Determination of circulating blood volume by continuously monitoring hematocrit during hemodialysis

Volume Assessment in Patients Undergoing Long-Term Dialysis

Accurate assessment of fluid status is a priority for patients with kidney failure undergoing long-term dialysis. There is wide variation in current volume-related practices between dialysis units and an urgent need to develop better evidence to guide practice. Clinical decisions relating to volume management are implicitly based on assessment of volume status, and there are numerous different but imperfect methods of assessment. Isotope-based dilutions are impractical for clinical use and may not be a gold standard for patients with kidney failure. Individual trends in body weight and BP have been used as a pragmatic surrogate marker for volume status. Probing the target weight based on BP is still widely practiced but may pose risks related to volume depletion and accelerated loss of residual kidney function. Clinical signs, such as elevated jugular venous pressure and leg edema, are readily accessible but have poor diagnostic accuracy and wide interobserver variability that limit their reproducibility for volume assessment in clinical trials. Lung ultrasound and bioelectrical impedance analysis have a sound scientific rationale for the assessment of extracellular volume and are appropriately associated with clinical outcomes, but neither approach has demonstrated convincingly favorable clinical outcomes in clinical trials. Other technologies for volume assessment exist but require further assessment in clinical trials. Advancements in clinical care can be made with existing technologies through comparative effectiveness trials of different fluid management strategies, routine and standardized measurement of volumetric parameters and individual patient preferences, and innovative integration of existing volume assessment methods. A systematic and globally coordinated approach to improving volume assessment and management is required to improve outcomes in patients receiving long-term dialysis.

Assessment of the renal function of patients with anorexia nervosa

BACKGROUND

A decreased glomerular filtration rate (GFR), estimated using creatinine (Cr- eGFR), is often found at the initial presentation of anorexia nervosa (AN). Its pathophysiology has been explained mainly by dehydration, and chronic hypokalemia is also thought to be a cause. However, because we have often experienced cases of AN with decreased Cr-eGFR without these conditions, we must consider different etiologies. The focus of this paper is on low free triiodothyronine (FT3) syndrome. We also discuss the utility of eGFR, estimated using cystatin-C (CysC-eGFR), for these patients.

METHODS

The data of 39 patients diagnosed with AN between January 2005 and December 2023 was available for study. The characteristics of patients at the lowest and highest body mass index standard deviation score (BMI-SDS) were examined. Data on the parameters Cr-eGFR, CysC-eGFR, dehydration markers, potassium (K), and hormonal data and BMI-SDS were assessed during the treatment course to evaluate the correlations in these parameters. Blood hematocrit, uric acid (UA), blood urine nitrogen (BUN) level, and urine specific gravity were adopted as dehydration markers; FT3, free thyroxine, thyroid stimulating hormone, and insulin-like growth factor were adopted as hormonal data. Cr-eGFR and simultaneously evaluated dehydration markers, K, or hormonal data were extracted and correlations associated with the changes in BMI-SDS were examined. Furthermore, Cr-eGFR and simultaneously assessed CysC-eGFR were compared.

RESULTS

When the BMI-SDS was at the lowest value, low-FT3 syndrome was shown. Severe hypokalemia was not found in our study. A linear relation was not found between Cr-eGFR and BMI-SDS. A statistically significant correlation was found between Cr-eGFR and FT3 (p = 0.0025). Among the dehydration markers, statistically significant correlations were found between Cr-eGFR and BUN or UA. The difference between Cr-eGFR and CysC-eGFR was prominent, and CysC-eGFR showed much higher values.

CONCLUSIONS

Our data indicates that low-FT3 syndrome and dehydration were related to the renal function of our patients with AN. Furthermore, our data suggest that caution is needed in the interpretation of kidney function evaluation when using CysC-eGFR in cases of AN.

Haematocrit monitoring and blood volume estimation during continuous renal replacement therapy

BACKGROUND

Continuous haemoglobin, venous blood oxygen saturation, and haematocrit (Hct) monitoring is currently not applied during continuous renal replacement therapy (CRRT). Such Hct monitoring enables estimation of changes in blood volume as percentage change (ΔBV%) from therapy start time and is incorporated into intermittent haemodialysis machines but not CRRT machines despite its potential to optimise fluid management in CRRT patients.

METHODS

To overcome this problem, we used a standalone monitor (CRIT-LINE®IV, Fresenius Medical Care, Concord, USA) with an associated in-line blood chamber (CRIT-LINE®IV Blood Chamber, Fresenius Medical Care, Concord, USA) and designed our own adaptor connection piece (TekMed and Morriset, Melbourne and Brisbane, Australia) to allow these readings at the vascular access outflow and recorded data for estimated Hct and derived ΔBV% during CRRT.

RESULTS

We report on this technique with an illustrative case example and 12 h of CRRT data on the fluid loss rate prescribed, hourly net patient fluid loss (range: 0-308 mL/h), mean arterial pressure, norepinephrine dose (range: 5-14 mcg/min), estimated continuous Hct and ΔBV%, and the otherwise undetected diagnosis of an approximate 15 % decrease in blood volume during the CRRT.

CONCLUSION

We have described a technical CRRT circuit modification that can facilitate a previously unavailable assessment of fluid shifts during CRRT. Further application in clinical trials is now possible.

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.

Hemodialysis-induced changes in hematocrit, hemoglobin and total protein: Implications for relative blood volume monitoring

Background

Relative blood volume (RBV) changes during hemodialysis (HD) are typically estimated based on online measurements of hematocrit, hemoglobin or total blood protein. The aim of this study was to assess changes in the above parameters during HD in order to compare the potential differences in the RBV changes estimated by individual methods.

Methods

25 anuric maintenance HD patients were monitored during a 1-week conventional HD treatment. Blood samples were collected from the arterial dialysis blood line at the beginning and at the end of each HD session. The analysis of blood samples was performed using the hematology analyzer Advia 2120 and clinical chemistry analyzer Advia 1800 (Siemens Healthcare).

Results

During the analyzed 30 HD sessions with ultrafiltration in the range 0.7–4.0 L (2.5 ± 0.8 L) hematocrit (HCT) increased by 9.1 ± 7.0% (mean ± SD), hemoglobin (HGB) increased by 10.6 ± 6.3%, total plasma protein (TPP) increased by 15.6 ± 9.5%, total blood protein (TBP) increased by 10.4 ± 5.8%, red blood cell count (RBC) increased by 10.8 ± 7.1%, while mean corpuscular red cell volume (MCV) decreased by 1.5 ± 1.1% (all changes statistically significant, p < 0.001). HGB increased on average by 1.5% more than HCT (p < 0.001). The difference between HGB and TBP increase was insignificant (p = 0.16).

Conclusions

Tracking HGB or TBP can be treated as equivalent for the purpose of estimating RBV changes during HD. Due to the reduction of MCV, the HCT-based estimate of RBV changes may underestimate the actual blood volume changes.

