Comparison of blood volume biofeedback hemodialysis and conventional hemodialysis on cardiovascular stability and blood pressure control in hemodialysis patients: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Despite the improvements in hemodialysis (HD) technology, 20-30% of sessions are still complicated by hypotension or hypotension-related symptoms. Biofeedback systems have proven to reduce the occurrence of such events, but no conclusive findings can lead to wider adoption of these systems. We conducted this systematic review and meta-analysis of randomized clinical trials to establish whether the use of blood volume tracking systems compared to conventional hemodialysis (C-HD) reduces the occurrence of intradialytic hypotension.

METHODS

The PRISMA guidelines were used to carry out this systematic review. Randomized clinical trials that evaluated the incidence of intradialytic hypotension during C-HD and blood volume tracking-HD were searched in the current literature. PROSPERO registration number: CRD42023426328.

RESULTS

Ninety-seven randomized clinical trials were retrieved. Nine studies, including 347 participants and 13,274 HD treatments were considered eligible for this systematic review. The results showed that the use of biofeedback systems reduces the risk of intradialytic hypotension (log odds ratio = 0.63, p = 0.03) in hypotension-prone patients (log odds ratio = 0.54, p = 0.04). When analysis was limited to fluid overloaded or hypertensive patients, it did not show the same effect (log odds ratio = 0.79, p = 0.38). No correlation was found in systolic blood pressure drop during dialysis and in post-dialysis blood pressure.

CONCLUSIONS

The use of blood volume tracking systems may be effective in reducing the incidence of intradialytic hypotension and allowing for easier attainment of the patients' ideal dry body weight. New studies to examine the long-term effects of the use of blood volume tracking systems on real hard endpoints are needed.

The Nephrologist's Role in the Collaborative Multi-Specialist Network Taking Care of Patients with Diabetes on Maintenance Hemodialysis: An Overview

Diabetes mellitus is the leading cause of renal failure in incident dialysis patients in several countries around the world. The quality of life for patients with diabetes in maintenance hemodialysis (HD) treatment is in general poor due to disease complications. Nephrologists have to cope with all these problems because of the “total care model” and strive to improve their patients’ outcome. In this review, an updated overview of the aspects the nephrologist must face in the management of these patients is reported. The conventional marker of glycemic control, hemoglobin A1c (HbA1c), is unreliable. HD itself may be responsible for dangerous hypoglycemic events. New methods of glucose control could be used even during dialysis, such as a continuous glucose monitoring (CGM) device. The pharmacological control of diabetes is another complex topic. Because of the risk of hypoglycemia, insulin and other medications used to treat diabetes may need dose adjustment. The new class of antidiabetic drugs dipeptidyl peptidase 4 (DPP-4) inhibitors can safely be used in non-insulin-dependent end-stage renal disease (ESRD) patients. Nephrologists should take care to improve the hemodynamic tolerance to HD treatment, frequently compromised by the high level of ultrafiltration needed to counter high interdialytic weight gain. Kidney and pancreas transplantation, in selected patients with diabetes, is the best therapy and is the only approach able to free patients from both dialysis and insulin therapy.

A New Method to Evaluate Patient Characteristic Response to Ultrafiltration during Hemodialysis

Background.

Several factors are involved in the pathogenesis of dialysis discomfort interfering with optimal fluid removal and reducing the efficacy of the treatment; the most important one is a decrease in blood volume caused by an imbalance between ultrafiltration (UF) and plasma refilling (PR) rates.

Objectives.

This study is aimed at devising a method to tailor the dialysis therapy to each individual patient, by analyzing the relationship between PR and UF during the sessions in stable patients and widening the knowledge of fluid exchanges during the treatment.

Methods.

Thirty stable patients undergoing maintenance hemodialysis were enrolled. Three dialysis sessions were monitored for each patient; systemic pressure, blood composition, blood volume % variation, weight loss and conductivity were recorded repeatedly. A Plasma Refilling Index (PRI), defined and calculated by means of parameters measured throughout the dialysis, was introduced as a novel instrument to study plasma refilling phenomena.

Results.

The PRI provides understanding of patient response (in terms of plasma refilling) to the set UF. In the monitored sessions, the PRI trend is found to be characteristic of each patient; a PRI course that is at variance with the characteristic trend is a signal of inadequate or unusual dialysis scheduling. Moreover, statistical analysis highlights two different PRI trends during the first hour and during the rest of the treatment, suggesting the presence of different treatment phases.

Conclusion.

