Preventing and Managing Hypotension

Machine Learning Analysis of Time-Dependent Features for Predicting Adverse Events During Hemodialysis Therapy: Model Development and Validation Study

BACKGROUND

Hemodialysis (HD) therapy is an indispensable tool used in critical care management. Patients undergoing HD are at risk for intradialytic adverse events, ranging from muscle cramps to cardiac arrest. So far, there is no effective HD device-integrated algorithm to assist medical staff in response to these adverse events a step earlier during HD.

OBJECTIVE

We aimed to develop machine learning algorithms to predict intradialytic adverse events in an unbiased manner.

METHODS

Three-month dialysis and physiological time-series data were collected from all patients who underwent maintenance HD therapy at a tertiary care referral center. Dialysis data were collected automatically by HD devices, and physiological data were recorded by medical staff. Intradialytic adverse events were documented by medical staff according to patient complaints. Features extracted from the time series data sets by linear and differential analyses were used for machine learning to predict adverse events during HD.

RESULTS

Time series dialysis data were collected during the 4-hour HD session in 108 patients who underwent maintenance HD therapy. There were a total of 4221 HD sessions, 406 of which involved at least one intradialytic adverse event. Models were built by classification algorithms and evaluated by four-fold cross-validation. The developed algorithm predicted overall intradialytic adverse events, with an area under the curve (AUC) of 0.83, sensitivity of 0.53, and specificity of 0.96. The algorithm also predicted muscle cramps, with an AUC of 0.85, and blood pressure elevation, with an AUC of 0.93. In addition, the model built based on ultrafiltration-unrelated features predicted all types of adverse events, with an AUC of 0.81, indicating that ultrafiltration-unrelated factors also contribute to the onset of adverse events.

CONCLUSIONS

Our results demonstrated that algorithms combining linear and differential analyses with two-class classification machine learning can predict intradialytic adverse events in quasi-real time with high AUCs. Such a methodology implemented with local cloud computation and real-time optimization by personalized HD data could warn clinicians to take timely actions in advance.

Cardiovascular autonomic nervous system dysfunction in chronic kidney disease and end-stage kidney disease: disruption of the complementary forces

PURPOSE OF REVIEW

Several nontraditional risk factors have been the focus of research in an attempt to understand the disproportionately high cardiovascular morbidity and mortality in chronic kidney disease (CKD) and end-stage kidney disease (ESKD) populations. One such category of risk factors is cardiovascular autonomic dysfunction. Its true prevalence in the CKD/ESKD population is unknown but existing evidence suggests it is common. Due to lack of standardized diagnostic and treatment options, this condition remains undiagnosed and untreated in many patients. In this review, we discuss current evidence pointing toward the role of autonomic nervous system (ANS) dysfunction in CKD, building off of crucial historical evidence and thereby highlighting the areas in need for future research interest.

RECENT FINDINGS

There are several key mediators and pathways leading to cardiovascular autonomic dysfunction in CKD and ESKD. We review studies exploring the mechanisms involved and discuss the current measurement tools and indices to evaluate the ANS and their pitfalls. There is a strong line of evidence establishing the temporal sequence of worsening autonomic function and kidney function and vice versa. Evidence linking ANS dysfunction and arrhythmia, sudden cardiac death, intradialytic hypotension, heart failure and hypertension are discussed.

SUMMARY

There is a need for early recognition and referral of CKD and ESKD patients suspected of cardiovascular ANS dysfunction to prevent the downstream effects described in this review.There are many unknowns in this area and a clear need for further research.

Implementation of an Algorithm Utilizing Saline Versus Albumin for the Treatment of Intradialytic Hypotension

Background: Intradialytic hypotension (IDH) is the most commonly reported complication of hemodialysis (HD) treatment. At our institution, dialysis patients often have both 25% albumin and normal saline ordered as rescue options for management of IDH, without specification of which agent to use first. Objective: The purpose of this study was to determine the effect of an algorithm for IDH management. Methods: A retrospective study was conducted in HD patients who experienced IDH. The primary end point was to evaluate albumin use. Secondary end points included albumin costs, study fluid use per dialysis session, compliance with algorithm, efficacy of hypotension reversal to mean arterial pressure (MAP) ⩾60 mm Hg, percentage of target ultrafiltration achieved, time required to restore systolic blood pressure ⩾90 mm Hg, blood pressure post–study fluids, IDH treatment failure rate, and early termination of dialysis as a result of persistent IDH. Results: Implementation of the algorithm was observed in 94% of patients (n = 90). Total albumin use was significantly reduced from 11 400 to 4700 mL in the pre– (n = 90) and post–algorithm implementation group (n = 90; P < 0.001). The associated total cost of albumin was reduced by 59% ($10 534 vs $4343; P < 0.001). No statistical differences were observed between the 2 groups regarding efficacy of hypotension reversal to MAP ⩾60 mm Hg, early HD termination, or treatment failure rates (all P = 0.99). Conclusion and Relevance: Implementation of an evidence-based, standardized algorithm and pharmacy education to nursing staff can result in a reduction in albumin use and its associated drug costs for IDH management without compromising efficacy of IDH reversal.

An Algorithm for the Rational Choice of Sodium Profile during Hemodialysis

The incidence of intradialytic disequilibrium syndrome and symptomatic hypotension has increased significantly among dialysis patients over the last ten years. Profiled hemodialysis (PHD) is a new technique, based on the intradialytic modulation of dialysate sodium concentration, which aspires to reduce to previous imbalances.

This paper presents a new algorithm for the determination of a rational dialysate sodium profile during PHD. A mathematical model of solute kinetics, monocompartmental for sodium and bicompartmental for urea is used. The algorithm allows the sodium profile to be elaborated a priori before each dialysis session, respecting the individual sodium mass removal and weight gain. A procedure allowing the adjustment of the method to the individual characteristics, on the basis of routine measurements performed before each session is also presented.

