Relative Blood Volume Monitoring Research Articles

Scattering effect for relative blood volume monitoring during hemodialysis

The long-term survival rate of hemodialysis patients is limited by hemodialysis-related complications, which are attributed to the inappropriate level of relative blood volume (RBV) after treatment. For the conventional optical monitoring methods, the RBV is usually overestimated, especially when the RBV varies in a wide range. Here, we find that the scattering effect of blood on incident light is the dominant factor of nonlinear measurement errors according to the numerical simulation results. Then a computational model considering both the absorption and scattering effect of blood is proposed and applied to a relative blood volume monitoring system (RBVMS). Finally, the RBVMS is validated in a commercial hemodialysis machine, showing a relatively low measurement error of 6.9 %. This result indicates the potential of the system for RBV monitoring during hemodialysis.

Use of Relative Blood Volume Monitoring to Reduce Intradialytic Hypotension in Hospitalized Patients Receiving Dialysis

Use of Relative Blood Volume Monitoring to Reduce Intradialytic Hypotension in Hospitalized Patients Receiving Dialysis

Dynamics of vascular refilling in extended nocturnal hemodialysis.

Long dialysis treatments are generally assumed to mitigate the ultrafiltration (UF) induced volume perturbation and to improve vascular refilling because of reduced UF rates and sufficient time for volume re-equilibration. The time course of vascular refilling was therefore examined during extended nocturnal dialysis. For each hour of dialysis, vascular refilling volume was calculated from the absolute blood volume changes and UF volume removed. Absolute blood volume was estimated by indicator dilution at the beginning of dialysis and then tracked with a relative blood volume monitor. The refilling fraction was defined as the ratio of refilling volume to UF volume. Ten stable chronic hemodialysis (HD) patients were studied during extended (7h) nocturnal treatment sessions. Specific UF rate was 4.8 ± 1.8ml/kg/h. In the 1 h, refilling volume amounted to only 23% of UF volume. Thereafter, refilling fraction steeply increased and reached maximum values in the 2, 3 and 4 h at about mean 90% (91.5%, 88.7%, and 91.1% respectively). From the 5 h on, refilling volume decreased (5 h 81.3%, 6 h 72.5%, 7 h 70.0% of UF volume). Cumulative refilling reached 73.6% of UF volume after 4h of treatment time. This did not change during the further course of HD. Cumulative refilling volume showed a strong correlation (r=0.94; p < 0.001) with UF volume. The ratio of blood volume to extracellular volume (Rbex ) was 0.306 ± 0.029 before and slightly but significantly increased to 0.326 ± 0.030 after UF. In spite of low-UF rates and extended treatment times, overall refilling fraction reached only 74% and was not different from the refilling fraction observed in regular HD. This value seems to represent a point where UF-induced volume perturbation is adequately compensated by physiologic control mechanisms.

Changes in total and segmental extracellular and intracellular volumes with hypotension during hemodialysis measured with bioimpedance spectroscopy.

Bioelectrical impedance analysis (BIA) devices have been advocated to guide volume management in hemodialysis (HD) patients. We hypothesized that understanding the dynamics of fluid shifts in different body segments may provide additional insight on preventive measures to reduce the risk of intradialytic hypotension. A prospective observational study was conducted among 42 HD patients at risk of hypotension who were admitted as emergencies inpatient. A total of 191 BIA measurements were made during the 42 HD sessions, and hypotension occurred during 52 measurements (27%). The extracellular water (ECW) to intracellular water ratio (EIR) was measured in different body segments and declined significantly only in the non-access arm with increasing HD session duration (β=-0.04; 95% confidence interval (CI): -0.05 to -0.03, p<0.01). There was no significant association between EIR and hypotension with respect to the different body segments. Only pre-HD N-terminal-pro b-type natriuretic peptide was significantly associated with hypotension (β=0.20, 95% CI: 0.04 to 0.89, p=0.04). There was no association between relative blood volume monitoring change and EIR. In summary, we found that segmental BIA during HD was unable to detect or predict hypotension during dialysis. Although BIA is able to provide information about ECW and guide clinical assessment of volume in HD patients prior to dialysis, our findings did not suggest the use of serial measurements of changes in EIR in different body segments during HD provided sufficient information to predict intradialytic hypotension. Similarly, changes in EIR did not provide information on changes in plasma volume that could potentially trigger interventions to prevent or reduce intra-dialytic hypotension.

