Bicarbonate hemodialysis: influence on plasma refilling and hemodynamic stability

Predicting anemia using NIR spectrum of spent dialysis fluid in hemodialysis patients

Anemia is commonly present in hemodialysis (HD) patients and significantly affects their survival and quality of life. NIR spectroscopy and machine learning were used as a method to detect anemia in hemodialysis patients. The aim of this investigation has been to evaluate the near-infrared spectroscopy (NIRS) as a method for non-invasive on-line detection of anemia parameters from HD effluent by assessing the correlation between the spectrum of spent dialysate in the wavelength range of 700–1700 nm and the levels of hemoglobin (Hb), red blood cells (RBC), hematocrit (Hct), iron (Fe), total iron binding capacity (TIBC), ferritin (FER), mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) in patient blood. The obtained correlation coefficient (R) for RBC was 0.93, for Hb 0.92, for Fe 0.94, for TIBC 0.96, for FER 0.91, for Hct 0.94, for MCV 0.92, for MCHC 0.92 and for MCH 0.93. The observed high correlations between the NIR spectrum of the dialysate fluid and the levels of the studied variables support the use of NIRS as a promising method for on-line monitoring of anemia and iron saturation parameters in HD patients.

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.

Regulation of Plasma Aldosterone during Hemodialysis

In order to clarify the influence of serum potassium, serum sodium and plasma angiotensin II concentrations on aldosterone release during hemodialysis (HD), six chronic hemodialysis patients were studied during HD with varying dialysate sodium concentrations and different buffers. Plasma aldosterone concentrations were higher during acetate than bicarbonate HD, during low sodium compared to high sodium HD, and were correlated inversely to serum sodium concentrations. The decline in plasma aldosterone concentrations during HD paralleled the decrease in serum potassium concentrations, and plasma aldosterone concentrations were correlated with serum potassium concentrations. In addition, plasma aldosterone and plasma angiotensin II concentrations were correlated significantly. It is proposed that serum potassium and the renin-angiotensin system are the main factors of aldosterone release during hemodialysis, while serum sodium per se seems to be of less importance. The dialysate buffer employed also plays a role in aldosterone regulation (via the renin-angiotensin system)

Subcutaneous interstitial pressure and volume characteristics in renal impairment associated with edema

The kidneys and the interstitial compartment play a vital role in body fluid regulation. The latter may be significantly altered in renal dysfunction, but experimental studies are lacking. To help define this we measured the subcutaneous interstitial pressure, bioimpedance volumes, and edema characteristics in 10 healthy subjects and 21 patients with obvious edema and chronic kidney disease (CKD). Interstitial edema was quantified by the time taken for a medial malleolar thumb pit to refill and termed the edema refill time. Interstitial pressure was significantly raised in CKD compared to healthy subjects. Total body water (TBW), extracellular fluid volume (ECFV), interstitial fluid volume, the ratio of the ECFV to the TBW, and segmental extracellular fluid volume were raised in CKD. The ratio of the ECFV to the TBW and the interstitial fluid volume were the best predictors of interstitial pressure. Significantly higher interstitial pressures were noted in edema of 2 weeks or less duration. A significant nonlinear relationship defined interstitial pressure and interstitial fluid volume. Edema refill time was significantly inversely related to interstitial pressure, interstitial compartment volumes, and edema vintage. Elevated interstitial pressure in CKD with obvious edema is a combined function of accumulated interstitial compartment fluid volumes, edema vintage, and tissue mechanical properties. The edema refill time may represent an important parameter in the clinical assessment of edema, providing additional information about interstitial pathophysiology in patients with CKD and fluid retention.

Van Beaumont's formula is valid during haemodialysis. Spectrophotometric determination of body circulating haemoglobin

Van Beaumont's formula is a convenient method to calculate changes in plasma volume from changes in haematocrit. The calculation is based on the assumption of a constant body red-cell volume. In order to evaluate the validity of this assumption during isovolaemic haemodialysis, we measured body circulating haemoglobin, blood volume and plasma volume by carbon monoxide dilution. No change in body circulating haemoglobin or plasma volume occurred by either method. Therefore, we conclude that van Beaumont's formula is valid during isovolaemic haemodialysis.

Extracorporeal treatment of acute renal failure in the intensive care unit: a critical view

Acute renal failure in critically ill patients is seldom an isolated problem but is more usually associated with multiple organ failure. When choosing an extracorporeal kidney replacement therapy, these other failing organs must be taken into account. Therefore the choice of an artificial kidney in patients requiring intensive care depends on both the efficacy of the technique and its possible adverse effects on cerebral, pulmonary and cardiovascular function. The most important pathogenic factors in the development of dysequilibrium syndromes, arterial hypoxemia and hypotension are treatment timing, diffusive solute transfer, bio-incompatible membranes and some specific dialysate components (buffer, electrolyte concentrations). It is important to understand the mechanisms by which these factors exert their adverse effects. Application of these pathophysiological mechanisms to the cardiopulmonary and neurologic status of the individual patient permits the prediction of their clinical outcome. This approach will lead to individualised treatment selection, thereby avoiding deleterious side-effects without loss of efficacy.