Physiological responses to heat stress in two genetically distinct chicken inbred lines

High ambient temperature is one of the most important environmental factors negatively impacting poultry production and health. Genetics is an important contributor in mitigating the stress response to heat. Two genetically distinct highly inbred lines of similar body size (Leghorn and Fayoumi) were characterized for phenotypic differences in response to heat. At 14 days of age, birds were exposed to 38°C with 50% humidity for 4 hours, then 35°C until the conclusion of the experiment. Non-treated individuals were kept at 29.4°C for the first week and then 25°C throughout the experiment. Birds in the heat-stress group were inoculated at day (d) 21 with Newcastle disease virus (NDV) La Sota strain to investigate the effects of heat stress and NDV infection. Thirteen blood parameters were measured using the iSTAT blood analyzer at three stages: 4 h, 6 d, and 9 d post heat-stress treatment, representing acute heat (AH) exposure, chronic heat (CH1) exposure, and chronic heat exposure after virus infection (CH2), respectively. Most blood parameters were significantly changed with heat stress in Leghorns at AH and in Fayoumis at CH1 and CH2. The Leghorn line had significant acute responses with disrupted acid-base balance and metabolic disorders. The heat-resilient Fayoumis maintained a relatively well-balanced acid-base balance. The current study provides the comprehensive profile of biomarker signatures in blood associated with heat tolerance and suggests that PO2, TCO2, HCO3, and base excess can be served as potential biomarkers that can be used to genetically improve heat tolerance in poultry.

The top tertile of hematocrit change during hospitalization is associated with lower risk of mortality in acute heart failure patients

BACKGROUND

Hemoconcentration has been proposed as surrogate for changes in volume status among patients hospitalized with acute heart failure (AHF) and is associated with a favorable outcome. However, there is a dearth of research assessing the clinical outcomes of hospitalized patients with hemoconcentration, hemodilution and unchanged volume status.

METHODS

We enrolled 510 consecutive patients hospitalized for AHF from April 2011 to July 2015. Hematocrit (HCT) levels were measured at admission and either at discharge or on approximately the seventh day of admission. Patients were stratified by delta HCT tertitles into hemodilution (ΔHCT ≤ - 1.6%), no change (NC, -1.6% < ΔHCT ≤1.5%) and hemoconcentration (ΔHCT >1.5%) groups. The endpoint was all-cause death, with a median follow-up duration of 18.9 months.

RESULTS

Hemoconcentration was associated with lower left ventricle ejection fraction, as compared with NC and hemodilution groups, while renal function at entry, New York Heart Association class IV, and in-hospital worsening renal function (WRF) were not significantly different across the three groups. After multivariable adjustment, hemoconcentration had a lower risk of mortality as compared with hemodilution [hazard ratio (HR) 0.39, 95% confidence interval (CI) 0.24-0.63, P < 0.001], or NC (HR 0.54, 95% CI 0.33-0.88, P = 0.015], while hemodilution and NC did not have significantly differ in mortality (HR 0.72, 95% CI 0.48-1.10, P = 0.130).

CONCLUSIONS

In patients hospitalized with AHF, an increased HCT during hospitalization is associated with a lower risk of all-cause mortality than a decreased or unchanged HCT. Furthermore, all-cause mortality does not differ significantly between patients with unchanged and decreased HCT values.

Comparison of multiple fluid status assessment methods in patients on chronic hemodialysis

PURPOSE

Control of hydration status is an important constituent of adequate and efficient hemodialysis (HD) treatment. Nevertheless, there are no precise clinical indices for early recognition of small changes in fluid status of patients undergoing chronic hemodialysis therapy. This study aimed to evaluate and compare the widely used and reliable method of indexed inferior vena cava diameter (IVCDi) with established and more recently available techniques (bioelectrical impedance analysis [BIA], continuous blood volume monitoring [Crit-line], and the B-line score [BLS] with lung ultrasonography) for estimating the hydration status of patients on HD.

METHODS

Fifty-three patients undergoing chronic HD thrice weekly were included in the study. Evaluation of hydration status methods (IVCDi, BLS, BIA, and Crit-line) was performed thrice weekly before and after HD. Receiver operating characteristic curve analysis was performed to evaluate the discriminative power of (methods) the BLS, BIA, and Crit-line for predicting over- and underhydration of patients, as determined by the reference method, IVCDi.

RESULTS

BLS showed the most promising results in predicting overhydration, as determined by IVCDi, compared with BIA and Crit-line and presented a sensitivity of 77% and specificity of 74%. The accuracy of the BLS was higher than that of BIA (0.81 vs. 0.71, p = 0.032) and Crit-line (0.61, p = 0.001). BLS also showed more promising results in predicting underhydration, as determined by IVCDi, than BIA and Crit-line and presented a sensitivity of 78% and a specificity of 73%. The accuracy of the BLS was higher than that of BIA (0.83 vs. 0.76, p = 0.035) and Crit-line (0.50, p < 0.001).

CONCLUSIONS

The BLS is a useful and easily performed technique that has recently become available for accurate evaluation of dry weight and fluid status in patients with end-stage renal disease undergoing chronic HD. This method might help recognize asymptomatic lung congestion in these patients.

Measurement of Cardiac Output and Blood Volume During Hemodialysis with Fluorescent Dye Dilution Technique

Intradialytic hypotensive events (IDH) accompanied by deleterious decreases of the cardiac output complicate up to 25% of hemodialysis treatments. Monitoring options available to track hemodynamic changes during hemodialysis have been found ineffective to anticipate the occurrence of IDH. We have assembled opto-electronic instrumentation that uses the fluorescence of a small bolus of indocyanine green dye injected in the hemodialysis circuit to estimate cardiac output and blood volume based on indicator dilution principles in patients receiving hemodialysis. The instrument and technique were tested in 24 adult end-stage renal failure subjects during 64 hemodialysis sessions. A single calibration factor could be used across subjects and across time. Intra-subject variability of the measurements over time was <10%. Stroke volume index (SVI) (mean ± SEM = 34 ± 1 vs. 39 ± 2 mL m^-2) and central blood volume (CBV) index (783 ± 36 vs. 881 ± 33 mL m^-2) were lower at the beginning of the sessions in which IDH eventually occurred. Cardiac index, SVI, and CBV index decreased with hemodialysis in all treatment sessions but the decrease was more intense in the IDH sessions. We conclude that hemodynamic monitoring can be implemented in patients receiving hemodialysis with minimal disruption of the treatment and could help understand intradialytic hypotension.

Online Hemoglobin and Oxygen Saturation Sensing During Continuous Renal Replacement Therapy with Regional Citrate Anticoagulation

Optical hemoglobin and oxygen saturation sensor (OHOS) monitor when used in combination with other hemodynamic tools may be useful for continuous hemodynamic monitoring during ultrafiltration. The stand-alone OHOS monitor can easily be deployed predialyzer into the extracorporeal circuit of continuous renal replacement therapy (CRRT) systems. To maximize the accuracy of the OHOS in 24 hr CRRT systems, clotting in the optical blood chamber and the presensor dilution incurred by replacement fluid should be minimized. Sustained low-efficiency dialysis (SLED) with regional citrate anticoagulation is a therapy that incorporates an OHOS and maintains the overall reliability of hemoglobin (Hb) and saturation sensing. The system operates at a blood flow rate of 60 ml/min and a fixed acid citrate infusion rate of 150 ml/hr. The presensor dilution incurred by concentrated citrate infusion would result in a minimal Hb dilution (<0.7 g/dl) while minimizing optical blood chamber clotting during 24 hr SLED.