The main advantage of the PRI index is that it is non-invasive peculiar to each patient and easy to compute in a dialysis routine based on online data recorded by the monitor. A deviation from the characteristic trend may be a warning for the clinician. The analysis of the PRI trend also suggests how to modulate UF as a function of interstitial to intravascular fluid removal balance during dialysis.

Intra-dialytic blood oxygen saturation (SO2): association with dialysis hypotension (the SOGLIA Study)

BACKGROUND

Intradialytic hypotension (IDH) has a dramatic impact on the main outcomes of dialysis patients. Early warning of hemodynamic worsening during dialysis would enable preventive measures to be taken. Blood oxygen saturation (SO₂) is used for hemodynamic monitoring in the critical care setting and may provide useful information about IDH onset.

AIM

To evaluate whether short- and medium-term variations in the SO₂ signal (ST-SO_2var, MT-SO_2var,) during dialysis are a predictor of IDH.

METHODS

In this 3-month observational cohort study, 51 hypotension-prone chronic hemodialysis (HD) patients, with vascular access by arteriovenous fistula (AVF) or central venous catheter (CVC), were enrolled. Continuous non-invasive blood SO₂ was monitored (fc = 0.2 Hz) by an optical sensor on the arterial line of the extracorporeal circulation; blood pressure (every 30 min), symptoms and their time of appearance were noted. Predictive power of IDH was expressed by the area under curve (AUC) sensitivity and specificity based on intradialytic variations in SO₂.

RESULTS

A total of 1290 HD sessions were analyzed. Overall, off-line ST-SO_2var analysis proved able to correctly predict IDH in 67 % of the sessions where IDH occurred. The best predictive performance was found in the presence of highly arterialized AVF (SO₂ > 95 %) (75 % sensitivity; AUC 0.825; p < 0.05). On the contrary, in sessions with CVC, IDH prediction proved more efficient by MT-SO_2var (AUC 0.575; p = 0.01).

CONCLUSIONS

Intradialytic SO₂ variability could be a valid parameter to detect in advance the hemodynamic worsening that precedes IDH. Appropriate timely intervention could help prevent IDH onset.

Cardiovascular dialysis instability and convective therapies

Acute hypotension is a frequent hemodialysis complication. Intratreatment vascular instability is a multifactorial process in which procedure-related and patient-related factors may influence the decrease in plasma volume and induce an impairment of cardiovascular regulatory mechanisms. Identification of the most susceptible patients and of the various risk factors may contribute to significantly improve cardiovascular stability during dialysis. In some high-risk patients, monitoring and biofeedback of the various hemodynamic variables, together with an extensive use of convection, can prevent the appearance of symptomatic hypotension and help in averting its onset.

Effect of High and Low Ultrafiltration Volume during Hemodialysis on Relative Blood Volume

Achieving an optimal post-hemodialysis hydration status may be difficult because objective criteria for dry weight are lacking. Both relative blood volume changes (DeltaRBV) at the end of hemodialysis and DeltaRBV normalized for ultrafiltration volume (DeltaRBV/UF ratio) have been reported to indicate post-hemodialysis volume status. A parameter for volume status should not be influenced by variations in ultrafiltration volume. However, if the volume that has to be ultrafiltrated to reach dry weight varies as a result of variations in pre-hemodialysis weight, either DeltaRBV or the DeltaRBV/UF ratio (or both) must change. To elucidate the relation between intradialytic ultrafiltration volume versus DeltaRBV and its derivative, the DeltaRBV/UF ratio, we studied the effect of a relatively high (mean+/- SD, 2.7+/- 0.5 l) and low (1.5+/- 0.3 l) intradialytic ultrafiltration volume on these parameters in eight patients. Post-hemodialysis weight was comparable in low and high ultrafiltration volume sessions. The average end-hemodialysis DeltaRBV did not differ between high (-6.7+/- 2.5%) and low ultrafiltration volume sessions (-7.3+/- 1.0%; NS), but the intraindividual variation was considerable. The DeltaRBV/UF ratio differed markedly (p<0.001) between high (-2.4+/- 0.8 %/l) and low (-4.9+/- 1.3 %/l) ultrafiltration volume sessions. In conclusion, the considerable random intraindividual variation of DeltaRBV and the systematic change of the DeltaRBV/UF ratio with variations in intradialytic ultrafiltration volume limit the use of these parameters as an aid to assess hydration status in hemodialysis patients.

On-line monitoring of solutes in dialysate using absorption of ultraviolet radiation: technique description

PURPOSE

The aim of this work was to describe a new optical method for monitoring solutes in a spent dialysate using absorption of UV radiation.