Beta 2-microglobulin kinetics in maintenance hemodialysis: a comparison of conventional and high-flux dialyzers and the effects of dialyzer reuse

beta 2-Microglobulin (beta 2M) forms synovial and bony amyloid deposits in long-term hemodialysis patients. To define the kinetics of beta 2M during hemodialysis and the effects of dialyzer reprocessing, we measured serum beta 2M, plasma C3a, and neutrophil counts immediately predialysis; 15, 90, and 180 minutes after beginning dialysis; and 15 minutes postdialysis in ten chronic hemodialysis patients. The studies were performed during first and third uses of cuprammonium rayon and polysulfone dialyzers processed by rinsing with water, then bleach, in an automated system (Seratronics DRS 4) and then packed in 1.5% formaldehyde. Mean serum beta 2M (corrected for ultrafiltration) decreased by 16.6% +/- 18.1% with new cuprammonium dialyzers and 57.1% +/- 12.8% with new polysulfone dialyzers. Dialyzer reprocessing had no significant effect on this decline. Predialysis serum beta 2M decreased by 30.4% +/- 15.5% 1 month after switching from cuprammonium to polysulfone dialyzers; these levels remained stable after 3 months of dialysis with polysulfone. Complement activation and neutropenia during dialysis were significantly more marked with cuprammonium, but were not affected by reprocessing of either dialyzer. In vitro adsorption of 124I-beta 2M to polysulfone fibers was greater than to cuprammonium; adsorption was not influenced by dialyzer reprocessing.

Is dialysis hypotension caused by an abnormality of venous tone?

The role of peripheral vascular tone in the development of hypotension induced by dialysis was investigated in eight patients undergoing haemodialysis with acetate or bicarbonate buffered fluid. Each patient had two sessions of dialysis with acetate fluid and two with bicarbonate fluid in the order acetate, bicarbonate, bicarbonate, acetate or bicarbonate, acetate, acetate, bicarbonate. Mean arterial blood pressure fell at a mean rate of 3.9 mm Hg/hour during dialysis with acetate fluid and 1.4 mm Hg/hour during dialysis with bicarbonate fluid. The rate of fall was significantly greater during dialysis with acetate fluid compared with bicarbonate fluid. Heart rate increased by a mean rate of 2.6 beats/min/hour during dialysis with both acetate and bicarbonate fluid. Vascular resistance in the forearm increased at a rate of 3.6 units/hour during dialysis with acetate fluid and 4.5 units/hour during dialysis with bicarbonate fluid, but the venous bed of the forearm dilated. The index of venous tone rose at a mean rate of 0.23 ml/dl [corrected] over 40 mm Hg/hour during dialysis with acetate fluid and 0.20 ml/dl over 40 mm Hg/hour during dialysis with bicarbonate fluid. Inappropriate peripheral venodilatation may be important in the development of hypotension induced by dialysis.

Unexpected seizures during hemodialysis. Effect of dialysate prescription

To assess the effects of the dialysate prescription on the intradialytic neurological stability of children requiring chronic hemodialysis (HD), continuous EEG monitoring (CEM) was performed on five children before, during and after HD against: (1) low sodium acetate (LAc: Na 132 mEq/l, acetate 38 mEq/l); (2) high sodium acetate (HAc: Na 144 mEq/l, acetate 41 mEq/l), and (3) low sodium bicarbonate (LBi: Na 133 mEq/l, bicarbonate 35 mEq/l) dialysate. Three children, two with clinically well-controlled seizure disorders and one with no seizure history, exhibited subclinical seizures on LAc and HAc but improved neurological stability on LBi. Two children had essentially unchanged CEM studies on any HD regimen. Symptoms of disequilibrium were noted in four of the five children on LAc, two of the five on HAc and only one of the five on LBi. The data suggest that bicarbonate HD may enhance intradialytic neurological stability, particularly in children with known seizure disorders. Furthermore, CEM was found to be a useful tool for evaluating the neurological stability of children during HD.

Effect of dialysate composition on intercompartmental fluid shift

Effect of dialysate composition on intercompartmental fluid shift and hemodynamics was studied in 12 patients during 1.5 or 2 hours of hemodialysis without net ultrafiltration, using high (H;Na 154 mmol/liter), normal (N;Na 140 mmol/liter) or low (L:Na 126 mmol/liter) concentration dialysate. H dialysate was associated with a small (0.9%) increase in blood volume, a larger increase in plasma volume and a decrease in erythrocyte volume. L dialysate resulted in a 2.3% decrease in blood volume, a larger decrease in plasma volume and an increase in erythrocyte volume. N dialysate gave results which were intermediately between the other two dialysis conditions. There was no difference in the post-dialysis mean arterial pressure between the groups, although heart rate increased more during H dialysis than during the other two conditions. Change in blood and erythrocyte volume correlated significantly with change in plasma Na concentration and osmolality, but not with change in plasma urea concentration. We conclude that dialysate composition affects the movement of water into and out of the plasma and erythrocytes in a manner that can be accounted for by altered plasma concentrations of osmotically active substances.