Continuous blood volume monitoring and "dry weight" assessment.

There are two distinct facets of adequate fluid balance control in haemodialysis patients--estimation of dry weight (DW) as the target and adequate ultrafiltration (UF) strategy, i.e. the way to reach the target in a possibly symptom-free way. The article reviews the continuous blood volume monitoring (CBVM) based procedures to deal with the former facet-DW determination. The existing approaches are divided in three groups--methods defining certain alert value of relative blood volume (RBV) reduction, methods working with RBV response to constant UF rate, and methods evaluating dynamics of RBV response to UF pulse or chain of UF pulses. While the first and the third approaches are relatively easy to automate, the second group of methods are suitable mainly for observational evaluations only. All the discussed methods, without exception, need large-scale verification, as they all were evaluated in the majority by their authors only and on small patient cohorts.

[Resting energy expenditure during hemodialysis]. / Klidový energetický výdei pri hemodialýze.

Very few studies have so far reported about resting energy expenditure (REE) in chronic renal failure and there is no information available on REE during hemodialysis (HD). Hypothetically, we can expect an increase in REE during HD procedure (due to the inflammatory response to extracorporeal blood circuit). However, such increase in REE could be modified by thermal balance of the procedure. In our study, REE was measured by indirect calorimetry (Deltatrac Datex) in a group of 13 HD patients (7 males and 6 females, mean age 59.8 +/- 13.5 years). In each patient, REE was assessed during two HD sessions: one isothermic and one thermoneutral. All other HD parameters were kept constant. The control group consisted of 14 healthy subjects (4 males and 10 females, mean age 41.3 +/- 20.5 years) with normal renal function. There was a significant difference in thermal balance between the two HD settings: -199 kJ/HD in isothermic and -4kJ/HD in thermoneutral HD sessions (p < 0.01). Measured REE values obtained in HD patients before HD session (7 316 +/- 919 kJ/day/1.73 m2) did not differ significantly from those of the healthy controls (7 264 +/- 1 016 kJ/day/1.73 m2). Similarly, there was no significant difference in calculated EE values (Harris-Benedict equation). In the 10th minute of the HD session, there was a slight, transitory decrease in REE (mean decrease by 3.2% during isothermic and by 2.8% during thermoneutral HD session, ns). In the 70th minute, REE returned to pre-dialysis values. After a light meal in the 110th minute REE increased by 8% during isothermic and by 6.3% during thermoneutral HD session. At the end of the HD session (i.e. in the 215th minute) REE again returned to pre-dialysis values. Intra-dialysis changes in REE were similar in both isothermic and thermoneutral HD sessions. The results of our study did not confirm the expected influence of HD procedure on REE in the two different thermal HD settings. We conclude that there is no significant difference between REE in HD patients and healthy controls and that REE values are not significantly influenced by hemodialysis procedure.

[Management of vascular access: monitoring and surveillance]. / Management des Gefässzugangs: Beobachtung und Uberwachung.

This article reviews vascular access (VA) assessment methods and procedures. It gives an overview of the existing methods for bed-side VA assessment by means of pressures, recirculation and access flow measurement. Pros and cons of the methods are discussed and additional benefits of a combined recirculation and access flow measurement are explained. Present vascular access care guidelines are discussed, namely the K/DOQI and EVAS documents. Practical setup of a vascular access monitoring and surveillance system is illustrated with data from the authors' own unit where such a system has been in use since 1999. The issue of adequate target setting is analysed in view of published works on clinical impact of access surveillance system introduction (timely detection of access stenosis and access patency). Critical re-evaluation is needed especially in current QVA threshold and intervention timing.

Simple pressure measurement is not reliable in detection of access stenosis in native AV fistulas.