The method was validated during seven dialysis sessions. Comparison between data measured in vivo and those predicted by the model showed standard deviations corresponding to the range of laboratory measurement errors: 1.50 mEq/L for sodium and 0.87 mmol/L for urea. In vivo implementation of PHD by our algorithm allows one to remove an amount of sodium close to that established a priori on the basis of patient's need.

Reduced Complications during Hemodialysis by Automatic Blood Volume Controlled Ultrafiltration

Background

Intradialytic morbid events (IMEs, mostly hypotension) are frequent complications during hemodialysis (HD). This study investigated whether automatic feedback control via adjustment of the ultrafiltration rate reduces IME frequency.

Methods

In this multi-center cross-over study, 56 hypotension-prone patients were treated both with standard HD (sHD, applying a constant ultrafiltration rate) and HD applying a blood volume controlled ultrafiltration rate (cHD). The relative blood volume (RBV) was continuously monitored. The individual relative blood volume limit (RBVcrit) was determined from the measured RBV during initial sHD. During cHD, the ultrafiltration rate was automatically adjusted to keep the actual RBV above RBVcrit.

Results

In 3,081 HD treatments, slightly fewer IMEs were observed during cHD than during sHD (0.785±0.613 versus 0.695±0.547 per treatment, P=0.144). Less symptomatic events were seen during cHD: -13% for symptomatic hypotension (0.594 versus 0.685 per treatment, P=0.120), and -32% for cramps (0.049 versus 0.072 per treatment, P=0.009). Thirty-one patients with the highest IME rate (IME in at least every second treatment) especially benefited from cHD: 1.185±0.554 versus 0.979±0.543 IME per treatment (P=0.004). The reduction in blood pressure (BP) and the increase in heart rate were lower during the treatments with cHD than with sHD: systolic BP: -18.8±26.7 versus -22.2±28.9 mmHg (P=0.007), diastolic BP: -7.8±14.8 versus -9.1±15.3 mmHg (P=0.064), heart rate: 1.8±10.4 versus 2.3±11.6 per minute (P=0.014). Neither treatment duration nor ultrafiltration volume was significantly different between cHD and sHD.

Conclusion

For cHD, less intradialytic morbid events were observed than for sHD, and pre- to post-dialytic changes in blood pressure and heart rate were less pronounced.

Prevalence of intradialytic hypotension, clinical symptoms and nursing interventions--a three-months, prospective study of 3818 haemodialysis sessions

Background

Intradialytic hypotension (IDH) is considered one of the most frequent complications of haemodialysis with an estimated prevalence of 20–50 %, but studies investigating its exact prevalence are scarce. A complicating factor is that several definitions of IDH are used. The goal of this study was, to assess the prevalence of IDH, primarily in reference to the European Best Practice Guideline (EBPG) on haemodynamic instability: A decrease in systolic blood pressure (SBP) ≥20 mmHg or in mean arterial pressure (MAP) ≥10 mmHg associated with a clinical event and the need for nursing intervention.

Methods

During 3 months we prospectively collected haemodynamic data, clinical events, and nursing interventions of 3818 haemodialysis sessions from 124 prevalent patients who dialyzed with constant ultrafiltration rate and dialysate conductivity. Patients were considered as having frequent IDH if it occurred in >20 % of dialysis sessions.

Results

Decreases in SBP ≥20 mmHg or MAP ≥10 mmHg occurred in 77.7 %, clinical symptoms occurred in 21.4 %, and nursing interventions were performed in 8.5 % of dialysis sessions. Dialysis hypotension according to the full EBPG definition occurred in only 6.7 % of dialysis sessions. Eight percent of patients had frequent IDH.

Conclusions

The prevalence of IDH according to the EBPG definition is low. The dominant determinant of the EBPG definition was nursing intervention since this was the component with the lowest prevalence. IDH seems to be less common than indicated in the literature but a proper comparison with previous studies is complicated by the lack of a uniform definition.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0231-9) contains supplementary material, which is available to authorized users.

Physiological monitoring and control in hemodialysis: state of the art and outlook

Medical devices for monitoring and feedback control of physiological parameters of the dialysis patient were introduced in the early 1990s. They have a wide range of applications, aiming at increasing the safety and ensuring the efficiency of the treatment, and at an improved restoration of physiological conditions, leading to an overall reduction in morbidity and mortality. Such devices include sensors for the measurement of temperature, optical parameters and sound speed in blood, and electrical characteristics of the human body, and other parameters. Essential for the development of these devices is a detailed understanding of the pathophysiological background of a therapeutical problem. There is still a large potential to introduce new devices for further therapy improvement and automation. Also, the size of the hemodialysis market appears attractive; however, a new product has to meet several specific requirements in order to also become commercially successful. This review describes the therapeutic and technical principles of several available devices, reports on concepts for possible future devices, and presents a short overview on the market environment.

Absolute blood volume in hemodialysis patients: why is it relevant, and how to measure it?

Intradialytic hypotension (IDH) is the most common complication during hemodialysis and is associated with significant morbidity. It occurs as a consequence of a reduction in blood volume during ultrafiltration. Today, devices for monitoring relative blood volume (i.e. the intradialytic blood volume as a fraction of the blood volume at the start of the dialysis treatment) are routinely available and have been used to analyze the relationship between changes in relative blood volume and the occurrence of IDH in an attempt to derive critical thresholds that, when observed, would help avoid hypotensive episodes during the treatment. However, the results have been unsatisfactory in many patients. Here we illustrate the importance of absolute blood volume in hemodialysis patients, summarize the acute physiologic mechanisms involved in the preservation of adequate circulation during ultrafiltration, and outline why hemodialysis patients are often particularly vulnerable to reductions in blood volume. We then discuss the shortcomings of relative blood volume measurements, make a case for the superiority of absolute blood volume measurements, and introduce the reader to a mathematical concept that allows relative blood volume devices to be used for the estimation of absolute blood volume. Finally, we discuss the implications of absolute blood volume beyond IDH and propose a paradigm shift in the approach to dry weight attainment.