Monitoring relative blood volume changes during hemodialysis: Impact of the priming procedure.

The monitoring of relative blood volume (RBV) changes during hemodialysis is increasingly used to evaluate the effect of dialyzer ultrafiltration on intravascular volume to guide the removal of excess fluid in a manner that maintains hemodynamic stability of the patient. RBV monitoring is typically based on an optical or acoustic sensor placed in the arterial blood line that measures a marker of hemoconcentration, such as hematocrit, hemoglobin, or total blood protein. However, the accuracy of RBV monitors and the impact of their clinical use remain the subject of ongoing debate. Here, we show that, depending on the procedure of filling the extracorporeal circuit with the patient's blood at the beginning of the dialysis session, theindications of an RBV monitor may be misleading as to the actual changes of the intravascular volume. When the blood is first pumped into the dialyzer, the priming fluid (saline) that fills the circuit may be either infused into the patient or disposed of to a drain bag. In the latter case, the intravascular volume is suddenly reduced, which is not accounted for by RBV monitors that track only the subsequent reductions in blood volume due to dialyzer ultrafiltration. Weanalyzed this general aspect of RBV monitoring using model-based simulations and showed quantitatively how RBV changes calculated using hematocrit differ depending on the priming procedure.

Relative blood volume changes during haemodialysis estimated from haemoconcentration markers

Relative blood volume (RBV) monitoring is frequently used in haemodialysis patients to help guide fluid management and improve cardiovascular stability. RBV changes are typically estimated based on online measurements of certain haemoconcentration markers, such as haematocrit (HCT), haemoglobin (HGB) or total blood protein concentration (TBP). The beginning of a haemodialysis procedure, i.e. filling the extracorporeal circuit with the patient’s blood (with the priming saline being infused to the patient or discarded) may be associated with relatively dynamic changes in the circulation, and hence the observed RBV changes may depend on the exact moment of starting the measurements. The aim of this study was to use a mathematical model to assess this issue quantitatively. The model-based simulations indicate that when the priming saline is not discarded but infused to the patient, a few-minute difference in the moment of starting RBV tracking through measurements of HCT, HGB or TBP may substantially affect the RBV changes observed throughout the dialysis session, especially with large priming volumes. A possible overestimation of the actual RBV changes is the highest when the measurements are started within a couple of minutes after the infusion of priming saline is completed.

P1524ABSOLUTE BLOOD VOLUME AND VASCULAR REFILLING IN HAEMODIALYSIS PATIENTS

Abstract Background and Aims The imbalance between UF and refilling rate is considered a major cause for intradialytic hypotension. Recent studies report a feasable and noninvasive method to estimate vascular refilling by determining absolute blood volume. It was the aim of this study to analyze absolute blood volume in a group of haemodialysis patients and to examine vascular refilling volume. Method Thirty stable chronic HD patients were studied (36,7% female, 63,3% male), aged 71,07 ± 13,31 years. Dialysis duration and UF requirements were based on physician prescription. Vascular refilling was calculated as: VREF = VUF – ΔV, where ΔV is the difference between absolute blood volume at the beginning and the end of dialysis. Relative blood volume monitor (BVM) was used. Hemodial Int. 2016;20(3):484–91. Results Absolute blood volume at the beginning of the dialysis was 6,27 ± 2,78 L (92,44 ± 32,66 ml/kg) and at the end 5,83 ± 2,77 L (85,94 ± 30,44 ml/kg). Ultrafiltration (UF) volume was 2,64 ± 0,82 L (11,14 ± 4,02 ml/kg/h). Vascular refilling was calculated as 2,24 ± 0,74 L, with a refilling fraction of 85,33 ± 11,07%. We found a strong correlation between refilling volume and UF volume (r2 0,861) (Figure 1), and a mild correlation between refilling volume and predialysis volume overload (r2 0,529). Conclusion Measurement of absolute blood volume is easy and noninvasive, and it allows us to study refilling volume. We found a strong correlation between UF volume and refilling volume.