Dynamic arterial and venous pressures (PA, PV) are used as the simplest tools to assess vascular access quality (VAQ). An increased PV over three consecutive dialyses is believed to indicate a stenosis, a rule devised for synthetic grafts (AVG) but not adequately validated for AV fistulas (AVF). In this study dynamic PV and static intra-access pressure (calculated by means of the simplified formula PIA=(PA+PV)/2) changes were evaluated in 46 accesses in which balloon angioplasty had to eventually be performed. The whole group consisted of 30 forearm AVF, 5 upper arm AVF and 11 AVG. Pressures were compared in each patient at a time of satisfactory access flow (QVA) and immediately before the angioplasty and pressure difference over that period (deltaPV, deltaPIA) evaluated. Despite a significant drop in QVA over the follow-up interval in both AVF and AVG, the mean deltaPV and deltaPIA in AVF were only several mm Hg and the chosen threshold limit of 20 mmHg was exceeded in approximately 10% of patients only. The results in the AVG group were, however, very different: The mean deltaPV and deltaPIA were close to 20 mmHg and almost 60% of patients in the AVG group exceeded this limit. Evaluation of PIA did not improve stenosis detection in either group. It is concluded that PV and/or PIA monitoring may be useful to detect a stenosis in AVG but not in AVF.

Comparison of different techniques of hemodialysis vascular access flow evaluation.

Measurement of vascular access flow (QVA) has been suggested as a method of choice for vascular access quality (VAQ) monitoring. Besides traditional duplex Doppler, a number of bedside methods based mostly on the Krivitski principle of QVA evaluation from recirculation at reversed needles (RX), have been developed. This work compares ultrasonic dilution (UD), taken as a reference, HD01, Transonic Systems; duplex Doppler (DD); thermodilution (TD), BTM, Fresenius; optodilutional RX measurement (ORX), Critline III, R-mode, HemaMetrics; direct optodilutional QVA evaluation from jumpwise changes in ultrafiltration rate at both normal and reversed needles connection (OABF), Critline III, ABF-mode; and direct transcutaneous optodilutional QVA evaluation (TQA), Critline III TQA. Firstly, reproducibility of each method was assessed by duplicate measurement at unchanged conditions. This was followed by paired measurement with each method performed at controlled change in relevant measurement condition (two different extracorporeal blood flows in UD and TD, changed sensor position in TQA). Finally paired measurements by each method and the reference method performed at identical conditions were evaluated to assess accuracy of each method. The simple Krivitski formula QVA= QB(1-RX)/RX was used wherever manual QVA calculation was needed. Very high reproducibility was seen in UD, both for measurement at the same extra corporeal blood flow (QB) (correlation coefficient of duplicate measurement r= 0.9702, n= 58) and for measurement at two different QB (r= 0.9735, n= 24), justifying its current status of a reference method in QVA evaluation. Slightly lower reproducibility of TD measurement at the same QB (r= 0.9197, n= 40) and at two different QB (r= 0.8508, n= 168) can be easily overcome by duplicate measurement with averaging. High correlation of TD vs. UD (r= 0.9543, n= 54) makes TD a viable clinical alternative in QVA evaluation. Consistently different QVA obtained at two different QB should prompt closer investigation of anatomical conditions of the access. Use of the simple Krivitski formula in TD (which measures total recirculation, i.e. sum of access recirculation and cardiopulmonary recirculation) brings about underestimation of QVA, which progressively increases from QVA of about 600 ml/min up. Good correlation, although with significant scatter (r= 0.8691, n= 27) was found between the DD- and UD-based QVA. By far the worst reproducibility at the same QB from among the investigated methods was found in ORX (0.6430, n= 23). Also the correlation of ORX vs. UD was lower than in other methods (r= 0.702, n=33) and general overestimation of QVA by about 25% was noted. Correlation of OABF vs. UD (r= 0.6957, n= 26) was slightly better than that of ORX and it gave less overestimated values. The TQA method showed very high reproducibility (r= 0.9712, n= 85), however only for unchanged sensor position. Correlation of QVA measured at two different sensor positions was much worse (r= 0.7255, n= 22). Correspondence of TQA vs. UD was satisfactory (r= 0.8077, n= 36). Skilled and experienced operators are a must with this method.

Vascular access quality monitoring.