Association of intradialytic hypotension and convective volume in hemodiafiltration: results from a retrospective cohort study

Background

Hemodiafiltration (HDF), as a convective blood purification technique, has been associated with favorable outcomes improved phosphate control, removal of middle-molecules such as Beta2-microglobulin and the occurrence of intradialytic hypotension (IDH) as compared to diffusive techniques. The aim of this retrospective cohort study in dialysis patients receiving HDF in one urban dialysis facility in Mexico City was to investigate the occurrence of IDH during HDF treatments with varying convective volume prescriptions.

Methods

Subjects were stratified into equal groups of percentiles of convective volume prescription: Group 1 of 0 to 7.53 liters, group 2 of 7.54 to 14.8 liters, group 3 of 14.9 to 16.96 liters, group 4 of 16.97 to 18.9 liters, group 5 of 21 to 19.9 liters and group 6 of 21.1 to 30 liters. Logistic Regression with and without adjustment for confounding factors was used to evaluate factors associated with the occurrence of IDH.

Results

2276 treatments of 154 patients were analyzed. IDH occurred during 239 HDF treatments (10.5% of all treatments). Group 1 showed 31 treatments (8.2%) with IDH whereas group 6 showed IDH in only 15 sessions (4% of all treatments). Odds Ratio of IDH for Group 6 was 0.47 (95% CI 0.25 to 0.88) as compared to Group 1 after adjustment.

Conclusions

In summary the data of this retrospective cohort study shows an inverse correlation between the occurrence of IDH and convective volume prescription. Further research in prospective settings is needed to confirm these findings.

Simultaneous Blood Temperature Control and Blood Volume Control Reduces Intradialytic Symptoms

Purpose

Intra-dialytic morbid events (IME; e.g. hypotension, cramps, headaches) are frequent complications during hemodialysis (HD), known to be associated with ultrafiltration-induced hypovolemia and body temperature changes. Feedback control of blood volume adjusts the ultrafiltration rate in order to keep the blood volume above the patient's individual limit; feedback control of blood temperature maintains the mean arterial blood temperature at the individual pre-dialytic level. Each of these methods reduces the frequency of IME.

Methods

In a randomized clinical trial the simultaneous application of both feedback controls was investigated for the first time. In 15 weeks, each patient went through 3 study phases: an observational screening phase, a standard phase (STD), and a blood temperature- and blood volume-control phase (CTL). Patients with at least 5 sessions with IME out of 15 sessions in the screening phase were eligible for the study and randomized either into sequence STD-CTL or CTL-STD.

Results

26 patients completed the study according to protocol, and 778 HD treatments were analyzed. The general treatment parameters were similar in both study phases: treatment duration (STD: 244 min, CTL: 243 min, NS), pre-dialytic weight (STD: 72.3 kg, CTL: 72.2 kg, NS), and weight loss due to ultrafiltration (STD: 3.26 kg, CTL: 3.15 kg, NS). The proportion of HD treatments with IME was 32.8% during STD and 18.0% during CTL (p=0.024).

Conclusions

The frequency of HD sessions with IME was significantly reduced by 45% compared to standard HD in this randomized clinical trial by use of individualized HD treatments with simultaneous feedback control of blood volume and blood temperature.

Midodrine-induced vascular ischemia in a hemodialysis patient: a case report and literature review

Midodrine is an alpha-agonist that causes peripheral vasoconstriction, resulting in increased blood pressure. It has been reported to be safe and effective in patients with end stage renal disease (ESRD) and is widely used for hemodialysis-associated hypotension. We report a case report of midodrine-induced ischemia in a patient on hemodialysis and review the literature relating to the safety of midodrine in patients with end stage renal disease.

Adenosine A1 receptor antagonist improves intradialytic hypotension

Intradialytic hypotension is a most frequent complication of hemodialysis and may contribute to cardiovascular events and high mortality. There is a hypothesis that an increase in adenosine generation during hemodialysis may cause vasodilation and a decrease in cardiac output, which results in systemic hypotension. We studied whether this can be blocked by an adenosine A1 receptor antagonist. We investigated the effects of an A1 antagonist, FK352, injection in 30 chronic hemodialysis patients with frequent intradialytic hypotension by a prospective, multicenter, double-blind placebo-controlled study for 4 weeks after 4 weeks of the observation period. Intradialytic hypotension was defined as systolic blood pressure (SBP) less than 110 mmHg, with SBP drop of more than 30 mmHg from the predialysis level. The efficacy of FK352 was primarily assessed by the reduction rate of dialysis hypotension between the FK352 and placebo groups. Incidence of emergency treatments caused by hypotension was evaluated. FK352 (50 mg, intravenous) or an equivalent placebo was injected into the dialysis circuit 1 h after starting dialysis. Blood pressure and heart rate were monitored every 30 min during dialysis. FK352 significantly improved intradialytic hypotension (P=0.046), in that the reduction rates of intradialytic hypotension in the FK352 and placebo groups were -12.8% (Q1 (first quantile), Q3 (third quantile): -27.5, -1.7), and +8.3% (Q1, Q3: -16.6, +16.7), respectively. The frequency of discontinuation of dialysis was significantly reduced by FK352. No apparent side effects were observed from treatment with FK352. In conclusion, the A1 antagonist FK352 may offer a novel therapeutic option for chronic dialysis patients associated with intradialytic hypotension.

Discordance of influence of hypertension on mortality and cardiovascular risk in hemodialysis patients

BACKGROUND

Hemodialysis patients are at significantly increased risk for both morbidity and mortality from cardiovascular disease. However, most recent reports have indicated elevated mortality risk associated with low blood pressure, rather than high blood pressure. We added nonfatal cardiovascular events as an outcome in addition to cardiovascular and all-cause mortality to analyze the risk of hypertension.