Discordance Between Hemoconcentration and Clinical Assessment of Decongestion in Acute Heart Failure

INTRODUCTION

Hemoconcentration has been proposed as a surrogate for successful decongestion in acute heart failure (AHF). The aim of the present study was to evaluate the relationship between hemoconcentration and clinical measures of congestion.

METHODS AND RESULTS

We studied 704 patients with AHF and volume overload. A composite congestion score was calculated at admission and discharge, with a score >1 denoting persistent congestion. Hemoconcentration was defined as any increase in hematocrit and hemoglobin levels between baseline and discharge. Of 276 patient with hemoconcentration, 66 (23.9%) had persistent congestion. Conversely, of 428 patients without hemoconcentration, 304 (71.0%) had no clinical evidence of congestion. Mean hematocrit changes were similar with and without persistent congestion (0.18 ± 3.4% and -0.19 ± 3.6%, respectively; P = .17). There was no correlation between the decline in congestion score and the change in hematocrit (P = .93). Hemoconcentration predicted lower mortality (hazard ratio 0.70, 95% confidence interval 0.54-0.90; P = .006). Persistent congestion was associated with increased mortality independent of hemoconcentration (Ptrend = .0003 for increasing levels of congestion score).

CONCLUSIONS

Hemoconcentration is weakly related to congestion as assessed clinically. Persistent congestion at discharge is associated with increased mortality regardless of hemoconcentration. Hemoconcentration is associated with better outcome but cannot substitute for clinically derived estimates of congestion to determine whether decongestion has been achieved.

Modifiable factors associated with achievement of high-volume post-dilution hemodiafiltration: results from an international study

BACKGROUND

The aim was to investigate factors associated with the successful achievement of ≥21 l/session of substitution fluid volume in patients on post-dilution hemodiafiltration.

METHODS

3315 patients treated in 6 European countries with the Fresenius 5008 CorDiax machine including the AutoSub Plus feature were considered. Variables that showed a relationship with convection volume were entered in a multivariable logistic regression model.

RESULTS

Mean blood flow was 379 ± 68 ml/min. Median substitution volume was 24.7 L (IQR 22.0-27.4 L). Mean filtration fraction was 28.3 ± 4.1%. 81.5% of sessions qualified as high-volume HDF (substitution volumes ≥21 L). Higher age, dialyzer surface area, blood flow and treatment time were positively associated with the achievement of ≥21 L substitution volume; higher body mass index, male gender, higher hematocrit, graft or catheter vs. fistula, and start of week vs. mid-week were negatively associated.

CONCLUSIONS

Dialysis center policy in terms of blood flow, treatment time, filter size, and perhaps even hemoglobin targets plays a key role in achieving high-volume HDF. All of these are modifiable factors that can help in prescribing an optimal combination of dialyzer size, achievable blood flows, and treatment times.

CRIT-LINE: a noninvasive tool to monitor hemoglobin levels in pediatric hemodialysis patients

BACKGROUND

The national average for achieving the KDOQI-recommended hemoglobin (Hgb) target level of 11-12 g/dL is low with the current anemia management protocol of measuring Hgb levels every 2-4 weeks to guide intervention. The objective of this study was to correlate initial Hgb readings from the CRIT-LINE monitor with actual serum Hgb levels in pediatric patients on hemodialysis (HD).

METHODS

Data were collected from pediatric HD patients who had Hgb tests ordered for routine and/or clinical reasons. Hgb concentrations were read with the CRIT-LINE after 0.5 or 1 L of blood had been processed by HD in patients with a body weight of ≤20 or >20 kg, respectively. Ultrafiltration was kept at a minimum until the CRIT-LINE Hgb was read.

RESULTS

In total, 217 Hgb readings from 23 HD patients were analyzed. Results showed a statistically significant correlation between CRIT-LINE readings and laboratory Hgb measurements (r = 0.94, p < 0.0001) using Pearson correlation coefficients for well-distributed data. The mean Hgb levels measured by CRIT-LINE and the laboratory were 11.12 ± 1.63 and 11.31 ± 1.69 g/dL, respectively.

CONCLUSIONS

The CRIT-LINE monitor is an accurate instrument for monitoring Hgb levels in HD patients. Further studies will be needed to evaluate whether using CRIT-LINE Hgb levels to guide anemia management will improve the percentage of children with Hgb levels within target.

A novel approach to drug development in heart failure: towards personalized medicine

Evidence-based treatment has succeeded in improving clinical outcomes in heart failure. Nevertheless, morbidity, mortality, and the economic burden associated with the syndrome remain unsatisfactorily high. Most landmark heart failure studies included broad study populations, and thus current recommendations dictate standardized, universal therapy. While most patients included in recent trials benefit from this background treatment, exceeding this already significant gain has proven to be a challenge. The early identification of responders and nonresponders to treatment could result in improved therapeutic effectiveness, while reduction of unnecessary exposure may limit harmful and unpleasant side effects. In this review, we examine the potential value of currently available information on differential responses to heart failure therapy-a first step toward personalized medicine in the management of heart failure.

Timing of hemoconcentration during treatment of acute decompensated heart failure and subsequent survival: importance of sustained decongestion

OBJECTIVES

This study sought to determine if the timing of hemoconcentration influences associated survival.

BACKGROUND

Indicating a reduction in intravascular volume, hemoconcentration during the treatment of decompensated heart failure has been associated with reduced mortality. However, it is unclear if this survival advantage stems from the improved intravascular volume or if healthier patients are simply more responsive to diuretics. Rapid diuresis early in the hospitalization should similarly identify diuretic responsiveness, but hemoconcentration this early would not indicate euvolemia if extravascular fluid has not yet equilibrated.

METHODS

Consecutive admissions at a single center with a primary discharge diagnosis of heart failure were reviewed (N = 845). Hemoconcentration was defined as an increase in both hemoglobin and hematocrit levels, then further dichotomized into early or late hemoconcentration by using the midway point of the hospitalization.

RESULTS

Hemoconcentration occurred in 422 (49.9%) patients (41.5% early and 58.5% late). Patients with late versus early hemoconcentration had similar baseline characteristics, cumulative in-hospital loop diuretic administered, and worsening of renal function. However, patients with late hemoconcentration versus early hemoconcentration had higher average daily loop diuretic doses (p = 0.001), greater weight loss (p < 0.001), later transition to oral diuretics (p = 0.03), and shorter length of stay (p < 0.001). Late hemoconcentration conferred a significant survival advantage (hazard ratio: 0.74 [95% confidence interval: 0.59 to 0.93]; p = 0.009), whereas early hemoconcentration offered no significant mortality benefit (hazard ratio: 1.0 [95% confidence interval: 0.80 to 1.3]; p = 0.93) over no hemoconcentration.

CONCLUSIONS

Only hemoconcentration occurring late in the hospitalization was associated with improved survival. These results provide further support for the importance of achieving sustained decongestion during treatment of decompensated heart failure.

The Evaluation of Filtration Coefficients of Microvasculature for the Assessment of Fluid Status in Hemodialysis Patients

Purpose

Bioimpedance spectroscopy (BIS) is widely used to assess fluid status in hemodialysis (HD) patients. Our purpose is to evaluate filtration coefficients (Lpst) as an alternative test to assess fluid status by utilizing BIS as a reference test.