P1124A NOVEL ALGORITHM TO IDENTIFY PRESUMABLY FLUID OVERLOADED HEMODIALYSIS PATIENTS

Abstract Background and Aims Adequate volume control is a major challenge in hemodialysis (HD) patients, as both fluid overload and depletion are associated with increased morbidity and mortality. In many cases, fluid overloaded patients may require further interventions, e.g. increasing ultrafiltration volume, treatment time or additional HD sessions to achieve their prescribed target weight. Relative blood volume (RBV) monitoring is widely used in HD patients, and past evidence suggests that flat RBV slopes indicate fluid overload [1,2]. The goal of this study was to develop an algorithm that would allow clinicians to identify presumably fluid overloaded HD patients based on a small number of consecutive RBV recordings. Method We based our analysis on the 842 prevalent HD patients enrolled in our previously published multicenter study [1], where RBV (Crit-Line®, Fresenius Medical Care, Waltham, MA) was assessed over a 6-month baseline period and all-cause mortality recorded during a median follow-up of 30.8 months; we found in this study that attainment of a RBV between 86 and 92% three hours into the HD session was associated with significantly better patient survival. The goal of our current research was to develop an algorithm that would require an observation period much shorter than 6 months yet yield clinically meaningful sensitivity and specificity to identify (presumably fluid overloaded) patients with flat RBV profiles (“flat” being defined as RBV &amp;gt; 92% at 3 hours.) We categorized patients in study [1] as either “positive” (their mean RBV at 3 hours was &amp;gt;92%) or “negative”. We computed sensitivities and specificities relative to the “positive” and “negative” cases for 1 to 15 HD sessions and various rates of treatments with flat RBV curves (30, 40, 50 and 60%). Results Sensitivities, specificities, and Youden’s indices (= sensitivity + specificity – 1) for 1 to 15 treatments and across the different rates of “positive” RBV curves are shown (Figure 1). We found a sensitivity of 92%, a specificity of 80%, and a Youden’s index of 73% when &amp;gt;=50% of 10 preceding treatments were “positive”. Based on these results we propose an RBV based algorithm to identify “positive” cases (i.e. patients with a flat RBV profile) (Figure 2). Conclusion Our algorithm requires only a small number (10) of RBV readings to identify presumably fluid overloaded patients with a clinically acceptable sensitivity (92%) and specificity (80%). It would be of interest to compare the performance of this algorithm with volume status as determined by bioimpedance; however, bioimpedance has not yet been approved for use in HD patients in the U.S.

P1090DETERMINATION OF ABSOLUTE BLOOD VOLUME USING ONLINE DIALYSATE DILUTION: WHEN SHOULD BE MEASURED?

Abstract Background and Aims Current on-line haemodiafiltration (HDF) machines equipped with a blood volume monitor (BVM) and an on-line bolus function have the potential for measuring absolute blood volume (aBV). Recently, we developed a simple method to determine absolute BV in everyday dialysis sessions. The aim of the present study was to evaluate the reproducibility of measurements. Method Intra-individual reproducibility was studied in 10 patients during a single dialysis session by 4 measurements of absolute BV: immediately after beginning before ultrafiltration (UF) was started, and after one, two and three hours. ABV was determined by indicator dilution. A defined volume bolus of 240 mL dialysate was infused into the venous blood line by pressing the emergency button of the HDF machine 5008 (FMC). For this reason, total UF volume was increased by 1L. UF was automatically stopped during and after the infusion. The resulting increase in relative blood volume (RBVpost-RBVpre) was measured by the ultrasonic relative BVM incorporated in the dialysis machine. ABV was measured in hourly intervals and for assessment of reproducibility the volume at treatment start (t=0) where RBV is 100% was calculated for all measurements as: aBV in mL = bolus volume 240 mL x 100% / increase RBV in % ABV data were normalized for body mass at dry weight (in mL/kg). Additionally, in 5 patients the RBV graph was monitored immediately at the beginning of dialysis without UF in a separate dialysis session. Results ABV at t=0 were consistently larger when calculated from measurements done immediately after the beginning compared to measurements obtained after 1 h (6.52 ± 1.40 L or 80.6 ± 14.5 mL/kg vs. 5.16 ± 1.40 L or 63.9 ± 14.3 mL/kg). Specific BV derived from 2 and 3 h measurements did not significantly differ from the measured volumes after 1 hour (61.4 ± 13.8 mL/kg, and 60.9 ± 13.9 mL/kg). The standard deviations of the 3 examinations in the same study patient during a further course of dialysis were between 0.6 and 5.3 ml/kg (ø 2.6 ml/kg). In a separate session, RBV decreases without UF at the beginning of dialysis in the first 3 minutes by 0.5 % and in 5 minutes by 0.6 %. Conclusion If BV is diluted by additional priming volume and bolus volume, a part of this volume will leave the circulation. This represented the time frame where the bolus was initially infused and the measurements were carried out. This loss is caused by the reduction in plasma colloid osmotic pressure induced by the dilution thereby changing the microvascular filtration equilibrium. The increase in RBV display is not solely caused by the bolus volume in this time and, and therefore, calculated BV would be overestimated by about 17 mL/kg. If measurement is performed at a later time, UF will take place and, consequently, refilling. This inward drive matches the outward bolus escape as a counterforce. BV measurement during a further course of dialysis is well reproducible with a deviation of only ± 2.6 ml/kg. The method would therefore be sufficiently precise in clinical practice. Therefore, we propose the determination of aBV only after 1 hour dialysis when a sufficient refilling takes place. With a software modification, the BV measurement could be routinely automated during each dialysis treatment. Manufacturers are asked to implement this technology in their devices.