METHODS

One hundred sixty-four patients receiving regular hemodialysis between January and December 1998 were examined and prospectively followed up until the end of 2003. The primary end point was hospital admission or death from cardiovascular disease. Secondary end points were cardiovascular and all-cause mortality.

RESULTS

During the 5-year follow-up period, 52 patients experienced cardiovascular events and 45 patients died (18 patients, from cardiovascular disease). Based on Cox analysis, high systolic blood pressure (relative risk [RR], 1.23; 95% confidence interval [CI], 1.07 to 1.43; P = 0.004) and older age were independently associated with cardiovascular events. Elevated systolic blood pressure (RR, 1.25; 95% CI, 0.99 to 1.59; P = 0.063) was a marginal predictor for cardiovascular mortality. Age, serum albumin level, malignant neoplasm, and diabetes were independent risk factors for all-cause mortality, whereas there was no association between blood pressure and all-cause mortality. The hazard ratio for cardiovascular events after adjustment for age, sex, and diabetes was lowest in patients with systolic blood pressure of 140.1 mm Hg or less and progressively increased with the increase in systolic blood pressure.

CONCLUSION

Hypertension is a potent risk factor for cardiovascular disease in hemodialysis patients, as in the general population, whereas there is no association of hypertension with mortality. Active reduction in systolic blood pressure is important to minimize the occurrence of cardiovascular events.

Addition of sertraline to other therapies to reduce dialysis-associated hypotension

Sertraline has shown promise in the treatment of dialysis-associated hypotension (DAH) in a limited number of end-stage renal disease patients. We undertook a study to evaluate the effect of adding sertraline to other therapies for patients with documented DAH. We also measured the effect of sertraline on intradialytic haemodynamics. We used the ultrasound dilution technique (HD01 monitor) to measure cardiac output (CO), central blood volume (CBV) and peripheral vascular resistance (PVR) in these patients. The study was performed in two phases. Phase 1 was a control, while the second phase consisted of treatment with sertraline (50 mg/day). Cardiac output and central blood volume were measured 30 min following the initiation of dialysis and 30 min prior to the termination of dialysis. Blood pressure (BP) was monitored during haemodynamic measurements and throughout dialysis. Eighteen patients with documented DAH completed the study. Cardiac output, CBV and PVR were no different in the sertraline phase as compared with the control phase. The declines in systolic BP, diastolic BP and mean arterial pressures from pre-haemodialysis (HD) to lowest intradialytic and pre-HD to post-HD were not significantly different for the sertraline phase versus the control phase. In conclusion, it appears that sertraline has no additive effect on intradialytic haemodynamics to improve blood pressure in patients with DAH who are under therapy (with sodium modelling, cool dialysate and midodrine).

Characteristics of hypotension-prone haemodialysis patients: is there a critical relative blood volume?

BACKGROUND

Intradialytic morbid events (IME, mostly hypotension) mainly due to ultrafiltration-induced hypovolaemia still are the most frequent complication during haemodialysis (HD). This study was performed to test the hypothesis that there is an individual critical relative blood volume (RBV(crit)) in IME-prone HD patients.

METHODS

In this prospective international multicentre study, 60 IME-prone patients from nine dialysis centres were observed during up to 21 standard HD sessions without trial-specific intervention. The RBV was monitored continuously by an ultrasonic method (BVM; blood volume monitor). Also, the ultrafiltration rate was registered continuously. Blood pressure was measured at regular intervals, and more frequently during IME. All IME and specific therapeutic interventions were noted.

RESULTS

In total, 537 IME, some with more than one symptom, were documented during 585 HD sessions. The occurrence of IME increased up to 10-fold from the start to the end of the HD session. RBV(crit) showed a wide inter-individual range, varying from 71 to 98%. However, the intra-individual RBV limit was relatively stable, with an SD of <5% in three-quarters of the patients. In patients with congestive heart failure, cardiac arrhythmia, advanced age, low ultrafiltration volume and low diastolic blood pressure, higher values of RBV(crit) were observed. While all correlations between RBV(crit) and patient characteristics alone were found to be of weak or medium strength, the combination of diastolic blood pressure, ultrafiltration volume and age resulted in a strong correlation with RBV(crit): the linear equation with these parameters allows an estimation of RBV(crit) in patients not yet monitored with a BVM.

CONCLUSIONS

An individual RBV limit exists for nearly all patients. In most IME-prone patients, these RBV values were stable with only narrow variability, thus making it a useful indicator to mark the individual window of haemodynamic instabilities.

Efficacy and safety of midodrine in the treatment of dialysis-associated hypotension

Dialysis-associated hypotension is a morbid problem in haemodialysis patients. Employment of midodrine at the start of dialysis has reduced the severity and frequency of hypotensive episodes in these patients. Through selective alpha(1)-adrenergic receptor-binding, desglymidodrine, the active metabolite of midodrine, raises blood pressure by enhancing venous and arterial tone. This medication has been demonstrated to be effective and safe in the acute and chronic treatment of haemodialysis-associated hypotension in end stage renal disease patients.

The role of blood volume reduction in the genesis of intradialytic hypotension

BACKGROUND

The aim of this multicenter prospective study was to investigate the role of relative blood volume (RBV) reduction on intradialytic hypotension.

METHODS

One hundred twenty-three patients on chronic hemodialysis therapy were considered a priori normotensive (reference group A), intradialytic hypotension prone (group B), and hypertensive (group C). RBV was continuously monitored, and diastolic and systolic blood pressure (SBP) and heart rate (HR) were measured at 20-minute intervals during three dialysis sessions.

