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      Hemoglobin Changes at the Initiation of High-Flux Hemodialysis

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          Background: The aim of the present study was to assess hemoglobin changes occurring at the beginning of high-flux hemodialysis (HD). Methods: In a group of 20 chronic HD patients (group A), total hemoglobin (tHb), hematocrit (Hct) and total serum proteins (TP) were measured in blood samples drawn from an arterial fistula needle before the initiation of high-flux HD, and from an arterial line 5 min after HD with the dialysate in the bypass mode. 31 chronic stable HD patients (group B) served as controls. In group B patients, tHb was measured in blood samples drawn from an arterial fistula needle before the initiation of high-flux HD, and from arterial and venous lines simultaneously 5 min later. Blood flow rates in groups A and B were set from the beginning of the study to 300 ml/min, while the bicarbonate dialysate flow rate and ultrafiltration rate in group B patients was set to 700 ml/min and zero, respectively. The same high-flux dialyzer was used for all patients (FLX-18, membrane PEPA 1.8 m<sup>2</sup>). Results: A comparison of baseline (pre-dialysis) values with those derived from an analysis of the arterial line in groups A and B at 5 min revealed that tHb decreased by 0.6 ± 0.2 g/dl (5.2 ± 1.7%, p < 0.001) and 0.7 ± 0.7 g/dl (5.4 ± 6.2%, p < 0.001), respectively. At the same time, Hct and TP in group A decreased by 1.32 ± 0.7% (3.8 ± 2.0%, p <0.001) and 0.3 ± 0.1 g/dl (4.8 ± 1.4%, p < 0.001), respectively. Blood volume (BV) and plasma volume (PV) in group A patients at 5 min as calculated from tHb and TP values increased by 5.6 ± 1.9 and 5.2 ± 1.7%, respectively, while BV in group B patients increased by 6.1 ± 7.0% (not significant when compared to group A). tHb did not change significantly in 14 patients (group C) studied immediately after adopting the supine position and 5 min later in the absence of HD. Conclusion: A 5% decrease in tHb was observed 5 min after the initiation of high-flux HD with a zero ultrafiltration rate, and was due to an increase in BV.

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          Most cited references 5

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          Variability of relative blood volume during haemodialysis.

           R Nette,  W. Weimar,  H Krepel (2000)
          A decrease in blood volume is thought to play a role in dialysis-related hypotension. Changes in relative blood volume (RBV) can be assessed by means of continuous haematocrit measurement. We studied the variability of RBV changes, and the relation between RBV and ultrafiltration volume (UV), blood pressure, heart rate, and inferior caval vein (ICV) diameter. In 10 patients on chronic haemodialysis, RBV measurement was performed during a total of one hundred 4-h haemodialysis sessions. Blood pressure and heart rate were measured at 5-min intervals. ICV diameter was assessed at the start and at the end of dialysis using ultrasonography. The changes in RBV showed considerable inter-individual variability. The average change in RBV ranged from -0.5 to -8.2% at 60 min and from -3.7 to -14.5% at 240 min (coefficient of variation (CV) 0.66 and 0.35 respectively). Intra-individual variability was also high (CV at 60 min 0.93; CV at 240 min 0.33). Inter-individual as well as intra-individual variability showed only minor improvement when RBV was corrected for UV. We found a significant correlation between RBV and UV at 60 (r= -0.69; P<0.001) and at 240 min (r= -0.63; P<0.001). There was a significant correlation between RBV and heart rate (r= -0.39; P<0.001), but not between RBV or UV and blood pressure. The level of RBV reduction at which hypotension occurred was also highly variable. ICV diameter decreased from 10.3+/-1.7 mm/m(2) to 7.3+/-1. 5 mm/m(2). There was only a slight, although significant, correlation between ICV diameter and RBV (r= -0.23; P<0.05). The change in ICV-diameter showed a wide variation. RBV changes during haemodialysis showed a considerable intra- and inter-individual variability that could not be explained by differences in UV. No correlation was observed between UV or changes in RBV and either blood pressure or the incidence of hypotension. Heart rate, however, was significantly correlated with RBV. Moreover, IVC diameter was only poorly correlated with RBV, suggesting a redistribution of blood towards the central venous compartment. These data indicate that RBV monitoring is of limited use in the prevention of dialysis-related hypotension, and that the critical level of reduction in RBV at which hypotension occurs depends on cardiovascular defence mechanisms such as sympathetic drive.
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            Haemodialysis with on-line monitoring equipment: tools or toys?