Access dysfunction presents a risk for haemodialysis patients and is costly for health care providers. Regular vascular access quality (VAQ) monitoring enables the detection of adverse access conditions early allowing timely interventions, which will presumably be less invasive, more successful and cheaper. This paper reviews all currently used assessment parameters: dynamic and static pressures, recirculation and blood flow through the access--and analyses pros and cons of each of them. Based on this overview it is concluded that access flow monitoring should be the method of choice, possibly combined with monitoring of another parameter to further enlarge diagnostic possibilities of the monitoring. The VAQ monitoring system developed and used currently in the author's dialysis centre is briefly described as an example. The issue of access flow related to haemodynamics is briefly mentioned. With the introduction of any VAQ monitoring system, one has to acknowledge a change in structure of interventions and that the demand for surgical procedures decreases with a concurrent increase in percutaneous interventions.

Monitoring parameters of dialysis dose.

In order to deliver a specific dialysis dose (Kt/V) to all patients, their product Kt (urea clearance K multiplied by dialysis time t) should be individually adjusted according to total body water (V) of each patient. With dialysis time being fixed in most centres for organisational reasons, such individualization can be accomplished by individually set blood flow (QB). For a given t, the value of QB also defines the magnitude of the cumulative blood volume (VB = QB*t), i.e. the volume of blood perfused through the dialyser during the whole dialysis time. VB is displayed by every contemporary dialysis machine but not used. The aim of this work was to derive an easy to use approach to QB individualization based on patient's body weight and dialysis time to obtain a desired Kt/V value which would also be easy to check after dialysis by looking at the obtained VB value. Statistically significant correlation was found between the QB-based Kt/V estimation and Kt/V determined by the other two methods demonstrating practical feasibility of the novel approach. Kt/V values obtained with the QB prescribed according to patient's body weight tended to be better in females and patients with higher body mass index.

Comparison of different techniques of hemodialysis vascular access flow evaluation.

Measurement of vascular access flow (QVA) has been suggested as a method of choice for vascular access quality (VAQ) monitoring. Besides traditional duplex Doppler, a number of bedside methods based mostly on the Krivitski principle of QVA evaluation from recirculation at reversed needles (RX), have been developed. This work compares ultrasonic dilution (UD), taken as a reference, HD01, Transonic Systems; duplex Doppler (DD); thermodilution (TD), BTM, Fresenius; optodilutional RX measurement (ORX), Critline III, R-mode, HemaMetrics; direct optodilutional QVA evaluation from jumpwise changes in ultrafiltration rate at both normal and reversed needles connection (OABF), Critline III, ABF-mode; and direct transcutaneous optodilutional QVA evaluation (TQA), Critline III TQA. Firstly, reproducibility of each method was assessed by duplicate measurement at unchanged conditions. This was followed by paired measurement with each method performed at controlled change in relevant measurement condition (two different extracorporeal blood flows in UD and TD, changed sensor position in TQA). Finally paired measurements by each method and the reference method performed at identical conditions were evaluated to assess accuracy of each method. The simple Krivitski formula QVA=QB(1-RX)/RX was used wherever manual QVA calculation was needed. Very high reproducibility was seen in UD, both for measurement at the same extra corporeal blood flow (QB) (correlation coefficient of duplicate measurement r=0.9702, n=58) and for measurement at two different QB (r=0.9735, n=24), justifying its current status of a reference method in QVA evaluation. Slightly lower reproducibility of TD measurement at the same QB (r=0.9197, n=40) and at two different QB (r=0.8508, n=168) can be easily overcome by duplicate measurement with averaging. High correlation of TD vs. UD (r=0.9543, n=54) makes TD a viable clinical alternative in QVA evaluation. Consistently different QVA obtained at two different QB should prompt closer investigation of anatomical conditions of the access. Use of the simple Krivitski formula in TD (which measures total recirculation, i.e. sum of access recirculation and cardiopulmonary recirculation) brings about underestimation of QVA, which progressively increases from QVA of about 600 mL/min up. Good correlation, although with significant scatter (r=0.8691, n=27) was found between the DD- and UD-based QVA. By far the worst reproducibility at the same QB from among the investigated methods was found in ORX (0.6430, n 23). Also the correlation of ORX vs. UD was lower than in other methods (r=0.702, n=33) and general overestimation of QVA by about 25% was noted. Correlation of OABF vs. UD (r=0.6957, n=26) was slightly better than that of ORX and it gave less overestimated values. The TQA method showed very high reproducibility (r=0.9712, n=85), however only for unchanged sensor position. Correlation of QVA measured at two different sensor positions was much worse (r=0.7255, n=22). Correspondence of TQA vs. UD was satisfactory (r=0.8077, n=36). Skilled and experienced operators are a must with this method.