RESULTS

Intradialytic RBV reduction was -13.8% +/- 7.0% and similar in the three groups (P = 0.841). SBP and RBV decreased during dialysis, with a sharp initial decrease (in the first 20 minutes for SBP and the first 40 minutes for RBV), followed by a slower decrease. The lying bradycardic response before dialysis was less in group B than group A (a decrease of 3 +/- 7 versus 9 +/- 9 beats/min; P < 0.001). When symptomatic hypotension occurred, RBV reduction was not significantly different from that recorded at the same time during hypotension-free sessions (-13.9% +/- 6.4% versus -12.7% +/- 5.2%; P = 0.149). Group, baseline plasma-dialysate sodium gradient, RBV line irregularity, and early RBV and HR reduction during dialysis influenced the relative risk for symptomatic hypotension with a sensitivity of 80% versus 30% for RBV alone.

CONCLUSION

We found no difference in reduction in RBV in the three groups and no critical RBV level for the appearance of symptomatic hypotension. With variables easily available within 40 minutes of dialysis, RBV monitoring increases the prediction of symptomatic hypotension.

Hemodynamics in patients with intradialytic hypotension treated with cool dialysate or midodrine

Cool dialysate and midodrine have been used successfully to treat intradialytic hypotension (IDH) in the end-stage renal disease population. However, the exact mechanisms by which these interventions improve hemodynamic stability are not well known. We undertook a study to evaluate the effect of these modalities on intradialytic hemodynamics in patients with documented dialysis-associated hypotension. We used the ultrasound dilution technique to measure cardiac output (CO), central blood volume (CBV), and peripheral vascular resistance (PVR) in these patients. The study was performed in two phases. Phase 1 consisted of control (1A) and cool dialysate (1B) studies, whereas phase 2 consisted of control (2A) and midodrine (2B) studies. CO, CBV, and PVR were measured 30 minutes after the initiation of hemodialysis (HD) and 30 minutes before the termination of HD using the HD01 monitor. Blood pressure was measured pre-HD and post-HD. Fourteen patients with documented IDH completed the study. CO and CBV were significantly more preserved in the cool dialysate and midodrine phases compared with control phases. PVR increased in all phases of the study. Declines in mean arterial pressures from pre-HD to post-HD were less with cool dialysate versus control and midodrine versus control. Ultrafiltration volumes were not significantly different between phases. Cool dialysate and midodrine appear to improve intradialytic hemodynamics in patients with dialysis-associated hypotension, mainly through the preservation of CBV and CO, rather than significantly elevating PVR.

Pharmacologic options available to treat symptomatic intradialytic hypotension

Treatment of symptomatic intradialytic hypotension (IDH) is a difficult task for the practicing nephrologist. Minimizing patient factors that precipitate IDH as well as dialysis procedure-related components that lower blood pressure are the initial approaches to this problem. However, despite these maneuvers, hypotension often persists in a group of high-risk patients. Pharmacologic interventions are often used to reduce IDH. Unfortunately, many of the available therapies are marginally effective and/or poorly tolerated. A few therapies appear to be efficacious and well tolerated-carnitine, sertraline, and midodrine. This article reviews the various pharmacologic therapies used for IDH and makes recommendations for treatment of this difficult problem.

Efficacy and safety of haemodialysis treatment with the Hemocontrol biofeedback system: a prospective medium-term study

BACKGROUND

Hypovolaemia has been implicated as a major causal factor of morbidity during haemodialysis (HD). A model biofeedback control system for intra-HD blood volume (BV) changes modelling has been developed (Hemocontrol), Hospal Italy) to prevent destabilizing hypovolaemia. It is based on an adaptive controller incorporated in a HD machine (Integra), Hospal Italy). The Hemocontrol biofeedback system (HBS) monitors BV contraction during HD with an optical device. HBS modulates BV contraction rates by adjusting the ultrafiltration rate (UFR) and the refilling rate by adjusting dialysate conductivity (DC) in order to obtain the desired pre-determined BV trajectories.

METHODS

Nineteen hypotension-prone uraemic patients (seven males, 12 females; mean age 64.5+/-3.0 SEM years; on maintenance HD for 80.5+/-13.2 months) volunteered for the present prospective study that compared the efficacy and safety of bicarbonate HD treatment equipped with HBS, as a whole, with the gold-standard bicarbonate treatment equipped with a constant UFR and DC (BD). The study included three phases: Medium-term studies started with one period of 6 months of BD and always had a follow-up period of HBS treatment ranging from 14 to 30 months (mean 24.0+/-1.6); short-term studies started in September 1999, when all patients went back to BD treatment for a wash-out period of 4 weeks and a short-term study period of a further 3 weeks (phase A). Afterwards, they once again started HBS treatment for a wash-out period of 4 weeks and a short-term study period of a further 3 weeks (phase B). Every patient underwent acute studies during a single HD run, once during phase A and once in phase B. Resistance (R) and reactance (Xc) measurements were obtained utilizing a single-frequency (50 kHz) tetrapolar bioimpedance analysis (BIA). Extracellular fluid volume (ECV) was calculated from R, Xc, and height and body weight measurements using the conventional BIA regression equations.

RESULTS

The overall occurrence of symptomatic hypotension and muscle cramps was significantly less in HBS treatment in both medium- and short-term studies. Self-evaluation of intra- and inter-HD symptoms (worst score=0, best score=10) revealed a statistically significant difference, as far as post-HD asthenia was concerned (6.2+/-0.2 in HBS treatment vs 4.3+/-0.1 in BD treatment, P<0.0001). No difference was observed between the two treatments when comparing pre- and post-HD lying blood pressure, heart rate, body weights and body weight changes in medium- and short-term studies. The residual BV%/ Delta ECV% ratio, expression of the vascular refilling, was significantly higher during HBS treatment in acute studies.

CONCLUSIONS

HBS treatment is effective in lowering hypovolaemia-associated morbidity compared with BD treatment; this could be related to a greater ECV stability. Furthermore, HBS is a safe treatment in the medium-term because these results are not achieved through potentially harmful changes in blood pressure, body weight, and serum sodium concentration.