            On-line monitoring of chemical/physical signals during haemodialysis (HD) and bio-feedback represents the first step towards a 'physiological' HD system incorporating adaptive and logic controls in order to achieve pre-set treatment targets. Discussions took place to achieve a consensus on key points relating to on-line monitoring and bio-feedback, focusing on the clinical applications. The relative blood volume (BV) reduction during HD can be monitored by optic devices detecting the variations in concentration of haemoglobin/haematocrit. BV changes result from an equilibrium between ultrafiltration and the refilling capacity. However, BV reduction has little power in predicting intra-HD hypotensive episodes, while the combination of the patient-dialysate sodium gradient, the relative BV reduction between the 20th and 40th minute of HD, the irregularity of the profile of BV reduction over time and the heart rate decrease from the start to the 20th minute of HD predict intra-HD hypotension with a sensitivity of 82%, a specificity of 73% and an accuracy of 80%. A bio-feedback system drives the relative BV reduction according to desired values by instantaneously changing the ultrafiltration rate and the dialysate conductivity. This system has proved to reduce the incidence of intra-HD hypotension episodes significantly. Ionic dialysance and the patient's plasma conductivity can be calculated easily from on-line inlet and outlet dialysate conductivity measurements at two different steps of dialysate conductivity. Ionic dialysance is equivalent to urea clearance corrected for recirculation and is a tool for continuously monitoring the dialysis efficiency and detecting early problems with the delivery of the prescribed dose of dialysis. Given the strict and linear relationship between conductivity and sodium content, the conductivity values replace the sodium concentration values and this permits the development of a conductivity kinetic model, by means of which sodium balance can be achieved at each dialysis session. The conductivity kinetic model has been demonstrated to improve intra-HD cardiovascular stability in hypotension-prone patients significantly. Ionic dialysance is also a useful tool to monitor vascular access function, as it can be used to obtain serial measurements of vascular access blood flow. On-line urea monitors provide detailed information on intra-HD urea kinetics and delivered dialysis dose, but they are not in widespread use because of the costs related to the disposable materials (e.g. urease cartridge). The body temperature monitor measures the blood temperature at the arterial and venous lines of the extra-corporeal circuit and, thanks to a bio-feedback system, is able to modulate the dialysate temperature in order to influence the patient's core body temperature, which can be kept at constant values. This is associated with improved intra-HD cardiovascular stability. The module can also be used to quantify total recirculation. On-line monitoring devices and bio-feedback systems have evolved from toys for research use to tools for routine clinical application, particularly in patients with clinical complications. Conductivity monitoring appears the most versatile tool, as it permits quantification of delivered dialysis dose, achievement of sodium balance and surveillance of vascular access function, potentially at each dialysis session and without extra cost.
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              Rapid plasma volume decline upon quiet standing reflects large filtration capacity in dependent limbs.

              The plasma volume (PV) decline upon 1.5, 3, 5, 8, 10, 15 and 35 min periods of quiet standing was studied (Hb/Hct) in male volunteers (n = 7). This approach permitted detailed definition of the time-course of the volume change. PV decreased by as much as 8.5 +/- 0.4% (328 +/- 15 mL) after 3 min standing and by no less than 11.7 +/- 0.4% (466 +/- 22 mL) after 5 min. The reduction was 14.3 +/- 0.7, 16.8 +/- 0.8, 17.7 +/- 0.8 and 17.4 +/- 0.9% after 8, 10, 15 and 35 min, or 568 +/- 30, 671 +/- 39, 707 +/- 41 and 691 +/- 44 mL. These data, in conjunction with the 1.5 min experiments, indicated a very rapid approximately 125 mL min-1 fluid loss initially on standing. However, the PV loss showed marked decline with time and was virtually completed within 10 min. Finally, the observation was made that the rate of PV recovery after standing was inversely related to the duration of standing. It is suggested that (a) the transcapillary hydraulic conductivity in the dependent limbs, the predominant targets for fluid filtration on standing, is about 0.010 mL min-1 100 mL-1 mmHg-1 and much greater than indicated previously. However, protective mechanisms restrict rapid fluid loss to early phases of standing. (b) Decrease in PV may contribute importantly to haemodynamic stress and to orthostatic, fainting reactions during short quiet standing. Apparently, PV loss may be equally important as pooling of blood, traditionally regarded as a dominant cause of adverse orthostatic reactions. (c) The duration of standing, as such, may be critical for the rate of PV recovery after standing.

                Author and article information

                Nephron Clin Pract
                Nephron Clinical Practice
                S. Karger AG
                December 2006
                15 November 2006
                : 105
                : 1
                : c29-c34
                Renal Unit ‘G. Papanikolaou’ General Hospital, Thessaloniki, Greece
                96983 Nephron Clin Pract 2007;105:c29–c34
                © 2007 S. Karger AG, Basel

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                Page count
                Tables: 5, References: 13, Pages: 1
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/96983
                Original Paper

                Cardiovascular Medicine, Nephrology

                Hemoglobin, Blood volume, Hemodialysis


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