METHOD

The method utilises UV-absorbance determined in the spent dialysate using a spectrophotometrical set-up. Measurements were performed both on collected dialysate samples and on-line. During on-line monitoring, a spectrophotometer was connected to the fluid outlet of the dialysis machine, with all spent dialysate passing through a specially-designed cuvette for optical single-wavelength measurements. The concentrations of several substances of various molecular sizes, electrical charge, transport mechanism, etc. were determined in the dialysate and in the blood using standard laboratory techniques. The correlation coefficient between UV-absorbance of the spent dialysate and concentration of the substances in the spent dialysate and in the blood was calculated from data based on the collected samples.

RESULTS

The obtained on-line UV-absorbance curve demonstrates the possibility to follow a single hemodialysis session continuously and to monitor deviations in the dialysator performance using UV-absorbance. The experimental results indicate a very good correlation between UV-absorbance and several small waste solutes removed such as urea, creatinine and uric acid in the spent dialysate and in the blood for every individual treatment at a fixed wavelength of 285 nm. Moreover, a good correlation between the UV-absorbance and substances like potassium, phosphate and beta2-microglobulin was obtained. The lowest correlation was achieved for sodium, calcium, glucose, vitamin B12 and albumin.

CONCLUSIONS

A technique for on-line monitoring of solutes in the spent dialysate utilising the UV-absorbance was developed. On-line monitoring during a single hemodialysis session exploiting UV-absorbance represents a possibility to follow a single hemodialysis session continuously and monitor deviations in dialysis efficiency (e.g. changes in blood flow and clearance). The UV-absorbance correlates well to the concentration of several solutes known to accumulate in dialysis patients indicating that the technique can be used to estimate the removal of retained substances.

A new technique for establishing dry weight in hemodialysis patients via whole body bioimpedance

BACKGROUND

Quantitative techniques are necessary to achieve dry weight (DW) in patients with kidney failure. Bioimpedance spectroscopy (BIS) is a non-invasive method that determines the volume of body fluid compartments. The current work evaluates the use of BIS data in hemodialysis patients for the prediction of DW.

METHODS

A new technique has been devised for the estimation of DW that involves the intersection of two slopes, slope normovolemia (SNV) and slope hypervolemia (SHV). These slopes characterize the variation in extracellular water (ECW) with body weight (BW) in the states of normovolemia and hypervolemia, respectively. SNV was established via measurements of ECW and BW in 30 healthy subjects. In a longitudinal study in new hemodialysis patients, successive reduction of post-dialysis weight (PDW) was attempted until clinical signs of normovolemia were presented. Measurements of ECW and BW that were acquired at the beginning of each treatment were used to determine SHV.

RESULTS

SNV was found to be 0.239 L/kg and 0.214 L/kg for male and female healthy subjects, respectively. A significant DeltaPDW predicted by the new method (-4.98 kg) was highly correlated to the DeltaPDW achieved in the study (-5.85 kg, R = 0.839). Blood pressure was reduced (P < 0.001) and an 86% decrease in antihypertensive agents was achieved.

CONCLUSION

The method of intersecting slopes (SHV with SNV) via BIS is a new method for the prediction DW. This approach will offer considerable improvement for the routine management of DW in the dialysis setting.

A critical review of sodium profiling for hemodialysis

In sodium profiling, the sodium concentration in the dialysis fluid, instead of being constant, follows a time-dependent profile over the course of a hemodialysis session. The main aim of this manipulation is to avoid osmotic disequilibrium by keeping plasma osmolality in the physiological range. Further advantages of sodium profiling are a reduction in the incidence of muscle cramps, improved sodium removal, and improved vascular stability. Many different profiles have been used by various investigators. However, if sodium profiling is not appropriately conducted, sodium accumulation with resulting augmented thirst, increase of interdialytic weight gain, and hypertension may result. Sodium accumulation may, in fact, explain the reduced intradialytic morbidity reported in some short-term sodium profiling studies. Randomized, double-blind studies meeting strict statistical criteria and providing a careful control to maintain equivalent sodium balances between the compared treatments are difficult to perform and have not yet been published. However, because sodium profiling has potential benefits, provided that sodium balance is carefully controlled, it should nevertheless be regarded as a tool that experienced nephrologists can use for the treatment of patients who experience intolerable side effects during standard dialysis.