Effect of dialysate sodium concentration on interdialytic increase of potassium

To evaluate the role of plasma tonicity in the postdialysis increment of plasma potassium (p[K(+)]), the outcome of two hemodiafiltration treatments that differed only in the Na(+) level in dialysate (Na(D))-143 mmol/L (high dialysate sodium concentration [H-Na(D)]) and 138 mmol/L (low dialysate sodium concentration [L-Na(D)])-were compared in the same group of uremic patients from the end of treatment (T0) to the subsequent 30 to 120 min and up to 68 h. Kt/V and intradialytic K(+) removal were comparable. At T0, plasma [Na(+)] was 145+/-1 and 137+/-1 mmol/L after H-Na(D) and L-Na(D), respectively (P<0.001). The difference in plasma tonicity persisted from T0 to T68 h. At T120, p[K(+)] was increased from the T0 value of 3.7+/-0.2 to 4.7+/-0.2 mmol/L (P<0.05) after H-Na(D), whereas it was unchanged after L-Na(D). The change of p[K(+)] was still different after 68 h (+76+/-10% and +50+/-7% in H-Na(D) and L-Na(D), respectively; P<0.05). Of note, in the first 2 h after the end of treatment, bioimpedance analysis revealed only in H-Na(D) a significant 11+/-3% decrement of phase angle that is compatible with a decrease of intracellular fluid volume at the expense of the extracellular volume. Similarly, within the same time frame, in H-Na(D), a significant reduction of mean corpuscular volume of red cells, associated with a 2 +/-1% decrease of the intracellular [K(+)], was observed. In contrast, mean corpuscular volume of red cells did not change and erythrocyte [K(+)] increased by 6+/-1% after L-Na(D) (P<0.005 versus H-Na(D)). Thus, hypertonicity significantly contributes to the increase of p[K(+)] throughout the whole interdialytic period by determining intracellular fluid volume/extracellular volume redistribution of water and K(+).

Ultrafiltration profiling and measurement of relative blood volume as strategies to reduce hemodialysis-related side effects

Hemodialysis (HD) side effects, such as hypotension and muscle cramps, may be related to excessive ultrafiltration (UF) in relation to refilling of fluids from the extravascular space, resulting in hemoconcentration and reduction of relative blood volume (RBV). This study examines the suitability of RBV measurements and UF modeling to reduce the incidence of dialysis side effects. We followed up 188 dialysis sessions in 53 patients. RBV and incidence of side effects were evaluated. Six treatment regimens were examined: UF profile 0, with a constant UF rate; UF profile 1, with a linear decreasing UF rate; UF profile 2, with a stepwise decreasing UF rate; and UF profiles 3 through 5, with intermittent high UF rates interrupted by UF pauses. During dialyses with a constant UF rate (UF profile 0), 10.6% of the treatments were associated with symptomatic hypotension. UF profiles 2 through 5, intermittently using high UF rates, caused a marked increase in hypotensive episodes (18.4%). In contrast, UF profile 1, providing a continuously decreasing UF rate, showed a reduced incidence of hypotension at only 5.7%. Symptomatic hypotension occurred in 13 of 53 patients during one or more dialysis sessions. With the help of RBV measurements, a subgroup of 8 patients with hypovolemia-induced hypotension could be identified. In these patients, an individual threshold of RBV could be defined, below which 92.3% of all hypotensive episodes occurred. In the remaining 5 hypotension-prone patients, there was no correlation between the occurrence of symptomatic hypotension and low RBV during HD treatments. In conclusion, UF profiles intermittently using high UF pulses cannot be recommended. RBV measurements help define a subgroup of patients at risk for hypovolemia-induced hypotension. Only these patients may benefit from blood volume-controlled UF. The incidence of symptomatic hypotension can likely be reduced if an individual threshold of RBV is avoided during HD treatments, eg, using lower UF rates in these patients.

Electrolyte and pH dependence of heart rate during hemodialysis: a computer model analysis

The influence of hemodialysis-induced modifications in extracellular fluid characteristics on heart rate was investigated by using a detailed computer model of sinus-node electrical activity. Changes similar to those occurring in the course of hemodialysis in extracellular concentrations of sodium (from 138 to 140 mM), potassium (from 6 to 3.3 mM), and calcium (from 1.2 to 1.5 mM) ions as well as in pH (from 7.31 to 7.4) and intracellular volume were simulated. The model predicted that such changes may largely influence the rhythm of the sinoatrial node pacemaker, causing the heart rate to range from 69 to 86 bpm. Heart rate increases after removing potassium (up to 7 bpm) and also after calcium perfusion (up to 11 bpm) whereas restoring pH slows heart beat (up to 6 bpm). Extracellular sodium has no significant influence, but the heart rate strictly depends on intracellular sodium concentration (5 bpm/mM). A complex dependence of heart rate on electrolytes and pH was also recognized. Providing extracellular potassium concentration is maintained above 5 mM, heart rate exhibits low sensitivity to changes in calcium and potassium. When potassium concentration is reduced below 4.5 mM, heart rate sensitivity to calcium and potassium increases significantly to 10 and 30 bpm/mM, respectively. A sustained increase in heart rate always corresponds to an increase in intracellular sodium concentration.