Feedback control of absolute blood volume: A new technical approach in hemodialysis.

The success of automatic feedback control systems to improve hemodynamic stability by preventing relative blood volume from dropping beyond a critical value during dialysis is limited. The aim of this study was to use one of these systems for control of absolute rather than relative blood volume to prevent volume-dependent morbid events. Dialysis was delivered by a machine providing feedback control of ultrafiltration rates, relative blood volume monitoring, and accurate bolus infusion of 240 mL of dialysate to measure absolute blood volume at the beginning of dialysis. Critical relative blood volume required by the control algorithm was calculated from absolute blood volume at the beginning and a critical absolute blood volume of 67 mL/kg. In 40 stable patients, ultrafiltration was guided by blood volume using the feedback algorithm of the integrated program. Blood volume was maintained in a narrow range above the prespecified minimal value of 67 mL/kg. At the end of dialysis, absolute blood volume ranged from 67.5 to 72.5 mL/kg (69.4 ± 1.3 mL/kg). No volume-dependent intradialytic morbid event occurred. A feedback control system for relative blood volume-controlled ultrafiltration can be used for control of absolute blood volume. A prescribed target of absolute blood volume can be converted into relative blood volume, and this can subsequently be reached automatically with the integrated feedback system of the dialysis machine. Intradialytic morbid events could be considerably reduced. The whole procedure could be completely automated without altering the hardware of the dialysis device.

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

BackgroundRelative 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.Methods25 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).ResultsDuring 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).ConclusionsTracking 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.

47 Impacts of a Fluid Management Quality Improvement (QI) Project Utilizing Relative Blood Volume Monitoring (RBV-M) Among Patients with Large Intradialytic Weight Gains

47 Impacts of a Fluid Management Quality Improvement (QI) Project Utilizing Relative Blood Volume Monitoring (RBV-M) Among Patients with Large Intradialytic Weight Gains

Relative blood volume monitoring in hemodialysis patients: identifying its appropriate role.

Relative blood volume monitoring in hemodialysis patients: identifying its appropriate role.

Time to Reconsider the Role of Relative Blood Volume Monitoring for Fluid Management in Hemodialysis.

Relative blood volume (RBV) monitoring during hemodialysis has been used to help guide fluid management for decades, although with little supporting evidence. The technique relies on the assumption that variation in RBV during fluid removal reflects the capacity for vascular refilling and that efficient refilling is related to fluid overload. This study investigated the relationship between RBV variation and bioimpedance-based fluid overload in 47 patients on stable hemodialysis. Mean treatment ultrafiltration volume (UFV) was 1.7 L and RBV reduction was 3.2%/hour. Relative blood volume slopes were grouped based on trajectory: flatline (no decrease), linear decrease, or linear decrease followed by flatline. Fluid overload was similar (p > 0.05) across groups pre-dialysis (1.0, 2.2, and 1.6 L, respectively) and post-dialysis (-0.8, -0.1, and -0.1 L), whereas UFV was higher in patients with a linear decrease (1.8, 2.5, and 1.6 L; p = 0.02). Specific ultrafiltration rate, but not fluid overload, was associated with RBV change over dialysis. At least half the patients in each group finished dialysis fluid depleted based on bioimpedance, suggesting that the link between refilling and fluid overload is not as straightforward as previously assumed. These results question the assumptions that the absence of an appreciable decrease in RBV indicates fluid overload, and a rapid fall suggests fluid depletion.