Methods

106 HD patients (determined group) were divided into two groups with (EX group: 53) or without excess fluid mass (ExF). ExF calculated from extracellular water and intracellular water measured by BIS. Multiple linear regression equation of Lpst was made using ExF (ExF/DW) and ultrafiltration rate (UFR/DW) to adjust Lpst (AdjLpst). The cut-off values of the tests for detection of EX were determined by receiver-operator characteristic curve analysis. Lpst, AdjLpst, serum atrial natriuretic peptide concentration (ANP), ultrasonically measured inferior vena cava diameter (IVCe/BSA), and blood volume change (ΔBV/TUF/DW) were examined. The detection abilities of these tests were evaluated in the distinct 61 patients (evaluated group).

Results

Patients of the EX group numbered 29 in the evaluated group. The correlation between AdjLpst and ExF/DW was the highest. The sensitivity of AdjLpst and specificity of Lpst were the highest. The specificity of AdjLpst was equivalent to that of Lpst. Unadjusted and adjusted odds ratios of AdjLpst were the higher (20.80, 95% CI, 5.61-77.10, 16.06, 95% CI 4.00-64.59, respectively) than those of the other tests.

Conclusions

AdjLpst can detect patients of the EX group more accurately than other tests. Because AdjLpst is related to plasma refilling, it may indicate removable fluid overload. AdjLpst in conjunction with BIS may contribute to more adequate fluid management.

Determinants and short-term reproducibility of relative plasma volume slopes during hemodialysis

BACKGROUND AND OBJECTIVES

Hypervolemia is a major cause of morbidity, in part because of the lack of well characterized diagnostic tests. The hypothesis was that relative plasma volume (RPV) slopes are influenced by ultrafiltration rate, directly associate with improvement in arterial oxygen saturation, and are reproducible.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

RPV slopes were measured on three consecutive hemodialysis sessions. Various relationships were tested using mixed models. Reproducibility was assessed by the intraclass correlation coefficient.

RESULTS

RPV slopes averaged 1.37 ± 1.45% per hour. The mean RPV slopes were steeper on the first dialysis of the week, which correlated with a higher ultrafiltration rate; RPV slope and ultrafiltration rate were directly related. Increasing ultrafiltration rate quartiles were associated with similar change in RPV in the first 1 hour of dialysis but steeper changes in RPV subsequently. A direct relationship emerged between increasing RPV slopes and increasing arterial oxygen saturation slopes. The intraclass correlation coefficient for the relative plasma volume slope was 0.77.

CONCLUSIONS

Although ultrafiltration rate is a major determinant of RPV slope, similar ultrafiltration rates are associated with varying RPV between individuals. Because RPV is associated with little change by ultrafiltration rate during the first 1 hour of dialysis, probing dry weight during the earlier part of dialysis may be safer. RPV slopes are physiologically meaningful, because they are associated with parallel changes in arterial oxygenation saturation slopes. RPV slopes are reproducible, and therefore, RPV may serve as a useful marker to judge changes in volume status within an individual.

Analyzing near-infrared scattering from human skin to monitor changes in hematocrit

Probing tissue with near-infrared radiation (NIR) simultaneously produces remitted fluorescence and Raman scattering (IE) plus Rayleigh∕Mie light scattering (EE) that noninvasively give chemical and physical information about the materials and objects within. We model tissue as a three-phase system: plasma and red blood cell (RBC) phases that are mobile and a static tissue phase. In vivo, any volume of tissue naturally experiences spatial and temporal fluctuations of blood plasma and RBC content. Plasma and RBC fractions may be discriminated from each other on the basis of their physical, chemical, and optical properties. Thus, IE and EE from NIR probing yield information about these fractions. Assuming there is no void volume in viable tissue, or that void volume is constant, changes in plasma and RBC volume fractions may be calculated from simultaneous measurements of the two observables, EE and IE. In a previously published analysis we showed the underlying phenomenology but did not provide an algorithm for calculating volume fractions from experimental data. Now, we present a simple analysis that allows monitoring of fluid fraction and hematocrit (Hct) changes by measuring IE and EE, and apply it to some experimental in vivo measurements.

Hypervolemia is associated with increased mortality among hemodialysis patients

Among chronic hemodialysis patients, 217 hospitalizations per 1000 patient-years are attributed to congestive heart failure; some are attributable to unrecognized hypervolemia. Hypervolemia can be detected by relative plasma volume (RPV) monitoring. The purpose of this study was to examine among 308 patients on long-term hemodialysis the value of slope of RPV compared with either ultrafiltration (UF) volume or UF rate index in determining all-cause mortality. RPV slopes were calculated by least-squares regression. These slopes were related to all-cause mortality in unadjusted and adjusted Cox proportional hazards models. Over a median follow-up of 30 months (interquartile range: 14 to 54 months) 96 patients (31%) died, yielding a crude mortality rate of 113/1000 patient-years. We found the following: (1) RPV slope measurements were of prognostic significance (hazard ratio of flatter slopes [>1.39%/h]: 1.72; P=0.01); (2) the UF volume alone was not prognostically informative (hazard ratio of higher UF volume [>2.7 L of dialysis]: 0.78; P=0.23); (3) the UF rate index alone was also not prognostically informative (hazard ratio of higher UF rate index [>8.4 mL/kg per hour]: 0.89; P=0.6); and (4) the prognostic relationship of RPV slope to mortality was independent of conventional and unconventional cardiovascular risk factors including the UF volume, UF rate, or UF volume per kilogram of postweight. RPV monitoring yields information that is prognostically important and independent of several risk factors including UF volume, aggressiveness of UF, and interdialytic ambulatory blood pressure. Its use to assess excess volume-related morbidity among chronic hemodialysis patients should be tested in randomized, controlled trials.

Potential effects of aggressive decongestion during the treatment of decompensated heart failure on renal function and survival

BACKGROUND

Overly aggressive diuresis leading to intravascular volume depletion has been proposed as a cause for worsening renal function during the treatment of decompensated heart failure. If diuresis occurs at a rate greater than extravascular fluid can refill the intravascular space, the concentration of such intravascular substances as hemoglobin and plasma proteins increases. We hypothesized that hemoconcentration would be associated with worsening renal function and possibly would provide insight into the relationship between aggressive decongestion and outcomes.

METHODS AND RESULTS

Subjects in the Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness trial limited data set with a baseline/discharge pair of hematocrit, albumin, or total protein values were included (336 patients). Baseline-to-discharge increases in these parameters were evaluated, and patients with >or=2 in the top tertile were considered to have evidence of hemoconcentration. The group experiencing hemoconcentration received higher doses of loop diuretics, lost more weight/fluid, and had greater reductions in filling pressures (P<0.05 for all). Hemoconcentration was strongly associated with worsening renal function (odds ratio, 5.3; P<0.001), whereas changes in right atrial pressure (P=0.36) and pulmonary capillary wedge pressure (P=0.53) were not. Patients with hemoconcentration had significantly lower 180-day mortality (hazard ratio, 0.31; P=0.013). This relationship persisted after adjustment for baseline characteristics (hazard ratio, 0.16; P=0.001).

