Cl–, urea, HCO–3, H+, CO2), acid-base equilibrium through two buffer systems (bicarbonate and non-carbonic buffers) and a three-compartment model of body fluids (plasma, interstitial and intracellular). The main model parameters can be individually assigned a priori, on the basis of body weight and plasma concentration values measured before beginning the session.

Model predictions are compared with clinical data obtained during 11 different hemodialysis sessions performed on six patients with profiled sodium concentration in the dialysate and profiled ultrafiltration rate. In all cases, the agreement between the time pattern of model solute concentrations in plasma and clinical data turns out fairly good as to urea, sodium, chloride and potassium kinetics. Finally, the time patterns of plasma bicarbonate concentration and pH can be reproduced fairly well with the model, provided CO2 concentration remains constant. Only in two sessions, blood volume was directly measured in the patient, and in both cases the agreement with model predictions was good.

In conclusion, the model allows a priori computation of the amount of sodium removed during hemodialysis, and may enable the prediction of plasma volume changes and plasma osmolarity changes induced by a given sodium concentration profile in the dialysate and by a given ultrafiltration profile. Hence, it can be used to improve the dialysis session taking the characteristics of individual patients into account, in order to minimize intradialytic imbalances (such as hypotension or disequilibrium syndrome).

Clinical Application of Sodium Profiling in the Treatment of Intradialytic Hypotension

Background

Intradialytic hypotension is mainly induced by the removal of extracellular sodium during dialysis, which impairs intravascular fluid refilling and reduces blood volume. To counter this complication we tested a new kind of profiled hemodialysis (PHD) consisting of the intradialytic modulation of dialysate sodium concentration according to individual profiles set up using a new mathematical model for intradialytic solutes and water kinetics. The clinical aim of this PHD is to stabilize blood pressure maintaining higher blood volume values than standard dialysis treatments. We clinically validated PHD in comparison with constant dialysate sodium dialysis (CHD).

Methods

Twenty hypotensive dialysis patients underwent one PHD and one CHD session maintaining the same dialysis length, sodium mass removal and body weight decrease. A new mathematical model was used to define both the dialysate sodium profiles for PHD and the constant dialysate sodium for CHD. Percent blood volume variation (Crit-line), mean blood pressure, heart rate, cardiac output (Doppler-echocardiography) were monitored intradialitically.

Results

Cardiovascular stability improved on PHD as compared with CHD sessions; blood volume and cardiac output during PHD showed a lower decrease than on CHD, the differences statistically significant (from 30' and 60' respectively). Mean blood pressure was, at all time intervals, more stable on PHD than on CHD and was accompanied, on PHD, by a lower heart rate increase (differences statistically significant).

Conclusions

This study shows that PHD performed using dialysate sodium profiles elaborated by our mathematical model obtains, in hypotensive patients, a higher hemodynamic intradialytic stability than CHD, probably due to a higher stabilization of blood volume.

Does bicarbonate transfer have relevant hemodynamic consequences in standard hemodialysis?

BACKGROUND

In a previous study we demonstrated that mild metabolic alkalosis resulting from standard bicarbonate hemodialysis induces hypotension. This study aimed to compare hemodynamic consequences of either a decrease in the dialysate bicarbonate from 32 to 26 mmol/l or an increase in the dialysate calcium of 0.25 mmol/l and to verify whether the calcium shift secondary to alkalemia explains the consequences on blood pressure.

METHODS

In this randomized controlled trial with a single-blind, cross-over design, we used dialysis liquids with two different bicarbonate (32 mmol/l in modalities A and C, and 26 mmol/l in modality B) and calcium (1.25 mmol/l in modalities A and B, and 1.50 mmol/l in modality C) concentrations, and in 27 patients, 243 dialysis sessions, compared blood pressure, heart rate and the incidence of hypotension.