Hemodynamic patterns and spectral analysis of heart rate variability during dialysis hypotension

Intradialytic hypotension, a major source of morbidity during hemodialysis and ultrafiltration, is often accompanied by paradoxical bradycardia. Relatively little is known about the sequential changes in autonomic nervous system activity up to and during the hypotensive episode. Continuous, beat-to-beat measurements of BP and heart rate were made during hemodialysis in patients prone (n = 8) and not prone (n = 11) to develop intradialytic hypotension. Off-line spectral analysis of heart rate variability (HRV) was performed to assess changes in autonomic nervous system activity during dialysis sessions both with and without hypotension. The low frequency (LF) component of HRV is thought to correlate with sympathetic nervous system activity, the high frequency (HF) component with that of the parasympathetic nervous system. In the sessions not complicated by symptomatic hypotension (n = 26), mean arterial BP (MAP) hardly fell, whereas heart rate increased from 77 +/- 2 to 89 +/- 5 bpm (P < 0.05). The LF component of HRV increased from 45.2 +/- 5.0 normalized units (nu) to 59.9 +/- 4.9 nu (P < 0.05), whereas the HF component fell from 54.8 +/- 5.0 to 40.2 +/- 4.4 nu (P < 0.05). These changes agree with compensatory baroreflex-mediated activation of the sympathetic nervous system (and suppressed parasympathetic activity) during ultrafiltration-induced intravascular volume depletion. In the sessions complicated by severe symptomatic hypotension (n = 22), the changes in heart rate and the results of spectral analysis of HRV were similar to those reported above up to the moment of sudden symptomatic (nausea, vomiting, dizziness, cramps) hypotension, whereas MAP had already fallen gradually from 94 +/- 3 to 85 +/- 3 mmHg (P < 0.05). The sudden further reduction in MAP (to 55 +/- 2 mmHg, P < 0.02) was invariably accompanied by bradycardia (heart rate directly before hypotension 90 +/- 2 bpm, during hypotension 69 +/- 3 bpm, P < 0.002). The LF component of HRV fell from 62.8 +/- 4.6 nu directly before to 40.0 +/- 3.7 nu (P < 0.05) during hypotension, whereas the HF component increased from 37.9 +/- 4.7 to 60.3 +/- 3.7 nu (P < 0.05). These findings agree with activation of the cardiodepressor reflex, involving decreased sympathetic and increased parasympathetic nervous system activity, respectively. These findings indicate that activation of the sympatho-inhibitory cardiodepressor reflex (Bezold-Jarisch reflex), which is a physiologic response to a critical reduction in intravascular volume and cardiac filling, is the cause of sudden intradialytic hypotension.

Clinical use of profiled hemodialysis

The new population on dialysis today consists mainly of high risk patients (the elderly, diabetics, etc.) with high cardiovascular scores, and such vascular pathology is the most important predisposing factor for the occurrence of a frequent intradialytic clinical complication, vascular instability syndrome, which covers a range of clinical problems. Recently a new dialysis technique, profiled hemodialysis (PHD), has been set up and proposed for routine use. PHD consists of the clinical use of preestablished individual dialysis profiles aimed at antagonizing the changes in intradialytic plasma osmolarity by continuous modulation of dialysate sodium concentration throughout the whole extracorporeal session. In particular, PHD aims at reducing the fall of plasma osmolarity in the first half of the session (when it is higher) by reducing the sodium removal rate through increasing its dialysate concentration while taking into account the desired individual sodium balance to be reached at the end of the session. In this work, we report clinical experience with PHD compared to standard hemodialysis with constant sodium dialysate (SHD) in terms of its efficacy to maintain a more stable intradialytic blood volume (BV) and more stable hemodynamics. The PHD used in this work has been implemented by a mathematical model for computing the individual dialysate sodium profile which we have recently validated (Ursino M, Coli L, La Manna G, Grilli Cicilioni M, Dalmastri V, Guidicissi A, Masotti P, Avanzolini G, Stefani S, Bonomini V. A simple mathematical model of intradialytic sodium kinetics: "in vivo" validation during hemodialysis with constant or variable sodium. Int J Artif Organs 1996;19:393-403.). Eleven uremic patients affected by hypotension at the beginning of dialysis treatment were studied. Each patient first underwent an SHD treatment and 1 week later a PHD treatment. The 2 extracorporeal sessions (one on SHD and the other on PHD) were performed in each individual patient under identical operative conditions including the sodium mass removal by the end of the session and the ultrafiltration rate. The crit line and Doppler echocardiography were used to determine BV, cardiac output (CO), and stroke volume (SV) throughout the sessions. The mean blood pressure (MBP) and heart rate (HR) were simultaneously monitored. PHD was associated with a more stable intradialytic BV and more stable hemodynamics compared to SHD. The higher stability of BV and cardiac function (in terms of SV and CO maintenance) which was obtained above all in the first half of the PHD session was associated with a higher stability of the MBP and the HR. This resulted in an enhancement in cardiovascular tolerance to ultrafiltration throughout the session in all tested patients. In contrast, SHD in the same patients was characterized by early significant changes in BV and cardiovascular parameters resulting in a significant decrease of the MBP and a significant increase of the HR throughout the session and also 1 h after the end of dialysis. Our results indicate that PHD may represent an efficient approach for the treatment of patients suffering from intradialytic vascular instability. If long-term clinical practice confirms the efficacy of PHD in controlling dialysis intolerance symptoms, it will have great scope as a routine procedure.

Intradialytic hypotension: is midodrine beneficial in symptomatic hemodialysis patients?

Symptomatic hypotension during hemodialysis is a disabling complication in end-stage renal disease (ESRD) patients, especially in certain groups of patients who are at higher risk for this problem. Autonomic dysfunction is thought to play a significant role. We evaluated the efficacy of midodrine, an oral agent with selective alpha-adrenergic agonist activity used in the treatment of neurogenic orthostatic hypotension, on 10 hemodialysis patients with persistent intradialytic hypotension. The patients were given a dose of midodrine (mean dose, 5.5 mg; range, 5 to 10 mg) 30 minutes before each hemodialysis session. We compared blood pressure, pulse, body weight, and laboratory values for 10 consecutive dialysis sessions off and on midodrine therapy. There was a statistically significant improvement in lowest intradialytic systolic blood pressure (from 96.6 to 114.7 mm Hg; P < 0.001), lowest intradialytic diastolic blood pressure (from 53.2 to 59.0 mm Hg; P = 0.002), lowest intradialytic mean arterial pressure (from 67.7 to 77.6 mm Hg; P < 0.001), posthemodialysis systolic blood pressure (from 116.5 to 127.1 mm Hg; P < 0.001), posthemodialysis diastolic blood pressure (from 66.6 to 69.7 mm Hg; P = 0.040), and posthemodialysis mean arterial pressure (from 83.2 to 88.8 mm Hg; P = 0.001) after patients were placed on midodrine. There also was a small but statistically significant decrease in intradialytic pulse rate (from 86.3 to 81 beats/min; P = 0.021) and posthemodialysis pulse rate (from 87.4 to 81.7 beats/min; P = 0.024) after initiation of midodrine therapy. There was no significant difference in any of the prehemodialysis blood pressure measurements or pulse rate off or on midodrine therapy. The improvements in intradialytic and posthemodialysis blood pressure were associated with a uniform subjective improvement in symptoms associated with dialysis hypotension, such as cramps, fatigue, dizziness, and weakness. Other than scalp paresthesia in one patient, no adverse effects were noted. Our results suggest that the administration of a single dose of midodrine before hemodialysis is an effective therapy for intradialytic hypotension. A prospective trial with adequate patient numbers and long-term follow-up would be useful to evaluate this drug's efficacy and safety profile in patients with ESRD.