Blood Pressure Management in Hemodialysis Patients: What We Know And What Questions Remain.

Despite having thousands of blood pressure (BP) readings on individual dialysis patients over the course of a year, our knowledge about the optimal assessment of BP, the mechanisms underlying hypertension and its management remain incomplete. Observational studies reveal that BP is lower at home than when measured in the dialysis unit. However, we do not know if using home vs. in-center measurements to guide treatment decisions improves BP control and/or clinical outcomes. Moreover, a recent US study suggests that typical hemodialysis patients are unlikely to adhere to home monitoring over the long term. Volume excess is one of probably many factors mediating hypertension in this population. A randomized clinical trial of aggressively challenging dry weight in patients without overt signs of fluid overload was shown to reduce BP, but there was an increase in vascular access thrombosis and intradialytic hypotension episodes. Long-term studies have not been done; thus, we do not know whether "squeezing dry weight" as a means to control BP is of more benefit than harm. Daily or prolonged nocturnal dialysis consistently has been shown to lower BP. To what extent this is a result of enhanced solute clearance vs. removal of excess volume is not clear. Use of bioimpedance or relative blood volume monitoring to guide fluid management has been tested in small studies, but more data are needed to determine whether their use impacts clinical outcomes. Well-designed clinical trials to determine whether a specific antihypertensive drug class is of benefit, independent of BP lowering, are lacking. The BP target that optimizes outcomes HD patients is also unknown. Observational studies consistently show poorer survival with predialysis BP <140/90 mmHg, although such studies likely are confounded by low BP due to cardiovascular disease and other comorbidities. In this review, we discuss what is known and the questions that remain regarding the epidemiology, diagnosis, etiology, and management of hypertension in hemodialysis patients.

Techniques for assessing fluids status in patients with kidney disease.

The aim of this article is to present current information on techniques for fluid status assessment in patients with kidney disease. The methods can be broadly categorized into biomarkers, ultrasound, blood volume monitoring, and bioimpedance. Biomarkers including atrial natriuretic peptide and B-type natriuretic peptide have been shown to provide information about relative changes in fluid status. Ultrasound is applied to measure inferior vena cava indices, pulmonary indicators, and vascular indicators of fluid overload. Relative blood volume monitoring is used to measure change in intravascular fluid during hemodialysis. While in principle appealing, measurement of absolute blood volume has seen limited use to date. Bioimpedance techniques such as vector analysis, whole body, and regional bioimpedance spectroscopy, have shown their ability to estimate fluid status. The interpretation of biomarkers is complicated by the presence of cardiac disease. All ultrasound methods have some correlation with fluid status; however, operator dependency limits their routine use. Bioimpedance methods and relative blood volume monitoring are increasingly used to assess fluid status in patients with acute or chronic kidney disease. Measurement of absolute blood volume holds promise for the future.

Intradialytic hypotension.

This review focuses on recent advances in our understanding of intradialytic hypotension (IDH) and measures that may reduce its frequency. The frequency and severity of IDH predict the risk for adverse clinical outcomes. The highest mortality risks associated with IDH were observed when the intradialytic systolic blood pressure (SBP) nadirs were <90 and <100 mmHg and the predialysis SBP were ≤159 mmHg or ≥160 mmHg, respectively. Interdialytic weight gain (IDWG) ≥3 kg occurs more frequently among patients with IDH. Prolonged and possibly more frequent dialysis, use of biofeedback devices, dialysate cooling and limiting sodium loading are useful measures to reduce the frequency of IDH. Frequent IDH is associated with high IDWGs and a poor prognosis. Studies on prolonged dialysis, biofeedback devices and cooled dialysate have yielded promising results. Intradialytic relative blood volume monitoring devices have been investigated in preventing IDH but results are mixed. Administration of a sodium/hydrogen exchange isoform 3 inhibitor increases stool sodium but has not been shown to decrease IDWG. IDH continues to be a significant dialysis complication deserving of further investigation.