Age-related extracellular to total body water volume ratio (Ecv/TBW)--can it be used for "dry weight" determination in dialysis patients? Application of multifrequency bioimpedance measurement.

The article suggests a novel method for quantitative determination of optimal dry weight in dialysis patient based on their extracellular volume (ECV) to total body water (TBW) ratio and its relation to age. Values of ECV and TBW are evaluated by means of whole body multifrequency bioimpedometry. In an effort to find a suitable marker of hydration status in an individual from bioimpedance data, significant correlation has been found between ECV/TBW ratio and age in health. Assuming that all excess fluid in dialysis patients is stored exclusively in ECV and that distribution of their TBW at the state of optimal dry weight corresponds to that of a healthy person of the same age, the pre-dialysis ECV/TBW could be used for quantitative determination of optimal dry weight and/or of the ultrafiltration to reach this weight. Practical bioimpedance measurement of ECV/TBW in a group of dialysis patients both pre- and post-dialysis confirmed both above assumptions, i.e. nearly exclusively extracellular origin of ultrafiltration as well as normalisation of the ECV/TBW ratio towards the end of dialysis. Supporting evidence of increasing ECV/TBW value with age was also found in literature. Although the suggested method needs detailed analysis of possible disturbing factors (ethnic "specificity" of the reference ECV/TBW vs. age characteristics in health, possible difference in "biological" and "physical" age of dialysis patient and others), the article is published at this early stage to enable wider testing of the proposed novel method by different investigators.

Vascular access monitoring evaluated from automated recirculation measurement.

Vascular access quality monitoring by means of vascular access blood flow (QVA) evaluated from automated thermodilutional measurement of recirculation with reverse needle position is described. This method provides significant advantages over conventional methods based on simple monitoring of pressures in the extracorporeal circuit and/or measurement of recirculation with normal needle position. AQVA evaluation protocol was developed and introduced into the system of primary nursing. The QVA values were found independent of the extracorporeal blood flow used during the recirculation measurement. QVA values from below 200 ml/min to over 2 l/min were seen. In general, lower values were found in diabetics compared to non-diabetics and in females compared to males. While blood flow below 600 ml/min is considered risky for synthetic vascular grafts, native AV-fistulae seem to remain stable and patent at a flow of 400 ml/min or even below. The method is able to detect erroneous needle placement in looped grafts, stenosis between needles, and is also well suited for effective evaluation of success/failure of interventions on access.

Treating and monitoring water for dialysis in Europe.

The quality of water used for dialysis is not subject to any mandatory regulations in most European countries. A survey of haemodialysis facilities in 14 countries carried out by the European Dialysis and Transplant Nurses Association/European Renal Care Association (EDTNA/ERCA) showed that the majority of centres aimed to meet the requirements of the European Pharmacopoeia, but only 50% carried out tests to check compliance. The wide variation in policies for maintaining and monitoring the equipment and the distribution system indicates that guidelines for water treatment are urgently needed in Europe.

[Evaluation of vascular access for hemodialysis using combined measurement of recirculation in normal and inverted needle placement and determination of blood flow through the access]. / Hodnocení stavu cévního prístupu pro hemodialýzu kombinovaným merením recirkulace pri normálním a invertovaném zapojení jehel a stanovení prutoku krve prístupem.