CONCLUSIONS

Hemoconcentration is significantly associated with measures of aggressive fluid removal and deterioration in renal function. Despite this relationship, hemoconcentration is associated with substantially improved survival. These observations raise the question of whether aggressive decongestion, even in the setting of worsening renal function, can positively affect survival.

Optical measurement of blood hematocrit on medical tubing with dual wavelength and detector model

Blood hematocrit (Hct) is a clinically important index to detect death-dealing symptoms such as anemia and thrombosis, especially for patients with artificial heart, in dialysis and during open-heart surgery. Optical technology has been applied to monitor hematocrit noninvasively, continuously and conveniently, however, it was not well established for actual use. The purpose of this study is to develop an accurate and stable optical hematocrit measurement without any calibrations for device-mounting errors. To this end, we propose a theoretical method. In this method, disturbances are cancelled by using dual detector and optical path changes are calibrated by dual wavelength so that we can measure hematocrit without calibrations of these. Based on the method, a measurement unit that has two LEDs (805/1300[nm]) and four photo detectors was developed. Then, we performed experiments with 38 blood samples from five bovines' blood (Hct: 19-55%). These blood samples were circulated in a mock-up circuit by a blood pump. During the experiment, we measured hematocrit on medical tubing with the developed measurement system. As a result, we could measure hematocrit within 1.7 Hct% mean errors for 38 blood samples without any calibrations. The result indicates that the proposed method is applicable for hematocrit measurement on medical tube in enough small error. We found this proposed method is effective for developments of clinically workable hematocrit measurement/monitoring system.

Use of 12x/month haemoglobin monitoring with a computer algorithm reduces haemoglobin variability

BACKGROUND

Haemoglobin variability may be associated with increased death. Frequent haemoglobin monitoring may allow earlier detection of trends in haemoglobin slopes, alerting staff to intercurrent events. The more frequent haemoglobin values may provide early evidence of response to erythropoietin (EPO) doses, and allow more appropriate anaemia management. Our objective is to assess whether frequent haemoglobin monitoring data (12x/month) using a computer algorithm (AMIE, Leeds, UK) will reduce haemoglobin variability compared with 1x/month monitoring.

METHODS

We performed an observational case-control study of 44 unselected patients, comprising one dialysis facility measuring Crit-Line haemoglobin, lab haemoglobin, standard deviation of residuals as surrogate of haemoglobin variability and EPO dosing.

RESULTS

Haemoglobin variability and 'percent in target haemoglobin range' significantly improved with 12x/month haemoglobin results using a computer algorithm. There was also a non-significant trend toward for lower EPO doses.

CONCLUSION

Use of a computer algorithm to analyse 12x/month haemoglobin values provides early evidence of haemoglobin trends and allows more appropriate anaemia management, with decreased haemoglobin variability, lower EPO doses and more patients achieving target haemoglobin.

Relative plasma volume monitoring during hemodialysis AIDS the assessment of dry weight

Among hemodialysis patients, the assessment of dry weight remains a matter of clinical judgment because tests to assess dry weight have not been validated. The objective of this study was to evaluate and validate relative plasma volume (RPV) monitoring as a marker of dry weight. We performed RPV monitoring using the Crit-Line monitor at baseline and at 8 weeks in 150 patients participating in the Dry-Weight Reduction in Hypertensive Hemodialysis Patients Trial. The intervention group of 100 patients had dry weight probed, whereas 50 patients served as time controls. RPV slopes were defined as flat when they were less than the median (1.33% per hour) at the baseline visit. Among predominantly (87%) black hemodialysis patients, we found that flat RPV slopes suggest a volume-overloaded state for the following reasons: (1) probing dry weight in these patients led to steeper slopes; (2) those with flatter slopes at baseline had greater weight loss; (3) both baseline RPV slopes and the intensity of weight loss were found to be important for subsequent change in RPV slopes; and, most importantly, (4) RPV slopes predicted the subsequent reduction in interdialytic ambulatory systolic blood pressure. Those with the flattest slopes had the greatest decline in blood pressure on probing dry weight. Both baseline RPV slopes and the change in RPV slopes were important for subsequent changes in ambulatory systolic blood pressure. We conclude that RPV slope monitoring is a valid method to assess dry weight among hypertensive hemodialysis patients.

Estimation of indocyanine green concentration in blood from fluorescence emission: application to hemodynamic assessment during hemodialysis

There is considerable interest in assessing cardiovascular function noninvasively in patients receiving hemodialysis. A possible approach is to measure the blood concentration of bolus-injected indocyanine green dye and to apply the dye-dilution method for estimating cardiac output and blood volume. Blood ICG concentration can be derived from a measurement of the ICG fluorescence through the dialysis tubing if a simple and unique calibration relationship can be established between transmural fluorescence intensity and blood ICG concentration. We investigated this relationship using Monte Carlo simulations of light transport in blood with varying hematocrit and ICG concentrations and performed empiric measurements of optical absorption and ICG fluorescence emission to confirm our findings. The ICG fluorescence intensity measured at the blood surface, as well as the light intensity remitted by the blood, varied as hematocrit changes modified the absorption and scattering characteristics of the blood. Calibration relationships were developed between fluorescence intensity and ICG concentration that accounted for hematocrit changes. Combining the backreflected fluorescence and the reflected light measured near the point of illumination provided optimal signal intensity, linearity, and robustness to hematocrit changes. These results provide a basis for developing a noninvasive approach to derive optically circulating blood ICG concentration in hemodialysis circuits.

Blood volume monitoring to adjust dry weight in hypertensive pediatric hemodialysis patients

The aim of this study was to adjust dry weight by short-term blood volume monitoring (BVM)-guided ultrafiltration and evaluate the effects of optimizing dry weight on blood pressure (BP) control and intradialytic symptoms (IDS) in a group of hypertensive hemodialysis (HD) patients. The study was performed in four sequential phases, each of which lasted for 1 week, on nine hypertensive HD patients (six girls, age 16.9 +/- 3.1 years). In phase I, patients were observed by BVM. In phase II, BVM was used to guide ultrafiltration to adjust dry weight. Antihypertensive drugs were gradually tapered or withheld in phase III, when the patients were hypotensive and/or their IDS increased. In phase IV, this particular weight was maintained without any intervention. Pre- and post-HD body weight, pre-HD, post-HD, 30 min after HD casual BP values, and IDS in each HD session were recorded. The BP was also assessed by 44-h ambulatory BP monitoring (ABPM), which is an ideal method to determine BP changes throughout the interdialytic period at the beginning of phase I and at the end of phase IV. There was a decrease in mean dry weight, all casual systolic BPs, and systolic/diastolic ABPM at the end of the study (all p < or = 0.05). Antihypertensive drugs were stopped in five patients and reduced in two during phase III of the study. The IDS was more frequent (36%) in phase IV than in phase I (16%); however, this increase did not reach statistical significance. The results of this study suggest that short-term BVM guided-ultrafiltration may be a useful tool to diagnose volume overload and to adjust dry weight and, consequently, to achieve a better control of BP in pediatric HD patients.

Diagnostic utility of blood volume monitoring in hemodialysis patients

BACKGROUND

Assessment of volume state is difficult in hemodialysis patients. Whether continuous blood volume monitoring can improve the assessment of volume state is unclear.