Continuous Blood Volume Monitoring and Ultrafiltration Control

Continuous blood volume monitoring (CBVM) is believed to be a promising method for making the determination of patients' "dry weight" more objective, and ultrafiltration (UF) control more appropriate. Although blood volume response to UF and the interrelation between blood volume changes and changes in hemodynamic parameters are highly individual, certain principles of this response and interrelation can be identified and exploited for effective use of CBVM. The present work summarizes the authors' findings from practical CBVM application over the past 5 years and their opinions on the future development of this method. Four distinct types of blood volume response to constant UF rate were identified: Type 1, flat line throughout the whole session; Type 2, flat line during the first part of dialysis, followed by a linear decrease during the remaining time; Type 3, linear decrease right from dialysis start; and Type 4, linear decrease first, followed by a flat line during the remaining time. The possibility of a shift from one type to the other was verified. Blood volume reduction due to UF was found to have a static and a dynamic component. The most important factors affecting both components were found to be, by sensitivity analysis of a three-pool kinetic model, degree of overhydration, vascular system compliance, and UF volume (for the static component); and UF coefficient of the capillary wall and UF rate (for the dynamic component). Type 3 response, induced by more vigorous UF, was found to significantly decrease the volume of residual daily diuresis on the first postdialysis day. If confirmed, this finding may serve as a basis for the response type choice in patients with still significant residual renal function. Exploitation of the existence of dynamic blood volume reduction component for the first generation of automated biofeedback UF controllers may be complemented by automated identification of patient's plasma refilling capacity and/or position of his/her point on the Guytonian pressure/volume characteristics curves, and thus may more advanced "intelligent" UF controllers be constructed in the future.

Hemodynamic monitoring during hemodialysis

Intradialytic monitoring of hemodynamic parameters is an active area of research; future developments in this field will decrease intradialytic morbidity and the mortality of end-stage renal disease patients treated by hemodialysis. Recent investigations have been assisted by the development of devices that can continuously and noninvasively measure hematocrit and plasma protein concentration during the treatment. Intradialytic morbidity, fluid overload, and hypertension in chronic hemodialysis patients have been shown to be associated with either large or small intradialytic decreases in blood or plasma volume that can be routinely measured by these devices. The use of intradialytic changes in blood volume as a feedback control parameter to vary the ultrafiltration rate and dialysate sodium concentration, so called profiling, is now possible, but further research in this area is necessary to show how to optimize the control algorithms. Other, more preliminary studies suggest that monitoring of central blood volume, extracellular volume, and cardiac output during hemodialysis may permit improved hemodynamic stability during treatment and better control of blood pressure. Although optimal application of these techniques and devices remains to be shown, their routine use during maintenance hemodialysis therapy will likely be the standard of care in the near future.

Blood volume regulation during hemodialysis

Hemodialysis (HD)-induced hypotension may be precipitated by severe hypovolemia. To avoid the appearance of destabilizing hypovolemias, we have developed a biofeedback control system for intradialytic blood volume (BV)-changes modeling. The system, incorporated in a dialysis machine, is based on a multivariable closed-loop control with a dependent output variable, the BV changes, and two independent control variables, the ultrafiltration rate (Qf) and dialysate conductivity (DC). The relative BV changes occurring during HD are measured by an optical device. The Qf and DC are continuously adjusted by the control model during the treatment to minimize any discrepancies between the ideal targets for the BV, the patient's body weight reductions, and the experimentally obtained results. The system manages three kinds of errors: in BV changes, the total weight loss, and the sodium balance. The latter is controlled by a dedicated kinetic model that continuously calculates the equivalent DC and, by the end of the session, tends to make the sodium balance the same as the one obtained in conventional HD with constant DC. This system's capacity to improve intradialytic hemodynamic tolerance has been assessed in a crossover study of eight highly symptomatic patients. Conventional HD (CHD; period A) was compared with blood volume-controlled dialysis sessions (BV-CHD; period B) following a protocol with an A1-B-A2 sequence, with each period lasting 1 month. A lower decrease in BV (-10.6%) was obtained during BV-CHD (period B) compared with CHD (-12.3% in period A1 and -12.5% in period A2). The predialysis to postdialysis systolic arterial pressure changes were lower in period B (-12.4%) than in period A (-20% in A1 and -17.5% in A2; P < 0.05) despite similar total Qf and mean treatment times. A significant reduction in the number of severe hypotensive episodes (three in period B v 26 in period A1 and 16 in period A2; P < 0.05) and the overall incidence of complaints, especially of muscular cramps, was found in BV-CHD. These results were reflected in a reduced need for therapeutically administered isotonic saline in each session (60 mL in B v160 mL in A1 and 95 mL in A2; P < 0.05). In conclusion, the proposed biofeedback system for intradialytic BV control may be useful to avoid severe hypovolemic states, to stabilize BV by modeling its trend, and to avoid reaching individual critical BV thresholds in hypotension-prone patients.