The article describes novel method of vascular access quality assessment by means of combined measurement of recirculation with normal and inverse needles placement and calculation of vascular access blood flow from the recirculation data. Blood flow values seen in a large group of patients ranged from as low as 200 ml/min up to as high as 2 l/min. Females and diabetics exhibited lower values as compared to males and non-diabetics. The method enables to detect a number of anomalous sates which cannot be detected by conventional means based on monitoring of pressures or recirculation measurement at normal needles placement only (stenosis between both needles, uintentionally erroneous placement of needles in accesses with a loop). Assessment of access blood flow is suitable also for evaluation of interventions on the access, such as percutaneous transluminal angioplasty or surgical narrowing of anastomosis in case of too high blood flow.

[The method of calculating the numeric value of the KT/V index in the evaluation of effectiveness of peritoneal dialysis]. / Závislost císelné hodnoty indexu KT/V pri hodnocení úcinnosti peritoneální dialýzy na metodice výpoctu.

BACKGROUND: For evaluation of the adequacy of peritoneal and haemodialyzation treatment the BP/V index is used. In the literature there is so far no uniform view on the procedure of calculation. The objective was to test whether and to what extent the results of different procedures differ. METHODS AND RESULTS: The authors demonstrated that the method of calculation of this index has a marked impact on the result. The greatest discrepancy was due to differences in the distribution volume of urea (or total body water) where the mean difference was 10% of the absolute value. Also the procedure used to assess the residual renal function can influence the result. Differences due to the method of collection of the dialysate for assessment of the urea concentration are insignificant. The mean difference between the maximal and minimal BP/V index, when different methods of calculation are used, was in the same patient 0.45, which is cca 25% of the total value. CONCLUSIONS: The BP/V index must be assessed always by the same method with maximum accuracy. When presenting results or comparing results of different departments, the method of calculation must be stated.

Computational analysis of blood volume dynamics during hemodialysis.

The recently introduced continuous blood volume monitoring (CBVM) technique enables real time observation of the blood volume (BV) response to ultrafiltration. This response differs quite widely among patients even under otherwise comparable conditions. Assessing the clinical recordings of over 100 CBVM measurements, identification of a static and a dynamic component of the overall BV reduction was made. Computational analysis of the factors that influence BV response variability was then performed by means of a three-pool model of sodium, potassium, and urea kinetics with the following results. The blood volume profile contains clinically highly interesting yet cumulative information. Except for the small change and flat BV profiles the static component is predominant. From the external factors, the static component of BV reduction during hemodialysis is influenced by the total ultrafiltered volume and by the degree of overhydration. From the patient's internal factors, compliance of his cardiovascular system is dominant. BV is also more reduced in patients with lower values of total plasma protein content and/or lower hematocrit. The BV reduction dynamic component is primarily influenced by the applied ultrafiltration rate. A certain influence is also exerted by the ultrafiltration coefficient of the capillary wall which may vary in different individuals.

Clinical use of continuous blood volume monitoring.

Our department has been using continuous blood volume monitoring (Critline instrument, In-line Diagnostics, Riverdale, USA) for over two years now. First during research on sodium concentration control in haemodialysis (HD), later in the project on assessment and control of hydration in HD patients.

Use of continuous blood volume monitoring to detect inadequately high dry weight.

A continuous blood volume monitoring (CBVM) device (Inline Diagnostics, Riverdale, USA) was used to study response to prescribed ultrafiltration during haemodialysis (HD) in 66 stabilised HD patients. Fifty percent of patients showed the expected linear decrease in BV right from the beginning of HD (group 1), 32% exhibited no decrease at all (group 2), while eighteen percent formed the transient group 3 which showed a plateau of varying length after which a decrease occurred. The correct setting of dry weight was verified through evaluation of the ratio of extracellular fluid volume to total body water (VEC/TBW) in 26 patients by means of whole body multifrequency impedometry MFI (Xitron Tech., San Diego, USA) and through measurement of the Vena Cava Inferior diameter (VCID) pre and post HD (in 6 and 5 patients from groups 1 and 3 and from group 2, respectively). The mean VEC/TBW in groups 1 and 3 was 0.56 pre and 0.51 post HD as compared to 0.583 and 0.551 in group 2. VCID decreased on average by 14.1% in groups 1 and 3 but remained stable in group 2. Both findings thus confirmed inadequately high estimation of dry weight. Since CBVM is extremely easy to perform it can be used as a method of choice in detecting inadequately high prescribed dry weight. The status of the cardiovascular system must always be considered before final judgement is made.