Blood volume changes during three different profiles of dialysate sodium variation with similar intradialytic sodium balances in chronic hemodialyzed patients

The aim of this study was to evaluate the effects on blood volume (BV) preservation of three different profiles of dialysate sodium variation with similar intradialytic sodium balances. Ten uremic patients aged 50 +/- 11 years receiving regular bicarbonate hemodialysis for 49 +/- 57 months were studied. Each patient underwent three hemodialysis treatments with different modalities of dialysate sodium profiles: constant sodium hemodialysis (CHD), high-low sodium hemodialysis (H-LHD), and low-high sodium hemodialysis (L-HHD). In CHD, the dialysate sodium concentration was 141 mEq/L and did not change during treatment. In H-LHD and L-HHD, the dialysate sodium concentration at the start of dialysis was 160 mEq/L and 133 mEq/L, respectively, and remained constant for 60 minutes. At this time, a single-step break point of variation of dialysate sodium concentration occurred. The dialysate sodium concentration changed according to a model aimed to keep identical the amount of dialysate sodium exchanged in the three different dialysis procedures. The duration of hemodialysis, the blood flow rate, the dialysate flow rate, and the dialysis membrane were the same for all three different hemodialysis modalities. The ultrafiltration rate was kept constant during treatment. Total dialysate collection and intradialytic sodium balance were calculated for each hemodialysis session. Blood pressure and heart rate were monitored at 10-minute intervals; percent reductions of BV (%R-BV) were continuously monitored by an online optical reflection method (Hemoscan; Hospal-Dasco, Medolla, Italy). The results have shown a lower intradialytic %R-BV with H-LHD compared with L-HHD and CHD. No differences in total ultrafiltration rate, systolic and diastolic blood pressures, and heart rate were observed among the three different dialysis procedures. The total dialysate sodium collected and the intradialytic sodium balances were very similar among the three different dialysis procedures, confirming the accuracy of the precision of the sodium model used. The H-LHD sodium profile may be a useful tool in the prevention of excessive %R-BV and of dialysis intolerance episodes.

Dialysate sodium delivery can alter chronic blood pressure management

Low dialysate sodium concentrations can reduce postdialysis thirst and serum sodium activity, but patients typically experience dialysis hypotension, fatigue, disequilibrium, and cramps. "High-sodium" hemodialysis minimizes dialysis disequilibrium but increases the serum sodium activity of most patients. Programmed "variable-sodium" dialysis can minimize dialysis discomfort but may also alter the sodium kinetics from those of "high-sodium" dialysis. We designed a cross-over study with random order assignment to determine whether a "variable-sodium" dialysis program could reduce the blood pressure of dialysis patients without increasing dialysis morbidity. Dialysis with a dialysate sodium of 140 mEq/L was compared with dialysis with a programmed exponential decrease of dialysate sodium from 155 mEq/L to 135 mEq/L. Dialysate sodium was then held constant at 135 mEq/L for the final half hour of dialysis. Eighteen patients completed the 7-month study, each receiving 3.5 months of experimental and 3.5 months of standard therapy. Programmed "variable-sodium" dialysis resulted in a reduction in antihypertensive drug use without alterations in predialysis blood pressure, interdialytic weight gain, ultrafiltration tolerance, or the frequency of symptomatic dialysis cramps or hypotension. Patients did, however, have lower postdialysis standing blood pressures and higher postdialysis target weights during programmed "variable-sodium" dialysis.

Reducing symptoms during hemodialysis by continuously monitoring the hematocrit

Previous studies have demonstrated that patients on hemodialysis develop intradialytic symptoms when the blood volume decreases to a critical level. Using a continuous monitor (CRIT-LINE; In-Line Diagnostics, Riverdale, UT) to determine the instantaneous hematocrit and blood volume, we observed that certain intradialytic symptoms occurred at a patient-specific hematocrit. In the present study, we exploited this hematocrit threshold concept to decrease the occurrence of lightheadedness, cramping, and nausea, regardless of blood pressure changes. In the first phase of the study, hematocrit threshold was established in six hypotension-prone patients. Five patients entered into the second phase in which ultrafiltration rates were increased 25 percent above prescribed values at the beginning of the experimental sessions. Subsequently during the experimental sessions, ultrafiltration rates were manipulated to maintain the instantaneous hematocrit value 2 units below the established hematocrit threshold. Sessions without ultrafiltration rate adjustments based on hematocrit served as controls. There were no differences between experimental (n = 27) and control (n = 28) sessions with respect to treatment time (230 minutes v 229 minutes), fluid volume removed (3,351 mL v 3,383 mL), and maximum percentage change in systemic blood pressure (-26 percent v -24 percent). However, there were less symptoms during the experimental sessions (26 percent v 57 percent; P = 0.038). These data suggest that a twofold reduction in intradialytic symptoms can be achieved using continuous hematocrit monitoring without altering treatment times or volume removed in hypotension-prone patients.