STUDY DESIGN

Diagnostic test study.

SETTINGS & PARTICIPANTS

Asymptomatic long-term hemodialysis patients (n = 150) in 4 university-affiliated hemodialysis units.

INDEX TESTS

Ultrafiltration rate (UFR) divided by postdialysis weight (UFR index), slopes of relative blood volume (RBV), RBV slope corrected for UFR and weight (volume index).

REFERENCE TESTS

Dialysis-related symptoms and echocardiographic signs of volume excess and volume depletion, assessed by using inferior vena cava (IVC) diameter after dialysis and its collapse on inspiration. Volume excess was defined as values in the upper third of IVC diameter or lower third of IVC collapse on inspiration. Volume depletion was defined as values in the lower third of IVC diameter or upper third of IVC collapse on inspiration.

RESULTS

Mean UFR was 8.3 +/- 3.8 (SD) mL/h/kg. Mean RBV slope was -2.32% +/- 1.50%/h. Mean volume index was -0.25% +/- 0.17%/h/mL/h ultrafiltration/kg. Volume index provided the best fit of observed RBV slopes. Volume index was related to dizziness, the need to decrease UFR, and placement in Trendelenburg position. RBV and volume index, but not UFR index, were related to echocardiographic markers of volume excess and depletion. Areas under the receiver operating characteristic curve to predict volume excess were 0.48 (95% confidence interval [CI], 0.33 to 0.63) for UFR index, 0.71 (95% CI, 0.60 to 0.83) for RBV slope, and 0.73 (95% CI, 0.59 to 0.86) for volume index. Areas under the receiver operating characteristic curve to predict volume depletion were 0.56 (95% CI, 0.38 to 0.74) for UFR index, 0.55 (95% CI, 0.38 to 0.72) for RBV slope, and 0.62 (95% CI, 0.48 to 0.76) for volume index.

LIMITATIONS

Dialysis-related symptoms and echocardiographic findings are not validated measures of volume. Our results were not adjusted for demographic or clinical characteristics; performance characteristics of the indices may differ across populations.

CONCLUSIONS

Volume index appears to be a novel marker of volume, but requires validation studies, and its utility needs to be tested in clinical trials.

Physiological changes during hemodialysis in patients with intradialysis hypertension

Intradialysis hypertension is a frustrating complication among hemodialysis (HD) patients. This study was conducted to investigate the physiological changes during intradialytic hypertension. The beat-to-beat continuous heart rate, hematocrit (Hct) changes during HD, serum levels of nitric oxide, plasma levels of catecholamine, renin, endothelin (ET-1), cardiac output (CO), and peripheral vascular resistance (PVR) were measured before and after HD in patients prone to develop intradialysis hypertension (n = 30) and from age, sex-matched control HD subjects (n = 30). It was found that the baseline values of Hct, serum levels of nitric oxide, plasma levels of catecholamine, renin, and ET-1, CO, PVR, and power index (low frequency/high frequency ratios) of heart rate variability were not significantly different between the patients and control subjects. In the hypertension-prone group, the plasma levels of catecholamine, renin, and the serial measurements of power index, did not show significant changes. However, the patients showed a significant elevation of systemic vascular resistance (56.8 +/- 9.2% vs 17.7 +/- 9.5; P < 0.05), ET-1 (510.9 +/- 43.3 vs 276.7 +/- 30.1 pg/ml; P < 0.05) and a significant decrease of nitric oxide (NO)/ET-1 balance (0.018 +/- 0.003 vs 0.034 +/- 0.005; P < 0.05) at the end of HD compared with the control patients. It was found that the physiological changes in intradialysis hypertension patients were characterized by inappropriately increased PVR through mechanisms that did not involve sympathetic stimulation or renin activation but might be related with altered NO/ET-1 balance.

Non-invasive Monitoring of Hemodynamic Changes During Hemodialysis by the Use of a Newly Developed Admittance Cardiograph

Only a little information is available for the evaluation of the complex hemodynamic changes that occur during hemodialysis. Recently, we developed the transthoracic electrical admittance cardiograph for repeated measurements of cardiac output, and monitored hemodynamic changes during hemodialysis by the use of this device. We measured cardiovascular hemodynamic and autonomic parameters non-invasively during 210 min of hemodialysis in 19 chronic hemodialysis patients who for more than 2 months had no history of cardiovascular collapses during hemodialysis. Blood pressure was monitored every 10 min using a cuff-oscillometric device (TM-2425; A & D, Tokyo, Japan). Cardiac output was monitored on a beat-by-beat basis by a newly developed electrical admittance cardiograph (NICOVIEW PA1100; NEC, Tokyo, Japan). Electrocardiogram R-R intervals were also monitored by the TM-2425. Power spectral analysis of R-R intervals was performed to obtain the low-frequency (LF; 0.05-0.15 Hz) and the high-frequency (HF; 0.15-0.40 Hz) components based on an autoregressive model. Change in circulatory blood volume was also monitored by a CRIT-LINE (In-Line Diagnostics, Riverdale, UT, USA). Although blood volume declined significantly by 16.3 +/- 1.4% (mean +/- SE) during hemodialysis (P < 0.0001), mean blood pressure did not change significantly. Heart rate increased significantly from the initial values of 76.3 +/- 3.4-86.4 +/- 4.9 beats/min (P = 0.03). Cardiac output and stroke volume decreased significantly from 4.47 +/- 0.30 to 2.91 +/- 0.32 L/min (P < 0.0001), and from 57.0 +/- 3.7 to 33.9 +/- 3.1 mL (P < 0.0001), respectively. Total peripheral vascular resistance increased significantly from 1940 +/- 146 to 3117 +/- 280 dyne x s x cm(5) (P < 0.0001). The LF component did not show significant change, while the HF component decreased significantly (P = 0.007), and the LF/HF ratio increased significantly (P = 0.03). These results suggest that a reduction in parasympathetic nerve activity and sympathetic nerve activation and a marked increase in total peripheral vascular resistance are responsible for the maintenance of blood pressure during hemodialysis in chronic hemodialysis patients. The admittance cardiograph seems to be one of the best options for serial measurements of cardiac output.

Methods of assessment of volume status and intercompartmental fluid shifts in hemodialysis patients: implications in clinical practice

Determining dry weight and assessing extracellular fluid volume in hemodialysis (HD) patients is one of the greatest challenges to practicing nephrologists. The clinical examination has limited accuracy, so different strategies have been investigated to aid in this evaluation. Biochemical markers of volume overload (ANP, BNP, cGMP) are fraught with excessive variability and poor correlation with volume status. Inferior vena cava ultrasound is effective, but cumbersome and costly. Bioimpedance measurements of intra- and extracellular water have significant shortcomings when used as isolated measurements, but can be useful in following trends over time and have been shown to improve intradialytic symptoms and blood pressure control. Continuous blood volume monitoring is helpful in preventing intradialytic hypotension and may help identify patients who are volume overloaded and need increased ultrafiltration. In this review we discuss these different techniques and other developments in the evaluation of dry weight and volume status, which may enhance our ability to improve patient stability and well-being during HD sessions.