Multifrequency bioimpedance in assessment of dry weight in haemodialysis.

The use of multifrequency bioimpedance (MFB) for determination of dry weight (DW) in haemodialysis (HD) patients was evaluated in three studies. In Study 1, the fluid state [total body water (TBW) and extracellular volume (ECV)] was measured by MFB in 82 normotensive patients. 41 hypertensive patients and in 30 healthy subjects. TBW and ECV were expressed as per cent of body weight (BW). In Study 2, DW of five hypertensive HD patients was gradually decreased during 3 months and ECV (MFB) and blood pressure (48 h ambulatory blood pressure monitoring) were measured at the beginning and end of study. In Study 3, we measured the fluid status repeatedly by MFB and the diameter of the inferior vena cava (DIVC) by ultrasound before, during and 2 h post-HD. In Study 1, the hypertensive patients had significantly greater TBW (P < 0.05) than the normotensive patients before (50.3 +/- 6.5% vs 47.6 +/- 5.8%) and after HD (48.8 +/- 7.8% vs 45.7 +/- 6.4%) and ECV (P < 0.001) before (29.4 +/- 3.6% vs 26.8 +/- 3.5%) and after HD (27.0 +/- 4.0% vs 24.6 +/- 3.5%), Post-HD ECV in the normotensive patients was similar to that in the healthy subjects. In Study 2, more efficient ultrafiltration resulted in reduction of BW and ECV along with a decrease in blood pressure and need for antihypertensive medication. In Study 3, both ECV and DIVC decreased following the removal of fluid during HD. ECV maintained stable values during the post-HD period, unlike DIVC which increased significantly (P < 0.005) due to refilling from the interstitial space. We conclude that MFB is an appropriate non-invasive method for DW determination, which is highly reproducible and technically simple to use.

[Determination of dry weight of hemodialyzed patients on the basis of the ratio of extracellular fluid volume to total body fluid volume as measured by multifrequency impedance]. / Objektivizace stanovení suché váhy hemodialyzovaných pacientu na základe pomeru objemu extracelulární tekutiny ku objemu celkové telesné vody zjisteného multifrekvencní impedometrií.

Whole body impedometry is relatively new non-invasive method to measure the distribution of total body water (TBW) between extra- and intracellular compartment (VEC, VIC). Having applied linear regression analysis onto the relation of the ratio of the extracellular volume to the volume of total body water (VEC/TBW) and the age in a group of healthy individuals very narrow scatter from the regression line was found. This line can thus be used as an indicator of normohydration status with respect to age. Assuming that the relation of VEC/TBW vs. age is the same in dialysed patients and that the state of normohydration corresponds to the so called dry weight, the VEC/TBW value can be used as a novel indicator of dry weight. Any deviation of the pre-dialysis VEC/TBW value from normal could easily be used to establish the desired ultrafiltration and dry weight. With regard to the known inaccuracy with which the dry weight is determined from purely clinical assessment this approach may lead to substantial objectivisation in determination of this principal parameter. It may be especially helpful in case of newly admitted patients. The suggested new approach to dry weight determination is supported by the finding of statistically significant relation between post-dialysis deviation of the VEC/TBW ratio from the normal value vs. blood volume reduction at the end of the dialysis session. Patients classified at the end of a dialysis session as still overhydrated by their VEC/TBW deviation from normal showed little or no reduction in their blood volume. An investigation of the Vena Cava Inferior diameter in a subgroup of these patients confirmed this finding showing no decrease at the end of dialysis. On the contrary, the patients whose post-dialysis VEC/TBW value was normal or below normal showed both significant reduction in their blood volume as well as decrease in the Vena Cava Inferior diameter.