RESULTS

No significant differences were seen between A and B while an increase in systolic and diastolic blood pressures and a decrease in the incidence of hypotension (10.5 vs. 1.2%, p < 0.05) were documented in C. The subgroup of patients who with A showed a lower mean systolic blood pressure received more angiotensin-converting enzyme inhibitors or angiotensin II type-1 receptor blockers (36 vs. 0%, p<0.05) and in C showed a less important increase in systolic and diastolic pressures, but the incidence of hypotensive episodes between A and B was not significantly different (9.1 vs. 15.1%).

CONCLUSIONS

In the present study it was not possible to demonstrate hemo dynamic instability associated with mild metabolic alkalosis. Even in the subgroup showing a lower blood pressure with a higher dialysate bicarbonate, significant hemodynamic or clinical consequences were not noticed. The calcium shift (0.05 mmol/l) related to alkalemia would justify a mean decrease in systolic blood pressure of only about 1 mm Hg.

New Blood Volume Monitoring Method for Hemodialysis: A-V Pressure Gradient Measurement by Synchronized One-point Reading

During hemodialysis, rapid ultrafiltration often causes symptomatic hypotension. To predict the occurrence of volume-dependent hypotension as early as possible, continuous hematocrit monitoring with the Crit-Line noninvasive monitor has been widely used to measure blood volume changes during hemodialysis. As another potential method of monitoring blood volume variations, we studied blood viscosity, which is theoretically associated with the pressure gradient across the dialyzer. Blood viscosity (calculated by the Hugen-Poiseuille formula) is a major determinant of the blood flow rate and is associated with the pressure difference between the postpump arterial (A) and venous (V) pressures. The A-V pressure gradient fluctuates due to pump pulsation, so we minimized this noise by always reading the pressure gradient at the same point out of 1400 partitions on the rotary pump. To test this synchronized one-point reading method, the A-V pressure gradient was measured using 3 different xanthan gum solutions and was found to be linearly proportional to the model blood flow rate. In an experimental dialysis system using a xanthan gum solution (300 mg/L), the A-V pressure gradient showed a gradual linear increase along with the ultrafiltration rate up to 1 L/h as the viscosity slowly increased in the dialyzer. The changes of blood volume shown by this method were significantly correlated with data obtained using the Crit-Line in 8 patients undergoing hemodialysis. This simple and inexpensive method may allow monitoring of blood volume changes and thus provide data that are beneficial for fluid management in hemodialysis patients suffering from clinical dialysis intolerance.

Biofeedback regulation of ultrafiltration and dialysate conductivity for the prevention of hypotension during hemodialysis

Intradialytic hypotension remains a frequent complication of dialysis, occurring in up to 33% of patients. We tested a fully integrated biofeedback system (the Hemocontrol system) that monitors and regulates blood volume contraction during hemodialysis. Seven hypotension prone patients were selected for the study. We conducted a prospective crossover study alternating dialysis sessions using the blood volume regulation system and standard dialysis sessions. Event free sessions were defined as dialysis sessions not requiring any therapeutic intervention for hypotension related signs or symptoms. There was a significant improvement in the number of event free sessions with blood volume regulation compared with standard dialysis (50.8% of sessions vs. 29.2%; p < 0.01). Percentages of event free sessions and mean postdialysis systolic blood pressure improved progressively over the course of the study, indicating improved hemodynamic stability over the study period. Therefore, the use of a biofeedback system to monitor and regulate blood volume during dialysis was helpful in restoring cardiovascular stability in a population of hypotension prone hemodialysis patients. Further studies are needed to confirm these preliminary results and to establish the role of blood volume regulation systems in reducing the incidence of hypotension during hemodialysis.