Continuous haematocrit monitoring during intradialytic hypotension: precipitous decline in plasma refill rates

BACKGROUND

Intradialytic hypotension (IDH) during ultrafiltration remains a major source of haemodialysis related morbidity, despite technological advances including continuous haematocrit monitoring and automated blood volume controlled dialysis machines. We hypothesized that studying the relationship between ultrafiltration rate and plasma refill rate (UFR, PRR) before and during IDH would provide insight into its mechanism and possible prevention.

METHODS

We retrospectively identified 17 patients (mean age 50 years) with IDH treated solely by turning off the ultrafiltration, none having received hypertonic saline, mannitol or albumin. All patients had archived data for continuous haematocrits, UFR, ultrafiltration goal, vital signs and symptoms. We used the Crit-Line III optical haematocrit monitor to calculate the PRR for intervals preceding and during IDH.

RESULTS

Prior to IDH the PRR was 1360+/-550 ml/h; which was less than the UFR of 1471+/-602 ml/h and was associated with a 4.4% rise in haematocrit. However, during IDH the PRR was dramatically lower (P<0.001): only 242+/-151 ml/h. The PRR was not correlated (P>0.05) with the absolute, per cent change or rate of rise in haematocrit, UFR, ultrafiltration goal or heart rate.

CONCLUSIONS

On-line haematocrit monitoring allows for the calculation of plasma volume changes, UFR and PRR, and the mismatch in those rates helps explain the physiology of hypotension episodes. The precipitous fall in PRR during sudden IDH supports activation of the cardiodepressor Bezold-Jarisch reflex. As both the UFR and PRR variables can change during a single dialysis session, this supports the use of devices with automated continuous adjustments of the UFR and suggests additional profiling methodologies.

Developments in online monitoring of haemodialysis patients: towards global assessment of dialysis adequacy

PURPOSE OF REVIEW

Online monitoring of haemodialysis provides more detailed and more immediate measurement of parameters currently assessed during haemodialysis. It can also assess novel variables that are not routinely measured and could intensively monitor the haemodynamic response to dialysis. In an era of expanding numbers of increasingly dependent patients on dialysis, the ability to provide intensive and extensive monitoring of haemodialysis is a boon. The technology available to do this is rapidly becoming more sophisticated, more widely available and more diverse than ever before.

RECENT FINDINGS

Adequacy of urea removal is of crucial importance to mortality on haemodialysis, and online monitoring of urea removal is now achievable using a number of different methods. Some of these methods also measure sodium flux, allowing precise monitoring of sodium balance. Haemodynamic disturbance can be assessed using relative blood volume monitoring equipment, or more directly with non-invasive pulse-wave analysis giving a continuous blood pressure reading. The attributes of each of the separate technologies involved are examined.

SUMMARY

Online monitoring of a variety of pertinent parameters during haemodialysis provides an array of tools that are steadily being incorporated into routine clinical practice. Research is also benefiting from novel insights into the process of haemodialysis provided by this technology.

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.

Warning of high-flux hemodialysis

In order to estimate the influence of flux on plasma refilling during hemodialysis (HD), prospective crossover studies were performed in 10 HD patients with low-flux and high-flux dialyzers. Hematocrit was continuously monitored to assess changes in blood volume. In addition, plasma osmolarity and total protein concentration were measured. Intradialytic reductions in body weight (-5 +/- 1 vs -5 +/- 1%) and plasma osmolarity (-5 +/- 1 vs -5 +/- 1%) were similar in both conditions. Although mean blood pressure remained unchanged in either state, the decrease in blood volume was larger in high-flux HD (-13 +/- 2 vs -10 +/- 2%, p<0.05). In spite of greater contraction in blood volume during high-flux HD, total proteins were increased equally between low-flux and high-flux HD (11 +/- 4 vs 11 +/- 4%). Our data that although high-flux HD failed to induce significant drops in blood pressure, it elicited greater magnitude of decreases in blood volume, implicate the judicious application of high-flux HD.

Pathophysiology of dialysis hypotension: an update

Dialysis hypotension occurs because a large volume of blood water and solutes are removed over a short period of time, overwhelming normal compensatory mechanisms, including plasma refilling and reduction of venous capacity, due to reduction of pressure transmission to veins. In some patients, seemingly paradoxical and inappropriate reduction of sympathetic tone may occur, causing reduction of arteriolar resistance, increased transmission of pressure to veins, and corresponding increase in venous capacity. Increased sequestration of blood in veins under conditions of hypovolemia reduces cardiac filling, cardiac output, and, ultimately, blood pressure. Adenosine release due to tissue ischemia may participate in reducing norepinephrine release locally, and activation of the Bezold-Jarisch reflex, perhaps in patients with certain but as yet undefined cardiac pathology, may be responsible for sudden dialysis hypotension. Patients with diastolic dysfunction may be more sensitive to the effects of reduced cardiac filling. The ultimate solution is reducing the ultrafiltration rate by use of longer dialysis sessions, more frequent dialysis, or reduction in salt intake. Increasing dialysis solution sodium chloride levels helps maintain blood volume and refilling but ultimately increases thirst and interdialytic weight gain, with a possible adverse effect on hypertension. Blood volume monitoring with ultrafiltration or dialysis solution sodium feedback loops are promising new strategies. Maintaining tissue oxygenation via an adequate blood hemoglobin level seems to be important. Use of adenosine antagonists remains experimental. Given the importance of sympathetic withdrawal, the use of pharmacologic sympathetic agonists is theoretically an attractive therapeutic strategy.

Clinical case-based approach to understanding intradialytic hypotension

The approach to end-stage renal disease (ESRD) patients who develop intradialytic hypotension (IDH) encompasses an understanding of the pathophysiology, appropriate dialysis prescription modification, application of newer pharmacologic therapies, and development of strategies for prevention. Patients should have a "minimal data set" as part of their predialysis assessment. This information is critical to prescription modifications that may help decrease the risk for IDH. Individuals at "high risk" for IDH should be kept to a "safe zone" for dialysis ultrafiltration (</=3% of body weight). Specific maneuvers that may decrease the risk for IDH include adjustment of the dialysate sodium or calcium concentration and dialysate temperature. The first priority for patients developing IDH should be the stabilization of the blood pressure and improvement in the patient's symptomology. Pharmacologic intervention should be considered for patients who require repeat interventions for IDH. "At-risk" patients with a strong cardiac history should undergo an assessment of their cardiovascular status if IDH episodes occur. The use of pharmacologic therapy, ie, midodrine, alone or in combination with prescription modification, can be helpful in decreasing interventions required for IDH. Noncompliance and high interdialytic weight gain in the setting of left ventricular hypertrophy (LVH) and diastolic dysfunction can increase the risk of IDH. Assessment of antihypertensive medications should be performed on a regular basis to determine the correct dosing schedule for patients with hypertension who develop IDH. Coronary flow reserve may be compromised in patients with LVH, adding to the risk for perfusion injury with low blood pressure. Increasing the dialysate calcium concentration may decrease the incidence of arrhythmogenicity in certain patients. Patients with low body temperature may benefit most from cool dialysate. Unit personnel should be aware of the potential link between hypotension and the increased relative risk for death in ESRD patients. Clinical training sessions on IDH risk recognition and appropriate treatment should be implemented within the dialysis unit. Because repeated bouts of IDH can be disruptive to the smooth efficiency of unit operations, attention to prevention as well as acute intervention of IDH is important. Preventive strategies can be developed in each unit to decrease the number of future IDH events. Considering the importance of hypotension in overall patient survival, attention to identifying the percentage of patients in each unit who experience IDH and/or who present with low blood pressure (systolic <110 mm Hg) should be tracked as a quality assurance initiative.