Use of the Body Composition Monitor for Fluid Status Measurements in Subjects with High Body Mass Index

Background: Fluid management is a central aspect of haemodialysis (HD). Body composition monitor (BCM)-measured overhydration (OH) can improve fluid management strategies, but there remains uncertainty about its use in subjects with high body mass index (BMI). This study explored whether the observed tendency for HD patients with high BMI to complete dialysis fluid depleted according to BCM is associated with an artefact in the BCM models, or with systematic differences in the prescription and delivery of treatment. Methods: To isolate the effect of BMI from effects relating to treatment, BCM measurements were made on 20 healthy subjects with high BMI. Mean OH was compared with a previously reported cohort of healthy subjects with normal BMI. To further explore BCM-measured OH in HD patients, measurements were made pre- and post-dialysis on 10 patients with high BMI alongside relative blood volume monitoring. Body shape was classified to assess associations between shape and OH. Results: The mean OH for healthy subjects with high BMI was -0.1 litres, which was not different from that of healthy subjects with normal BMI. Median BCM-measured OH for HD patients was 1.8 and -1.8 litres pre- and post-dialysis respectively, while blood volume and blood pressure were maintained. Body shape correlated with OH in control subjects but not HD patients. Conclusions: We found no evidence of systematic bias in BCM-measured OH with high BMI in healthy subjects. BCM-measured post-dialysis fluid depletion in asymptomatic patients with high BMI appears to result from greater tolerance of ultrafiltration and ability to maintain blood volume.

Vascular refilling is independent of volume overload in hemodialysis with moderate ultrafiltration requirements.

Introduction Blood volume changes and vascular refilling during hemodialysis (HD) and ultrafiltration (UF) have been assumed to depend on volume overload (Vo ). It was the aim to study the magnitude of vascular refilling in stable HD patients with moderate volume expansion in everyday dialysis using novel technical approaches. Methods Patients were studied during routine dialysis and UF based on clinical dry weight assessment. Pre-dialysis Vo was independently measured by bioimpedance spectroscopy. Vascular refilling volume (Vref ) was calculated as: Vref = Vuf - ΔV, where ΔV is the absolute blood volume change determined by on-line dialysate dilution using a commercial on-line hemodiafiltration machine incorporating a relative blood volume monitor, and where Vuf is the prescribed UF volume. Findings Thirty patients (dry weight: 81.0 ± 17.8 kg) were studied. Pre-dialysis Vo was 2.46 ± 1.45 L. Vuf was 2.27 ± 0.71 L, specific UF rate was 6.45 ± 2.43 mL/kg/h, and since ΔV was 0.66 ± 0.31 L, Vref was determined as 1.61 ± 0.58 L, corresponding to a constant refilling fraction (Fref ) of 70.6 ± 10.6%. Vref strongly correlated with Vuf (r(2) = 0.82) but was independent of Vo and other volumes. Fref was also independent of Vo and other volumes normalized for various measures of body size. Discussion While vascular refilling and Fref is independent of Vo in treatments with moderate UF requirements, intravascular volume depletion increases with increasing UF requirements. The relationship between blood volume and Vo needs to be more closely examined in further studies to optimize volume control in everyday dialysis.

Relative Blood Volume Monitoring during Renal Replacement Therapy in Critically Ill Patients with Septic Shock: A Preliminary Report

Background: Volume management during renal replacement therapy (RRT) in septic shock is always in the conflict between aggravating hypovolemia by undue ultrafiltration (UF) and insufficient reduction of fluid overload which is associated with adverse outcome. Relative blood volume (RBV) monitoring could be helpful for timely transition from fluid resuscitation to fluid removal. Methods: Data of RBV were continuously monitored and used for guidance of UF and fluid resuscitation in 21 consecutive patients with severe septic multiple organ failure. RRT was applied with extended daily hemodiafiltration for median 11 h (range 6-23). Changes in RBV were analyzed during the first 4 treatment sessions. Results: During 26 treatments, RBV monitoring revealed an internal volume loss substituted by a median infusion volume of 2.38 l (maximum 8.07 l) per treatment to keep the RBV constant. In the remaining 40 sessions, a median net-UF of 1.00 l (range 0.40-4.40) was achieved. In the first 2 days predominantly substitution was necessary whereas from the third day UF became increasingly possible. The 28-day survival rate was 81%. Conclusion: Blood volume monitoring proved to be an easy and feasible tool for safe guidance of fluid management maintaining the balance between UF and vascular refilling. Video Journal Club ‘Cappuccino with Claudio Ronco' at http://www.karger.com/?doi=433415.