Individualizing the dialysate in the hemodialysis patient

In most outpatient centers the dialysate is prepared centrally such that the composition of the dialysate is the same for all patients. When delivered in this manner most patients tolerate the procedure well. However, there are patients who tolerate the procedure poorly, which has prompted a great deal of research focused on individualizing the composition of the dialysate in order to improve patient tolerability. Prescribing a patient-specific dialysate will become increasingly important as the age of and number of comorbid conditions increase in the dialysis population. Patients with end-stage renal disease (ESRD) depend on dialysis to maintain fluid and electrolyte balance. Hemodialysis allows for solutes to diffuse between blood and dialysate such that, over the course of the procedure, plasma composition is restored toward normal values. The makeup of the dialysate is of paramount importance in accomplishing this goal. In most out-patient settings patients receive hemodialysis using dialysate prepared in bulk and delivered via a central delivery system so that the composition of the dialysate is the same for all patients. While most patients tolerate the procedure when administered in this fashion, many patients suffer from hemodynamic instability or symptoms of dialysis disequilibrium. One strategy to improve the clinical tolerance to dialysis is to adjust the dialysate composition according to the individual characteristics of the patient. This article reviews recent developments on how the dialysate can be manipulated in order to improve patient tolerance. Individualizing the dialysate composition is likely to gain increasing importance given the advancing age and increasing number of comorbid conditions found in ESRD patients.

Impact of sodium and ultrafiltration profiling on hemodialysis-related symptoms

Dialysate sodium and ultrafiltration profiling are two methods to reduce symptoms during hemodialysis. The objective of the study was to determine the efficacy of combining these techniques to reduce symptoms in chronic hemodialysis patients. Blood volume changes were measured to determine whether any benefit of profiling could be explained through this mechanism. Patients were randomized to profiled dialysate sodium and ultrafiltration or constant dialysate sodium and ultrafiltration. The study was a two-period, two-treatment, crossover design with repeated measures. The primary outcome was hypotension and/or symptomatic events observed by the dialysis nurse. Secondary outcomes were symptom survey scores, weights, BP, and blood volume changes. Thirty-three patients were randomized. On standard treatment, 30.6% of dialysis sessions were symptomatic compared with 20.4% on profiled treatments. The odds ratio for the development of hypotension or symptomatic event on profiled treatments was 0.61 (95% confidence interval, 0.39 to 0.96) compared with standard treatment. Patients had lower symptom scores by questionnaire in both the intradialytic and the interdialytic periods during profiled treatments. Predialysis weight was greater during profiled treatments by 0.3 kg (P: = 0.008), but there were no differences in postdialysis weight, BP, or thirst. There was no difference in maximum decrease in blood volume during the two treatments (standard, -11.2%; profiled, -10.0%; P: = 0.08), but there was a significant difference in the rate of change in blood volume (standard, -2.96%/h; profiled, -1.96%/h; P: < 0.001). Decrease in blood volume, rate of change in blood volume, and predialysis weights were not associated with hypotension or symptomatic dialysis sessions. In conclusion, dialysate sodium and ultrafiltration profiling significantly reduces hemodialysis-related symptoms. Profiling reduces the slope of the blood volume curve during dialysis, but blood volume changes are not predictive of symptomatic events for an individual patient.

Computational analysis of blood volume curves and risk of intradialytic morbid events in hemodialysis

BACKGROUND

Blood volume (BV) curves have been used to prevent intradialytic morbid events (IMEs) caused by hypotensive episodes in hemodialysis treatment. However, no standardized parameter is available to describe BV dynamics and to enable online interference with ultrafiltration rates in unselected patients. Moreover, only time-dependent BV reduction and absolute hematocrit threshold, but not BV variability, have been suggested as markers of pending hypotension. The present study therefore deals with a computer-aided analysis of indices characterizing both BV reduction per time and BV variability in treatments of nonselected maintenance hemodialysis patients.

METHODS

The methodology uses indices obtained by mathematical analysis of BV curves and was designed to potentially enable automatic interference with ultrafiltration.

RESULTS

In 46 out of 380 treatments (12.1%), IMEs occurred. In these treatments, the indices for long- and short-term variability and slope of the curves were significantly lower than in treatments without IMEs. Moreover, the last 10 minutes before an IME were characterized by additionally decreased variability and slope. In a risk analysis of long-term variability and IMEs, we established an index below 16 to be associated with the highest risk of IMEs.

CONCLUSIONS

Using these kind of index thresholds and online analysis of BV curves, automatic management of ultrafiltration by BV dynamics could be a promising concept to avoid intradialytic morbidity.