Energy transfer is the single most important factor for the difference in vascular response between isolated ultrafiltration and hemodialysis

Differences in vascular reactivity between isolated ultrafiltration (i-UF) and hemodialysis (UF + HD) have been attributed to various factors, including differences in core temperature (CT) and energy transfer (ET). However, the relative importance of these thermal factors is not known. The aim of this study was to elucidate to what extent differences in ET are responsible for the divergent vascular response between i-UF and UF + HD. During four different dialysis treatments in 15 patients, four measurements were performed that consisted of 1 h of i-UF, UF + HD at a dialysate temperature (T(d)) of 37.5 degrees C (UF + HD(37.5)), UF + HD at T(d) 35.5 degrees C (UF + HD(35.5)), and UF + HD with a similar ET as during i-UF(UF + HD(ET-set)). The UF rate in all sessions was 1 L/h. CT ( degrees C) decreased significantly during i-UF and UF + HD(ET-set) (P < 0.05), increased significantly during UF + HD(37.5) (P < 0.05), and remained unchanged during UF + HD(35. 5) (NS). Forearm vascular reactivity increased significantly during i-UF, UF + HD(ET-set), and UF + HD(35.5) (P < 0.05), but not during UF + HD(37.5) (NS). Venous tone increased significantly during i-UF, UF + HD(35.5), and UF + HD(ET-set) (P < 0.05), and decreased significantly during UF + HD(37.5) (P < 0.05). When i-UF and UF + HD are matched for ET, all differences in vascular response disappear, showing that differences in ET are the single most important factor for the observed difference in vascular response between i-UF and UF + HD. In contrast to UF + HD(37.5), vascular reactivity was improved when the increase in CT was prevented during UF + HD(35.5) and appeared to increase more when CT was lowered. Preventing the increase in CT during UF + HD appears to be mandatory for optimization of hemodynamic stability during dialysis.

Effect of intravenous fluids on blood pressure course during hemodialysis in hypotensive-prone patients

Hypertonic and hyperoncotic solutions are generally used as acute treatment for symptomatic hypotension during dialysis. Administration of hydroxyethylstarch (HES) was recently shown to be an effective substitution fluid in preserving blood volume (BV) and systolic BP (SBP) in a group of stable dialysis patients during dialysis. In this study, in nine cardiac-compromised dialysis patients with frequent symptomatic hypotensive episodes, the efficacy of three fluids (hypertonic saline [3%], albumin [20%], and HES [10%]) was assessed during three treatment sessions with combined ultrafiltration and hemodialysis, which only differed in the type of fluid administered intravenously. Changes in SBP and relative BV were compared. Fluids were given when SBP was less than 100 mmHg or when the decrease in SBP was more than 25 mmHg versus the start of the treatment. The ultrafiltration was continued at the same rate. When comparing SBP at the end of the dialysis session (t = end) with that at the time of infusion (t = iv), SBP decreased with saline, increased with albumin, and increased significantly with HES. The change in SBP in t = end versus t = iv was significantly greater when using saline compared with HES, and tended to decrease more when using saline compared with albumin (P = 0.09). Between albumin and HES there were no significant differences. BV decreased significantly (t = end) versus baseline (t = 0) during ultrafiltration and hemodialysis in all three treatment sessions. The decrease was significantly higher when using saline compared with albumin and saline compared with HES. Between albumin and HES there were no significant differences. When the values at t = end were compared with those at t = iv, BV decreased, although not significantly, with saline and albumin, but remained unchanged with HES. It is concluded that HES is an effective fluid in maintaining SBP and preserving BV in hypotensive-prone dialysis patients, comparable to albumin but superior to hypertonic saline.

The effects of peracetic acid-hydrogen peroxide reprocessing on dialyzer solute and water permeability

We characterized the effects of peracetic acid-hydrogen peroxide (PAHP) reprocessing on hemodialyzer permeability to water and solutes of various molecular weights and compared these effects within and between dialyzers. An aqueous-based solution containing urea, creatinine, vancomycin, inulin, myoglobin, and albumin was dialyzed for 60 minutes with a hemodialyzer after undergoing 0, 1 , 5, 10, and 15 reuse cycles. Solute clearance, sieving coefficient (SC), and ultrafiltration coefficient were determined. We found that PAHP reprocessing significantly decreased water and solute removal (urea, creatinine, vancomycin, inulin) by cellulose triacetate dialyzers (CT190) over 15 reuses (p<0.05) but did not affect the permeability of polysulfone dialyzers (F80A). Inulin removal was significantly lower for F80A than for CT190 (p<0.0001 and p<0.001 for clearance and SC values, respectively). Myoglobin and albumin removal by CT190 significantly decreased over 15 reuses (p<0.05), but no protein was detected in dialysate or ultrafiltrate at any reuse number for F80A. Reprocessing with PAHP alters dialyzer permeability; the effect is more pronounced for the CT190 dialyzer, but removal of solutes with molecular weight above 1500 Da is significantly lower with F80A dialyzers than with CT190. These changes in dialyzer permeability should be considered when determining optimal reuse procedures.

Effect of intravenous saline, albumin, or hydroxyethylstarch on blood volume during combined ultrafiltration and hemodialysis

It is generally advocated to use saline or albumin infusions during symptomatic hypotension during dialysis. However, because of their side effects and/or costs, they are of limited use. Hydroxyethylstarch (HES), a synthetic colloid with a long-standing volume effect, is used in the management of hypovolemia. In this study, the efficacy of three fluids (isotonic saline [0.9%], albumin [20%], and HES [10%]) was assessed during three treatment sessions with combined ultrafiltration and hemodialysis, which differed in the type of fluid given intravenously. Changes in relative blood volume (BV), systolic BP (SBP), and vascular reactivity (venous tone [VT]) were compared. An intravenous infusion of 100 ml of fluid was given when the decrease in BV versus baseline was more than 10% as measured by a continuous optical reflection method. The ultrafiltration was continued. BV decreased significantly versus baseline independent of the intravenous fluid administration in all three treatment sessions. However, when we compared BV values at the end of the dialysis session with those at the time of infusion, BV continued to decrease significantly with saline (change in BV -4.56 +/- 2.75%; P < 0.05) and albumin (change in BV -2.13 +/- 2.51%; P < 0.05), but not with HES (change in BV -0.15 +/- 2.17%; NS). Between albumin and HES there were no significant differences in changes in BV (NS), whereas between HES and saline (P < 0.05) and between albumin and saline (P < 0.05) the differences in BV changes were significant. SBP remained unchanged within each session. Although SBP tended to decrease more with saline compared to albumin and HES, the difference was not significant. The higher decrease in BV and SBP with saline was counterbalanced by a significantly higher increase in VT, while VT remained unchanged in the other two sessions. It is concluded that HES is a promising fluid in preserving blood volume, comparable to albumin, but superior to saline.