Measurement of Blood Volume During Hemodialysis is a Useful Tool to Achieve Safely Adequate Dry Weight by Enhanced Ultrafiltration

A physiologically based model of vascular refilling during ultrafiltration in hemodialysis

An assessment of fluid status can be obtained by monitoring relative blood volume (RBV) during hemodialysis (HD) treatment. The dynamics of RBV is determined by fluid removal from the intravascular compartment by ultrafiltration (UF) and vascular refill from the interstitium. To characterize this dynamics, a two-compartment model describing the short-term dynamics of vascular refilling and UF is developed. Fluid movement between the compartments is governed by lymphatic and microvascular fluid shifts. Further, protein flux is described by convection, diffusion and the lymphatic protein flux. Patient specific parameters are identified based on hematocrit (Hct) measurements by the Crit-Line monitor (CLM). Different measurement frequencies and UF profiles are compared to determine data fidelity and influence on the quality of parameter estimates. This relevant information can be used to assess the (patho)physiological status of hemodialysis patients and could aid in individualizing therapy.

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.

A novel bioimpedance technique to monitor fluid volume state during hemodialysis treatment

Bioimpedance spectroscopy is a potential candidate for monitoring of body fluids during dialysis. In this article, the suitability of knee-to-knee (KK) as an alternative to wrist-to-ankle (WA) bioimpedance spectroscopy measurements during dialysis is evaluated. Measurements on eight patients (22 dialysis sessions) showed a good correlation between the change in extracellular resistance (Re) in KK and WA measurements. A deeper analysis indicated that the change in Re normalized for ultrafiltrated volume [DeltaRe/UFV (%/L)] depends on the characteristics of the patient: clinically stable patients [with a presumed lower extracellular fluid - total body volume (VB) relationship] show a higher DeltaRe/UFV (%/L) mean +/- standard deviation (WA: 8.90 +/- 1.9 and KK: 8.29 +/- 2.2) than clinically unstable patients with pitting peripheral edema (WA: 2.10 +/- 0.8 and KK: 2.07 +/- 0.2). Simulations based on bioimpedance equations considering Hanai theory confirm the results. The KK method, especially in combination with proper use of the introduced DeltaRe/UFV (%/L) normalization could possibly offer new options for comfortable online monitoring and the evaluation of fluid volume state during dialysis.

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.

Influence of Ultrafiltration Volume on Blood Volume Changes During Hemodialysis as Observed in Day-of-the-Week Analysis of Hemodialysis Sessions

Monitoring of relative blood volume changes (DeltaRBV) has been propagated for the prevention of hemodialysis hypotension. Although the influence of ultrafiltration volume on DeltaRBV is well-known, there is no mention in the literature that DeltaRBV results should be interpreted differently for the first, second, or third hemodialysis session of the week. To elucidate whether DeltaRBV and its derivative, DeltaRBV normalized for ultrafiltration volume (DeltaRBV/ultrafiltration ratio), vary systematically over the week, we separately analyzed these parameters for the first, second, and third hemodialysis session of the week in 13 chronic hemodialysis patients over a 17-week period. As expected, mean (+/-SD) ultrafiltration volume was significantly (p < 0.001) higher during the first session than during the second and third hemodialysis sessions (3163 +/- 615, 2622 +/- 674 and 2607 +/- 638 ml, respectively). DeltaRBV was significantly (p < 0.01) more negative at the first session than at the second and third hemodialysis sessions (-10.1 +/- 2.7, -9.3 +/- 3.0 and -9.3 +/- 3.1%, respectively). The DeltaRBV/ultrafiltration ratio was significantly (p < 0.01) less negative at the first session than at the second and third hemodialysis sessions (-3.2 +/- 0.6, -3.5 +/- 0.8 and -3.6 +/- 0.6%/l, respectively). In conclusion, DeltaRBV and the DeltaRBV/ultrafiltration ratio differ systematically between the first and other hemodialysis sessions in patients on a thrice-weekly hemodialysis schedule, most likely as a result of different ultrafiltration volumes.

Evaluation of Markers to Estimate Volume Status in Hemodialysis Patients: Atrial Natriuretic Peptide, Inferior Vena Cava Diameter, Blood Volume Changes and Filtration Coefficients of Microvasculature

Relationships among five markers of volume status - cardio-thoracic ratio (CTR), atrial natriuretic peptide (ANP), inferior vena cava diameter at quiet expiration (IVCe), blood volume change (Delta BV/TUF) during ultrafiltration and filtration coefficients of microvasculature (Lpst) - were investigated. Fifty stable hemodialysis patients were enrolled. The CTR was measured before hemodialysis (HD), and ultrasonic measurement of IVCe and sample collection for ANP were performed shortly after HD. Lpst and Delta BV/TUF were calculated using a CRIT-LINE monitor. Overhydrated patients determined by each marker (OVERctr, OVERivc, OVERanp, OVERlp and OVERbv) were compared. The agreement of volume status determined by each marker was assessed by kappa value, and the sensitivity and specificity of each marker to distinguish overhydrated patients were analyzed by a receiver-operating characteristic (ROC) curve. IVCe, ANP, Delta BV/TUF and Lpst, significantly correlated with each other. The correlation coefficients of Lpst with IVCe, ANP and Delta BV/TUF were higher than the others. The kappa value between ANP and Lpst was the highest. OVERanp was the highest, then OVERlp, OVERivc and OVERbv, in this order. The OVERlp and OVERivc patients were completely included in OVERanp. All patients, except one OVERbv patient, were included in OVERlp. The relatively high distinguishing ability of Lpst was demonstrated by ROC analysis. These results suggest that the determination of overhydration solely by ANP was an overestimation and by Delta BV/TUF was an underestimation. The relatively high correlation coefficients of Lpst with other markers, as well as its distinguishing ability, suggest that Lpst fluctuates in close relation to other markers.

Mortality risk for patients receiving hemodiafiltration versus hemodialysis: European results from the DOPPS

Hemodiafiltration (HDF) is used sporadically for renal replacement therapy in Europe but not in the US. Characteristics and outcomes were compared for patients receiving HDF versus hemodialysis (HD) in five European countries in the Dialysis Outcomes and Practice Patterns Study. The study followed 2165 patients from 1998 to 2001, stratified into four groups: low- and high-flux HD, and low- and high-efficiency HDF. Patient characteristics including age, sex, 14 comorbid conditions, and time on dialysis were compared between each group using multivariate logistic regression. Cox proportional hazards regression assessed adjusted differences in mortality risk. Prevalence of HDF ranged from 1.8% in Spain to 20.1% in Italy. Compared to low-flux HD, patients receiving low-efficiency HDF had significantly longer average duration of end-stage renal disease (7.0 versus 4.7 years), more history of cancer (15.4 versus 8.7%), and lower phosphorus (5.3 versus 5.6 mg/dl); patients receiving high-efficiency HDF had significantly more lung disease (15.5 versus 10.2%) and received a higher single-pool Kt/V (1.44 versus 1.35). High-efficiency HDF patients had lower crude mortality rates than low-flux HD patients. After adjustment, high-efficiency HDF patients had a significant 35% lower mortality risk than those receiving low-flux HD (relative risk=0.65, P=0.01). These observational results suggest that HDF may improve patient survival independently of its higher dialysis dose. Owing to possible selection bias, the potential benefits of HDF must be tested by controlled clinical trials before recommendations can be made for clinical practice.

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

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